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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | FILES | SEE ALSO | NOTES | COLOPHON |
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SYSTEMD-P...E.SERVICE(8) systemd-pcrphase.serviceSYSTEMD-P...E.SERVICE(8)
systemd-pcrphase.service, systemd-pcrphase-sysinit.service,
systemd-pcrphase-initrd.service, systemd-pcrmachine.service,
systemd-pcrfs-root.service, systemd-pcrfs@.service, systemd-
pcrextend - Measure boot phase into TPM2 PCR 11, machine ID and
file system identity into PCR 15
systemd-pcrphase.service
systemd-pcrphase-sysinit.service
systemd-pcrphase-initrd.service
systemd-pcrmachine.service
systemd-pcrfs-root.service
systemd-pcrfs@.service
/usr/lib/systemd/systemd-pcrextend [STRING]
systemd-pcrphase.service, systemd-pcrphase-sysinit.service, and
systemd-pcrphase-initrd.service are system services that measure
specific strings into TPM2 PCR 11 during boot at various
milestones of the boot process.
systemd-pcrmachine.service is a system service that measures the
machine ID (see machine-id(5)) into PCR 15.
systemd-pcrfs-root.service and systemd-pcrfs@.service are services
that measure file system identity information (i.e. mount point,
file system type, label and UUID, partition label and UUID) into
PCR 15. systemd-pcrfs-root.service does so for the root file
system, systemd-pcrfs@.service is a template unit that measures
the file system indicated by its instance identifier instead.
These services require systemd-stub(7) to be used in a unified
kernel image (UKI). They execute no operation when the stub has
not been used to invoke the kernel. The stub will measure the
invoked kernel and associated vendor resources into PCR 11 before
handing control to it; once userspace is invoked these services
then will extend TPM2 PCR 11 with certain literal strings
indicating phases of the boot process. During a regular boot
process PCR 11 is extended with the following strings:
1. "enter-initrd" — early when the initrd initializes, before
activating system extension images for the initrd. It acts as
a barrier between the time where the kernel initializes and
where the initrd starts operating and enables system extension
images, i.e. code shipped outside of the UKI. (This extension
happens when the systemd-pcrphase-initrd.service(8) service is
started.)
2. "leave-initrd" — when the initrd is about to transition into
the host file system. It acts as barrier between initrd code
and host OS code. (This extension happens when the
systemd-pcrphase-sysinit.service(8) service is stopped.)
3. "sysinit" — when basic system initialization is complete
(which includes local file systems having been mounted), and
the system begins starting regular system services. (This
extension happens when the systemd-pcrphase-sysinit.service(8)
service is started.)
4. "ready" — during later boot-up, after remote file systems have
been activated (i.e. after remote-fs.target), but before users
are permitted to log in (i.e. before
systemd-user-sessions.service). It acts as barrier between the
time where unprivileged regular users are still prohibited to
log in and where they are allowed to log in. (This extension
happens when the systemd-pcrphase-sysinit.service(8) service
is started.)
5. "shutdown" — when the system shutdown begins. It acts as
barrier between the time the system is fully up and running
and where it is about to shut down. (This extension happens
when the systemd-pcrphase.service service is stopped.)
6. "final" — at the end of system shutdown. It acts as barrier
between the time the service manager still runs and when it
transitions into the final shutdown phase where service
management is not available anymore. (This extension happens
when the systemd-pcrphase-sysinit.service(8) service is
stopped.)
During a regular system lifecycle, PCR 11 is extended with the
strings "enter-initrd", "leave-initrd", "sysinit", "ready",
"shutdown", and "final".
Specific phases of the boot process may be referenced via the
series of strings measured, separated by colons (the "phase
path"). For example, the phase path for the regular system runtime
is "enter-initrd:leave-initrd:sysinit:ready", while the one for
the initrd is just "enter-initrd". The phase path for the boot
phase before the initrd is an empty string; because that's hard to
pass around a single colon (":") may be used instead. Note that
the aforementioned six strings are just the default strings and
individual systems might measure other strings at other times, and
thus implement different and more fine-grained boot phases to bind
policy to.
By binding policy of TPM2 objects to a specific phase path it is
possible to restrict access to them to specific phases of the boot
process, for example making it impossible to access the root file
system's encryption key after the system transitioned from the
initrd into the host root file system.
Use systemd-measure(1) to pre-calculate expected PCR 11 values for
specific boot phases (via the --phase= switch).
systemd-pcrfs-root.service and systemd-pcrfs@.service are
automatically pulled into the initial transaction by
systemd-gpt-auto-generator(8) for the root and /var/ file systems.
systemd-fstab-generator(8) will do this for all mounts with the
x-systemd.pcrfs mount option in /etc/fstab.
The /usr/lib/systemd/system-pcrextend executable may also be
invoked from the command line, where it expects the word to extend
into PCR 11, as well as the following switches:
--bank=
Takes the PCR banks to extend the specified word into. If not
specified, the tool automatically determines all enabled PCR
banks and measures the word into all of them.
Added in version 252.
--pcr=
Takes the index of the PCR to extend. If --machine-id or
--file-system= are specified defaults to 15, otherwise
defaults to 11.
Added in version 255.
--tpm2-device=PATH
Controls which TPM2 device to use. Expects a device node path
referring to the TPM2 chip (e.g. /dev/tpmrm0). Alternatively
the special value "auto" may be specified, in order to
automatically determine the device node of a suitable TPM2
device (of which there must be exactly one). The special value
"list" may be used to enumerate all suitable TPM2 devices
currently discovered.
Added in version 252.
--graceful
If no TPM2 firmware, kernel subsystem, kernel driver or device
support is found, exit with exit status 0 (i.e. indicate
success). If this is not specified, any attempt to measure
without a TPM2 device will cause the invocation to fail.
Added in version 253.
--machine-id
Instead of measuring a word specified on the command line into
PCR 11, measure the host's machine ID into PCR 15.
Added in version 253.
--file-system=
Instead of measuring a word specified on the command line into
PCR 11, measure identity information of the specified file
system into PCR 15. The parameter must be the path to the
established mount point of the file system to measure.
Added in version 253.
-h, --help
Print a short help text and exit.
--version
Print a short version string and exit.
/run/log/systemd/tpm2-measure.log
Measurements are logged into an event log file maintained in
/run/log/systemd/tpm2-measure.log, which contains a
JSON-SEQ[1] series of objects that follow the general
structure of the TCG Canonical Event Log Format (CEL-JSON)[2]
event objects (but lack the "recnum" field).
A LOCK_EX BSD file lock (flock(2)) on the log file is acquired
while the measurement is made and the file is updated. Thus,
applications that intend to acquire a consistent quote from
the TPM with the associated snapshot of the event log should
acquire a LOCK_SH lock while doing so.
Added in version 252.
systemd(1), systemd-stub(7), systemd-measure(1),
systemd-gpt-auto-generator(8), systemd-fstab-generator(8), TPM2
PCR Measurements Made by systemd[3]
1. JSON-SEQ
https://www.rfc-editor.org/rfc/rfc7464.html
2. TCG Canonical Event Log Format (CEL-JSON)
https://trustedcomputinggroup.org/resource/canonical-event-log-format/
3. TPM2 PCR Measurements Made by systemd
https://systemd.io/TPM2_PCR_MEASUREMENTS
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-P...E.SERVICE(8)
Pages that refer to this page: systemd-cryptenroll(1), systemd-measure(1), ukify(1), systemd.mount(5), systemd.pcrlock(5), systemd.directives(7), systemd.index(7), systemd-gpt-auto-generator(8), systemd-pcrlock(8), systemd-pcrphase.service(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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