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SYSTEMD.EXEC(5) systemd.exec SYSTEMD.EXEC(5)
systemd.exec - Execution environment configuration
service.service, socket.socket, mount.mount, swap.swap
Unit configuration files for services, sockets, mount points, and
swap devices share a subset of configuration options which define
the execution environment of spawned processes.
This man page lists the configuration options shared by these four
unit types. See systemd.unit(5) for the common options of all unit
configuration files, and systemd.service(5), systemd.socket(5),
systemd.swap(5), and systemd.mount(5) for more information on the
specific unit configuration files. The execution specific
configuration options are configured in the [Service], [Socket],
[Mount], or [Swap] sections, depending on the unit type.
In addition, options which control resources through Linux Control
Groups (cgroups) are listed in systemd.resource-control(5). Those
options complement options listed here.
A few execution parameters result in additional, automatic
dependencies to be added:
• Units with WorkingDirectory=, RootDirectory=, RootImage=,
RuntimeDirectory=, StateDirectory=, CacheDirectory=,
LogsDirectory= or ConfigurationDirectory= set automatically
gain dependencies of type Requires= and After= on all mount
units required to access the specified paths. This is
equivalent to having them listed explicitly in
RequiresMountsFor=.
• Units with PrivateTmp=yes automatically gain dependencies of
type Wants= and After= on all mounts required to access /tmp/
and /var/tmp/. They will also gain an automatic After=
dependency on systemd-tmpfiles-setup.service(8).
• Units with PrivateTmp=disconnected automatically gain
dependencies of type Wants= and After= on the mount required
to access /var/, unless DefaultDependencies=no and/or
RootDirectory=/RootImage= are specified.
• Units whose standard output or error output is connected to
journal or kmsg (or their combinations with console output,
see below) automatically acquire dependencies of type After=
on systemd-journald.socket.
• Units using LogNamespace= will automatically gain ordering and
requirement dependencies on the two socket units associated
with systemd-journald@.service instances.
The following settings may be used to change a service's view of
the filesystem. Please note that the paths must be absolute and
must not contain a ".." path component.
ExecSearchPath=
Takes a colon separated list of absolute paths relative to
which the executable used by the Exec*= (e.g. ExecStart=,
ExecStop=, etc.) properties can be found. ExecSearchPath=
overrides $PATH if $PATH is not supplied by the user through
Environment=, EnvironmentFile= or PassEnvironment=. Assigning
an empty string removes previous assignments and setting
ExecSearchPath= to a value multiple times will append to the
previous setting.
Added in version 250.
WorkingDirectory=
Takes a directory path relative to the service's root
directory specified by RootDirectory=, or the special value
"~". Sets the working directory for executed processes. If set
to "~", the home directory of the user specified in User= is
used. If not set, defaults to the root directory when systemd
is running as a system instance and the respective user's home
directory if run as user. If the setting is prefixed with the
"-" character, a missing working directory is not considered
fatal. If RootDirectory=/RootImage= is not set, then
WorkingDirectory= is relative to the root of the system
running the service manager. Note that setting this parameter
might result in additional dependencies to be added to the
unit (see above).
RootDirectory=
Takes a directory path relative to the host's root directory
(i.e. the root of the system running the service manager).
Sets the root directory for executed processes, with the
pivot_root(2) or chroot(2) system call. If this is used, it
must be ensured that the process binary and all its auxiliary
files are available in the new root. Note that setting this
parameter might result in additional dependencies to be added
to the unit (see above).
The MountAPIVFS= and PrivateUsers= settings are particularly
useful in conjunction with RootDirectory=. For details, see
below.
If RootDirectory=/RootImage= are used together with
NotifyAccess= the notification socket is automatically mounted
from the host into the root environment, to ensure the
notification interface can work correctly.
Note that services using RootDirectory=/RootImage= will not be
able to log via the syslog or journal protocols to the host
logging infrastructure, unless the relevant sockets are
mounted from the host, specifically:
The host's os-release(5) file will be made available for the
service (read-only) as /run/host/os-release. It will be
updated automatically on soft reboot (see:
systemd-soft-reboot.service(8)), in case the service is
configured to survive it.
Example 1. Mounting logging sockets into root environment
BindReadOnlyPaths=/dev/log /run/systemd/journal/socket /run/systemd/journal/stdout
In place of the directory path a ".v/" versioned directory may
be specified, see systemd.v(7) for details.
This option is only available for system services, or for
services running in per-user instances of the service manager
in which case PrivateUsers= is implicitly enabled (requires
unprivileged user namespaces support to be enabled in the
kernel via the "kernel.unprivileged_userns_clone=" sysctl).
RootImage=
Takes a path to a block device node or regular file as
argument. This call is similar to RootDirectory= however
mounts a file system hierarchy from a block device node or
loopback file instead of a directory. The device node or file
system image file needs to contain a file system without a
partition table, or a file system within an MBR/MS-DOS or GPT
partition table with only a single Linux-compatible partition,
or a set of file systems within a GPT partition table that
follows the Discoverable Partitions Specification[1].
When DevicePolicy= is set to "closed" or "strict", or set to
"auto" and DeviceAllow= is set, then this setting adds
/dev/loop-control with rw mode, "block-loop" and
"block-blkext" with rwm mode to DeviceAllow=. See
systemd.resource-control(5) for the details about
DevicePolicy= or DeviceAllow=. Also, see PrivateDevices=
below, as it may change the setting of DevicePolicy=.
Units making use of RootImage= automatically gain an After=
dependency on systemd-udevd.service.
The host's os-release(5) file will be made available for the
service (read-only) as /run/host/os-release. It will be
updated automatically on soft reboot (see:
systemd-soft-reboot.service(8)), in case the service is
configured to survive it.
In place of the image path a ".v/" versioned directory may be
specified, see systemd.v(7) for details.
This option is only available for system services and is not
supported for services running in per-user instances of the
service manager.
Added in version 233.
RootImageOptions=
Takes a comma-separated list of mount options that will be
used on disk images specified by RootImage=. Optionally a
partition name can be prefixed, followed by colon, in case the
image has multiple partitions, otherwise partition name "root"
is implied. Options for multiple partitions can be specified
in a single line with space separators. Assigning an empty
string removes previous assignments. Duplicated options are
ignored. For a list of valid mount options, please refer to
mount(8).
Valid partition names follow the Discoverable Partitions
Specification[1]: root, usr, home, srv, esp, xbootldr, tmp,
var.
This option is only available for system services and is not
supported for services running in per-user instances of the
service manager.
Added in version 247.
RootEphemeral=
Takes a boolean argument. If enabled, executed processes will
run in an ephemeral copy of the root directory or root image.
The ephemeral copy is placed in
/var/lib/systemd/ephemeral-trees/ while the service is active
and is cleaned up when the service is stopped or restarted. If
RootDirectory= is used and the root directory is a subvolume,
the ephemeral copy will be created by making a snapshot of the
subvolume.
To make sure making ephemeral copies can be made efficiently,
the root directory or root image should be located on the same
filesystem as /var/lib/systemd/ephemeral-trees/. When using
RootEphemeral= with root directories, btrfs(5) should be used
as the filesystem and the root directory should ideally be a
subvolume which systemd can snapshot to make the ephemeral
copy. For root images, a filesystem with support for reflinks
should be used to ensure an efficient ephemeral copy.
This option is only available for system services and is not
supported for services running in per-user instances of the
service manager.
Added in version 254.
RootHash=
Takes a data integrity (dm-verity) root hash specified in
hexadecimal, or the path to a file containing a root hash in
ASCII hexadecimal format. This option enables data integrity
checks using dm-verity, if the used image contains the
appropriate integrity data (see above) or if RootVerity= is
used. The specified hash must match the root hash of integrity
data, and is usually at least 256 bits (and hence 64 formatted
hexadecimal characters) long (in case of SHA256 for example).
If this option is not specified, but the image file carries
the "user.verity.roothash" extended file attribute (see
xattr(7)), then the root hash is read from it, also as
formatted hexadecimal characters. If the extended file
attribute is not found (or is not supported by the underlying
file system), but a file with the .roothash suffix is found
next to the image file, bearing otherwise the same name
(except if the image has the .raw suffix, in which case the
root hash file must not have it in its name), the root hash is
read from it and automatically used, also as formatted
hexadecimal characters.
If the disk image contains a separate /usr/ partition it may
also be Verity protected, in which case the root hash may
configured via an extended attribute "user.verity.usrhash" or
a .usrhash file adjacent to the disk image. There's currently
no option to configure the root hash for the /usr/ file system
via the unit file directly.
This option is only available for system services and is not
supported for services running in per-user instances of the
service manager.
Added in version 246.
RootHashSignature=
Takes a PKCS7 signature of the RootHash= option as a path to a
DER-encoded signature file, or as an ASCII base64 string
encoding of a DER-encoded signature prefixed by "base64:". The
dm-verity volume will only be opened if the signature of the
root hash is valid and signed by a public key present in the
kernel keyring. If this option is not specified, but a file
with the .roothash.p7s suffix is found next to the image file,
bearing otherwise the same name (except if the image has the
.raw suffix, in which case the signature file must not have it
in its name), the signature is read from it and automatically
used.
If the disk image contains a separate /usr/ partition it may
also be Verity protected, in which case the signature for the
root hash may configured via a .usrhash.p7s file adjacent to
the disk image. There's currently no option to configure the
root hash signature for the /usr/ via the unit file directly.
This option is only available for system services and is not
supported for services running in per-user instances of the
service manager.
Added in version 246.
RootVerity=
Takes the path to a data integrity (dm-verity) file. This
option enables data integrity checks using dm-verity, if
RootImage= is used and a root-hash is passed and if the used
image itself does not contain the integrity data. The
integrity data must be matched by the root hash. If this
option is not specified, but a file with the .verity suffix is
found next to the image file, bearing otherwise the same name
(except if the image has the .raw suffix, in which case the
verity data file must not have it in its name), the verity
data is read from it and automatically used.
This option is supported only for disk images that contain a
single file system, without an enveloping partition table.
Images that contain a GPT partition table should instead
include both root file system and matching Verity data in the
same image, implementing the Discoverable Partitions
Specification[1].
This option is only available for system services and is not
supported for services running in per-user instances of the
service manager.
Added in version 246.
RootImagePolicy=, MountImagePolicy=, ExtensionImagePolicy=
Takes an image policy string as per systemd.image-policy(7) to
use when mounting the disk images (DDI) specified in
RootImage=, MountImage=, ExtensionImage=, respectively. If not
specified the following policy string is the default for
RootImagePolicy= and MountImagePolicy:
root=verity+signed+encrypted+unprotected+absent: \
usr=verity+signed+encrypted+unprotected+absent: \
home=encrypted+unprotected+absent: \
srv=encrypted+unprotected+absent: \
tmp=encrypted+unprotected+absent: \
var=encrypted+unprotected+absent
The default policy for ExtensionImagePolicy= is:
root=verity+signed+encrypted+unprotected+absent: \
usr=verity+signed+encrypted+unprotected+absent
Added in version 254.
MountAPIVFS=
Takes a boolean argument. If on, a private mount namespace for
the unit's processes is created and the API file systems
/proc/, /sys/, /dev/ and /run/ (as an empty "tmpfs") are
mounted inside of it, unless they are already mounted. Note
that this option has no effect unless used in conjunction with
RootDirectory=/RootImage= as these four mounts are generally
mounted in the host anyway, and unless the root directory is
changed, the private mount namespace will be a 1:1 copy of the
host's, and include these four mounts. Note that the /dev/
file system of the host is bind mounted if this option is used
without PrivateDevices=. To run the service with a private,
minimal version of /dev/, combine this option with
PrivateDevices=.
In order to allow propagating mounts at runtime in a safe
manner, /run/systemd/propagate/ on the host will be used to
set up new mounts, and /run/host/incoming/ in the private
namespace will be used as an intermediate step to store them
before being moved to the final mount point.
Added in version 233.
BindLogSockets=
Takes a boolean argument. If true, sockets from
systemd-journald.socket(8) will be bind mounted into the mount
namespace. This is particularly useful when a different
instance of /run/ is employed, to make sure processes running
in the namespace can still make use of sd-journal(3).
This option is implied when LogNamespace= is used, when
MountAPIVFS=yes, or when PrivateDevices=yes is used in
conjunction with either RootDirectory= or RootImage=.
Added in version 257.
ProtectProc=
Takes one of "noaccess", "invisible", "ptraceable" or
"default" (which it defaults to). When set, this controls the
"hidepid=" mount option of the "procfs" instance for the unit
that controls which directories with process metainformation
(/proc/PID) are visible and accessible: when set to "noaccess"
the ability to access most of other users' process metadata in
/proc/ is taken away for processes of the service. When set to
"invisible" processes owned by other users are hidden from
/proc/. If "ptraceable" all processes that cannot be
ptrace()'ed by a process are hidden to it. If "default" no
restrictions on /proc/ access or visibility are made. For
further details see The /proc Filesystem[2]. It is generally
recommended to run most system services with this option set
to "invisible". This option is implemented via file system
namespacing, and thus cannot be used with services that shall
be able to install mount points in the host file system
hierarchy. Note that the root user is unaffected by this
option, so to be effective it has to be used together with
User= or DynamicUser=yes, and also without the
"CAP_SYS_PTRACE" capability, which also allows a process to
bypass this feature. It cannot be used for services that need
to access metainformation about other users' processes. This
option implies MountAPIVFS=.
If the kernel does not support per-mount point hidepid= mount
options this setting remains without effect, and the unit's
processes will be able to access and see other process as if
the option was not used.
This option is only available for system services and is not
supported for services running in per-user instances of the
service manager.
Added in version 247.
ProcSubset=
Takes one of "all" (the default) and "pid". If "pid", all
files and directories not directly associated with process
management and introspection are made invisible in the /proc/
file system configured for the unit's processes. This controls
the "subset=" mount option of the "procfs" instance for the
unit. For further details see The /proc Filesystem[2]. Note
that Linux exposes various kernel APIs via /proc/, which are
made unavailable with this setting. Since these APIs are used
frequently this option is useful only in a few, specific
cases, and is not suitable for most non-trivial programs.
Much like ProtectProc= above, this is implemented via file
system mount namespacing, and hence the same restrictions
apply: it is only available to system services, it disables
mount propagation to the host mount table, and it implies
MountAPIVFS=. Also, like ProtectProc= this setting is
gracefully disabled if the used kernel does not support the
"subset=" mount option of "procfs".
Added in version 247.
BindPaths=, BindReadOnlyPaths=
Configures unit-specific bind mounts. A bind mount makes a
particular file or directory available at an additional place
in the unit's view of the file system. Any bind mounts created
with this option are specific to the unit, and are not visible
in the host's mount table. This option expects a whitespace
separated list of bind mount definitions. Each definition
consists of a colon-separated triple of source path,
destination path and option string, where the latter two are
optional. If only a source path is specified the source and
destination is taken to be the same. The option string may be
either "rbind" or "norbind" for configuring a recursive or
non-recursive bind mount. If the destination path is omitted,
the option string must be omitted too. Each bind mount
definition may be prefixed with "-", in which case it will be
ignored when its source path does not exist.
BindPaths= creates regular writable bind mounts (unless the
source file system mount is already marked read-only), while
BindReadOnlyPaths= creates read-only bind mounts. These
settings may be used more than once, each usage appends to the
unit's list of bind mounts. If the empty string is assigned to
either of these two options the entire list of bind mounts
defined prior to this is reset. Note that, in this case, both
read-only and regular bind mounts are reset, regardless which
of the two settings is used.
Using this option implies that a mount namespace is allocated
for the unit, i.e. it implies the effect of PrivateMounts=
(see below).
This option is particularly useful when
RootDirectory=/RootImage= is used. In this case, the source
path refers to a path on the host file system, while the
destination path refers to a path below the root directory of
the unit.
Note that the destination directory must exist or systemd must
be able to create it. Thus, it is not possible to use those
options for mount points nested underneath paths specified in
InaccessiblePaths=, or under /home/ and other protected
directories if ProtectHome=yes is specified.
TemporaryFileSystem= with ":ro" or ProtectHome=tmpfs should be
used instead.
Added in version 233.
MountImages=
This setting is similar to RootImage= in that it mounts a file
system hierarchy from a block device node or loopback file,
but the destination directory can be specified as well as
mount options. This option expects a whitespace separated list
of mount definitions. Each definition consists of a
colon-separated tuple of source path and destination
definitions, optionally followed by another colon and a list
of mount options.
Mount options may be defined as a single comma-separated list
of options, in which case they will be implicitly applied to
the root partition on the image, or a series of
colon-separated tuples of partition name and mount options.
Valid partition names and mount options are the same as for
RootImageOptions= setting described above.
Each mount definition may be prefixed with "-", in which case
it will be ignored when its source path does not exist. The
source argument is a path to a block device node or regular
file. If source or destination contain a ":", it needs to be
escaped as "\:". The device node or file system image file
needs to follow the same rules as specified for RootImage=.
Any mounts created with this option are specific to the unit,
and are not visible in the host's mount table.
These settings may be used more than once, each usage appends
to the unit's list of mount paths. If the empty string is
assigned, the entire list of mount paths defined prior to this
is reset.
Note that the destination directory must exist or systemd must
be able to create it. Thus, it is not possible to use those
options for mount points nested underneath paths specified in
InaccessiblePaths=, or under /home/ and other protected
directories if ProtectHome=yes is specified.
When DevicePolicy= is set to "closed" or "strict", or set to
"auto" and DeviceAllow= is set, then this setting adds
/dev/loop-control with rw mode, "block-loop" and
"block-blkext" with rwm mode to DeviceAllow=. See
systemd.resource-control(5) for the details about
DevicePolicy= or DeviceAllow=. Also, see PrivateDevices=
below, as it may change the setting of DevicePolicy=.
This option is only available for system services and is not
supported for services running in per-user instances of the
service manager.
Added in version 247.
ExtensionImages=
This setting is similar to MountImages= in that it mounts a
file system hierarchy from a block device node or loopback
file, but instead of providing a destination path, an overlay
will be set up. This option expects a whitespace separated
list of mount definitions. Each definition consists of a
source path, optionally followed by a colon and a list of
mount options.
A read-only OverlayFS will be set up on top of /usr/ and /opt/
hierarchies for sysext images and /etc/ hierarchy for confext
images. The order in which the images are listed will
determine the order in which the overlay is laid down: images
specified first to last will result in overlayfs layers bottom
to top.
Mount options may be defined as a single comma-separated list
of options, in which case they will be implicitly applied to
the root partition on the image, or a series of
colon-separated tuples of partition name and mount options.
Valid partition names and mount options are the same as for
RootImageOptions= setting described above.
Each mount definition may be prefixed with "-", in which case
it will be ignored when its source path does not exist. The
source argument is a path to a block device node or regular
file. If the source path contains a ":", it needs to be
escaped as "\:". The device node or file system image file
needs to follow the same rules as specified for RootImage=.
Any mounts created with this option are specific to the unit,
and are not visible in the host's mount table.
These settings may be used more than once, each usage appends
to the unit's list of image paths. If the empty string is
assigned, the entire list of mount paths defined prior to this
is reset.
Each sysext image must carry a
/usr/lib/extension-release.d/extension-release.IMAGE file
while each confext image must carry a
/etc/extension-release.d/extension-release.IMAGE file, with
the appropriate metadata which matches
RootImage=/RootDirectory= or the host. See: os-release(5). To
disable the safety check that the extension-release file name
matches the image file name, the
x-systemd.relax-extension-release-check mount option may be
appended.
This option can be used together with a notify-reload service
type and systemd.v(7) to manage configuration updates. When
such a service carrying confext images is reloaded via
systemctl reload foo.service or equivalent D-Bus method, the
confext itself will be reloaded to pick up any changes. This
only applies to confext extensions. Note that in case a
service has this configuration enabled at first, and then it
is subsequently removed in an update followed by a
daemon-reload operation, reloading the confexts will be a
no-op, and a full service restart is required instead. See
systemd.service(5) also for details.
When DevicePolicy= is set to "closed" or "strict", or set to
"auto" and DeviceAllow= is set, then this setting adds
/dev/loop-control with rw mode, "block-loop" and
"block-blkext" with rwm mode to DeviceAllow=. See
systemd.resource-control(5) for the details about
DevicePolicy= or DeviceAllow=. Also, see PrivateDevices=
below, as it may change the setting of DevicePolicy=.
In place of the image path a ".v/" versioned directory may be
specified, see systemd.v(7) for details.
This option is only available for system services and is not
supported for services running in per-user instances of the
service manager.
Added in version 248.
ExtensionDirectories=
This setting is similar to BindReadOnlyPaths= in that it
mounts a file system hierarchy from a directory, but instead
of providing a destination path, an overlay will be set up.
This option expects a whitespace separated list of source
directories.
A read-only OverlayFS will be set up on top of /usr/ and /opt/
hierarchies for sysext images and /etc/ hierarchy for confext
images. The order in which the directories are listed will
determine the order in which the overlay is laid down:
directories specified first to last will result in overlayfs
layers bottom to top.
Each directory listed in ExtensionDirectories= may be prefixed
with "-", in which case it will be ignored when its source
path does not exist. Any mounts created with this option are
specific to the unit, and are not visible in the host's mount
table.
These settings may be used more than once, each usage appends
to the unit's list of directories paths. If the empty string
is assigned, the entire list of mount paths defined prior to
this is reset.
Each sysext directory must contain a
/usr/lib/extension-release.d/extension-release.IMAGE file
while each confext directory must carry a
/etc/extension-release.d/extension-release.IMAGE file, with
the appropriate metadata which matches
RootImage=/RootDirectory= or the host. See: os-release(5).
This option can be used together with a notify-reload service
type and systemd.v(7) to manage configuration updates. When
such a service carrying confext directories is reloaded via
systemctl reload foo.service or equivalent D-Bus method, the
confext itself will be reloaded to pick up any changes. This
only applies to confext extensions. Note that in case a
service has this configuration enabled at first, and then it
is subsequently removed in an update followed by a
daemon-reload operation, reloading the confexts will be a
no-op, and a full service restart is required instead. See
systemd.service(5) also for details.
Note that usage from user units requires overlayfs support in
unprivileged user namespaces, which was first introduced in
kernel v5.11.
In place of the directory path a ".v/" versioned directory may
be specified, see systemd.v(7) for details.
This option is only available for system services, or for
services running in per-user instances of the service manager
in which case PrivateUsers= is implicitly enabled (requires
unprivileged user namespaces support to be enabled in the
kernel via the "kernel.unprivileged_userns_clone=" sysctl).
Added in version 251.
These options are only available for system services and are not
supported for services running in per-user instances of the
service manager.
User=, Group=
Set the UNIX user or group that the processes are executed as,
respectively. Takes a single user or group name, or a numeric
ID as argument. For system services (services run by the
system service manager, i.e. managed by PID 1) and for user
services of the root user (services managed by root's instance
of systemd --user), the default is "root", but User= may be
used to specify a different user. For user services of any
other user, switching user identity is not permitted, hence
the only valid setting is the same user the user's service
manager is running as. If no group is set, the default group
of the user is used. This setting does not affect commands
whose command line is prefixed with "+".
Note that this enforces only weak restrictions on the
user/group name syntax, but will generate warnings in many
cases where user/group names do not adhere to the following
rules: the specified name should consist only of the
characters a-z, A-Z, 0-9, "_" and "-", except for the first
character which must be one of a-z, A-Z and "_" (i.e. digits
and "-" are not permitted as first character). The user/group
name must have at least one character, and at most 31. These
restrictions are made in order to avoid ambiguities and to
ensure user/group names and unit files remain portable among
Linux systems. For further details on the names accepted and
the names warned about see User/Group Name Syntax[3].
When used in conjunction with DynamicUser= the user/group name
specified is dynamically allocated at the time the service is
started, and released at the time the service is stopped —
unless it is already allocated statically (see below). If
DynamicUser= is not used the specified user and group must
have been created statically in the user database no later
than the moment the service is started, for example using the
sysusers.d(5) facility, which is applied at boot or package
install time. If the user does not exist by then program
invocation will fail.
If the User= setting is used the supplementary group list is
initialized from the specified user's default group list, as
defined in the system's user and group database. Additional
groups may be configured through the SupplementaryGroups=
setting (see below).
DynamicUser=
Takes a boolean parameter. If set, a UNIX user and group pair
is allocated dynamically when the unit is started, and
released as soon as it is stopped. The user and group will not
be added to /etc/passwd or /etc/group, but are managed
transiently during runtime. The nss-systemd(8) glibc NSS
module provides integration of these dynamic users/groups into
the system's user and group databases. The user and group name
to use may be configured via User= and Group= (see above). If
these options are not used and dynamic user/group allocation
is enabled for a unit, the name of the dynamic user/group is
implicitly derived from the unit name. If the unit name
without the type suffix qualifies as valid user name it is
used directly, otherwise a name incorporating a hash of it is
used. If a statically allocated user or group of the
configured name already exists, it is used and no dynamic
user/group is allocated. Note that if User= is specified and
the static group with the name exists, then it is required
that the static user with the name already exists. Similarly,
if Group= is specified and the static user with the name
exists, then it is required that the static group with the
name already exists. Dynamic users/groups are allocated from
the UID/GID range 61184...65519. It is recommended to avoid
this range for regular system or login users. At any point in
time each UID/GID from this range is only assigned to zero or
one dynamically allocated users/groups in use. However,
UID/GIDs are recycled after a unit is terminated. Care should
be taken that any processes running as part of a unit for
which dynamic users/groups are enabled do not leave files or
directories owned by these users/groups around, as a different
unit might get the same UID/GID assigned later on, and thus
gain access to these files or directories. If DynamicUser= is
enabled, RemoveIPC= is implied (and cannot be turned off).
This ensures that the lifetime of IPC objects and temporary
files created by the executed processes is bound to the
runtime of the service, and hence the lifetime of the dynamic
user/group. Since /tmp/ and /var/tmp/ are usually the only
world-writable directories on a system, unless PrivateTmp= is
manually set to "true", "disconnected" would be implied. This
ensures that a unit making use of dynamic user/group
allocation cannot leave files around after unit termination.
Furthermore NoNewPrivileges= and RestrictSUIDSGID= are
implicitly enabled (and cannot be disabled), to ensure that
processes invoked cannot take benefit or create SUID/SGID
files or directories. Moreover, ProtectSystem=strict and
ProtectHome=read-only are implied, thus prohibiting the
service to write to arbitrary file system locations. In order
to allow the service to write to certain directories, they
have to be allow-listed using ReadWritePaths=, but care must
be taken so that UID/GID recycling does not create security
issues involving files created by the service. Use
RuntimeDirectory= (see below) in order to assign a writable
runtime directory to a service, owned by the dynamic
user/group and removed automatically when the unit is
terminated. Use StateDirectory=, CacheDirectory= and
LogsDirectory= in order to assign a set of writable
directories for specific purposes to the service in a way that
they are protected from vulnerabilities due to UID reuse (see
below). If this option is enabled, care should be taken that
the unit's processes do not get access to directories outside
of these explicitly configured and managed ones. Specifically,
do not use BindPaths= and be careful with AF_UNIX file
descriptor passing for directory file descriptors, as this
would permit processes to create files or directories owned by
the dynamic user/group that are not subject to the lifecycle
and access guarantees of the service. Note that this option is
currently incompatible with D-Bus policies, thus a service
using this option may currently not allocate a D-Bus service
name (note that this does not affect calling into other D-Bus
services). Defaults to off.
Added in version 232.
SupplementaryGroups=
Sets the supplementary Unix groups the processes are executed
as. This takes a space-separated list of group names or IDs.
This option may be specified more than once, in which case all
listed groups are set as supplementary groups. When the empty
string is assigned, the list of supplementary groups is reset,
and all assignments prior to this one will have no effect. In
any way, this option does not override, but extends the list
of supplementary groups configured in the system group
database for the user. This does not affect commands prefixed
with "+".
SetLoginEnvironment=
Takes a boolean parameter that controls whether to set the
$HOME, $LOGNAME, and $SHELL environment variables. If not set,
this defaults to true if User=, DynamicUser= or PAMName= are
set, false otherwise. If set to true, the variables will
always be set for system services, i.e. even when the default
user "root" is used. If set to false, the mentioned variables
are not set by the service manager, no matter whether User=,
DynamicUser=, or PAMName= are used or not. This option
normally has no effect on services of the per-user service
manager, since in that case these variables are typically
inherited from user manager's own environment anyway.
Added in version 255.
PAMName=
Sets the PAM service name to set up a session as. If set, the
executed process will be registered as a PAM session under the
specified service name. This is only useful in conjunction
with the User= setting, and is otherwise ignored. If not set,
no PAM session will be opened for the executed processes. See
pam(8) for details.
Note that for each unit making use of this option a PAM
session handler process will be maintained as part of the unit
and stays around as long as the unit is active, to ensure that
appropriate actions can be taken when the unit and hence the
PAM session terminates. This process is named "(sd-pam)" and
is an immediate child process of the unit's main process.
Note that when this option is used for a unit it is very
likely (depending on PAM configuration) that the main unit
process will be migrated to its own session scope unit when it
is activated. This process will hence be associated with two
units: the unit it was originally started from (and for which
PAMName= was configured), and the session scope unit. Any
child processes of that process will however be associated
with the session scope unit only. This has implications when
used in combination with NotifyAccess=all, as these child
processes will not be able to affect changes in the original
unit through notification messages. These messages will be
considered belonging to the session scope unit and not the
original unit. It is hence not recommended to use PAMName= in
combination with NotifyAccess=all.
If a PAM module interactively requests input (a password or
suchlike) it will be attempted to be read from a service
credential (as configured via SetCredential=,
ImportCredential= and related calls) under the name
pam.authtok.pamservice, where pamservice is replaced by the
PAM service name as configured with PAMName=. (Note that the
credential remains accessible for the runtime of the service!)
If no matching credential is set, the user is prompted for it
interactively via the Password Agent[4] logic.
These options are only available for system services, or for
services running in per-user instances of the service manager in
which case PrivateUsers= is implicitly enabled (requires
unprivileged user namespaces support to be enabled in the kernel
via the "kernel.unprivileged_userns_clone=" sysctl).
CapabilityBoundingSet=
Controls which capabilities to include in the capability
bounding set for the executed process. See capabilities(7) for
details. Takes a whitespace-separated list of capability
names, e.g. CAP_SYS_ADMIN, CAP_DAC_OVERRIDE, CAP_SYS_PTRACE.
Capabilities listed will be included in the bounding set, all
others are removed. If the list of capabilities is prefixed
with "~", all but the listed capabilities will be included,
the effect of the assignment inverted. Note that this option
also affects the respective capabilities in the effective,
permitted and inheritable capability sets. If this option is
not used, the capability bounding set is not modified on
process execution, hence no limits on the capabilities of the
process are enforced. This option may appear more than once,
in which case the bounding sets are merged by OR, or by AND if
the lines are prefixed with "~" (see below). If the empty
string is assigned to this option, the bounding set is reset
to the empty capability set, and all prior settings have no
effect. If set to "~" (without any further argument), the
bounding set is reset to the full set of available
capabilities, also undoing any previous settings. This does
not affect commands prefixed with "+".
Use systemd-analyze(1)'s capability command to retrieve a list
of capabilities defined on the local system.
Example: if a unit has the following,
CapabilityBoundingSet=CAP_A CAP_B
CapabilityBoundingSet=CAP_B CAP_C
then CAP_A, CAP_B, and CAP_C are set. If the second line is
prefixed with "~", e.g.,
CapabilityBoundingSet=CAP_A CAP_B
CapabilityBoundingSet=~CAP_B CAP_C
then, only CAP_A is set.
AmbientCapabilities=
Controls which capabilities to include in the ambient
capability set for the executed process. Takes a
whitespace-separated list of capability names, e.g.
CAP_SYS_ADMIN, CAP_DAC_OVERRIDE, CAP_SYS_PTRACE. This option
may appear more than once, in which case the ambient
capability sets are merged (see the above examples in
CapabilityBoundingSet=). If the list of capabilities is
prefixed with "~", all but the listed capabilities will be
included, the effect of the assignment inverted. If the empty
string is assigned to this option, the ambient capability set
is reset to the empty capability set, and all prior settings
have no effect. If set to "~" (without any further argument),
the ambient capability set is reset to the full set of
available capabilities, also undoing any previous settings.
Note that adding capabilities to the ambient capability set
adds them to the process's inherited capability set.
Ambient capability sets are useful if you want to execute a
process as a non-privileged user but still want to give it
some capabilities. Note that, in this case, option keep-caps
is automatically added to SecureBits= to retain the
capabilities over the user change. AmbientCapabilities= does
not affect commands prefixed with "+".
Added in version 229.
NoNewPrivileges=
Takes a boolean argument. If true, ensures that the service
process and all its children can never gain new privileges
through execve() (e.g. via setuid or setgid bits, or
filesystem capabilities). This is the simplest and most
effective way to ensure that a process and its children can
never elevate privileges again. Defaults to false. In case the
service will be run in a new mount namespace anyway and
SELinux is disabled, all file systems are mounted with
MS_NOSUID flag. Also see No New Privileges Flag[5].
Note that this setting only has an effect on the unit's
processes themselves (or any processes directly or indirectly
forked off them). It has no effect on processes potentially
invoked on request of them through tools such as at(1),
crontab(1), systemd-run(1), or arbitrary IPC services.
Added in version 187.
SecureBits=
Controls the secure bits set for the executed process. Takes a
space-separated combination of options from the following
list: keep-caps, keep-caps-locked, no-setuid-fixup,
no-setuid-fixup-locked, noroot, and noroot-locked. This option
may appear more than once, in which case the secure bits are
ORed. If the empty string is assigned to this option, the bits
are reset to 0. This does not affect commands prefixed with
"+". See capabilities(7) for details.
SELinuxContext=
Set the SELinux security context of the executed process. If
set, this will override the automated domain transition.
However, the policy still needs to authorize the transition.
This directive is ignored if SELinux is disabled. If prefixed
by "-", failing to set the SELinux security context will be
ignored, but it is still possible that the subsequent execve()
may fail if the policy does not allow the transition for the
non-overridden context. This does not affect commands prefixed
with "+". See setexeccon(3) for details.
Added in version 209.
AppArmorProfile=
Takes a profile name as argument. The process executed by the
unit will switch to this profile when started. Profiles must
already be loaded in the kernel, or the unit will fail. If
prefixed by "-", all errors will be ignored. This setting has
no effect if AppArmor is not enabled. This setting does not
affect commands prefixed with "+".
This option is only available for system services and is not
supported for services running in per-user instances of the
service manager.
Added in version 210.
SmackProcessLabel=
Takes a SMACK64 security label as argument. The process
executed by the unit will be started under this label and
SMACK will decide whether the process is allowed to run or
not, based on it. The process will continue to run under the
label specified here unless the executable has its own
SMACK64EXEC label, in which case the process will transition
to run under that label. When not specified, the label that
systemd is running under is used. This directive is ignored if
SMACK is disabled.
The value may be prefixed by "-", in which case all errors
will be ignored. An empty value may be specified to unset
previous assignments. This does not affect commands prefixed
with "+".
This option is only available for system services and is not
supported for services running in per-user instances of the
service manager.
Added in version 218.
LimitCPU=, LimitFSIZE=, LimitDATA=, LimitSTACK=, LimitCORE=,
LimitRSS=, LimitNOFILE=, LimitAS=, LimitNPROC=, LimitMEMLOCK=,
LimitLOCKS=, LimitSIGPENDING=, LimitMSGQUEUE=, LimitNICE=,
LimitRTPRIO=, LimitRTTIME=
Set soft and hard limits on various resources for executed
processes. See setrlimit(2) for details on the process
resource limit concept. Process resource limits may be
specified in two formats: either as single value to set a
specific soft and hard limit to the same value, or as
colon-separated pair soft:hard to set both limits individually
(e.g. "LimitAS=4G:16G"). Use the string infinity to configure
no limit on a specific resource. The multiplicative suffixes
K, M, G, T, P and E (to the base 1024) may be used for
resource limits measured in bytes (e.g. "LimitAS=16G"). For
the limits referring to time values, the usual time units ms,
s, min, h and so on may be used (see systemd.time(7) for
details). Note that if no time unit is specified for LimitCPU=
the default unit of seconds is implied, while for LimitRTTIME=
the default unit of microseconds is implied. Also, note that
the effective granularity of the limits might influence their
enforcement. For example, time limits specified for LimitCPU=
will be rounded up implicitly to multiples of 1s. For
LimitNICE= the value may be specified in two syntaxes: if
prefixed with "+" or "-", the value is understood as regular
Linux nice value in the range -20...19. If not prefixed like
this the value is understood as raw resource limit parameter
in the range 0...40 (with 0 being equivalent to 1).
Note that most process resource limits configured with these
options are per-process, and processes may fork in order to
acquire a new set of resources that are accounted
independently of the original process, and may thus escape
limits set. Also note that LimitRSS= is not implemented on
Linux, and setting it has no effect. Often it is advisable to
prefer the resource controls listed in
systemd.resource-control(5) over these per-process limits, as
they apply to services as a whole, may be altered dynamically
at runtime, and are generally more expressive. For example,
MemoryMax= is a more powerful (and working) replacement for
LimitRSS=.
Note that LimitNPROC= will limit the number of processes from
one (real) UID and not the number of processes started
(forked) by the service. Therefore the limit is cumulative for
all processes running under the same UID. Please also note
that the LimitNPROC= will not be enforced if the service is
running as root (and not dropping privileges). Due to these
limitations, TasksMax= (see systemd.resource-control(5)) is
typically a better choice than LimitNPROC=.
Resource limits not configured explicitly for a unit default
to the value configured in the various DefaultLimitCPU=,
DefaultLimitFSIZE=, ... options available in
systemd-system.conf(5), and – if not configured there – the
kernel or per-user defaults, as defined by the OS (the latter
only for user services, see below).
For system units these resource limits may be chosen freely.
When these settings are configured in a user service (i.e. a
service run by the per-user instance of the service manager)
they cannot be used to raise the limits above those set for
the user manager itself when it was first invoked, as the
user's service manager generally lacks the privileges to do
so. In user context these configuration options are hence only
useful to lower the limits passed in or to raise the soft
limit to the maximum of the hard limit as configured for the
user. To raise the user's limits further, the available
configuration mechanisms differ between operating systems, but
typically require privileges. In most cases it is possible to
configure higher per-user resource limits via PAM or by
setting limits on the system service encapsulating the user's
service manager, i.e. the user's instance of user@.service.
After making such changes, make sure to restart the user's
service manager.
Table 1. Resource limit directives, their equivalent ulimit
shell commands and the unit used
┌──────────────────┬────────────┬─────────────────┬──────────────────────────────┐
│ Directive │ ulimit │ Unit │ Notes │
│ │ equivalent │ │ │
├──────────────────┼────────────┼─────────────────┼──────────────────────────────┤
│ LimitCPU= │ ulimit -t │ Seconds │ - │
├──────────────────┼────────────┼─────────────────┼──────────────────────────────┤
│ LimitFSIZE= │ ulimit -f │ Bytes │ - │
├──────────────────┼────────────┼─────────────────┼──────────────────────────────┤
│ LimitDATA= │ ulimit -d │ Bytes │ Do not use. │
│ │ │ │ This limits the │
│ │ │ │ allowed address │
│ │ │ │ range, not │
│ │ │ │ memory use! │
│ │ │ │ Defaults to │
│ │ │ │ unlimited and │
│ │ │ │ should not be │
│ │ │ │ lowered. To │
│ │ │ │ limit memory │
│ │ │ │ use, see │
│ │ │ │ MemoryMax= in │
│ │ │ │ systemd.resource-control(5). │
├──────────────────┼────────────┼─────────────────┼──────────────────────────────┤
│ LimitSTACK= │ ulimit -s │ Bytes │ - │
├──────────────────┼────────────┼─────────────────┼──────────────────────────────┤
│ LimitCORE= │ ulimit -c │ Bytes │ - │
├──────────────────┼────────────┼─────────────────┼──────────────────────────────┤
│ LimitRSS= │ ulimit -m │ Bytes │ Do not use. No effect on │
│ │ │ │ Linux. │
├──────────────────┼────────────┼─────────────────┼──────────────────────────────┤
│ LimitNOFILE= │ ulimit -n │ Number of File │ Do not use. Be careful when │
│ │ │ Descriptors │ raising the soft limit above │
│ │ │ │ 1024, since select(2) cannot │
│ │ │ │ function with file │
│ │ │ │ descriptors above 1023 on │
│ │ │ │ Linux. Nowadays, the hard │
│ │ │ │ limit defaults to 524288, a │
│ │ │ │ very high value compared to │
│ │ │ │ historical defaults. │
│ │ │ │ Typically applications │
│ │ │ │ should increase their soft │
│ │ │ │ limit to the hard limit on │
│ │ │ │ their own, if they are OK │
│ │ │ │ with working with file │
│ │ │ │ descriptors above 1023, i.e. │
│ │ │ │ do not use select(2). Note │
│ │ │ │ that file descriptors are │
│ │ │ │ nowadays accounted like any │
│ │ │ │ other form of memory, thus │
│ │ │ │ there should not be any need │
│ │ │ │ to lower the hard limit. Use │
│ │ │ │ MemoryMax= to control │
│ │ │ │ overall service memory use, │
│ │ │ │ including file descriptor │
│ │ │ │ memory. │
├──────────────────┼────────────┼─────────────────┼──────────────────────────────┤
│ LimitAS= │ ulimit -v │ Bytes │ Do not use. This limits the │
│ │ │ │ allowed address range, not │
│ │ │ │ memory use! Defaults to │
│ │ │ │ unlimited and should not be │
│ │ │ │ lowered. To limit memory │
│ │ │ │ use, see MemoryMax= in │
│ │ │ │ systemd.resource-control(5). │
├──────────────────┼────────────┼─────────────────┼──────────────────────────────┤
│ LimitNPROC= │ ulimit -u │ Number of │ This limit is enforced based │
│ │ │ Processes │ on the number of processes │
│ │ │ │ belonging to the user. │
│ │ │ │ Typically it is better to │
│ │ │ │ track processes per service, │
│ │ │ │ i.e. use TasksMax=, see │
│ │ │ │ systemd.resource-control(5). │
├──────────────────┼────────────┼─────────────────┼──────────────────────────────┤
│ LimitMEMLOCK= │ ulimit -l │ Bytes │ - │
├──────────────────┼────────────┼─────────────────┼──────────────────────────────┤
│ LimitLOCKS= │ ulimit -x │ Number of Locks │ - │
├──────────────────┼────────────┼─────────────────┼──────────────────────────────┤
│ LimitSIGPENDING= │ ulimit -i │ Number of │ - │
│ │ │ Queued Signals │ │
├──────────────────┼────────────┼─────────────────┼──────────────────────────────┤
│ LimitMSGQUEUE= │ ulimit -q │ Bytes │ - │
├──────────────────┼────────────┼─────────────────┼──────────────────────────────┤
│ LimitNICE= │ ulimit -e │ Nice Level │ - │
├──────────────────┼────────────┼─────────────────┼──────────────────────────────┤
│ LimitRTPRIO= │ ulimit -r │ Realtime │ - │
│ │ │ Priority │ │
├──────────────────┼────────────┼─────────────────┼──────────────────────────────┤
│ LimitRTTIME= │ ulimit -R │ Microseconds │ - │
└──────────────────┴────────────┴─────────────────┴──────────────────────────────┘
UMask=
Controls the file mode creation mask. Takes an access mode in
octal notation. See umask(2) for details. Defaults to 0022 for
system units. For user units the default value is inherited
from the per-user service manager (whose default is in turn
inherited from the system service manager, and thus typically
also is 0022 — unless overridden by a PAM module). In order to
change the per-user mask for all user services, consider
setting the UMask= setting of the user's user@.service system
service instance. The per-user umask may also be set via the
umask field of a user's JSON User Record[6] (for users managed
by systemd-homed.service(8) this field may be controlled via
homectl --umask=). It may also be set via a PAM module, such
as pam_umask(8).
CoredumpFilter=
Controls which types of memory mappings will be saved if the
process dumps core (using the /proc/pid/coredump_filter file).
Takes a whitespace-separated combination of mapping type names
or numbers (with the default base 16). Mapping type names are
private-anonymous, shared-anonymous, private-file-backed,
shared-file-backed, elf-headers, private-huge, shared-huge,
private-dax, shared-dax, and the special values all (all
types) and default (the kernel default of "private-anonymous
shared-anonymous elf-headers private-huge"). See core(5) for
the meaning of the mapping types. When specified multiple
times, all specified masks are ORed. When not set, or if the
empty value is assigned, the inherited value is not changed.
Example 2. Add DAX pages to the dump filter
CoredumpFilter=default private-dax shared-dax
Added in version 246.
KeyringMode=
Controls how the kernel session keyring is set up for the
service (see session-keyring(7) for details on the session
keyring). Takes one of inherit, private, shared. If set to
inherit no special keyring setup is done, and the kernel's
default behaviour is applied. If private is used a new session
keyring is allocated when a service process is invoked, and it
is not linked up with any user keyring. This is the
recommended setting for system services, as this ensures that
multiple services running under the same system user ID (in
particular the root user) do not share their key material
among each other. If shared is used a new session keyring is
allocated as for private, but the user keyring of the user
configured with User= is linked into it, so that keys assigned
to the user may be requested by the unit's processes. In this
mode multiple units running processes under the same user ID
may share key material. Unless inherit is selected the unique
invocation ID for the unit (see below) is added as a protected
key by the name "invocation_id" to the newly created session
keyring. Defaults to private for services of the system
service manager and to inherit for non-service units and for
services of the user service manager.
Added in version 235.
OOMScoreAdjust=
Sets the adjustment value for the Linux kernel's Out-Of-Memory
(OOM) killer score for executed processes. Takes an integer
between -1000 (to disable OOM killing of processes of this
unit) and 1000 (to make killing of processes of this unit
under memory pressure very likely). See The /proc
Filesystem[7] for details. If not specified, defaults to the
OOM score adjustment level of the service manager itself,
which is normally at 0.
Use the OOMPolicy= setting of service units to configure how
the service manager shall react to the kernel OOM killer or
systemd-oomd terminating a process of the service. See
systemd.service(5) for details.
TimerSlackNSec=
Sets the timer slack in nanoseconds for the executed
processes. The timer slack controls the accuracy of wake-ups
triggered by timers. See prctl(2) for more information. Note
that in contrast to most other time span definitions this
parameter takes an integer value in nano-seconds if no unit is
specified. The usual time units are understood too.
Personality=
Controls which kernel architecture uname(2) shall report, when
invoked by unit processes. Takes one of the architecture
identifiers arm64, arm64-be, arm, arm-be, x86, x86-64, ppc,
ppc-le, ppc64, ppc64-le, s390 or s390x. Which personality
architectures are supported depends on the kernel's native
architecture. Usually the 64-bit versions of the various
system architectures support their immediate 32-bit
personality architecture counterpart, but no others. For
example, x86-64 systems support the x86-64 and x86
personalities but no others. The personality feature is useful
when running 32-bit services on a 64-bit host system. If not
specified, the personality is left unmodified and thus
reflects the personality of the host system's kernel. This
option is not useful on architectures for which only one
native word width was ever available, such as m68k (32-bit
only) or alpha (64-bit only).
Added in version 209.
IgnoreSIGPIPE=
Takes a boolean argument. If true, SIGPIPE is ignored in the
executed process. Defaults to true since SIGPIPE is generally
only useful in shell pipelines.
Nice=
Sets the default nice level (scheduling priority) for executed
processes. Takes an integer between -20 (highest priority) and
19 (lowest priority). In case of resource contention, smaller
values mean more resources will be made available to the
unit's processes, larger values mean less resources will be
made available. See setpriority(2) for details.
CPUSchedulingPolicy=
Sets the CPU scheduling policy for executed processes. Takes
one of other, batch, idle, fifo or rr. See
sched_setscheduler(2) for details.
CPUSchedulingPriority=
Sets the CPU scheduling priority for executed processes. The
available priority range depends on the selected CPU
scheduling policy (see above). For real-time scheduling
policies an integer between 1 (lowest priority) and 99
(highest priority) can be used. In case of CPU resource
contention, smaller values mean less CPU time is made
available to the service, larger values mean more. See
sched_setscheduler(2) for details.
CPUSchedulingResetOnFork=
Takes a boolean argument. If true, elevated CPU scheduling
priorities and policies will be reset when the executed
processes call fork(2), and can hence not leak into child
processes. See sched_setscheduler(2) for details. Defaults to
false.
CPUAffinity=
Controls the CPU affinity of the executed processes. Takes a
list of CPU indices or ranges separated by either whitespace
or commas. Alternatively, takes a special "numa" value in
which case systemd automatically derives allowed CPU range
based on the value of NUMAMask= option. CPU ranges are
specified by the lower and upper CPU indices separated by a
dash. This option may be specified more than once, in which
case the specified CPU affinity masks are merged. If the empty
string is assigned, the mask is reset, all assignments prior
to this will have no effect. See sched_setaffinity(2) for
details.
NUMAPolicy=
Controls the NUMA memory policy of the executed processes.
Takes a policy type, one of: default, preferred, bind,
interleave and local. A list of NUMA nodes that should be
associated with the policy must be specified in NUMAMask=. For
more details on each policy please see, set_mempolicy(2). For
overall overview of NUMA support in Linux see, numa(7).
Added in version 243.
NUMAMask=
Controls the NUMA node list which will be applied alongside
with selected NUMA policy. Takes a list of NUMA nodes and has
the same syntax as a list of CPUs for CPUAffinity= option or
special "all" value which will include all available NUMA
nodes in the mask. Note that the list of NUMA nodes is not
required for default and local policies and for preferred
policy we expect a single NUMA node.
Added in version 243.
IOSchedulingClass=
Sets the I/O scheduling class for executed processes. Takes
one of the strings realtime, best-effort or idle. The kernel's
default scheduling class is best-effort at a priority of 4. If
the empty string is assigned to this option, all prior
assignments to both IOSchedulingClass= and
IOSchedulingPriority= have no effect. See ioprio_set(2) for
details.
IOSchedulingPriority=
Sets the I/O scheduling priority for executed processes. Takes
an integer between 0 (highest priority) and 7 (lowest
priority). In case of I/O contention, smaller values mean more
I/O bandwidth is made available to the unit's processes,
larger values mean less bandwidth. The available priorities
depend on the selected I/O scheduling class (see above). If
the empty string is assigned to this option, all prior
assignments to both IOSchedulingClass= and
IOSchedulingPriority= have no effect. For the kernel's default
scheduling class (best-effort) this defaults to 4. See
ioprio_set(2) for details.
The following sandboxing options are an effective way to limit the
exposure of the system towards the unit's processes. It is
recommended to turn on as many of these options for each unit as
is possible without negatively affecting the process' ability to
operate. Note that many of these sandboxing features are
gracefully turned off on systems where the underlying security
mechanism is not available. For example, ProtectSystem= has no
effect if the kernel is built without file system namespacing or
if the service manager runs in a container manager that makes file
system namespacing unavailable to its payload. Similarly,
RestrictRealtime= has no effect on systems that lack support for
SECCOMP system call filtering, or in containers where support for
this is turned off.
Also note that some sandboxing functionality is generally not
available in user services (i.e. services run by the per-user
service manager). Specifically, the various settings requiring
file system namespacing support (such as ProtectSystem=) are not
available, as the underlying kernel functionality is only
accessible to privileged processes. However, most namespacing
settings, that will not work on their own in user services, will
work when used in conjunction with PrivateUsers=true.
Note that the various options that turn directories read-only
(such as ProtectSystem=, ReadOnlyPaths=, ...) do not affect the
ability for programs to connect to and communicate with AF_UNIX
sockets in these directories. These options cannot be used to lock
down access to IPC services hence.
ProtectSystem=
Takes a boolean argument or the special values "full" or
"strict". If true, mounts the /usr/ and the boot loader
directories (/boot and /efi) read-only for processes invoked
by this unit. If set to "full", the /etc/ directory is mounted
read-only, too. If set to "strict" the entire file system
hierarchy is mounted read-only, except for the API file system
subtrees /dev/, /proc/ and /sys/ (protect these directories
using PrivateDevices=, ProtectKernelTunables=,
ProtectControlGroups=). This setting ensures that any
modification of the vendor-supplied operating system (and
optionally its configuration, and local mounts) is prohibited
for the service. It is recommended to enable this setting for
all long-running services, unless they are involved with
system updates or need to modify the operating system in other
ways. If this option is used, ReadWritePaths= may be used to
exclude specific directories from being made read-only.
Similar, StateDirectory=, LogsDirectory=, ... and related
directory settings (see below) also exclude the specific
directories from the effect of ProtectSystem=. This setting is
implied if DynamicUser= is set. This setting cannot ensure
protection in all cases. In general it has the same
limitations as ReadOnlyPaths=, see below. Defaults to off.
Note that if ProtectSystem= is set to "strict" and PrivateTmp=
is enabled, then /tmp/ and /var/tmp/ will be writable.
Added in version 214.
ProtectHome=
Takes a boolean argument or the special values "read-only" or
"tmpfs". If true, the directories /home/, /root, and /run/user
are made inaccessible and empty for processes invoked by this
unit. If set to "read-only", the three directories are made
read-only instead. If set to "tmpfs", temporary file systems
are mounted on the three directories in read-only mode. The
value "tmpfs" is useful to hide home directories not relevant
to the processes invoked by the unit, while still allowing
necessary directories to be made visible when listed in
BindPaths= or BindReadOnlyPaths=.
Setting this to "yes" is mostly equivalent to setting the
three directories in InaccessiblePaths=. Similarly,
"read-only" is mostly equivalent to ReadOnlyPaths=, and
"tmpfs" is mostly equivalent to TemporaryFileSystem= with
":ro".
It is recommended to enable this setting for all long-running
services (in particular network-facing ones), to ensure they
cannot get access to private user data, unless the services
actually require access to the user's private data. This
setting is implied if DynamicUser= is set. This setting cannot
ensure protection in all cases. In general it has the same
limitations as ReadOnlyPaths=, see below.
This option is only available for system services, or for
services running in per-user instances of the service manager
in which case PrivateUsers= is implicitly enabled (requires
unprivileged user namespaces support to be enabled in the
kernel via the "kernel.unprivileged_userns_clone=" sysctl).
Added in version 214.
RuntimeDirectory=, StateDirectory=, CacheDirectory=,
LogsDirectory=, ConfigurationDirectory=
These options take a whitespace-separated list of directory
names. The specified directory names must be relative, and may
not include "..". If set, when the unit is started, one or
more directories by the specified names will be created
(including their parents) below the locations defined in the
following table. Also, the corresponding environment variable
will be defined with the full paths of the directories. If
multiple directories are set, then in the environment variable
the paths are concatenated with colon (":").
If DynamicUser= is used, and if the kernel version supports
id-mapped mounts[8], the specified directories will be owned
by "nobody" in the host namespace and will be mapped to (and
will be owned by) the service's UID/GID in its own namespace.
For backward compatibility, existing directories created
without id-mapped mounts will be kept untouched.
Table 2. Automatic directory creation and environment
variables
┌─────────────────────────┬────────────────┬──────────────────────┬──────────────────────────┐
│ Directory │ Below path for │ Below path for │ Environment │
│ │ system units │ user units │ variable set │
├─────────────────────────┼────────────────┼──────────────────────┼──────────────────────────┤
│ RuntimeDirectory= │ /run/ │ $XDG_RUNTIME_DIR │ $RUNTIME_DIRECTORY │
├─────────────────────────┼────────────────┼──────────────────────┼──────────────────────────┤
│ StateDirectory= │ /var/lib/ │ $XDG_STATE_HOME │ $STATE_DIRECTORY │
├─────────────────────────┼────────────────┼──────────────────────┼──────────────────────────┤
│ CacheDirectory= │ /var/cache/ │ $XDG_CACHE_HOME │ $CACHE_DIRECTORY │
├─────────────────────────┼────────────────┼──────────────────────┼──────────────────────────┤
│ LogsDirectory= │ /var/log/ │ $XDG_STATE_HOME/log/ │ $LOGS_DIRECTORY │
├─────────────────────────┼────────────────┼──────────────────────┼──────────────────────────┤
│ ConfigurationDirectory= │ /etc/ │ $XDG_CONFIG_HOME │ $CONFIGURATION_DIRECTORY │
└─────────────────────────┴────────────────┴──────────────────────┴──────────────────────────┘
In case of RuntimeDirectory= the innermost subdirectories are
removed when the unit is stopped. It is possible to preserve
the specified directories in this case if
RuntimeDirectoryPreserve= is configured to restart or yes (see
below). The directories specified with StateDirectory=,
CacheDirectory=, LogsDirectory=, ConfigurationDirectory= are
not removed when the unit is stopped.
Except in case of ConfigurationDirectory=, the innermost
specified directories will be owned by the user and group
specified in User= and Group=. If the specified directories
already exist and their owning user or group do not match the
configured ones, all files and directories below the specified
directories as well as the directories themselves will have
their file ownership recursively changed to match what is
configured. As an optimization, if the specified directories
are already owned by the right user and group, files and
directories below of them are left as-is, even if they do not
match what is requested. The innermost specified directories
will have their access mode adjusted to the what is specified
in RuntimeDirectoryMode=, StateDirectoryMode=,
CacheDirectoryMode=, LogsDirectoryMode= and
ConfigurationDirectoryMode=.
These options imply BindPaths= for the specified paths. When
combined with RootDirectory= or RootImage= these paths always
reside on the host and are mounted from there into the unit's
file system namespace.
If DynamicUser= is used, the logic for CacheDirectory=,
LogsDirectory= and StateDirectory= is slightly altered: the
directories are created below /var/cache/private,
/var/log/private and /var/lib/private, respectively, which are
host directories made inaccessible to unprivileged users,
which ensures that access to these directories cannot be
gained through dynamic user ID recycling. Symbolic links are
created to hide this difference in behaviour. Both from
perspective of the host and from inside the unit, the relevant
directories hence always appear directly below /var/cache,
/var/log and /var/lib.
Use RuntimeDirectory= to manage one or more runtime
directories for the unit and bind their lifetime to the daemon
runtime. This is particularly useful for unprivileged daemons
that cannot create runtime directories in /run/ due to lack of
privileges, and to make sure the runtime directory is cleaned
up automatically after use. For runtime directories that
require more complex or different configuration or lifetime
guarantees, please consider using tmpfiles.d(5).
RuntimeDirectory=, StateDirectory=, CacheDirectory= and
LogsDirectory= optionally support two more parameters,
separated by ":". The second parameter will be interpreted as
a destination path that will be created as a symlink to the
directory. The symlinks will be created after any BindPaths=
or TemporaryFileSystem= options have been set up, to make
ephemeral symlinking possible. The same source can have
multiple symlinks, by using the same first parameter, but a
different second parameter. The third parameter is a flags
field, and since v257 can take a value of ro to make the
directory read only for the service. This is also supported
for ConfigurationDirectory=. If multiple symlinks are set up,
the directory will be read only if at least one is configured
to be read only. To pass a flag without a destination symlink,
the second parameter can be empty, for example:
ConfigurationDirectory=foo::ro
The directories defined by these options are always created
under the standard paths used by systemd (/var/, /run/, /etc/,
...). If the service needs directories in a different
location, a different mechanism has to be used to create them.
tmpfiles.d(5) provides functionality that overlaps with these
options. Using these options is recommended, because the
lifetime of the directories is tied directly to the lifetime
of the unit, and it is not necessary to ensure that the
tmpfiles.d configuration is executed before the unit is
started.
To remove any of the directories created by these settings,
use the systemctl clean ... command on the relevant units,
see systemctl(1) for details.
Example: if a system service unit has the following,
RuntimeDirectory=foo/bar baz
the service manager creates /run/foo (if it does not exist),
/run/foo/bar, and /run/baz. The directories /run/foo/bar and
/run/baz except /run/foo are owned by the user and group
specified in User= and Group=, and removed when the service is
stopped.
Example: if a system service unit has the following,
RuntimeDirectory=foo/bar
StateDirectory=aaa/bbb ccc
then the environment variable "RUNTIME_DIRECTORY" is set with
"/run/foo/bar", and "STATE_DIRECTORY" is set with
"/var/lib/aaa/bbb:/var/lib/ccc".
Example: if a system service unit has the following,
RuntimeDirectory=foo:bar foo:baz
the service manager creates /run/foo (if it does not exist),
and /run/bar plus /run/baz as symlinks to /run/foo.
Added in version 211.
RuntimeDirectoryMode=, StateDirectoryMode=, CacheDirectoryMode=,
LogsDirectoryMode=, ConfigurationDirectoryMode=
Specifies the access mode of the directories specified in
RuntimeDirectory=, StateDirectory=, CacheDirectory=,
LogsDirectory=, or ConfigurationDirectory=, respectively, as
an octal number. Defaults to 0755. See "Permissions" in
path_resolution(7) for a discussion of the meaning of
permission bits.
Added in version 234.
StateDirectoryQuota=, CacheDirectoryQuota=, LogsDirectoryQuota=
Specifies the storage limits for the directories specified in
StateDirectory=, CacheDirectory=, or LogsDirectory=
respectively.
The storage quota is defined in terms of disk blocks and
inodes, as per quotactl[9]. Takes an absolute size limit in
bytes. If the value is suffixed with K, M, G or T, the
specified size is parsed as Kilobytes, Megabytes, Gigabytes,
or Terabytes (with the base 1024), respectively. If an
absolute size limit is specified, only the block quota is set
(rounded up to the nearest block). Alternatively, a percentage
value may be specified, which applies the same percent quota
to both blocks and inodes. Defaults to off, in which case no
storage limits will be set.
Only hard limits are set, not soft limits. If the underlying
filesystem for the specified directories does not support
project quotas, the specified storage limits will not be set.
In addition to enabling per-unit quotas with these settings,
it is necessary to enable prjquota on the file system level as
well (i.e. tune2fs -Q prjquota). Quotas must also be turned
on with quotaon.[10]
Added in version 258.
StateDirectoryAccounting=, CacheDirectoryAccounting=,
LogsDirectoryAccounting=
Takes a boolean argument. If true, a project ID is assigned to
the directories specified in StateDirectory=, CacheDirectory=,
or LogsDirectory= respectively, which is used for tracking
disk usage when disk quotas are turned on (see repquota[11]).
Defaults to false.
To set and enforce disk quotas, StateDirectoryQuota=,
CacheDirectoryQuota=, or LogsDirectoryQuota= must be
specified.
Added in version 258.
RuntimeDirectoryPreserve=
Takes a boolean argument or restart. If set to no (the
default), the directories specified in RuntimeDirectory= are
always removed when the service stops. If set to restart the
directories are preserved when the service is both
automatically and manually restarted. Here, the automatic
restart means the operation specified in Restart=, and manual
restart means the one triggered by systemctl restart
foo.service. If set to yes, then the directories are not
removed when the service is stopped. Note that since the
runtime directory /run/ is a mount point of "tmpfs", then for
system services the directories specified in RuntimeDirectory=
are removed when the system is rebooted.
Added in version 235.
TimeoutCleanSec=
Configures a timeout on the clean-up operation requested
through systemctl clean ..., see systemctl(1) for details.
Takes the usual time values and defaults to infinity, i.e. by
default no timeout is applied. If a timeout is configured the
clean operation will be aborted forcibly when the timeout is
reached, potentially leaving resources on disk.
Added in version 244.
ReadWritePaths=, ReadOnlyPaths=, InaccessiblePaths=, ExecPaths=,
NoExecPaths=
Sets up a new file system namespace for executed processes.
These options may be used to limit access a process has to the
file system. Each setting takes a space-separated list of
paths relative to the host's root directory (i.e. the system
running the service manager). Note that if paths contain
symlinks, they are resolved relative to the root directory set
with RootDirectory=/RootImage=.
Paths listed in ReadWritePaths= are accessible from within the
namespace with the same access modes as from outside of it.
Paths listed in ReadOnlyPaths= are accessible for reading
only, writing will be refused even if the usual file access
controls would permit this. Nest ReadWritePaths= inside of
ReadOnlyPaths= in order to provide writable subdirectories
within read-only directories. Use ReadWritePaths= in order to
allow-list specific paths for write access if
ProtectSystem=strict is used. Note that ReadWritePaths= cannot
be used to gain write access to a file system whose superblock
is mounted read-only. On Linux, for each mount point write
access is granted only if the mount point itself and the file
system superblock backing it are not marked read-only.
ReadWritePaths= only controls the former, not the latter,
hence a read-only file system superblock remains protected.
Paths listed in InaccessiblePaths= will be made inaccessible
for processes inside the namespace along with everything below
them in the file system hierarchy. This may be more
restrictive than desired, because it is not possible to nest
ReadWritePaths=, ReadOnlyPaths=, BindPaths=, or
BindReadOnlyPaths= inside it. For a more flexible option, see
TemporaryFileSystem=.
Content in paths listed in NoExecPaths= are not executable
even if the usual file access controls would permit this. Nest
ExecPaths= inside of NoExecPaths= in order to provide
executable content within non-executable directories.
Non-directory paths may be specified as well. These options
may be specified more than once, in which case all paths
listed will have limited access from within the namespace. If
the empty string is assigned to this option, the specific list
is reset, and all prior assignments have no effect.
Paths in ReadWritePaths=, ReadOnlyPaths=, InaccessiblePaths=,
ExecPaths= and NoExecPaths= may be prefixed with "-", in which
case they will be ignored when they do not exist. If prefixed
with "+" the paths are taken relative to the root directory of
the unit, as configured with RootDirectory=/RootImage=,
instead of relative to the root directory of the host (see
above). When combining "-" and "+" on the same path make sure
to specify "-" first, and "+" second.
Note that these settings will disconnect propagation of mounts
from the unit's processes to the host. This means that this
setting may not be used for services which shall be able to
install mount points in the main mount namespace. For
ReadWritePaths= and ReadOnlyPaths=, propagation in the other
direction is not affected, i.e. mounts created on the host
generally appear in the unit processes' namespace, and mounts
removed on the host also disappear there too. In particular,
note that mount propagation from host to unit will result in
unmodified mounts to be created in the unit's namespace, i.e.
writable mounts appearing on the host will be writable in the
unit's namespace too, even when propagated below a path marked
with ReadOnlyPaths=! Restricting access with these options
hence does not extend to submounts of a directory that are
created later on. This means the lock-down offered by that
setting is not complete, and does not offer full protection.
Note that the effect of these settings may be undone by
privileged processes. In order to set up an effective
sandboxed environment for a unit it is thus recommended to
combine these settings with either
CapabilityBoundingSet=~CAP_SYS_ADMIN or
SystemCallFilter=~@mount.
Please be extra careful when applying these options to API
file systems (a list of them could be found in MountAPIVPS=),
since they may be required for basic system functionalities.
Moreover, /run/ needs to be writable for setting up mount
namespace and propagation.
Simple allow-list example using these directives:
[Service]
ReadOnlyPaths=/
ReadWritePaths=/var /run
InaccessiblePaths=-/lost+found
NoExecPaths=/
ExecPaths=/usr/sbin/my_daemon /usr/lib /usr/lib64
These options are only available for system services, or for
services running in per-user instances of the service manager
in which case PrivateUsers= is implicitly enabled (requires
unprivileged user namespaces support to be enabled in the
kernel via the "kernel.unprivileged_userns_clone=" sysctl).
Added in version 231.
TemporaryFileSystem=
Takes a space-separated list of mount points for temporary
file systems (tmpfs). If set, a new file system namespace is
set up for executed processes, and a temporary file system is
mounted on each mount point. This option may be specified more
than once, in which case temporary file systems are mounted on
all listed mount points. If the empty string is assigned to
this option, the list is reset, and all prior assignments have
no effect. Each mount point may optionally be suffixed with a
colon (":") and mount options such as "size=10%" or "ro". By
default, each temporary file system is mounted with
"nodev,strictatime,mode=0755". These can be disabled by
explicitly specifying the corresponding mount options, e.g.,
"dev" or "nostrictatime".
This is useful to hide files or directories not relevant to
the processes invoked by the unit, while necessary files or
directories can be still accessed by combining with BindPaths=
or BindReadOnlyPaths=:
Example: if a unit has the following,
TemporaryFileSystem=/var:ro
BindReadOnlyPaths=/var/lib/systemd
then the invoked processes by the unit cannot see any files or
directories under /var/ except for /var/lib/systemd or its
contents.
This option is only available for system services, or for
services running in per-user instances of the service manager
in which case PrivateUsers= is implicitly enabled (requires
unprivileged user namespaces support to be enabled in the
kernel via the "kernel.unprivileged_userns_clone=" sysctl).
Added in version 238.
PrivateTmp=
Takes a boolean argument, or "disconnected". If enabled, a new
file system namespace will be set up for the executed
processes, and /tmp/ and /var/tmp/ directories inside it are
not shared with processes outside of the namespace, plus all
temporary files created by a service in these directories will
be removed after the service is stopped. For this setting, the
same restrictions regarding mount propagation and privileges
apply as for ReadOnlyPaths= and related calls, see above. This
setting is useful to secure access to temporary files of the
process, but makes sharing between processes via /tmp/ or
/var/tmp/ impossible. If DynamicUser= is enabled,
"disconnected" is implied. Otherwise, defaults to false.
If "true", the backing storage of the private temporary
directories will remain on the host's /tmp/ and /var/tmp/
directories. It is possible to run two or more units within
the same private /tmp/ and /var/tmp/ namespace by using the
JoinsNamespaceOf= directive, see systemd.unit(5) for details.
This has the side effect of adding Wants= and After=
dependencies on all mount units necessary to access /tmp/ and
/var/tmp/ on the host. Moreover, an implicit After= ordering
on systemd-tmpfiles-setup.service(8) is added.
If "disconnected", the directories will be backed by a
completely new tmpfs instance, meaning that the storage is
fully disconnected from the host namespace. The tmpfs instance
does not shared with other units even if the JoinsNamespaceOf=
directive is used. If DefaultDependencies=no is specified,
RequiresMountsFor=/WantsMountsFor= for /var/ is not specified,
and RootDirectory=/RootImage= is not specified, then a new
tmpfs is mounted only on /tmp/, hence the host's /var/tmp is
still accessible from the unit. In that case, $TMPDIR
environment variable is set to "/tmp" to suggest the processes
in the unit to use /tmp/. This automatically adds
WantsMountsFor=/var/ dependency, unless DefaultDependencies=no
and/or RootDirectory=/RootImage= are specified.
Table 3. Summary for PrivateTmp=disconnected
┌───────────────────────────┬───────────┬──────────────┬──────────────────────┐
│ Other Settings │ tmpfs on │ $TMPVAR │ implied │
│ │ /var/tmp/ │ │ dependencies │
├───────────────────────────┼───────────┼──────────────┼──────────────────────┤
│ (none) │ yes │ (unset) │ WantsMountsFor=/var/ │
├───────────────────────────┼───────────┼──────────────┼──────────────────────┤
│ RootDirectory=/RootImage= │ yes │ (unset) │ (none) │
├───────────────────────────┼───────────┼──────────────┼──────────────────────┤
│ DefaultDependency=no, │ yes │ (unset) │ (none) │
│ RequiresMountsFor=/var/ │ │ │ │
├───────────────────────────┼───────────┼──────────────┼──────────────────────┤
│ DefaultDependency=no, │ yes │ (unset) │ (none) │
│ WantsMountsFor=/var/ │ │ │ │
├───────────────────────────┼───────────┼──────────────┼──────────────────────┤
│ DefaultDependency=no │ no │ $TMPDIR=/tmp │ (none) │
└───────────────────────────┴───────────┴──────────────┴──────────────────────┘
Note that the implementation of this setting might be
impossible (for example if mount namespaces are not
available), and the unit should be written in a way that does
not solely rely on this setting for security.
This option is only available for system services, or for
services running in per-user instances of the service manager
in which case PrivateUsers= is implicitly enabled (requires
unprivileged user namespaces support to be enabled in the
kernel via the "kernel.unprivileged_userns_clone=" sysctl).
PrivateDevices=
Takes a boolean argument. If true, sets up a new /dev/ mount
for the executed processes and only adds API pseudo devices
such as /dev/null, /dev/zero or /dev/random (as well as the
pseudo TTY subsystem) to it, but no physical devices such as
/dev/sda, system memory /dev/mem, system ports /dev/port and
others. This is useful to turn off physical device access by
the executed process. Defaults to false.
Enabling this option will install a system call filter to
block low-level I/O system calls that are grouped in the
@raw-io set, remove CAP_MKNOD and CAP_SYS_RAWIO from the
capability bounding set for the unit, and set
DevicePolicy=closed (see systemd.resource-control(5) for
details). Note that using this setting will disconnect
propagation of mounts from the service to the host
(propagation in the opposite direction continues to work).
This means that this setting may not be used for services
which shall be able to install mount points in the main mount
namespace. The new /dev/ will be mounted read-only and
'noexec'. The latter may break old programs which try to set
up executable memory by using mmap(2) of /dev/zero instead of
using MAP_ANON. For this setting the same restrictions
regarding mount propagation and privileges apply as for
ReadOnlyPaths= and related calls, see above.
Note that the implementation of this setting might be
impossible (for example if mount namespaces are not
available), and the unit should be written in a way that does
not solely rely on this setting for security.
This option is only available for system services, or for
services running in per-user instances of the service manager
in which case PrivateUsers= is implicitly enabled (requires
unprivileged user namespaces support to be enabled in the
kernel via the "kernel.unprivileged_userns_clone=" sysctl).
When access to some but not all devices must be possible, the
DeviceAllow= setting might be used instead. See
systemd.resource-control(5).
Added in version 209.
PrivateNetwork=
Takes a boolean argument. If true, sets up a new network
namespace for the executed processes and configures only the
loopback network device "lo" inside it. No other network
devices will be available to the executed process. This is
useful to turn off network access by the executed process.
Defaults to false. It is possible to run two or more units
within the same private network namespace by using the
JoinsNamespaceOf= directive, see systemd.unit(5) for details.
Note that this option will disconnect all socket families from
the host, including AF_NETLINK and AF_UNIX. Effectively, for
AF_NETLINK this means that device configuration events
received from systemd-udevd.service(8) are not delivered to
the unit's processes. And for AF_UNIX this has the effect that
AF_UNIX sockets in the abstract socket namespace of the host
will become unavailable to the unit's processes (however,
those located in the file system will continue to be
accessible).
Note that the implementation of this setting might be
impossible (for example if network namespaces are not
available), and the unit should be written in a way that does
not solely rely on this setting for security.
When this option is enabled, PrivateMounts= is implied unless
it is explicitly disabled, and /sys will be remounted to
associate it with the new network namespace.
When this option is used on a socket unit any sockets bound on
behalf of this unit will be bound within a private network
namespace. This may be combined with JoinsNamespaceOf= to
listen on sockets inside of network namespaces of other
services.
This option is only available for system services, or for
services running in per-user instances of the service manager
in which case PrivateUsers= is implicitly enabled (requires
unprivileged user namespaces support to be enabled in the
kernel via the "kernel.unprivileged_userns_clone=" sysctl).
NetworkNamespacePath=
Takes an absolute file system path referring to a Linux
network namespace pseudo-file (i.e. a file like
/proc/$PID/ns/net or a bind mount or symlink to one). When set
the invoked processes are added to the network namespace
referenced by that path. The path has to point to a valid
namespace file at the moment the processes are forked off. If
this option is used PrivateNetwork= has no effect. If this
option is used together with JoinsNamespaceOf= then it only
has an effect if this unit is started before any of the listed
units that have PrivateNetwork= or NetworkNamespacePath=
configured, as otherwise the network namespace of those units
is reused.
When this option is enabled, PrivateMounts= is implied unless
it is explicitly disabled, and /sys will be remounted to
associate it with the new network namespace.
When this option is used on a socket unit any sockets bound on
behalf of this unit will be bound within the specified network
namespace.
This option is only available for system services, or for
services running in per-user instances of the service manager
in which case PrivateUsers= is implicitly enabled (requires
unprivileged user namespaces support to be enabled in the
kernel via the "kernel.unprivileged_userns_clone=" sysctl).
Added in version 242.
PrivateIPC=
Takes a boolean argument. If true, sets up a new IPC namespace
for the executed processes. Each IPC namespace has its own set
of System V IPC identifiers and its own POSIX message queue
file system. This is useful to avoid name clash of IPC
identifiers. Defaults to false. It is possible to run two or
more units within the same private IPC namespace by using the
JoinsNamespaceOf= directive, see systemd.unit(5) for details.
Note that IPC namespacing does not have an effect on AF_UNIX
sockets, which are the most common form of IPC used on Linux.
Instead, AF_UNIX sockets in the file system are subject to
mount namespacing, and those in the abstract namespace are
subject to network namespacing. IPC namespacing only has an
effect on SysV IPC (which is mostly legacy) as well as POSIX
message queues (for which AF_UNIX/SOCK_SEQPACKET sockets are
typically a better replacement). IPC namespacing also has no
effect on POSIX shared memory (which is subject to mount
namespacing) either. See ipc_namespaces(7) for the details.
Note that the implementation of this setting might be
impossible (for example if IPC namespaces are not available),
and the unit should be written in a way that does not solely
rely on this setting for security.
This option is only available for system services, or for
services running in per-user instances of the service manager
in which case PrivateUsers= is implicitly enabled (requires
unprivileged user namespaces support to be enabled in the
kernel via the "kernel.unprivileged_userns_clone=" sysctl).
Added in version 248.
IPCNamespacePath=
Takes an absolute file system path referring to a Linux IPC
namespace pseudo-file (i.e. a file like /proc/$PID/ns/ipc or a
bind mount or symlink to one). When set the invoked processes
are added to the network namespace referenced by that path.
The path has to point to a valid namespace file at the moment
the processes are forked off. If this option is used
PrivateIPC= has no effect. If this option is used together
with JoinsNamespaceOf= then it only has an effect if this unit
is started before any of the listed units that have
PrivateIPC= or IPCNamespacePath= configured, as otherwise the
network namespace of those units is reused.
This option is only available for system services, or for
services running in per-user instances of the service manager
in which case PrivateUsers= is implicitly enabled (requires
unprivileged user namespaces support to be enabled in the
kernel via the "kernel.unprivileged_userns_clone=" sysctl).
Added in version 248.
MemoryKSM=
Takes a boolean argument. When set, it enables KSM (kernel
samepage merging) for the processes. KSM is a memory-saving
de-duplication feature. Anonymous memory pages with identical
content can be replaced by a single write-protected page. This
feature should only be enabled for jobs that share the same
security domain. For details, see Kernel Samepage Merging[12]
in the kernel documentation.
Note that this functionality might not be available, for
example if KSM is disabled in the kernel, or the kernel does
not support controlling KSM at the process level through
prctl(2).
Added in version 254.
PrivatePIDs=
Takes a boolean argument. Defaults to false. If enabled, sets
up a new PID namespace for the executed processes. Each
executed process is now PID 1 - the init process - in the new
namespace. /proc/ is mounted such that only processes in the
PID namespace are visible. If PrivatePIDs= is set,
MountAPIVFS=yes is implied.
PrivatePIDs= is only supported for service units. This setting
is not supported with Type=forking since the kernel will kill
all processes in the PID namespace if the init process
terminates.
This setting will be ignored if the kernel does not support
PID namespaces.
Note unprivileged user services (i.e. a service run by the
per-user instance of the service manager) will fail with
PrivatePIDs=yes if /proc/ is masked (i.e. /proc/kmsg is
over-mounted with tmpfs like systemd-nspawn(1) does). This is
due to a kernel restriction not allowing unprivileged user
namespaces to mount a less restrictive instance of /proc/.
Added in version 257.
PrivateUsers=
Takes a boolean argument or one of "self", "identity", or
"full". Defaults to false. If enabled, sets up a new user
namespace for the executed processes and configures a user and
group mapping. If set to a true value or "self", a minimal
user and group mapping is configured that maps the "root" user
and group as well as the unit's own user and group to
themselves and everything else to the "nobody" user and group.
This is useful to securely detach the user and group databases
used by the unit from the rest of the system, and thus to
create an effective sandbox environment. All files,
directories, processes, IPC objects and other resources owned
by users/groups not equaling "root" or the unit's own will
stay visible from within the unit but appear owned by the
"nobody" user and group.
If the parameter is "identity", user namespacing is set up
with an identity mapping for the first 65536 UIDs/GIDs. Any
UIDs/GIDs above 65536 will be mapped to the "nobody" user and
group, respectively. While this does not provide UID/GID
isolation, since all UIDs/GIDs are chosen identically it does
provide process capability isolation, and hence is often a
good choice if proper user namespacing with distinct UID maps
is not appropriate.
If the parameter is "full", user namespacing is set up with an
identity mapping for all UIDs/GIDs. In addition, for system
services, "full" allows the unit to call setgroups() system
calls (by setting /proc/pid/setgroups to "allow"). Similar to
"identity", this does not provide UID/GID isolation, but it
does provide process capability isolation.
If this mode is enabled, all unit processes are run without
privileges in the host user namespace (regardless of whether
the unit's own user/group is "root" or not). Specifically this
means that the process will have zero process capabilities on
the host's user namespace, but full capabilities within the
service's user namespace. Settings such as
CapabilityBoundingSet= will affect only the latter, and
there's no way to acquire additional capabilities in the
host's user namespace.
When this setting is set up by a per-user instance of the
service manager, the mapping of the "root" user and group to
itself is omitted (unless the user manager is root).
Additionally, in the per-user instance manager case, the user
namespace will be set up before most other namespaces. This
means that combining PrivateUsers=true with other namespaces
will enable use of features not normally supported by the
per-user instances of the service manager.
This setting is particularly useful in conjunction with
RootDirectory=/RootImage=, as the need to synchronize the user
and group databases in the root directory and on the host is
reduced, as the only users and groups who need to be matched
are "root", "nobody" and the unit's own user and group.
Added in version 232.
ProtectHostname=
Takes a boolean argument or "private". If enabled, sets up a
new UTS namespace for the executed processes. If enabled, a
hostname can be optionally specified following a colon (e.g.
"yes:foo" or "private:host.example.com"), and the hostname is
set in the new UTS namespace for the unit. If set to a true
value, changing hostname or domainname via sethostname() and
setdomainname() system calls is prevented. If set to
"private", changing hostname or domainname is allowed but only
affects the unit's UTS namespace. Defaults to off.
Note that the implementation of this setting might be
impossible (for example if UTS namespaces are not available),
and the unit should be written in a way that does not solely
rely on this setting for security.
Note that when this option is enabled for a service hostname
changes no longer propagate from the system into the service,
it is hence not suitable for services that need to take notice
of system hostname changes dynamically.
Note that this option does not prevent changing system
hostname via hostnamectl. However, User= and Group= may be
used to run as an unprivileged user to disallow changing
system hostname. See SetHostname() in
org.freedesktop.hostname1(5) for more details.
This option is only available for system services, or for
services running in per-user instances of the service manager
in which case PrivateUsers= is implicitly enabled (requires
unprivileged user namespaces support to be enabled in the
kernel via the "kernel.unprivileged_userns_clone=" sysctl).
Added in version 242.
ProtectClock=
Takes a boolean argument. If set, writes to the hardware clock
or system clock will be denied. Defaults to off. Enabling this
option removes CAP_SYS_TIME and CAP_WAKE_ALARM from the
capability bounding set for this unit, installs a system call
filter to block calls that can set the clock, and
DeviceAllow=char-rtc r is implied. Note that the system calls
are blocked altogether, the filter does not take into account
that some of the calls can be used to read the clock state
with some parameter combinations. Effectively, /dev/rtc0,
/dev/rtc1, etc. are made read-only to the service. See
systemd.resource-control(5) for the details about
DeviceAllow=.
It is recommended to turn this on for most services that do
not need modify the clock or check its state.
This option is only available for system services, or for
services running in per-user instances of the service manager
in which case PrivateUsers= is implicitly enabled (requires
unprivileged user namespaces support to be enabled in the
kernel via the "kernel.unprivileged_userns_clone=" sysctl).
Added in version 245.
ProtectKernelTunables=
Takes a boolean argument. If true, kernel variables accessible
through /proc/sys/, /sys/, /proc/sysrq-trigger,
/proc/latency_stats, /proc/acpi, /proc/timer_stats, /proc/fs
and /proc/irq will be made read-only and /proc/kallsyms as
well as /proc/kcore will be inaccessible to all processes of
the unit. Usually, tunable kernel variables should be
initialized only at boot-time, for example with the
sysctl.d(5) mechanism. Few services need to write to these at
runtime; it is hence recommended to turn this on for most
services. For this setting the same restrictions regarding
mount propagation and privileges apply as for ReadOnlyPaths=
and related calls, see above. Defaults to off. Note that this
option does not prevent indirect changes to kernel tunables
affected by IPC calls to other processes. However,
InaccessiblePaths= may be used to make relevant IPC file
system objects inaccessible. If ProtectKernelTunables= is set,
MountAPIVFS=yes is implied.
This option is only available for system services, or for
services running in per-user instances of the service manager
in which case PrivateUsers= is implicitly enabled (requires
unprivileged user namespaces support to be enabled in the
kernel via the "kernel.unprivileged_userns_clone=" sysctl).
Added in version 232.
ProtectKernelModules=
Takes a boolean argument. If true, explicit module loading
will be denied. This allows module load and unload operations
to be turned off on modular kernels. It is recommended to turn
this on for most services that do not need special file
systems or extra kernel modules to work. Defaults to off.
Enabling this option removes CAP_SYS_MODULE from the
capability bounding set for the unit, and installs a system
call filter to block module system calls, also
/usr/lib/modules is made inaccessible. For this setting the
same restrictions regarding mount propagation and privileges
apply as for ReadOnlyPaths= and related calls, see above. Note
that limited automatic module loading due to user
configuration or kernel mapping tables might still happen as
side effect of requested user operations, both privileged and
unprivileged. To disable module auto-load feature please see
sysctl.d(5) kernel.modules_disabled mechanism and
/proc/sys/kernel/modules_disabled documentation.
This option is only available for system services, or for
services running in per-user instances of the service manager
in which case PrivateUsers= is implicitly enabled (requires
unprivileged user namespaces support to be enabled in the
kernel via the "kernel.unprivileged_userns_clone=" sysctl).
Added in version 232.
ProtectKernelLogs=
Takes a boolean argument. If true, access to the kernel log
ring buffer will be denied. It is recommended to turn this on
for most services that do not need to read from or write to
the kernel log ring buffer. Enabling this option removes
CAP_SYSLOG from the capability bounding set for this unit, and
installs a system call filter to block the syslog(2) system
call (not to be confused with the libc API syslog(3) for
userspace logging). The kernel exposes its log buffer to
userspace via /dev/kmsg and /proc/kmsg. If enabled, these are
made inaccessible to all the processes in the unit.
This option is only available for system services, or for
services running in per-user instances of the service manager
in which case PrivateUsers= is implicitly enabled (requires
unprivileged user namespaces support to be enabled in the
kernel via the "kernel.unprivileged_userns_clone=" sysctl).
Added in version 244.
ProtectControlGroups=
Takes a boolean argument or the special values "private" or
"strict". If true, the Linux Control Groups (cgroups(7))
hierarchies accessible through /sys/fs/cgroup/ will be made
read-only to all processes of the unit. If set to "private",
the unit will run in a cgroup namespace with a private
writable mount of /sys/fs/cgroup/. If set to "strict", the
unit will run in a cgroup namespace with a private read-only
mount of /sys/fs/cgroup/. Defaults to off. If
ProtectControlGroups= is set, MountAPIVFS=yes is implied. Note
"private" and "strict" are downgraded to false and true
respectively unless the system is using the unified control
group hierarchy and the kernel supports cgroup namespaces.
Except for container managers no services should require write
access to the control groups hierarchies; it is hence
recommended to set ProtectControlGroups= to true or "strict"
for most services. For this setting the same restrictions
regarding mount propagation and privileges apply as for
ReadOnlyPaths= and related settings, see above.
This option is only available for system services and is not
supported for services running in per-user instances of the
service manager.
Added in version 232.
RestrictAddressFamilies=
Restricts the set of socket address families accessible to the
processes of this unit. Takes "none", or a space-separated
list of address family names to allow-list, such as AF_UNIX,
AF_INET or AF_INET6, see address_families(7) for all possible
options. When "none" is specified, then all address families
will be denied. When prefixed with "~" the listed address
families will be applied as deny list, otherwise as allow
list.
By default, no restrictions apply, all address families are
accessible to processes. If assigned the empty string, any
previous address family restriction changes are undone. This
setting does not affect commands prefixed with "+".
Use this option to limit exposure of processes to remote
access, in particular via exotic and sensitive network
protocols, such as AF_PACKET. Note that in most cases, the
local AF_UNIX address family should be included in the
configured allow list as it is frequently used for local
communication, including for syslog(2) logging.
Note that this restricts access to the socket(2) system call
only. Sockets passed into the process by other means (for
example, by using socket activation with socket units, see
systemd.socket(5)) are unaffected. Also, sockets created with
socketpair() (which creates connected AF_UNIX sockets) or the
io_uring(7) functions, are not affected. Thus, it is
recommended to combined this setting with
SystemCallFilter=@service, to only allow a limited subset of
system calls.
Note that this option is limited to some ABIs, in particular
x86-64, but currently has no effect on 32-bit x86, s390,
s390x, mips, mips-le, ppc, ppc-le, ppc64, or ppc64-le, and is
ignored. On systems supporting multiple ABIs (such as
x86/x86-64) it is recommended to turn off alternative ABIs for
services, so that they cannot be used to circumvent the
restrictions of this option. Specifically, it is recommended
to combine this option with SystemCallArchitectures=native or
similar.
Added in version 211.
RestrictFileSystems=
Restricts the set of filesystems processes of this unit can
open files on. Takes a space-separated list of filesystem
names. Any filesystem listed is made accessible to the unit's
processes, access to filesystem types not listed is prohibited
(allow-listing). If the first character of the list is "~",
the effect is inverted: access to the filesystems listed is
prohibited (deny-listing). If the empty string is assigned,
access to filesystems is not restricted.
If you specify both types of this option (i.e. allow-listing
and deny-listing), the first encountered will take precedence
and will dictate the default action (allow access to the
filesystem or deny it). Then the next occurrences of this
option will add or delete the listed filesystems from the set
of the restricted filesystems, depending on its type and the
default action.
Example: if a unit has the following,
RestrictFileSystems=ext4 tmpfs
RestrictFileSystems=ext2 ext4
then access to ext4, tmpfs, and ext2 is allowed and access to
other filesystems is denied.
Example: if a unit has the following,
RestrictFileSystems=ext4 tmpfs
RestrictFileSystems=~ext4
then only access tmpfs is allowed.
Example: if a unit has the following,
RestrictFileSystems=~ext4 tmpfs
RestrictFileSystems=ext4
then only access to tmpfs is denied.
As the number of possible filesystems is large, predefined
sets of filesystems are provided. A set starts with "@"
character, followed by name of the set.
Table 4. Currently predefined filesystem sets
┌───────────────────┬──────────────────────────┐
│ Set │ Description │
├───────────────────┼──────────────────────────┤
│ @basic-api │ Basic filesystem API. │
├───────────────────┼──────────────────────────┤
│ @auxiliary-api │ Auxiliary filesystem │
│ │ API. │
├───────────────────┼──────────────────────────┤
│ @common-block │ Common block device │
│ │ filesystems. │
├───────────────────┼──────────────────────────┤
│ @historical-block │ Historical block device │
│ │ filesystems. │
├───────────────────┼──────────────────────────┤
│ @network │ Well-known network │
│ │ filesystems. │
├───────────────────┼──────────────────────────┤
│ @privileged-api │ Privileged filesystem │
│ │ API. │
├───────────────────┼──────────────────────────┤
│ @temporary │ Temporary filesystems: │
│ │ tmpfs, ramfs. │
├───────────────────┼──────────────────────────┤
│ @known │ All known filesystems │
│ │ defined by the kernel. │
│ │ This list is defined │
│ │ statically in systemd │
│ │ based on a kernel │
│ │ version that was │
│ │ available when this │
│ │ systemd version was │
│ │ released. It will become │
│ │ progressively more │
│ │ out-of-date as the │
│ │ kernel is updated. │
└───────────────────┴──────────────────────────┘
Use systemd-analyze(1)'s filesystems command to retrieve a
list of filesystems defined on the local system.
Note that this setting might not be supported on some systems
(for example if the LSM eBPF hook is not enabled in the
underlying kernel or if not using the unified control group
hierarchy). In that case this setting has no effect.
This option cannot be bypassed by prefixing "+" to the
executable path in the service unit, as it applies to the
whole control group.
Added in version 250.
RestrictNamespaces=
Restricts access to Linux namespace functionality for the
processes of this unit. For details about Linux namespaces,
see namespaces(7). Either takes a boolean argument, or a
space-separated list of namespace type identifiers. If false
(the default), no restrictions on namespace creation and
switching are made. If true, access to any kind of namespacing
is prohibited. Otherwise, a space-separated list of namespace
type identifiers must be specified, consisting of any
combination of: cgroup, ipc, net, mnt, pid, user, uts, and
time. Any namespace type listed is made accessible to the
unit's processes, access to namespace types not listed is
prohibited (allow-listing). By prepending the list with a
single tilde character ("~") the effect may be inverted: only
the listed namespace types will be made inaccessible, all
unlisted ones are permitted (deny-listing). If the empty
string is assigned, the default namespace restrictions are
applied, which is equivalent to false. This option may appear
more than once, in which case the namespace types are merged
by OR, or by AND if the lines are prefixed with "~" (see
examples below). Internally, this setting limits access to the
unshare(2), clone(2) and setns(2) system calls, taking the
specified flags parameters into account. Note that — if this
option is used — in addition to restricting creation and
switching of the specified types of namespaces (or all of
them, if true) access to the setns() system call with a zero
flags parameter is prohibited. This setting is only supported
on x86, x86-64, mips, mips-le, mips64, mips64-le, mips64-n32,
mips64-le-n32, ppc64, ppc64-le, s390 and s390x, and enforces
no restrictions on other architectures.
Example: if a unit has the following,
RestrictNamespaces=cgroup ipc
RestrictNamespaces=cgroup net
then cgroup, ipc, and net are set. If the second line is
prefixed with "~", e.g.,
RestrictNamespaces=cgroup ipc
RestrictNamespaces=~cgroup net
then, only ipc is set.
Added in version 233.
DelegateNamespaces=
Delegates ownership of the given namespace types to the user
namespace of the processes of this unit. For details about
Linux namespaces, see namespaces(7). Either takes a boolean
argument, or a space-separated list of namespace type
identifiers. If false (the default), the unit's processes'
user namespace will not have ownership over any namespaces
created during setup of the unit's sandboxed environment. If
true, ownership of all namespace types (except for user
namespaces, where the concept doesn't apply) created during
setup of the unit's sandboxed environment is delegated to the
unit's processes' user namespace. Otherwise, a space-separated
list of namespace type identifiers must be specified,
consisting of any combination of: cgroup, ipc, net, mnt, pid,
and uts. All namespaces of the listed types will be owned by
the unit's processes' user namespace if they are created
during setup of the unit's sandboxed environment
(allow-listing). By prepending the list with a single tilde
character ("~") the effect may be inverted: all namespaces of
types not listed and created during setup of the unit's
sandboxed environment will be owned by the unit's processes'
user namespace (deny-listing). If the empty string is
assigned, the default namespace ownership is applied, which is
equivalent to false. This option may appear more than once, in
which case the namespace types are merged by OR, or by AND if
the lines are prefixed with "~" (see examples below).
Internally, this setting controls the order in which
namespaces are unshared by systemd. Namespace types that
should be owned by the unit's processes' user namespace will
be unshared after unsharing the user namespace. Internally,
this setting controls the order in which namespaces are
unshared. Delegated namespaces will be unshared after the user
namespace is unshared. Other namespaces will be unshared
before the user namespace is unshared.
Delegating any namespace with DelegateNamespaces= implies
PrivateUsers=self unless PrivateUsers= is explicitly enabled
already by the unit. Delegating a namespace does not imply
that the namespace is unshared, that is done with the
namespace specific unit setting such as PrivateNetwork= or
PrivateMounts=.
Note that some namespace sandboxing options might entail mount
namespace for private API VFS instances, such as PrivatePIDs=,
ProtectControlGroups=private/strict, or PrivateNetwork=. If
any of the mentioned options are enabled, mount namespace is
implicitly delegated.
Added in version 258.
PrivateBPF=
Takes a boolean argument. If set, mount a private instance of
the BPF filesystem on /sys/fs/bpf/, effectively hiding the
host bpffs which contains information about loaded programs
and maps. Otherwise, if ProtectKernelTunables= is set, the
instance from the host is inherited but mounted read-only.
Defaults to false.
This can be used together with the bpffs delegate feature to
choose what BPF functions are available to the unit's
processes. When mounting the BPF filesystem with the fsopen()
API, four mount options can be specified to set a list of BPF
commands, maps, programs and attachment types that are allowed
to be used. Processes needs to get a file descriptor for the
bpffs mountpoint and use that to get a token which will enable
for that user namespace the BPF functionalities chosen upon
bpffs mount. A more detailed explanation of the feature can be
found in this LWN post[13].
Added in version 258.
BPFDelegateCommands=
Accepts a list of BPF commands to allow or "any" to allow
everything. Defaults to none. The accepted values are:
BPFMapCreate BPFMapLookupElem BPFMapUpdateElem
BPFMapDeleteElem BPFMapGetNextKey BPFProgLoad BPFObjPin
BPFObjGet BPFProgAttach BPFProgDetach BPFProgTestRun
BPFProgGetNextId BPFMapGetNextId BPFProgGetFdById
BPFMapGetFdById BPFObjGetInfoByFd BPFProgQuery
BPFRawTracepointOpen BPFBtfLoad BPFBtfGetFdById BPFTaskFdQuery
BPFMapLookupAndDeleteElem BPFMapFreeze BPFBtfGetNextId
BPFMapLookupBatch BPFMapLookupAndDeleteBatch BPFMapUpdateBatch
BPFMapDeleteBatch BPFLinkCreate BPFLinkUpdate BPFLinkGetFdById
BPFLinkGetNextId BPFEnableStats BPFIterCreate BPFLinkDetach
BPFProgBindMap BPFTokenCreate This will set the delegate_cmds
bpffs mount option.
Requires PrivateBPF=yes to be effective, see PrivateBPF= more
details.
Added in version 258.
BPFDelegateMaps=
Accepts a list of BPF maps to allow or "any" to allow
everything. Defaults to none. The accepted values are:
BPFMapTypeUnspec BPFMapTypeHash BPFMapTypeArray
BPFMapTypeProgArray BPFMapTypePerfEventArray
BPFMapTypePercpuHash BPFMapTypePercpuArray
BPFMapTypeStackTrace BPFMapTypeCgroupArray BPFMapTypeLruHash
BPFMapTypeLruPercpuHash BPFMapTypeLpmTrie
BPFMapTypeArrayOfMaps BPFMapTypeHashOfMaps BPFMapTypeDevmap
BPFMapTypeSockmap BPFMapTypeCpumap BPFMapTypeXskmap
BPFMapTypeSockhash BPFMapTypeCgroupStorageDeprecated
BPFMapTypeReuseportSockarray
BPFMapTypePercpuCgroupStorageDeprecated BPFMapTypeQueue
BPFMapTypeStack BPFMapTypeSkStorage BPFMapTypeDevmapHash
BPFMapTypeStructOps BPFMapTypeRingbuf BPFMapTypeInodeStorage
BPFMapTypeTaskStorage BPFMapTypeBloomFilter
BPFMapTypeUserRingbuf BPFMapTypeCgrpStorage BPFMapTypeArena
This will set the delegate_maps bpffs mount option.
Requires PrivateBPF=yes to be effective, see PrivateBPF= more
details.
Added in version 258.
BPFDelegatePrograms=
Accepts a list of BPF programs to allow or "any" to allow
everything. Defaults to none. The accepted values are:
BPFProgTypeUnspec BPFProgTypeSocketFilter BPFProgTypeKprobe
BPFProgTypeSchedCls BPFProgTypeSchedAct BPFProgTypeTracepoint
BPFProgTypeXdp BPFProgTypePerfEvent BPFProgTypeCgroupSkb
BPFProgTypeCgroupSock BPFProgTypeLwtIn BPFProgTypeLwtOut
BPFProgTypeLwtXmit BPFProgTypeSockOps BPFProgTypeSkSkb
BPFProgTypeCgroupDevice BPFProgTypeSkMsg
BPFProgTypeRawTracepoint BPFProgTypeCgroupSockAddr
BPFProgTypeLwtSeg6local BPFProgTypeLircMode2
BPFProgTypeSkReuseport BPFProgTypeFlowDissector
BPFProgTypeCgroupSysctl BPFProgTypeRawTracepointWritable
BPFProgTypeCgroupSockopt BPFProgTypeTracing
BPFProgTypeStructOps BPFProgTypeExt BPFProgTypeLsm
BPFProgTypeSkLookup BPFProgTypeNetfilter This will set the
delegate_progs bpffs mount option.
Requires PrivateBPF=yes to be effective, see PrivateBPF= more
details.
Added in version 258.
BPFDelegateAttachments=
Accepts a list of BPF attach points to allow or "any" to allow
everything. Defaults to none. The accepted values are:
BPFCgroupInetIngress BPFCgroupInetEgress
BPFCgroupInetSockCreate BPFCgroupSockOps BPFSkSkbStreamParser
BPFSkSkbStreamVerdict BPFCgroupDevice BPFSkMsgVerdict
BPFCgroupInet4Bind BPFCgroupInet6Bind BPFCgroupInet4Connect
BPFCgroupInet6Connect BPFCgroupInet4PostBind
BPFCgroupInet6PostBind BPFCgroupUdp4Sendmsg
BPFCgroupUdp6Sendmsg BPFLircMode2 BPFFlowDissector
BPFCgroupSysctl BPFCgroupUdp4Recvmsg BPFCgroupUdp6Recvmsg
BPFCgroupGetsockopt BPFCgroupSetsockopt BPFTraceRawTp
BPFTraceFentry BPFTraceFexit BPFModifyReturn BPFLsmMac
BPFTraceIter BPFCgroupInet4Getpeername
BPFCgroupInet6Getpeername BPFCgroupInet4Getsockname
BPFCgroupInet6Getsockname BPFXdpDevmap
BPFCgroupInetSockRelease BPFXdpCpumap BPFSkLookup BPFXdp
BPFSkSkbVerdict BPFSkReuseportSelect
BPFSkReuseportSelectOrMigrate BPFPerfEvent BPFTraceKprobeMulti
BPFLsmCgroup BPFStructOps BPFNetfilter BPFTcxIngress
BPFTcxEgress BPFTraceUprobeMulti BPFCgroupUnixConnect
BPFCgroupUnixSendmsg BPFCgroupUnixRecvmsg
BPFCgroupUnixGetpeername BPFCgroupUnixGetsockname
BPFNetkitPrimary BPFNetkitPeer BPFTraceKprobeSession
BPFTraceUprobeSession This will set the delegate_attachs bpffs
mount option.
Requires PrivateBPF=yes to be effective, see PrivateBPF= more
details.
Added in version 258.
LockPersonality=
Takes a boolean argument. If set, locks down the
personality(2) system call so that the kernel execution domain
may not be changed from the default or the personality
selected with Personality= directive. This may be useful to
improve security, because odd personality emulations may be
poorly tested and source of vulnerabilities.
Added in version 235.
MemoryDenyWriteExecute=
Takes a boolean argument. If set, attempts to create memory
mappings that are writable and executable at the same time, or
to change existing memory mappings to become executable, or
mapping shared memory segments as executable, are prohibited.
Specifically, a system call filter is added (or preferably, an
equivalent kernel check is enabled with prctl(2)) that rejects
mmap(2) system calls with both PROT_EXEC and PROT_WRITE set,
mprotect(2) or pkey_mprotect(2) system calls with PROT_EXEC
set and shmat(2) system calls with SHM_EXEC set. Note that
this option is incompatible with programs and libraries that
generate program code dynamically at runtime, including JIT
execution engines, executable stacks, and code "trampoline"
feature of various C compilers. This option improves service
security, as it makes harder for software exploits to change
running code dynamically. However, the protection can be
circumvented, if the service can write to a filesystem, which
is not mounted with noexec (such as /dev/shm), or it can use
memfd_create(). This can be prevented by making such file
systems inaccessible to the service (e.g.
InaccessiblePaths=/dev/shm) and installing further system call
filters (SystemCallFilter=~memfd_create). Note that this
feature is fully available on x86-64, and partially on x86.
Specifically, the shmat() protection is not available on x86.
Note that on systems supporting multiple ABIs (such as
x86/x86-64) it is recommended to turn off alternative ABIs for
services, so that they cannot be used to circumvent the
restrictions of this option. Specifically, it is recommended
to combine this option with SystemCallArchitectures=native or
similar.
Added in version 231.
RestrictRealtime=
Takes a boolean argument. If set, any attempts to enable
realtime scheduling in a process of the unit are refused. This
restricts access to realtime task scheduling policies such as
SCHED_FIFO, SCHED_RR or SCHED_DEADLINE. See sched(7) for
details about these scheduling policies. Realtime scheduling
policies may be used to monopolize CPU time for longer periods
of time, and may hence be used to lock up or otherwise trigger
Denial-of-Service situations on the system. It is hence
recommended to restrict access to realtime scheduling to the
few programs that actually require them. Defaults to off.
Added in version 231.
RestrictSUIDSGID=
Takes a boolean argument. If set, any attempts to set the
set-user-ID (SUID) or set-group-ID (SGID) bits on files or
directories will be denied (for details on these bits see
inode(7)). As the SUID/SGID bits are mechanisms to elevate
privileges, and allow users to acquire the identity of other
users, it is recommended to restrict creation of SUID/SGID
files to the few programs that actually require them. Note
that this restricts marking of any type of file system object
with these bits, including both regular files and directories
(where the SGID is a different meaning than for files, see
documentation). This option is implied if DynamicUser= is
enabled.
In other cases, this setting defaults to the value set with
DefaultRestrictSUIDSGID= in systemd-system.conf(5), which
defaults to off.
Added in version 242.
RemoveIPC=
Takes a boolean parameter. If set, all System V and POSIX IPC
objects owned by the user and group the processes of this unit
are run as are removed when the unit is stopped. This setting
only has an effect if at least one of User=, Group= and
DynamicUser= are used. It has no effect on IPC objects owned
by the root user. Specifically, this removes System V
semaphores, as well as System V and POSIX shared memory
segments and message queues. If multiple units use the same
user or group the IPC objects are removed when the last of
these units is stopped. This setting is implied if
DynamicUser= is set.
This option is only available for system services and is not
supported for services running in per-user instances of the
service manager.
Added in version 232.
PrivateMounts=
Takes a boolean parameter. If set, the processes of this unit
will be run in their own private file system (mount) namespace
with all mount propagation from the processes towards the
host's main file system namespace turned off. This means any
file system mount points established or removed by the unit's
processes will be private to them and not be visible to the
host. However, file system mount points established or removed
on the host will be propagated to the unit's processes. See
mount_namespaces(7) for details on file system namespaces.
Defaults to off.
When turned on, this executes three operations for each
invoked process: a new CLONE_NEWNS namespace is created, after
which all existing mounts are remounted to MS_SLAVE to disable
propagation from the unit's processes to the host (but leaving
propagation in the opposite direction in effect). Finally, the
mounts are remounted again to the propagation mode configured
with MountFlags=, see below.
File system namespaces are set up individually for each
process forked off by the service manager. Mounts established
in the namespace of the process created by ExecStartPre= will
hence be cleaned up automatically as soon as that process
exits and will not be available to subsequent processes forked
off for ExecStart= (and similar applies to the various other
commands configured for units). Similarly, JoinsNamespaceOf=
does not permit sharing kernel mount namespaces between units,
it only enables sharing of the /tmp/ and /var/tmp/
directories.
Other file system namespace unit settings — PrivateTmp=,
PrivateDevices=, ProtectSystem=, ProtectHome=, ReadOnlyPaths=,
InaccessiblePaths=, ReadWritePaths=, BindPaths=,
BindReadOnlyPaths=, ... — also enable file system namespacing
in a fashion equivalent to this option. Hence it is primarily
useful to explicitly request this behaviour if none of the
other settings are used.
This option is only available for system services, or for
services running in per-user instances of the service manager
in which case PrivateUsers= is implicitly enabled (requires
unprivileged user namespaces support to be enabled in the
kernel via the "kernel.unprivileged_userns_clone=" sysctl).
Added in version 239.
MountFlags=
Takes a mount propagation setting: shared, slave or private,
which controls whether file system mount points in the file
system namespaces set up for this unit's processes will
receive or propagate mounts and unmounts from other file
system namespaces. See mount(2) for details on mount
propagation, and the three propagation flags in particular.
This setting only controls the final propagation setting in
effect on all mount points of the file system namespace
created for each process of this unit. Other file system
namespacing unit settings (see the discussion in
PrivateMounts= above) will implicitly disable mount and
unmount propagation from the unit's processes towards the host
by changing the propagation setting of all mount points in the
unit's file system namespace to slave first. Setting this
option to shared does not reestablish propagation in that
case.
If not set – but file system namespaces are enabled through
another file system namespace unit setting – shared mount
propagation is used, but — as mentioned — as slave is applied
first, propagation from the unit's processes to the host is
still turned off.
It is not recommended to use private mount propagation for
units, as this means temporary mounts (such as removable
media) of the host will stay mounted and thus indefinitely
busy in forked off processes, as unmount propagation events
will not be received by the file system namespace of the unit.
Usually, it is best to leave this setting unmodified, and use
higher level file system namespacing options instead, in
particular PrivateMounts=, see above.
This option is only available for system services, or for
services running in per-user instances of the service manager
in which case PrivateUsers= is implicitly enabled (requires
unprivileged user namespaces support to be enabled in the
kernel via the "kernel.unprivileged_userns_clone=" sysctl).
SystemCallFilter=
Takes a space-separated list of system call names or system
call groups. If this setting is used, system calls executed by
the unit processes except for the listed ones will result in
the system call being denied (allow-listing). If the first
character of the list is "~", the effect is inverted: only the
listed system calls will be denied (deny-listing). This option
may be specified more than once, in which case the filter
masks are merged. If the empty string is assigned, the filter
is reset, all prior assignments will have no effect.
Commands prefixed with "+" are not subject to filtering. The
execve(), exit(), exit_group(), getrlimit(), rt_sigreturn(),
sigreturn() system calls and the system calls for querying
time and sleeping are implicitly allow-listed and do not need
to be listed explicitly.
The default action when a system call is denied is to
terminate the processes with a SIGSYS signal. This can changed
using SystemCallErrorNumber=, see below. In addition,
deny-listed system calls and system call groups may optionally
be suffixed with a colon (":") and an argument in the same
format as SystemCallErrorNumber=, to take this action when the
matching system call is made. This takes precedence over the
action specified in SystemCallErrorNumber=.
This feature makes use of the Secure Computing Mode 2
interfaces of the kernel ('seccomp filtering') and is useful
for enforcing a minimal sandboxing environment.
Note that on systems supporting multiple ABIs (such as
x86/x86-64) it is recommended to turn off alternative ABIs for
services, so that they cannot be used to circumvent the
restrictions of this option. Specifically, it is recommended
to combine this option with SystemCallArchitectures=native or
similar.
Note that strict system call filters may impact execution and
error handling code paths of the service invocation.
Specifically, access to the execve() system call is required
for the execution of the service binary — if it is blocked
service invocation will necessarily fail. Also, if execution
of the service binary fails for some reason (for example:
missing service executable), the error handling logic might
require access to an additional set of system calls in order
to process and log this failure correctly. It might be
necessary to temporarily disable system call filters in order
to allow debugging of such failures.
If you specify both types of this option (i.e. allow-listing
and deny-listing), the first encountered will take precedence
and will dictate the default action (termination or approval
of a system call). Then the next occurrences of this option
will add or delete the listed system calls from the set of the
filtered system calls, depending of its type and the default
action. (For example, if you have started with an allow list
rule for read() and write(), and right after it add a deny
list rule for write(), then write() will be removed from the
set.)
As the number of possible system calls is large, predefined
groups of system calls are provided. A group starts with "@"
character, followed by name of the set.
Table 5. Currently predefined system call sets
┌─────────────────┬──────────────────────────┐
│ Set │ Description │
├─────────────────┼──────────────────────────┤
│ @aio │ Asynchronous I/O (‐ │
│ │ io_setup(2), │
│ │ io_submit(2), and │
│ │ related calls) │
├─────────────────┼──────────────────────────┤
│ @basic-io │ System calls for basic │
│ │ I/O: reading, writing, │
│ │ seeking, file descriptor │
│ │ duplication and closing │
│ │ (read(2), write(2), and │
│ │ related calls) │
├─────────────────┼──────────────────────────┤
│ @chown │ Changing file ownership │
│ │ (chown(2), fchownat(2), │
│ │ and related calls) │
├─────────────────┼──────────────────────────┤
│ @clock │ System calls for │
│ │ changing the system │
│ │ clock (adjtimex(2), │
│ │ settimeofday(2), and │
│ │ related calls) │
├─────────────────┼──────────────────────────┤
│ @cpu-emulation │ System calls for CPU │
│ │ emulation functionality │
│ │ (vm86(2) and related │
│ │ calls) │
├─────────────────┼──────────────────────────┤
│ @debug │ Debugging, performance │
│ │ monitoring and tracing │
│ │ functionality (‐ │
│ │ ptrace(2), │
│ │ perf_event_open(2) and │
│ │ related calls) │
├─────────────────┼──────────────────────────┤
│ @file-system │ File system operations: │
│ │ opening, creating files │
│ │ and directories for read │
│ │ and write, renaming and │
│ │ removing them, reading │
│ │ file properties, or │
│ │ creating hard and │
│ │ symbolic links │
├─────────────────┼──────────────────────────┤
│ @io-event │ Event loop system calls │
│ │ (poll(2), select(2), │
│ │ epoll(7), eventfd(2) and │
│ │ related calls) │
├─────────────────┼──────────────────────────┤
│ @ipc │ Pipes, SysV IPC, POSIX │
│ │ Message Queues and other │
│ │ IPC (mq_overview(7), │
│ │ svipc(7)) │
├─────────────────┼──────────────────────────┤
│ @keyring │ Kernel keyring access (‐ │
│ │ keyctl(2) and related │
│ │ calls) │
├─────────────────┼──────────────────────────┤
│ @memlock │ Locking of memory in RAM │
│ │ (mlock(2), mlockall(2) │
│ │ and related calls) │
├─────────────────┼──────────────────────────┤
│ @module │ Loading and unloading of │
│ │ kernel modules (‐ │
│ │ init_module(2), │
│ │ delete_module(2) and │
│ │ related calls) │
├─────────────────┼──────────────────────────┤
│ @mount │ Mounting and unmounting │
│ │ of file systems (‐ │
│ │ mount(2), chroot(2), and │
│ │ related calls) │
├─────────────────┼──────────────────────────┤
│ @network-io │ Socket I/O (including │
│ │ local AF_UNIX): │
│ │ socket(7), unix(7) │
├─────────────────┼──────────────────────────┤
│ @obsolete │ Unusual, obsolete or │
│ │ unimplemented (‐ │
│ │ create_module(2), │
│ │ gtty(2), ...) │
├─────────────────┼──────────────────────────┤
│ @pkey │ System calls that deal │
│ │ with memory protection │
│ │ keys (pkeys(7)) │
├─────────────────┼──────────────────────────┤
│ @privileged │ All system calls which │
│ │ need super-user │
│ │ capabilities (‐ │
│ │ capabilities(7)) │
├─────────────────┼──────────────────────────┤
│ @process │ Process control, │
│ │ execution, namespacing │
│ │ operations (clone(2), │
│ │ kill(2), namespaces(7), │
│ │ ...) │
├─────────────────┼──────────────────────────┤
│ @raw-io │ Raw I/O port access (‐ │
│ │ ioperm(2), iopl(2), │
│ │ pciconfig_read(), ...) │
├─────────────────┼──────────────────────────┤
│ @reboot │ System calls for │
│ │ rebooting and reboot │
│ │ preparation (reboot(2), │
│ │ kexec(), ...) │
├─────────────────┼──────────────────────────┤
│ @resources │ System calls for │
│ │ changing resource │
│ │ limits, memory and │
│ │ scheduling parameters (‐ │
│ │ setrlimit(2), │
│ │ setpriority(2), ...) │
├─────────────────┼──────────────────────────┤
│ @sandbox │ System calls for │
│ │ sandboxing programs (‐ │
│ │ seccomp(2), Landlock │
│ │ system calls, ...) │
├─────────────────┼──────────────────────────┤
│ @setuid │ System calls for │
│ │ changing user ID and │
│ │ group ID credentials, (‐ │
│ │ setuid(2), setgid(2), │
│ │ setresuid(2), ...) │
├─────────────────┼──────────────────────────┤
│ @signal │ System calls for │
│ │ manipulating and │
│ │ handling process signals │
│ │ (signal(2), │
│ │ sigprocmask(2), ...) │
├─────────────────┼──────────────────────────┤
│ @swap │ System calls for │
│ │ enabling/disabling swap │
│ │ devices (swapon(2), │
│ │ swapoff(2)) │
├─────────────────┼──────────────────────────┤
│ @sync │ Synchronizing files and │
│ │ memory to disk (‐ │
│ │ fsync(2), msync(2), and │
│ │ related calls) │
├─────────────────┼──────────────────────────┤
│ @system-service │ A reasonable set of │
│ │ system calls used by │
│ │ common system services, │
│ │ excluding any special │
│ │ purpose calls. This is │
│ │ the recommended starting │
│ │ point for allow-listing │
│ │ system calls for system │
│ │ services, as it contains │
│ │ what is typically needed │
│ │ by system services, but │
│ │ excludes overly specific │
│ │ interfaces. For example, │
│ │ the following APIs are │
│ │ excluded: "@clock", │
│ │ "@mount", "@swap", │
│ │ "@reboot". │
├─────────────────┼──────────────────────────┤
│ @timer │ System calls for │
│ │ scheduling operations by │
│ │ time (alarm(2), │
│ │ timer_create(2), ...) │
├─────────────────┼──────────────────────────┤
│ @known │ All system calls defined │
│ │ by the kernel. This list │
│ │ is defined statically in │
│ │ systemd based on a │
│ │ kernel version that was │
│ │ available when this │
│ │ systemd version was │
│ │ released. It will become │
│ │ progressively more │
│ │ out-of-date as the │
│ │ kernel is updated. │
└─────────────────┴──────────────────────────┘
Note, that as new system calls are added to the kernel,
additional system calls might be added to the groups above.
Contents of the sets may also change between systemd versions.
In addition, the list of system calls depends on the kernel
version and architecture for which systemd was compiled. Use
systemd-analyze syscall-filter to list the actual list of
system calls in each filter.
Generally, allow-listing system calls (rather than
deny-listing) is the safer mode of operation. It is
recommended to enforce system call allow lists for all
long-running system services. Specifically, the following
lines are a relatively safe basic choice for the majority of
system services:
[Service]
SystemCallFilter=@system-service
SystemCallErrorNumber=EPERM
Note that various kernel system calls are defined redundantly:
there are multiple system calls for executing the same
operation. For example, the pidfd_send_signal() system call
may be used to execute operations similar to what can be done
with the older kill() system call, hence blocking the latter
without the former only provides weak protection. Since new
system calls are added regularly to the kernel as development
progresses, keeping system call deny lists comprehensive
requires constant work. It is thus recommended to use
allow-listing instead, which offers the benefit that new
system calls are by default implicitly blocked until the allow
list is updated.
Also note that a number of system calls are required to be
accessible for the dynamic linker to work. The dynamic linker
is required for running most regular programs (specifically:
all dynamic ELF binaries, which is how most distributions
build packaged programs). This means that blocking these
system calls (which include open(), openat() or mmap()) will
make most programs typically shipped with generic
distributions unusable.
It is recommended to combine the file system namespacing
related options with SystemCallFilter=~@mount, in order to
prohibit the unit's processes to undo the mappings.
Specifically these are the options PrivateTmp=,
PrivateDevices=, ProtectSystem=, ProtectHome=,
ProtectKernelTunables=, ProtectControlGroups=,
ProtectKernelLogs=, ProtectClock=, ReadOnlyPaths=,
InaccessiblePaths= and ReadWritePaths=.
Added in version 187.
SystemCallErrorNumber=
Takes an "errno" error number (between 1 and 4095) or errno
name such as EPERM, EACCES or EUCLEAN, to return when the
system call filter configured with SystemCallFilter= is
triggered, instead of terminating the process immediately. See
errno(3) for a full list of error codes. When this setting is
not used, or when the empty string or the special setting
"kill" is assigned, the process will be terminated immediately
when the filter is triggered.
Added in version 209.
SystemCallArchitectures=
Takes a space-separated list of architecture identifiers to
include in the system call filter. The known architecture
identifiers are the same as for ConditionArchitecture=
described in systemd.unit(5), as well as x32, mips64-n32,
mips64-le-n32, and the special identifier native. The special
identifier native implicitly maps to the native architecture
of the system (or more precisely: to the architecture the
system manager is compiled for). By default, this option is
set to the empty list, i.e. no filtering is applied.
If this setting is used, processes of this unit will only be
permitted to call native system calls, and system calls of the
specified architectures. For the purposes of this option, the
x32 architecture is treated as including x86-64 system calls.
However, this setting still fulfills its purpose, as explained
below, on x32.
System call filtering is not equally effective on all
architectures. For example, on x86 filtering of network
socket-related calls is not possible, due to ABI limitations —
a limitation that x86-64 does not have, however. On systems
supporting multiple ABIs at the same time — such as x86/x86-64
— it is hence recommended to limit the set of permitted system
call architectures so that secondary ABIs may not be used to
circumvent the restrictions applied to the native ABI of the
system. In particular, setting SystemCallArchitectures=native
is a good choice for disabling non-native ABIs.
System call architectures may also be restricted system-wide
via the SystemCallArchitectures= option in the global
configuration. See systemd-system.conf(5) for details.
Added in version 209.
SystemCallLog=
Takes a space-separated list of system call names. If this
setting is used, all system calls executed by the unit
processes for the listed ones will be logged. If the first
character of the list is "~", the effect is inverted: all
system calls except the listed system calls will be logged.
This feature makes use of the Secure Computing Mode 2
interfaces of the kernel ('seccomp filtering') and is useful
for auditing or setting up a minimal sandboxing environment.
This option may be specified more than once, in which case the
filter masks are merged. If the empty string is assigned, the
filter is reset, all prior assignments will have no effect.
This does not affect commands prefixed with "+".
Added in version 247.
Environment=
Sets environment variables for executed processes. Each line
is unquoted using the rules described in "Quoting" section in
systemd.syntax(7) and becomes a list of variable assignments.
If you need to assign a value containing spaces or the equals
sign to a variable, put quotes around the whole assignment.
Variable expansion is not performed inside the strings and the
"$" character has no special meaning. Specifier expansion is
performed, see the "Specifiers" section in systemd.unit(5).
This option may be specified more than once, in which case all
listed variables will be set. If the same variable is listed
twice, the later setting will override the earlier setting. If
the empty string is assigned to this option, the list of
environment variables is reset, all prior assignments have no
effect.
The names of the variables can contain ASCII letters, digits,
and the underscore character. Variable names cannot be empty
or start with a digit. In variable values, most characters are
allowed, but non-printable characters are currently rejected.
Example:
Environment="VAR1=word1 word2" VAR2=word3 "VAR3=$word 5 6"
gives three variables "VAR1", "VAR2", "VAR3" with the values
"word1 word2", "word3", "$word 5 6".
See environ(7) for details about environment variables.
Note that environment variables are not suitable for passing
secrets (such as passwords, key material, ...) to service
processes. Environment variables set for a unit are exposed to
unprivileged clients via D-Bus IPC, and generally not
understood as being data that requires protection. Moreover,
environment variables are propagated down the process tree,
including across security boundaries (such as setuid/setgid
executables), and hence might leak to processes that should
not have access to the secret data. Use LoadCredential=,
LoadCredentialEncrypted= or SetCredentialEncrypted= (see
below) to pass data to unit processes securely.
EnvironmentFile=
Similar to Environment=, but reads the environment variables
from a text file. The text file should contain
newline-separated variable assignments. Empty lines, lines
without an "=" separator, or lines starting with ";" or "#"
will be ignored, which may be used for commenting. The file
must be encoded with UTF-8. Valid characters are unicode
scalar values[14] other than unicode noncharacters[15], U+0000
NUL, and U+FEFF unicode byte order mark[16]. Control codes
other than NUL are allowed.
In the file, an unquoted value after the "=" is parsed with
the same backslash-escape rules as POSIX shell unquoted
text[17], but unlike in a shell, interior whitespace is
preserved and quotes after the first non-whitespace character
are preserved. Leading and trailing whitespace (space, tab,
carriage return) is discarded, but interior whitespace within
the line is preserved verbatim. A line ending with a backslash
will be continued to the following one, with the newline
itself discarded. A backslash "\" followed by any character
other than newline will preserve the following character, so
that "\\" will become the value "\".
In the file, a "'"-quoted value after the "=" can span
multiple lines and contain any character verbatim other than
single quote, like POSIX shell single-quoted text[18]. No
backslash-escape sequences are recognized. Leading and
trailing whitespace outside of the single quotes is discarded.
In the file, a """-quoted value after the "=" can span
multiple lines, and the same escape sequences are recognized
as in POSIX shell double-quoted text[19]. Backslash ("\")
followed by any of ""\`$" will preserve that character. A
backslash followed by newline is a line continuation, and the
newline itself is discarded. A backslash followed by any other
character is ignored; both the backslash and the following
character are preserved verbatim. Leading and trailing
whitespace outside of the double quotes is discarded.
The argument passed should be an absolute filename or wildcard
expression, optionally prefixed with "-", which indicates that
if the file does not exist, it will not be read and no error
or warning message is logged. This option may be specified
more than once in which case all specified files are read. If
the empty string is assigned to this option, the list of file
to read is reset, all prior assignments have no effect.
The files listed with this directive will be read shortly
before the process is executed (more specifically, after all
processes from a previous unit state terminated. This means
you can generate these files in one unit state, and read it
with this option in the next. The files are read from the file
system of the service manager, before any file system changes
like bind mounts take place).
Settings from these files override settings made with
Environment=. If the same variable is set twice from these
files, the files will be read in the order they are specified
and the later setting will override the earlier setting.
PassEnvironment=
Pass environment variables set for the system service manager
to executed processes. Takes a space-separated list of
variable names. This option may be specified more than once,
in which case all listed variables will be passed. If the
empty string is assigned to this option, the list of
environment variables to pass is reset, all prior assignments
have no effect. Variables specified that are not set for the
system manager will not be passed and will be silently
ignored. Note that this option is only relevant for the system
service manager, as system services by default do not
automatically inherit any environment variables set for the
service manager itself. However, in case of the user service
manager all environment variables are passed to the executed
processes anyway, hence this option is without effect for the
user service manager.
Variables set for invoked processes due to this setting are
subject to being overridden by those configured with
Environment= or EnvironmentFile=.
Example:
PassEnvironment=VAR1 VAR2 VAR3
passes three variables "VAR1", "VAR2", "VAR3" with the values
set for those variables in PID1.
See environ(7) for details about environment variables.
Added in version 228.
UnsetEnvironment=
Explicitly unset environment variable assignments that would
normally be passed from the service manager to invoked
processes of this unit. Takes a space-separated list of
variable names or variable assignments. This option may be
specified more than once, in which case all listed
variables/assignments will be unset. If the empty string is
assigned to this option, the list of environment
variables/assignments to unset is reset. If a variable
assignment is specified (that is: a variable name, followed by
"=", followed by its value), then any environment variable
matching this precise assignment is removed. If a variable
name is specified (that is a variable name without any
following "=" or value), then any assignment matching the
variable name, regardless of its value is removed. Note that
the effect of UnsetEnvironment= is applied as final step when
the environment list passed to executed processes is compiled.
That means it may undo assignments from any configuration
source, including assignments made through Environment= or
EnvironmentFile=, inherited from the system manager's global
set of environment variables, inherited via PassEnvironment=,
set by the service manager itself (such as $NOTIFY_SOCKET and
such), or set by a PAM module (in case PAMName= is used).
See "Environment Variables in Spawned Processes" below for a
description of how those settings combine to form the
inherited environment. See environ(7) for general information
about environment variables.
Added in version 235.
StandardInput=
Controls where file descriptor 0 (STDIN) of the executed
processes is connected to. Takes one of null, tty, tty-force,
tty-fail, data, file:path, socket or fd:name.
If null is selected, standard input will be connected to
/dev/null, i.e. all read attempts by the process will result
in immediate EOF.
If tty is selected, standard input is connected to a TTY (as
configured by TTYPath=, see below) and the executed process
becomes the controlling process of the terminal. If the
terminal is already being controlled by another process, the
executed process waits until the current controlling process
releases the terminal.
tty-force is similar to tty, but the executed process is
forcefully and immediately made the controlling process of the
terminal, potentially removing previous controlling processes
from the terminal.
tty-fail is similar to tty, but if the terminal already has a
controlling process start-up of the executed process fails.
The data option may be used to configure arbitrary textual or
binary data to pass via standard input to the executed
process. The data to pass is configured via
StandardInputText=/StandardInputData= (see below). Note that
the actual file descriptor type passed (memory file, regular
file, UNIX pipe, ...) might depend on the kernel and available
privileges. In any case, the file descriptor is read-only, and
when read returns the specified data followed by EOF.
The file:path option may be used to connect a specific file
system object to standard input. An absolute path following
the ":" character is expected, which may refer to a regular
file, a FIFO or special file. If an AF_UNIX socket in the file
system is specified, a stream socket is connected to it. The
latter is useful for connecting standard input of processes to
arbitrary system services.
The socket option is valid in socket-activated services only,
and requires the relevant socket unit file (see
systemd.socket(5) for details) to have Accept=yes set, or to
specify a single socket only. If this option is set, standard
input will be connected to the socket the service was
activated from, which is primarily useful for compatibility
with daemons designed for use with the traditional inetd(8)
socket activation daemon ($LISTEN_FDS (and related)
environment variables are not passed when socket value is
configured).
The fd:name option connects standard input to a specific,
named file descriptor provided by a socket unit. The name may
be specified as part of this option, following a ":" character
(e.g. "fd:foobar"). If no name is specified, the name "stdin"
is implied (i.e. "fd" is equivalent to "fd:stdin"). At least
one socket unit defining the specified name must be provided
via the Sockets= option, and the file descriptor name may
differ from the name of its containing socket unit. If
multiple matches are found, the first one will be used. See
FileDescriptorName= in systemd.socket(5) for more details
about named file descriptors and their ordering.
This setting defaults to null, unless
StandardInputText=/StandardInputData= are set, in which case
it defaults to data.
StandardOutput=
Controls where file descriptor 1 (stdout) of the executed
processes is connected to. Takes one of inherit, null, tty,
journal, kmsg, journal+console, kmsg+console, file:path,
append:path, truncate:path, socket or fd:name.
inherit duplicates the file descriptor of standard input for
standard output.
null connects standard output to /dev/null, i.e. everything
written to it will be lost.
tty connects standard output to a tty (as configured via
TTYPath=, see below). If the TTY is used for output only, the
executed process will not become the controlling process of
the terminal, and will not fail or wait for other processes to
release the terminal. Note: if a unit tries to print multiple
lines to a TTY during bootup or shutdown, then there's a
chance that those lines will be broken up by status messages.
SetShowStatus() can be used to prevent this problem. See
org.freedesktop.systemd1(5) for details.
journal connects standard output with the journal, which is
accessible via journalctl(1). Note that everything that is
written to kmsg (see below) is implicitly stored in the
journal as well, the specific option listed below is hence a
superset of this one. (Also note that any external, additional
syslog daemons receive their log data from the journal, too,
hence this is the option to use when logging shall be
processed with such a daemon.)
kmsg connects standard output with the kernel log buffer which
is accessible via dmesg(1), in addition to the journal. The
journal daemon might be configured to send all logs to kmsg
anyway, in which case this option is no different from
journal.
journal+console and kmsg+console work in a similar way as the
two options above but copy the output to the system console as
well.
The file:path option may be used to connect a specific file
system object to standard output. The semantics are similar to
the same option of StandardInput=, see above. If path refers
to a regular file on the filesystem, it is opened (created if
it does not exist yet using privileges of the user executing
the systemd process) for writing at the beginning of the file,
but without truncating it. If standard input and output are
directed to the same file path, it is opened only once — for
reading as well as writing — and duplicated. This is
particularly useful when the specified path refers to an
AF_UNIX socket in the file system, as in that case only a
single stream connection is created for both input and output.
append:path is similar to file:path above, but it opens the
file in append mode.
truncate:path is similar to file:path above, but it truncates
the file when opening it. For units with multiple command
lines, e.g. Type=oneshot services with multiple ExecStart=,
or services with ExecCondition=, ExecStartPre= or
ExecStartPost=, the output file is reopened and therefore
re-truncated for each command line. If the output file is
truncated while another process still has the file open, e.g.
by an ExecReload= running concurrently with an ExecStart=, and
the other process continues writing to the file without
adjusting its offset, then the space between the file pointers
of the two processes may be filled with NUL bytes, producing a
sparse file. Thus, truncate:path is typically only useful for
units where only one process runs at a time, such as services
with a single ExecStart= and no ExecStartPost=, ExecReload=,
ExecStop= or similar.
socket connects standard output to a socket acquired via
socket activation. The semantics are similar to the same
option of StandardInput=, see above.
The fd:name option connects standard output to a specific,
named file descriptor provided by a socket unit. A name may be
specified as part of this option, following a ":" character
(e.g. "fd:foobar"). If no name is specified, the name
"stdout" is implied (i.e. "fd" is equivalent to "fd:stdout").
At least one socket unit defining the specified name must be
provided via the Sockets= option, and the file descriptor name
may differ from the name of its containing socket unit. If
multiple matches are found, the first one will be used. See
FileDescriptorName= in systemd.socket(5) for more details
about named descriptors and their ordering.
If the standard output (or error output, see below) of a unit
is connected to the journal or the kernel log buffer, the unit
will implicitly gain a dependency of type After= on
systemd-journald.socket (also see the "Implicit Dependencies"
section above). Also note that, in this case, stdout (or
stderr, see below) will be an AF_UNIX stream socket, and not a
pipe or FIFO that can be reopened. This means when executing
shell scripts the construct echo "hello" > /dev/stderr for
writing text to stderr will not work. To mitigate this use the
construct echo "hello" >&2 instead, which is mostly equivalent
and avoids this pitfall.
If StandardInput= is set to one of tty, tty-force, tty-fail,
socket, or fd:name, this setting defaults to inherit.
In other cases, this setting defaults to the value set with
DefaultStandardOutput= in systemd-system.conf(5), which
defaults to journal. Note that setting this parameter might
result in additional dependencies to be added to the unit (see
above).
StandardError=
Controls where file descriptor 2 (stderr) of the executed
processes is connected to. The available options are identical
to those of StandardOutput=, with some exceptions: if set to
inherit the file descriptor used for standard output is
duplicated for standard error, while fd:name will use a
default file descriptor name of "stderr".
This setting defaults to the value set with
DefaultStandardError= in systemd-system.conf(5), which
defaults to inherit. Note that setting this parameter might
result in additional dependencies to be added to the unit (see
above).
StandardInputText=, StandardInputData=
Configures arbitrary textual or binary data to pass via file
descriptor 0 (STDIN) to the executed processes. These settings
have no effect unless StandardInput= is set to data (which is
the default if StandardInput= is not set otherwise, but
StandardInputText=/StandardInputData= is). Use this option to
embed process input data directly in the unit file.
StandardInputText= accepts arbitrary textual data. C-style
escapes for special characters as well as the usual
"%"-specifiers are resolved. Each time this setting is used
the specified text is appended to the per-unit data buffer,
followed by a newline character (thus every use appends a new
line to the end of the buffer). Note that leading and trailing
whitespace of lines configured with this option is removed. If
an empty line is specified the buffer is cleared (hence, in
order to insert an empty line, add an additional "\n" to the
end or beginning of a line).
StandardInputData= accepts arbitrary binary data, encoded in
Base64[20]. No escape sequences or specifiers are resolved.
Any whitespace in the encoded version is ignored during
decoding.
Note that StandardInputText= and StandardInputData= operate on
the same data buffer, and may be mixed in order to configure
both binary and textual data for the same input stream. The
textual or binary data is joined strictly in the order the
settings appear in the unit file. Assigning an empty string to
either will reset the data buffer.
Please keep in mind that in order to maintain readability long
unit file settings may be split into multiple lines, by
suffixing each line (except for the last) with a "\" character
(see systemd.unit(5) for details). This is particularly useful
for large data configured with these two options. Example:
...
StandardInput=data
StandardInputData=V2XigLJyZSBubyBzdHJhbmdlcnMgdG8gbG92ZQpZb3Uga25vdyB0aGUgcnVsZXMgYW5kIHNvIGRv \
IEkKQSBmdWxsIGNvbW1pdG1lbnQncyB3aGF0IEnigLJtIHRoaW5raW5nIG9mCllvdSB3b3VsZG4n \
dCBnZXQgdGhpcyBmcm9tIGFueSBvdGhlciBndXkKSSBqdXN0IHdhbm5hIHRlbGwgeW91IGhvdyBJ \
J20gZmVlbGluZwpHb3R0YSBtYWtlIHlvdSB1bmRlcnN0YW5kCgpOZXZlciBnb25uYSBnaXZlIHlv \
dSB1cApOZXZlciBnb25uYSBsZXQgeW91IGRvd24KTmV2ZXIgZ29ubmEgcnVuIGFyb3VuZCBhbmQg \
ZGVzZXJ0IHlvdQpOZXZlciBnb25uYSBtYWtlIHlvdSBjcnkKTmV2ZXIgZ29ubmEgc2F5IGdvb2Ri \
eWUKTmV2ZXIgZ29ubmEgdGVsbCBhIGxpZSBhbmQgaHVydCB5b3UK
...
Added in version 236.
LogLevelMax=
Sets the maximum log level for log messages generated by this
unit. Takes a syslog log level, one of emerg (lowest log
level, only highest priority messages), alert, crit, err,
warning, notice, info, debug (highest log level, also lowest
priority messages). See syslog(3) for details. By default, the
maximum log level is not overridden.
This option can be used to configure the logging system to
drop log messages of a specific service above the specified
level. For example, set LogLevelMax=info in order to turn off
debug logging of a particularly chatty unit. Alternatively,
this option can be used to enable extra logging about a
specific unit by the system or user manager processes without
changing the global log level for the system or user manager
processes by setting LogLevelMax=debug.
Note that the configured level is applied to any log messages
written by any of the processes belonging to this unit, as
well as any log messages written by the system or user manager
processes in reference to this unit, sent via any supported
logging protocol. The override is applied early in the logging
pipeline, before any kind of further processing is done.
Moreover, messages which pass through this filter successfully
might still be dropped by filters applied at a later stage in
the logging subsystem. For example, MaxLevelStore= configured
in journald.conf(5) might prohibit messages of higher log
levels to be stored on disk, even though the per-unit
LogLevelMax= permitted it to be processed.
Added in version 236.
LogExtraFields=
Configures additional log metadata fields to include in all
log records generated by processes associated with this unit,
including systemd. This setting takes one or more journal
field assignments in the format "FIELD=VALUE" separated by
whitespace. See systemd.journal-fields(7) for details on the
journal field concept. Even though the underlying journal
implementation permits binary field values, this setting
accepts only valid UTF-8 values. To include space characters
in a journal field value, enclose the assignment in double
quotes ("). The usual specifiers are expanded in all
assignments (see below). Note that this setting is not only
useful for attaching additional metadata to log records of a
unit, but given that all fields and values are indexed may
also be used to implement cross-unit log record matching.
Assign an empty string to reset the list.
Note that this functionality is currently only available in
system services, not in per-user services.
Added in version 236.
LogRateLimitIntervalSec=, LogRateLimitBurst=
Configures the rate limiting that is applied to log messages
generated by this unit. If, in the time interval defined by
LogRateLimitIntervalSec=, more messages than specified in
LogRateLimitBurst= are logged by a service, all further
messages within the interval are dropped until the interval is
over. A message about the number of dropped messages is
generated. The time specification for LogRateLimitIntervalSec=
may be specified in the following units: "s", "min", "h",
"ms", "us". See systemd.time(7) for details. The default
settings are set by RateLimitIntervalSec= and RateLimitBurst=
configured in journald.conf(5). Note that this only applies to
log messages that are processed by the logging subsystem, i.e.
by systemd-journald.service(8). This means that if you connect
a service's stderr directly to a file via
StandardOutput=file:... or a similar setting, the rate
limiting will not be applied to messages written that way (but
it will be enforced for messages generated via syslog(3) and
similar functions).
Added in version 240.
LogFilterPatterns=
Define an extended regular expression to filter log messages
based on the MESSAGE= field of the structured message. If the
first character of the pattern is "~", log entries matching
the pattern should be discarded. This option takes a single
pattern as an argument but can be used multiple times to
create a list of allowed and denied patterns. If the empty
string is assigned, the filter is reset, and all prior
assignments will have no effect.
Because the "~" character is used to define denied patterns,
it must be replaced with "\x7e" to allow a message starting
with "~". For example, "~foobar" would add a pattern matching
"foobar" to the deny list, while "\x7efoobar" would add a
pattern matching "~foobar" to the allow list.
Log messages are tested against denied patterns (if any), then
against allowed patterns (if any). If a log message matches
any of the denied patterns, it is discarded immediately
without considering allowed patterns. Remaining log messages
are tested against allowed patterns. Messages matching against
none of the allowed pattern are discarded. If no allowed
patterns are defined, then all messages are processed directly
after going through denied filters.
Filtering is based on the unit for which LogFilterPatterns= is
defined, meaning log messages coming from systemd(1) about the
unit are not taken into account. Filtered log messages will
not be forwarded to traditional syslog daemons, the kernel log
buffer (kmsg), the systemd console, or sent as wall messages
to all logged-in users.
Note that this functionality is currently only available in
system services, not in per-user services.
Added in version 253.
LogNamespace=
Run the unit's processes in the specified journal namespace.
Expects a short user-defined string identifying the namespace.
If not used the processes of the service are run in the
default journal namespace, i.e. their log stream is collected
and processed by systemd-journald.service. If this option is
used any log data generated by processes of this unit
(regardless of whether via the syslog(), journal native
logging or stdout/stderr logging) is collected and processed
by an instance of the systemd-journald@.service template unit,
which manages the specified namespace. The log data is stored
in a data store independent from the default log namespace's
data store. See systemd-journald.service(8) for details about
journal namespaces.
Internally, journal namespaces are implemented through Linux
mount namespacing and over-mounting the directory that
contains the relevant AF_UNIX sockets used for logging in the
unit's mount namespace. Since mount namespaces are used this
setting disconnects propagation of mounts from the unit's
processes to the host, similarly to how ReadOnlyPaths= and
similar settings describe above work. Journal namespaces may
hence not be used for services that need to establish mount
points on the host.
When this option is used the unit will automatically gain
ordering and requirement dependencies on the two socket units
associated with the systemd-journald@.service instance so that
they are automatically established prior to the unit starting
up. Note that when this option is used log output of this
service does not appear in the regular journalctl(1) output,
unless the --namespace= option is used.
This option is only available for system services and is not
supported for services running in per-user instances of the
service manager.
Added in version 245.
SyslogIdentifier=
Sets the process name ("syslog tag") to prefix log lines sent
to the logging system or the kernel log buffer with. If not
set, defaults to the process name of the executed process.
This option is only useful when StandardOutput= or
StandardError= are set to journal or kmsg (or to the same
settings in combination with +console) and only applies to log
messages written to stdout or stderr.
SyslogFacility=
Sets the syslog facility identifier to use when logging. One
of kern, user, mail, daemon, auth, syslog, lpr, news, uucp,
cron, authpriv, ftp, local0, local1, local2, local3, local4,
local5, local6 or local7. See syslog(3) for details. This
option is only useful when StandardOutput= or StandardError=
are set to journal or kmsg (or to the same settings in
combination with +console), and only applies to log messages
written to stdout or stderr. Defaults to daemon.
SyslogLevel=
The default syslog log level to use when logging to the
logging system or the kernel log buffer. One of emerg, alert,
crit, err, warning, notice, info, debug. See syslog(3) for
details. This option is only useful when StandardOutput= or
StandardError= are set to journal or kmsg (or to the same
settings in combination with +console), and only applies to
log messages written to stdout or stderr. Note that individual
lines output by executed processes may be prefixed with a
different log level which can be used to override the default
log level specified here. The interpretation of these prefixes
may be disabled with SyslogLevelPrefix=, see below. For
details, see sd-daemon(3). Defaults to info.
SyslogLevelPrefix=
Takes a boolean argument. If true and StandardOutput= or
StandardError= are set to journal or kmsg (or to the same
settings in combination with +console), log lines written by
the executed process that are prefixed with a log level will
be processed with this log level set but the prefix removed.
If set to false, the interpretation of these prefixes is
disabled and the logged lines are passed on as-is. This only
applies to log messages written to stdout or stderr. For
details about this prefixing see sd-daemon(3). Defaults to
true.
TTYPath=
Sets the terminal device node to use if standard input,
output, or error are connected to a TTY (see above). Defaults
to /dev/console.
TTYReset=
Reset the terminal device specified with TTYPath= before and
after execution. This does not erase the screen (see
TTYVTDisallocate= below for that). Defaults to "no".
TTYVHangup=
Disconnect all clients which have opened the terminal device
specified with TTYPath= before and after execution. Defaults
to "no".
TTYColumns=, TTYRows=
Configure the size of the TTY specified with TTYPath=. If
unset or set to the empty string, it is attempted to retrieve
the dimensions of the terminal screen via ANSI sequences, and
if that fails the kernel defaults (typically 80x24) are used.
Added in version 250.
TTYVTDisallocate=
If the terminal device specified with TTYPath= is a virtual
console terminal, try to deallocate the TTY before and after
execution. This ensures that the screen and scrollback buffer
is cleared. If the terminal device is of any other type of TTY
an attempt is made to clear the screen via ANSI sequences.
Defaults to "no".
LoadCredential=ID[:PATH], LoadCredentialEncrypted=ID[:PATH]
Pass a credential to the unit. Credentials are limited-size
binary or textual objects that may be passed to unit
processes. They are primarily intended for passing
cryptographic keys (both public and private) or certificates,
user account information or identity information from host to
services, but can be freely used to pass any kind of
limited-size information to a service. The data is accessible
from the unit's processes via the file system, at a read-only
location that (if possible and permitted) is backed by
non-swappable memory. The data is only accessible to the user
associated with the unit, via the User=/DynamicUser= settings
(as well as the superuser). When available, the location of
credentials is exported as the $CREDENTIALS_DIRECTORY
environment variable to the unit's processes.
The LoadCredential= setting takes a textual ID to use as name
for a credential plus a file system path, separated by a
colon. The ID must be a short ASCII string suitable as
filename in the filesystem, and may be chosen freely by the
user. If the specified path is absolute it is opened as
regular file and the credential data is read from it. If the
absolute path refers to an AF_UNIX stream socket in the file
system a connection is made to it (once at process invocation)
and the credential data read from the connection, providing an
easy IPC integration point for dynamically transferring
credentials from other services.
If the specified path is not absolute and itself qualifies as
valid credential identifier it is attempted to find a
credential that the service manager itself received under the
specified name — which may be used to propagate credentials
from an invoking environment (e.g. a container manager that
invoked the service manager) into a service. If no matching
passed credential is found, the system service manager will
search the directories /etc/credstore/, /run/credstore/ and
/usr/lib/credstore/ for files under the credential's name —
which hence are recommended locations for credential data on
disk. If LoadCredentialEncrypted= is used
/run/credstore.encrypted/, /etc/credstore.encrypted/, and
/usr/lib/credstore.encrypted/ are searched as well. The
per-user service manager will search
$XDG_CONFIG_HOME/credstore/, $XDG_RUNTIME_DIR/credstore/,
$HOME/.local/lib/credstore/ (and the counterparts ending with
.../credstore.encrypted/) instead. The systemd-path(1) tool
may be used to query the precise credential store search path.
If the file system path is omitted it is chosen identical to
the credential name, i.e. this is a terse way to declare
credentials to inherit from the service manager or credstore
directories into a service. This option may be used multiple
times, each time defining an additional credential to pass to
the unit.
Note that if the path is not specified or a valid credential
identifier is given, i.e. in the above two cases, a missing
credential is not considered fatal.
If an absolute path referring to a directory is specified,
every file in that directory (recursively) will be loaded as a
separate credential. The ID for each credential will be the
provided ID suffixed with "_$FILENAME" (e.g., "Key_file1").
When loading from a directory, symlinks will be ignored.
The contents of the file/socket may be arbitrary binary or
textual data, including newline characters and NUL bytes.
The LoadCredentialEncrypted= setting is identical to
LoadCredential=, except that the credential data is decrypted
and authenticated before being passed on to the executed
processes. Specifically, the referenced path should refer to a
file or socket with an encrypted credential, as implemented by
systemd-creds(1). This credential is loaded, decrypted,
authenticated and then passed to the application in plaintext
form, in the same way a regular credential specified via
LoadCredential= would be. A credential configured this way may
be symmetrically encrypted/authenticated with a secret key
derived from the system's TPM2 security chip, or with a secret
key stored in /var/lib/systemd/credential.secret, or with
both. Using encrypted and authenticated credentials improves
security as credentials are not stored in plaintext and only
authenticated and decrypted into plaintext the moment a
service requiring them is started. Moreover, credentials may
be bound to the local hardware and installations, so that they
cannot easily be analyzed offline, or be generated externally.
See systemd.resource-control(5) for the details about
DevicePolicy= or DeviceAllow=.
Note that encrypted credentials targeted for services of the
per-user service manager must be encrypted with systemd-creds
encrypt --user, and those for the system service manager
without the --user switch. Encrypted credentials are always
targeted to a specific user or the system as a whole, and it
is ensured that per-user service managers cannot decrypt
secrets intended for the system or for other users.
The credential files/IPC sockets must be accessible to the
service manager, but do not have to be directly accessible to
the unit's processes: the credential data is read and copied
into separate, read-only copies for the unit that are
accessible to appropriately privileged processes. This is
particularly useful in combination with DynamicUser= as this
way privileged data can be made available to processes running
under a dynamic UID (i.e. not a previously known one) without
having to open up access to all users.
In order to reference the path a credential may be read from
within a ExecStart= command line use
"${CREDENTIALS_DIRECTORY}/mycred", e.g. "ExecStart=cat
${CREDENTIALS_DIRECTORY}/mycred". In order to reference the
path a credential may be read from within a Environment= line
use "%d/mycred", e.g. "Environment=MYCREDPATH=%d/mycred". For
system services the path may also be referenced as
"/run/credentials/UNITNAME" in cases where no interpolation is
possible, e.g. configuration files of software that does not
yet support credentials natively. $CREDENTIALS_DIRECTORY is
considered the primary interface to look for credentials,
though, since it also works for user services.
Currently, an accumulated credential size limit of 1 MB per
unit is enforced.
The service manager itself may receive system credentials that
can be propagated to services from a hosting container manager
or VM hypervisor. See the Container Interface[21]
documentation for details about the former. For the latter,
pass DMI/SMBIOS[22] OEM string table entries (field type 11)
with a prefix of "io.systemd.credential:" or
"io.systemd.credential.binary:". In both cases a key/value
pair separated by "=" is expected. In the latter case, the
right-hand side is Base64 decoded when parsed (thus permitting
binary data to be passed in). Example qemu[23] switch:
"-smbios type=11,value=io.systemd.credential:xx=yy", or
"-smbios
type=11,value=io.systemd.credential.binary:rick=TmV2ZXIgR29ubmEgR2l2ZSBZb3UgVXA=".
Alternatively, use the qemu "fw_cfg" node
"opt/io.systemd.credentials/". Example qemu switch: "-fw_cfg
name=opt/io.systemd.credentials/mycred,string=supersecret".
They may also be passed from the UEFI firmware environment via
systemd-stub(7), from the initrd (see systemd(1)), or be
specified on the kernel command line using the
"systemd.set_credential=" and "systemd.set_credential_binary="
switches (see systemd(1) – this is not recommended since
unprivileged userspace can read the kernel command line).
If referencing an AF_UNIX stream socket to connect to, the
connection will originate from an abstract namespace socket,
that includes information about the unit and the credential ID
in its socket name. Use getpeername(2) to query this
information. The returned socket name is formatted as NUL
RANDOM "/unit/" UNIT "/" ID, i.e. a NUL byte (as required for
abstract namespace socket names), followed by a random string
(consisting of alphadecimal characters), followed by the
literal string "/unit/", followed by the requesting unit name,
followed by the literal character "/", followed by the textual
credential ID requested. Example:
"\0adf9d86b6eda275e/unit/foobar.service/credx" in case the
credential "credx" is requested for a unit "foobar.service".
This functionality is useful for using a single listening
socket to serve credentials to multiple consumers.
For further information see System and Service Credentials[24]
documentation.
Added in version 247.
ImportCredential=GLOB
Pass one or more credentials to the unit. Takes a credential
name for which we will attempt to find a credential that the
service manager itself received under the specified name —
which may be used to propagate credentials from an invoking
environment (e.g. a container manager that invoked the service
manager) into a service. If the credential name is a glob, all
credentials matching the glob are passed to the unit. Matching
credentials are searched for in the system credentials, the
encrypted system credentials, and under /etc/credstore/,
/run/credstore/, /usr/lib/credstore/,
/run/credstore.encrypted/, /etc/credstore.encrypted/, and
/usr/lib/credstore.encrypted/ in that order. When multiple
credentials of the same name are found, the first one found is
used.
The globbing expression implements a restrictive subset of
glob(7): only a single trailing "*" wildcard may be specified.
Both "?" and "[]" wildcards are not permitted, nor are "*"
wildcards anywhere except at the end of the glob expression.
Optionally, the credential name or glob may be followed by a
colon followed by a rename pattern. If specified, all
credentials matching the credential name or glob are renamed
according to the given pattern. For example, if
"ImportCredential=my.original.cred:my.renamed.cred" is
specified, the service manager will read the
"my.original.cred" credential and make it available as the
"my.renamed.cred" credential to the service. Similarly, if
"ImportCredential=my.original.*:my.renamed." is specified,
the service manager will read all credentials starting with
"my.original." and make them available as "my.renamed.xxx" to
the service.
If ImportCredential= is specified multiple times and multiple
credentials end up with the same name after renaming, the
first one is kept and later ones are dropped.
When multiple credentials of the same name are found,
credentials found by LoadCredential= and
LoadCredentialEncrypted= take priority over credentials found
by ImportCredential=.
Added in version 254.
SetCredential=ID:VALUE, SetCredentialEncrypted=ID:VALUE
The SetCredential= setting is similar to LoadCredential= but
accepts a literal value to use as data for the credential,
instead of a file system path to read the data from. Do not
use this option for data that is supposed to be secret, as it
is accessible to unprivileged processes via IPC. It's only
safe to use this for user IDs, public key material and similar
non-sensitive data. For everything else use LoadCredential=.
In order to embed binary data into the credential data use
C-style escaping (i.e. "\n" to embed a newline, or "\x00" to
embed a NUL byte).
The SetCredentialEncrypted= setting is identical to
SetCredential= but expects an encrypted credential in literal
form as value. This allows embedding confidential credentials
securely directly in unit files. Use systemd-creds(1)' -p
switch to generate suitable SetCredentialEncrypted= lines
directly from plaintext credentials. For further details see
LoadCredentialEncrypted= above.
When multiple credentials of the same name are found,
credentials found by LoadCredential=, LoadCredentialEncrypted=
and ImportCredential= take priority over credentials found by
SetCredential=. As such, SetCredential= will act as default if
no credentials are found by any of the former. In this case,
not being able to retrieve the credential from the path
specified in LoadCredential= or LoadCredentialEncrypted= is
not considered fatal.
Added in version 247.
UtmpIdentifier=
Takes a four character identifier string for an utmp(5) and
wtmp entry for this service. This should only be set for
services such as getty implementations (such as agetty(8))
where utmp/wtmp entries must be created and cleared before and
after execution, or for services that shall be executed as if
they were run by a getty process (see below). If the
configured string is longer than four characters, it is
truncated and the terminal four characters are used. This
setting interprets %I style string replacements. This setting
is unset by default, i.e. no utmp/wtmp entries are created or
cleaned up for this service.
UtmpMode=
Takes one of "init", "login" or "user". If UtmpIdentifier= is
set, controls which type of utmp(5)/wtmp entries for this
service are generated. This setting has no effect unless
UtmpIdentifier= is set too. If "init" is set, only an
INIT_PROCESS entry is generated and the invoked process must
implement a getty-compatible utmp/wtmp logic. If "login" is
set, first an INIT_PROCESS entry, followed by a LOGIN_PROCESS
entry is generated. In this case, the invoked process must
implement a login(1)-compatible utmp/wtmp logic. If "user" is
set, first an INIT_PROCESS entry, then a LOGIN_PROCESS entry
and finally a USER_PROCESS entry is generated. In this case,
the invoked process may be any process that is suitable to be
run as session leader. Defaults to "init".
Added in version 225.
Processes started by the service manager are executed with an
environment variable block assembled from multiple sources.
Processes started by the system service manager generally do not
inherit environment variables set for the service manager itself
(but this may be altered via PassEnvironment=), but processes
started by the user service manager instances generally do inherit
all environment variables set for the service manager itself.
For each invoked process the list of environment variables set is
compiled from the following sources:
• Variables globally configured for the service manager, using
the DefaultEnvironment= setting in systemd-system.conf(5), the
kernel command line option systemd.setenv= understood by
systemd(1), or via systemctl(1) set-environment verb.
• Variables defined by the service manager itself (see the list
below).
• Variables set in the service manager's own environment
variable block (subject to PassEnvironment= for the system
service manager).
• Variables set via Environment= in the unit file.
• Variables read from files specified via EnvironmentFile= in
the unit file.
• Variables set by any PAM modules in case PAMName= is in
effect, cf. pam_env(8).
If the same environment variable is set by multiple of these
sources, the later source — according to the order of the list
above — wins. Note that as the final step all variables listed in
UnsetEnvironment= are removed from the compiled environment
variable list, immediately before it is passed to the executed
process.
The general philosophy is to expose a small curated list of
environment variables to processes. Services started by the system
manager (PID 1) will be started, without additional
service-specific configuration, with just a few environment
variables. The user manager inherits environment variables as any
other system service, but in addition may receive additional
environment variables from PAM, and, typically, additional
imported variables when the user starts a graphical session. It is
recommended to keep the environment blocks in both the system and
user managers lean. Importing all variables inherited by the
graphical session or by one of the user shells is strongly
discouraged.
Hint: systemd-run -P env and systemd-run --user -P env print the
effective system and user service environment blocks.
Environment Variables Set or Propagated by the Service Manager
The following environment variables are propagated by the service
manager or generated internally for each invoked process:
$PATH
Colon-separated list of directories to use when launching
executables. systemd uses a fixed value of
"/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin" in the
system manager. In case of the user manager, a different path
may be configured by the distribution. It is recommended to
not rely on the order of entries, and have only one program
with a given name in $PATH.
Added in version 208.
$LANG
Locale. Can be set in locale.conf(5) or on the kernel command
line (see systemd(1) and kernel-command-line(7)).
Added in version 208.
$USER, $LOGNAME, $HOME, $SHELL
User name (twice), home directory, and the login shell. $USER
is set unconditionally, while $HOME, $LOGNAME, and $SHELL are
only set for the units that have User= set and
SetLoginEnvironment= unset or set to true. For user services,
these variables are typically inherited from the user manager
itself. See passwd(5).
Added in version 208.
$INVOCATION_ID
Contains a randomized, unique 128-bit ID identifying each
runtime cycle of the unit, formatted as 32 character
hexadecimal string. A new ID is assigned each time the unit
changes from an inactive state into an activating or active
state, and may be used to identify this specific runtime
cycle, in particular in data stored offline, such as the
journal. The same ID is passed to all processes run as part of
the unit.
Added in version 232.
$XDG_RUNTIME_DIR
The directory to use for runtime objects (such as IPC objects)
and volatile state. Set for all services run by the user
systemd instance, as well as any system services that use
PAMName= with a PAM stack that includes pam_systemd. See below
and pam_systemd(8) for more information.
Added in version 208.
$RUNTIME_DIRECTORY, $STATE_DIRECTORY, $CACHE_DIRECTORY,
$LOGS_DIRECTORY, $CONFIGURATION_DIRECTORY
Absolute paths to the directories defined with
RuntimeDirectory=, StateDirectory=, CacheDirectory=,
LogsDirectory=, and ConfigurationDirectory= when those
settings are used.
Added in version 244.
$CREDENTIALS_DIRECTORY
An absolute path to the per-unit directory with credentials
configured via
ImportCredential=/LoadCredential=/SetCredential=. The
directory is marked read-only and is placed in unswappable
memory (if supported and permitted), and is only accessible to
the UID associated with the unit via User= or DynamicUser=
(and the superuser).
Added in version 247.
$TMPDIR
The environment variable is set to "/tmp" when
PrivateTmp=disconnected specified with DefaultDependencies=no
and without RootDirectory=/RootImage= and
RequiresMountsFor=/WantsMountsFor= for /var/. See explanation
for PrivateTmp= above.
Added in version 258.
$MAINPID
The UNIX process ID (PID) of the unit's main process if it is
known. This is only set for control processes as invoked by
ExecReload= and similar.
Added in version 209.
$MAINPIDFDID
The 64bit inode ID of the file descriptor returned by
pidfd_open(3) for the main process (if supported). This is
only set for control processes as invoked by ExecReload= and
similar.
Added in version 258.
$MANAGERPID
The PID of the per-user systemd service manager instance, set
for processes spawned by it.
Added in version 208.
$MANAGERPIDFDID
The pidfd_open() inode ID (see above) of the per-user systemd
service manager instance, set for processes spawned by it.
Added in version 258.
$LISTEN_FDS, $LISTEN_PID, $LISTEN_FDNAMES
Information about file descriptors passed to a service for
socket activation. See sd_listen_fds(3).
Added in version 208.
$NOTIFY_SOCKET
The socket sd_notify() talks to. See sd_notify(3).
Added in version 229.
$WATCHDOG_PID, $WATCHDOG_USEC
Information about watchdog keep-alive notifications. See
sd_watchdog_enabled(3).
Added in version 229.
$SYSTEMD_EXEC_PID
The PID of the unit process (e.g. process invoked by
ExecStart=). The child process can use this information to
determine whether the process is directly invoked by the
service manager or indirectly as a child of another process by
comparing this value with the current PID (similarly to the
scheme used in sd_listen_fds(3) with $LISTEN_PID and
$LISTEN_FDS).
Added in version 248.
$TERM
Terminal type, set only for units connected to a terminal
(StandardInput=tty, StandardOutput=tty, or StandardError=tty).
See termcap(5).
Added in version 209.
$LOG_NAMESPACE
Contains the name of the selected logging namespace when the
LogNamespace= service setting is used.
Added in version 246.
$JOURNAL_STREAM
If the standard output or standard error output of the
executed processes are connected to the journal (for example,
by setting StandardError=journal) $JOURNAL_STREAM contains the
device and inode numbers of the connection file descriptor,
formatted in decimal, separated by a colon (":"). This permits
invoked processes to safely detect whether their standard
output or standard error output are connected to the journal.
The device and inode numbers of the file descriptors should be
compared with the values set in the environment variable to
determine whether the process output is still connected to the
journal. Note that it is generally not sufficient to only
check whether $JOURNAL_STREAM is set at all as services might
invoke external processes replacing their standard output or
standard error output, without unsetting the environment
variable.
If both standard output and standard error of the executed
processes are connected to the journal via a stream socket,
this environment variable will contain information about the
standard error stream, as that's usually the preferred
destination for log data. (Note that typically the same stream
is used for both standard output and standard error, hence
very likely the environment variable contains device and inode
information matching both stream file descriptors.)
This environment variable is primarily useful to allow
services to optionally upgrade their used log protocol to the
native journal protocol (using sd_journal_print(3) and other
functions) if their standard output or standard error output
is connected to the journal anyway, thus enabling delivery of
structured metadata along with logged messages.
Added in version 231.
$SERVICE_RESULT
Only used for the service unit type. This environment variable
is passed to all ExecStop= and ExecStopPost= processes, and
encodes the service "result". Currently, the following values
are defined:
Table 6. Defined $SERVICE_RESULT values
┌───────────────────┬──────────────────────────┐
│ Value │ Meaning │
├───────────────────┼──────────────────────────┤
│ "success" │ The service ran │
│ │ successfully and exited │
│ │ cleanly. │
├───────────────────┼──────────────────────────┤
│ "protocol" │ A protocol violation │
│ │ occurred: the service │
│ │ did not take the steps │
│ │ required by its unit │
│ │ configuration │
│ │ (specifically what is │
│ │ configured in its Type= │
│ │ setting). │
├───────────────────┼──────────────────────────┤
│ "timeout" │ One of the steps timed │
│ │ out. │
├───────────────────┼──────────────────────────┤
│ "exit-code" │ Service process exited │
│ │ with a non-zero exit │
│ │ code; see $EXIT_CODE │
│ │ below for the actual │
│ │ exit code returned. │
├───────────────────┼──────────────────────────┤
│ "signal" │ A service process was │
│ │ terminated abnormally by │
│ │ a signal, without │
│ │ dumping core. See │
│ │ $EXIT_CODE below for the │
│ │ actual signal causing │
│ │ the termination. │
├───────────────────┼──────────────────────────┤
│ "core-dump" │ A service process │
│ │ terminated abnormally │
│ │ with a signal and dumped │
│ │ core. See $EXIT_CODE │
│ │ below for the signal │
│ │ causing the termination. │
├───────────────────┼──────────────────────────┤
│ "watchdog" │ Watchdog keep-alive ping │
│ │ was enabled for the │
│ │ service, but the │
│ │ deadline was missed. │
├───────────────────┼──────────────────────────┤
│ "exec-condition" │ Service did not run │
│ │ because ExecCondition= │
│ │ failed. │
├───────────────────┼──────────────────────────┤
│ "oom-kill" │ A service process was │
│ │ terminated by the │
│ │ Out-Of-Memory (OOM) │
│ │ killer. │
├───────────────────┼──────────────────────────┤
│ "start-limit-hit" │ A start limit was │
│ │ defined for the unit and │
│ │ it was hit, causing the │
│ │ unit to fail to start. │
│ │ See systemd.unit(5)'s │
│ │ StartLimitIntervalSec= │
│ │ and StartLimitBurst= for │
│ │ details. │
├───────────────────┼──────────────────────────┤
│ "resources" │ A catch-all condition in │
│ │ case a system operation │
│ │ failed. │
└───────────────────┴──────────────────────────┘
This environment variable is useful to monitor failure or
successful termination of a service. Even though this variable
is available in both ExecStop= and ExecStopPost=, it is
usually a better choice to place monitoring tools in the
latter, as the former is only invoked for services that
managed to start up correctly, and the latter covers both
services that failed during their start-up and those which
failed during their runtime.
Added in version 232.
$EXIT_CODE, $EXIT_STATUS
Only defined for the service unit type. These environment
variables are passed to all ExecStop=, ExecStopPost= processes
and contain exit status/code information of the main process
of the service. For the precise definition of the exit code
and status, see wait(2). $EXIT_CODE is one of "exited",
"killed", "dumped". $EXIT_STATUS contains the numeric exit
code formatted as string if $EXIT_CODE is "exited", and the
signal name in all other cases. Note that these environment
variables are only set if the service manager succeeded to
start and identify the main process of the service.
Table 7. Summary of possible service result variable values
┌───────────────────┬──────────────────┬──────────────────┐
│ $SERVICE_RESULT │ $EXIT_CODE │ $EXIT_STATUS │
├───────────────────┼──────────────────┼──────────────────┤
│ "success" │ "killed" │ "HUP", "INT", │
│ │ │ "TERM", "PIPE" │
│ ├──────────────────┼──────────────────┤
│ │ "exited" │ "0" │
├───────────────────┼──────────────────┼──────────────────┤
│ "protocol" │ not set │ not set │
│ ├──────────────────┼──────────────────┤
│ │ "exited" │ "0" │
├───────────────────┼──────────────────┼──────────────────┤
│ "timeout" │ "killed" │ "TERM", "KILL" │
│ ├──────────────────┼──────────────────┤
│ │ "exited" │ "0", "1", "2", │
│ │ │ "3", ..., "255" │
├───────────────────┼──────────────────┼──────────────────┤
│ "exit-code" │ "exited" │ "1", "2", "3", │
│ │ │ ..., "255" │
├───────────────────┼──────────────────┼──────────────────┤
│ "signal" │ "killed" │ "HUP", "INT", │
│ │ │ "KILL", ... │
├───────────────────┼──────────────────┼──────────────────┤
│ "core-dump" │ "dumped" │ "ABRT", "SEGV", │
│ │ │ "QUIT", ... │
├───────────────────┼──────────────────┼──────────────────┤
│ "watchdog" │ "dumped" │ "ABRT" │
│ ├──────────────────┼──────────────────┤
│ │ "killed" │ "TERM", "KILL" │
│ ├──────────────────┼──────────────────┤
│ │ "exited" │ "0", "1", "2", │
│ │ │ "3", ..., "255" │
├───────────────────┼──────────────────┼──────────────────┤
│ "exec-condition" │ "exited" │ "1", "2", "3", │
│ │ │ "4", ..., "254" │
├───────────────────┼──────────────────┼──────────────────┤
│ "oom-kill" │ "killed" │ "TERM", "KILL" │
├───────────────────┼──────────────────┼──────────────────┤
│ "start-limit-hit" │ not set │ not set │
├───────────────────┼──────────────────┼──────────────────┤
│ "resources" │ any of the above │ any of the above │
├───────────────────┴──────────────────┴──────────────────┤
│ Note: the process may be also terminated by a signal │
│ not sent by systemd. In particular the process may send │
│ an arbitrary signal to itself in a handler for any of │
│ the non-maskable signals. Nevertheless, in the │
│ "timeout" and "watchdog" rows above only the signals │
│ that systemd sends have been included. Moreover, using │
│ SuccessExitStatus= additional exit statuses may be │
│ declared to indicate clean termination, which is not │
│ reflected by this table. │
└─────────────────────────────────────────────────────────┘
Added in version 232.
$MONITOR_SERVICE_RESULT, $MONITOR_EXIT_CODE, $MONITOR_EXIT_STATUS,
$MONITOR_INVOCATION_ID, $MONITOR_UNIT
Only defined for the service unit type. Those environment
variables are passed to all ExecStart= and ExecStartPre=
processes which run in services triggered by OnFailure= or
OnSuccess= dependencies.
Variables $MONITOR_SERVICE_RESULT, $MONITOR_EXIT_CODE and
$MONITOR_EXIT_STATUS take the same values as for ExecStop= and
ExecStopPost= processes. Variables $MONITOR_INVOCATION_ID and
$MONITOR_UNIT are set to the invocation id and unit name of
the service which triggered the dependency.
Note that when multiple services specify the same unit as
their OnFailure= or OnSuccess= handler, those variables will
not be passed. Consider using a template handler unit for that
case instead: "OnFailure=handler@%n.service" for non-templated
units, or "OnFailure=handler@%p-%i.service" for templated
units.
Added in version 251.
$PIDFILE
The path to the configured PID file, in case the process is
forked off on behalf of a service that uses the PIDFile=
setting, see systemd.service(5) for details. Service code may
use this environment variable to automatically generate a PID
file at the location configured in the unit file. This field
is set to an absolute path in the file system.
Added in version 242.
$REMOTE_ADDR, $REMOTE_PORT
If this is a unit started via per-connection socket activation
(i.e. via a socket unit with Accept=yes), these environment
variables contain information about the remote peer of the
socket connection.
For IPv4 and IPv6 connections, $REMOTE_ADDR contains the IP
address, and $REMOTE_PORT contains the port number of the
remote peer.
For AF_UNIX socket connections, $REMOTE_ADDR contains either
the remote socket's file system path starting with a slash
("/"), its address in the abstract namespace starting with an
at symbol ("@"), or is unset in case of an unnamed socket.
$REMOTE_PORT is not set for AF_UNIX sockets.
Added in version 220.
$SO_COOKIE
If this is a unit started via per-connection socket activation
(i.e. via a socket unit with Accept=yes), this environment
variable contains the Linux socket cookie, formatted as
decimal integer. The socket cookie can otherwise be acquired
via getsockopt(7).
Added in version 258.
$TRIGGER_UNIT, $TRIGGER_PATH, $TRIGGER_TIMER_REALTIME_USEC,
$TRIGGER_TIMER_MONOTONIC_USEC
If the unit was activated dynamically (e.g.: a corresponding
path unit or timer unit), the unit that triggered it and other
type-dependent information will be passed via these variables.
Note that this information is provided in a best-effort way.
For example, multiple triggers happening one after another
will be coalesced and only one will be reported, with no
guarantee as to which one it will be. Because of this, in most
cases this variable will be primarily informational, i.e.
useful for debugging purposes, is lossy, and should not be
relied upon to propagate a comprehensive reason for
activation.
Added in version 252.
$MEMORY_PRESSURE_WATCH, $MEMORY_PRESSURE_WRITE
If memory pressure monitoring is enabled for this service
unit, the path to watch and the data to write into it. See
Memory Pressure Handling[25] for details about these variables
and the service protocol data they convey.
Added in version 254.
$FDSTORE
The maximum number of file descriptors that may be stored in
the manager for the service. This variable is set when the
file descriptor store is enabled for the service, i.e.
FileDescriptorStoreMax= is set to a non-zero value (see
systemd.service(5) for details). Applications may check this
environment variable before sending file descriptors to the
service manager via sd_pid_notify_with_fds(3).
Added in version 254.
$DEBUG_INVOCATION
If RestartMode=debug is set, and a previous attempt at
starting the unit failed, this variable will be passed to the
service to indicate that additional logging should be enabled
at startup. See systemd.service(5) for more details.
Added in version 257.
For system services, when PAMName= is enabled and pam_systemd is
part of the selected PAM stack, additional environment variables
defined by systemd may be set for services. Specifically, these
are $XDG_SEAT, $XDG_VTNR, see pam_systemd(8) for details.
When invoking a unit process the service manager possibly fails to
apply the execution parameters configured with the settings above.
In that case the already created service process will exit with a
non-zero exit code before the configured command line is executed.
(Or in other words, the child process possibly exits with these
error codes, after having been created by the fork(2) system call,
but before the matching execve(2) system call is called.)
Specifically, exit codes defined by the C library, by the LSB
specification and by the systemd service manager itself are used.
The following basic service exit codes are defined by the C
library.
Table 8. Basic C library exit codes
┌───────────┬───────────────┬────────────────────┐
│ Exit Code │ Symbolic Name │ Description │
├───────────┼───────────────┼────────────────────┤
│ 0 │ EXIT_SUCCESS │ Generic success │
│ │ │ code. │
├───────────┼───────────────┼────────────────────┤
│ 1 │ EXIT_FAILURE │ Generic failure or │
│ │ │ unspecified error. │
└───────────┴───────────────┴────────────────────┘
The following service exit codes are defined by the LSB
specification[26].
Table 9. LSB service exit codes
┌───────────┬──────────────────────┬────────────────────┐
│ Exit Code │ Symbolic Name │ Description │
├───────────┼──────────────────────┼────────────────────┤
│ 2 │ EXIT_INVALIDARGUMENT │ Invalid or excess │
│ │ │ arguments. │
├───────────┼──────────────────────┼────────────────────┤
│ 3 │ EXIT_NOTIMPLEMENTED │ Unimplemented │
│ │ │ feature. │
├───────────┼──────────────────────┼────────────────────┤
│ 4 │ EXIT_NOPERMISSION │ The user has │
│ │ │ insufficient │
│ │ │ privileges. │
├───────────┼──────────────────────┼────────────────────┤
│ 5 │ EXIT_NOTINSTALLED │ The program is not │
│ │ │ installed. │
├───────────┼──────────────────────┼────────────────────┤
│ 6 │ EXIT_NOTCONFIGURED │ The program is not │
│ │ │ configured. │
├───────────┼──────────────────────┼────────────────────┤
│ 7 │ EXIT_NOTRUNNING │ The program is not │
│ │ │ running. │
└───────────┴──────────────────────┴────────────────────┘
The LSB specification suggests that error codes 200 and above are
reserved for implementations. Some of them are used by the service
manager to indicate problems during process invocation:
Table 10. systemd-specific exit codes
┌───────────┬──────────────────────────────┬─────────────────────────────────────────────┐
│ Exit Code │ Symbolic Name │ Description │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 200 │ EXIT_CHDIR │ Changing to the │
│ │ │ requested working │
│ │ │ directory failed. │
│ │ │ See │
│ │ │ WorkingDirectory= │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 201 │ EXIT_NICE │ Failed to set up │
│ │ │ process scheduling │
│ │ │ priority (nice │
│ │ │ level). See Nice= │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 202 │ EXIT_FDS │ Failed to close │
│ │ │ unwanted file │
│ │ │ descriptors, or to │
│ │ │ adjust passed file │
│ │ │ descriptors. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 203 │ EXIT_EXEC │ The actual process │
│ │ │ execution failed │
│ │ │ (specifically, the │
│ │ │ execve(2) system │
│ │ │ call). Most likely │
│ │ │ this is caused by │
│ │ │ a missing or │
│ │ │ non-accessible │
│ │ │ executable file. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 204 │ EXIT_MEMORY │ Failed to perform │
│ │ │ an action due to │
│ │ │ memory shortage. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 205 │ EXIT_LIMITS │ Failed to adjust │
│ │ │ resource limits. │
│ │ │ See LimitCPU= and │
│ │ │ related settings │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 206 │ EXIT_OOM_ADJUST │ Failed to adjust │
│ │ │ the OOM setting. │
│ │ │ See │
│ │ │ OOMScoreAdjust= │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 207 │ EXIT_SIGNAL_MASK │ Failed to set │
│ │ │ process signal │
│ │ │ mask. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 208 │ EXIT_STDIN │ Failed to set up │
│ │ │ standard input. │
│ │ │ See StandardInput= │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 209 │ EXIT_STDOUT │ Failed to set up │
│ │ │ standard output. │
│ │ │ See │
│ │ │ StandardOutput= │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 210 │ EXIT_CHROOT │ Failed to change │
│ │ │ root directory (‐ │
│ │ │ chroot(2)). See │
│ │ │ RootDirectory=/RootImage= │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 211 │ EXIT_IOPRIO │ Failed to set up IO │
│ │ │ scheduling priority. See │
│ │ │ IOSchedulingClass=/IOSchedulingPriority= │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 212 │ EXIT_TIMERSLACK │ Failed to set up timer slack. See │
│ │ │ TimerSlackNSec= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 213 │ EXIT_SECUREBITS │ Failed to set process secure bits. See │
│ │ │ SecureBits= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 214 │ EXIT_SETSCHEDULER │ Failed to set up CPU scheduling. See │
│ │ │ CPUSchedulingPolicy=/CPUSchedulingPriority= │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 215 │ EXIT_CPUAFFINITY │ Failed to set up CPU affinity. See │
│ │ │ CPUAffinity= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 216 │ EXIT_GROUP │ Failed to determine or change group │
│ │ │ credentials. See │
│ │ │ Group=/SupplementaryGroups= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 217 │ EXIT_USER │ Failed to determine or change user │
│ │ │ credentials, or to set up user namespacing. │
│ │ │ See User=/PrivateUsers= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 218 │ EXIT_CAPABILITIES │ Failed to drop capabilities, or apply │
│ │ │ ambient capabilities. See │
│ │ │ CapabilityBoundingSet=/AmbientCapabilities= │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 219 │ EXIT_CGROUP │ Setting up the service control group │
│ │ │ failed. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 220 │ EXIT_SETSID │ Failed to create new process session. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 221 │ EXIT_CONFIRM │ Execution has been cancelled by the user. │
│ │ │ See the systemd.confirm_spawn= kernel │
│ │ │ command line setting on │
│ │ │ kernel-command-line(7) for details. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 222 │ EXIT_STDERR │ Failed to set up standard error output. See │
│ │ │ StandardError= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 224 │ EXIT_PAM │ Failed to set up PAM session. See PAMName= │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 225 │ EXIT_NETWORK │ Failed to set up network namespacing. See │
│ │ │ PrivateNetwork= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 226 │ EXIT_NAMESPACE │ Failed to set up mount, UTS, or IPC │
│ │ │ namespacing. See ReadOnlyPaths=, │
│ │ │ ProtectHostname=, PrivateIPC=, and related │
│ │ │ settings above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 227 │ EXIT_NO_NEW_PRIVILEGES │ Failed to disable new privileges. See │
│ │ │ NoNewPrivileges=yes above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 228 │ EXIT_SECCOMP │ Failed to apply system call filters. See │
│ │ │ SystemCallFilter= and related settings │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 229 │ EXIT_SELINUX_CONTEXT │ Determining or changing SELinux context │
│ │ │ failed. See SELinuxContext= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 230 │ EXIT_PERSONALITY │ Failed to set up an execution domain │
│ │ │ (personality). See Personality= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 231 │ EXIT_APPARMOR_PROFILE │ Failed to prepare changing AppArmor │
│ │ │ profile. See AppArmorProfile= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 232 │ EXIT_ADDRESS_FAMILIES │ Failed to restrict address families. See │
│ │ │ RestrictAddressFamilies= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 233 │ EXIT_RUNTIME_DIRECTORY │ Setting up runtime directory failed. See │
│ │ │ RuntimeDirectory= and related settings │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 235 │ EXIT_CHOWN │ Failed to adjust socket ownership. Used for │
│ │ │ socket units only. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 236 │ EXIT_SMACK_PROCESS_LABEL │ Failed to set SMACK label. See │
│ │ │ SmackProcessLabel= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 237 │ EXIT_KEYRING │ Failed to set up kernel keyring. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 238 │ EXIT_STATE_DIRECTORY │ Failed to set up unit's state directory. │
│ │ │ See StateDirectory= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 239 │ EXIT_CACHE_DIRECTORY │ Failed to set up unit's cache directory. │
│ │ │ See CacheDirectory= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 240 │ EXIT_LOGS_DIRECTORY │ Failed to set up unit's logging directory. │
│ │ │ See LogsDirectory= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 241 │ EXIT_CONFIGURATION_DIRECTORY │ Failed to set up unit's configuration │
│ │ │ directory. See ConfigurationDirectory= │
│ │ │ above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 242 │ EXIT_NUMA_POLICY │ Failed to set up unit's NUMA memory policy. │
│ │ │ See NUMAPolicy= and NUMAMask= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 243 │ EXIT_CREDENTIALS │ Failed to set up unit's credentials. See │
│ │ │ ImportCredential=, LoadCredential= and │
│ │ │ SetCredential= above. │
├───────────┼──────────────────────────────┼─────────────────────────────────────────────┤
│ 245 │ EXIT_BPF │ Failed to apply BPF restrictions. See │
│ │ │ RestrictFileSystems= above. │
└───────────┴──────────────────────────────┴─────────────────────────────────────────────┘
Finally, the BSD operating systems define a set of exit codes,
typically defined on Linux systems too:
Table 11. BSD exit codes
┌───────────┬────────────────┬────────────────────┐
│ Exit Code │ Symbolic Name │ Description │
├───────────┼────────────────┼────────────────────┤
│ 64 │ EX_USAGE │ Command line usage │
│ │ │ error │
├───────────┼────────────────┼────────────────────┤
│ 65 │ EX_DATAERR │ Data format error │
├───────────┼────────────────┼────────────────────┤
│ 66 │ EX_NOINPUT │ Cannot open input │
├───────────┼────────────────┼────────────────────┤
│ 67 │ EX_NOUSER │ Addressee unknown │
├───────────┼────────────────┼────────────────────┤
│ 68 │ EX_NOHOST │ Host name unknown │
├───────────┼────────────────┼────────────────────┤
│ 69 │ EX_UNAVAILABLE │ Service │
│ │ │ unavailable │
├───────────┼────────────────┼────────────────────┤
│ 70 │ EX_SOFTWARE │ internal software │
│ │ │ error │
├───────────┼────────────────┼────────────────────┤
│ 71 │ EX_OSERR │ System error │
│ │ │ (e.g., cannot │
│ │ │ fork) │
├───────────┼────────────────┼────────────────────┤
│ 72 │ EX_OSFILE │ Critical OS file │
│ │ │ missing │
├───────────┼────────────────┼────────────────────┤
│ 73 │ EX_CANTCREAT │ Cannot create │
│ │ │ (user) output file │
├───────────┼────────────────┼────────────────────┤
│ 74 │ EX_IOERR │ Input/output error │
├───────────┼────────────────┼────────────────────┤
│ 75 │ EX_TEMPFAIL │ Temporary failure; │
│ │ │ user is invited to │
│ │ │ retry │
├───────────┼────────────────┼────────────────────┤
│ 76 │ EX_PROTOCOL │ Remote error in │
│ │ │ protocol │
├───────────┼────────────────┼────────────────────┤
│ 77 │ EX_NOPERM │ Permission denied │
├───────────┼────────────────┼────────────────────┤
│ 78 │ EX_CONFIG │ Configuration │
│ │ │ error │
└───────────┴────────────────┴────────────────────┘
Example 3. $MONITOR_* usage
A service myfailer.service which can trigger an OnFailure=
dependency.
[Unit]
Description=Service which can trigger an OnFailure= dependency
OnFailure=myhandler.service
[Service]
ExecStart=/bin/myprogram
A service mysuccess.service which can trigger an OnSuccess=
dependency.
[Unit]
Description=Service which can trigger an OnSuccess= dependency
OnSuccess=myhandler.service
[Service]
ExecStart=/bin/mysecondprogram
A service myhandler.service which can be triggered by any of the
above services.
[Unit]
Description=Acts on service failing or succeeding
[Service]
ExecStart=/bin/bash -c "echo $MONITOR_SERVICE_RESULT $MONITOR_EXIT_CODE $MONITOR_EXIT_STATUS $MONITOR_INVOCATION_ID $MONITOR_UNIT"
If myfailer.service were to run and exit in failure, then
myhandler.service would be triggered and the monitor variables
would be set as follows:
MONITOR_SERVICE_RESULT=exit-code
MONITOR_EXIT_CODE=exited
MONITOR_EXIT_STATUS=1
MONITOR_INVOCATION_ID=cc8fdc149b2b4ca698d4f259f4054236
MONITOR_UNIT=myfailer.service
If mysuccess.service were to run and exit in success, then
myhandler.service would be triggered and the monitor variables
would be set as follows:
MONITOR_SERVICE_RESULT=success
MONITOR_EXIT_CODE=exited
MONITOR_EXIT_STATUS=0
MONITOR_INVOCATION_ID=6ab9af147b8c4a3ebe36e7a5f8611697
MONITOR_UNIT=mysuccess.service
systemd(1), systemctl(1), systemd-analyze(1), journalctl(1),
systemd-system.conf(5), systemd.unit(5), systemd.service(5),
systemd.socket(5), systemd.swap(5), systemd.mount(5),
systemd.kill(5), systemd.resource-control(5), systemd.time(7),
systemd.directives(7), tmpfiles.d(5), exec(3), fork(2)
1. Discoverable Partitions Specification
https://uapi-group.org/specifications/specs/discoverable_partitions_specification
2. The /proc Filesystem
https://docs.kernel.org/filesystems/proc.html#mount-options
3. User/Group Name Syntax
https://systemd.io/USER_NAMES
4. Password Agent
https://systemd.io/PASSWORD_AGENTS
5. No New Privileges Flag
https://docs.kernel.org/userspace-api/no_new_privs.html
6. JSON User Record
https://systemd.io/USER_RECORD
7. The /proc Filesystem
https://docs.kernel.org/filesystems/proc.html
8. id-mapped mounts
https://lwn.net/Articles/896255/
9. quotactl
https://man7.org/linux/man-pages/man2/quotactl.2.html
10. quotaon.
https://linux.die.net/man/8/quotaon
11. repquota
https://man7.org/linux/man-pages/man8/repquota.8.html
12. Kernel Samepage Merging
https://docs.kernel.org/admin-guide/mm/ksm.html
13. LWN post
https://lwn.net/Articles/947173/
14. unicode scalar values
https://www.unicode.org/glossary/#unicode_scalar_value
15. unicode noncharacters
https://www.unicode.org/glossary/#noncharacter
16. unicode byte order mark
https://www.unicode.org/glossary/#byte_order_mark
17. POSIX shell unquoted text
https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_02_01
18. POSIX shell single-quoted text
https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_02_02
19. POSIX shell double-quoted text
https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_02_03
20. Base64
https://tools.ietf.org/html/rfc2045#section-6.8
21. Container Interface
https://systemd.io/CONTAINER_INTERFACE
22. DMI/SMBIOS
https://www.dmtf.org/standards/smbios
23. qemu
https://www.qemu.org/docs/master/system/index.html
24. System and Service Credentials
https://systemd.io/CREDENTIALS
25. Memory Pressure Handling
https://systemd.io/MEMORY_PRESSURE
26. LSB specification
https://refspecs.linuxbase.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/iniscrptact.html
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a
bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-08-11.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
systemd 258~rc2 SYSTEMD.EXEC(5)
Pages that refer to this page: homectl(1), portablectl(1), systemctl(1), systemd(1), systemd-analyze(1), systemd-ask-password(1), systemd-creds(1), systemd-cryptenroll(1), systemd-dissect(1), systemd-firstboot(1), systemd-id128(1), systemd-nspawn(1), systemd-run(1), systemd-vmspawn(1), userdbctl(1), sd_bus_creds_get_pid(3), sd_id128_get_machine(3), sd_notify(3), sd_pidfd_get_inode_id(3), capsule@.service(5), journald.conf(5), org.freedesktop.portable1(5), org.freedesktop.systemd1(5), systemd.automount(5), systemd.kill(5), systemd.link(5), systemd.mount(5), systemd.netdev(5), systemd.path(5), systemd.resource-control(5), systemd.scope(5), systemd.service(5), systemd.socket(5), systemd.swap(5), systemd-system.conf(5), systemd.timer(5), systemd.unit(5), tmpfiles.d(5), user@.service(5), daemon(7), file-hierarchy(7), smbios-type-11(7), systemd.directives(7), systemd.generator(7), systemd.index(7), systemd.journal-fields(7), systemd-stub(7), systemd.v(7), nss-systemd(8), systemd-coredump(8), systemd-cryptsetup(8), systemd-fsck@.service(8), systemd-journald.service(8), systemd-network-generator.service(8), systemd-nsresourced.service(8), systemd-quotacheck@.service(8), systemd-resolved.service(8), systemd-sysctl.service(8), systemd-sysusers(8), systemd-tmpfiles(8), systemd-vconsole-setup.service(8)
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