sysfs(5) — Linux manual page


sysfs(5)                   File Formats Manual                  sysfs(5)

NAME         top

       sysfs - a filesystem for exporting kernel objects

DESCRIPTION         top

       The sysfs filesystem is a pseudo-filesystem which provides an
       interface to kernel data structures.  (More precisely, the files
       and directories in sysfs provide a view of the kobject structures
       defined internally within the kernel.)  The files under sysfs
       provide information about devices, kernel modules, filesystems,
       and other kernel components.

       The sysfs filesystem is commonly mounted at /sys.  Typically, it
       is mounted automatically by the system, but it can also be
       mounted manually using a command such as:

           mount -t sysfs sysfs /sys

       Many of the files in the sysfs filesystem are read-only, but some
       files are writable, allowing kernel variables to be changed.  To
       avoid redundancy, symbolic links are heavily used to connect
       entries across the filesystem tree.

   Files and directories
       The following list describes some of the files and directories
       under the /sys hierarchy.

              This subdirectory contains one symbolic link for each
              block device that has been discovered on the system.  The
              symbolic links point to corresponding directories under

              This directory contains one subdirectory for each of the
              bus types in the kernel.  Inside each of these directories
              are two subdirectories:

                     This subdirectory contains symbolic links to
                     entries in /sys/devices that correspond to the
                     devices discovered on this bus.

                     This subdirectory contains one subdirectory for
                     each device driver that is loaded on this bus.

              This subdirectory contains a single layer of further
              subdirectories for each of the device classes that have
              been registered on the system (e.g., terminals, network
              devices, block devices, graphics devices, sound devices,
              and so on).  Inside each of these subdirectories are
              symbolic links for each of the devices in this class.
              These symbolic links refer to entries in the /sys/devices

              Each of the entries in this directory is a symbolic link
              representing one of the real or virtual networking devices
              that are visible in the network namespace of the process
              that is accessing the directory.  Each of these symbolic
              links refers to entries in the /sys/devices directory.

              This directory contains two subdirectories block/ and
              char/, corresponding, respectively, to the block and
              character devices on the system.  Inside each of these
              subdirectories are symbolic links with names of the form
              major-ID:minor-ID, where the ID values correspond to the
              major and minor ID of a specific device.  Each symbolic
              link points to the sysfs directory for a device.  The
              symbolic links inside /sys/dev thus provide an easy way to
              look up the sysfs interface using the device IDs returned
              by a call to stat(2) (or similar).

              The following shell session shows an example from

                  $ stat -c "%t %T" /dev/null
                  1 3
                  $ readlink /sys/dev/char/1\:3
                  $ ls -Fd /sys/devices/virtual/mem/null
                  $ ls -d1 /sys/devices/virtual/mem/null/*

              This is a directory that contains a filesystem
              representation of the kernel device tree, which is a
              hierarchy of device structures within the kernel.

              This subdirectory contains interfaces for viewing and
              manipulating firmware-specific objects and attributes.

              This directory contains subdirectories for some
              filesystems.  A filesystem will have a subdirectory here
              only if it chose to explicitly create the subdirectory.

              This directory conventionally is used as a mount point for
              a tmpfs(5) filesystem containing mount points for
              cgroups(7) filesystems.

              The directory contains configuration files for the SMACK
              LSM.  See the kernel source file

              [To be documented]

              This subdirectory contains various files and
              subdirectories that provide information about the running

              For information about the files in this directory, see

              Mount point for the tracefs filesystem used by the
              kernel's ftrace facility.  (For information on ftrace, see
              the kernel source file Documentation/trace/ftrace.txt.)

              This subdirectory contains various files and
              subdirectories that provide information about the kernel's
              memory management subsystem.

              This subdirectory contains one subdirectory for each of
              the huge page sizes that the system supports.  The
              subdirectory name indicates the huge page size (e.g.,
              hugepages-2048kB).  Within each of these subdirectories is
              a set of files that can be used to view and (in some
              cases) change settings associated with that huge page
              size.  For further information, see the kernel source file

              This subdirectory contains one subdirectory for each
              module that is loaded into the kernel.  The name of each
              directory is the name of the module.  In each of the
              subdirectories, there may be following files:

                     [to be documented]

                     [to be documented]

                     [to be documented]

              refcnt [to be documented]

                     [to be documented]

              taint  [to be documented]

              uevent [to be documented]

                     [to be documented]

              In each of the subdirectories, there may be following

                     [To be documented]

                     [To be documented]

              notes  [To be documented]

                     This directory contains one file for each module
                     parameter, with each file containing the value of
                     the corresponding parameter.  Some of these files
                     are writable, allowing the

                     This subdirectories contains files with information
                     about module sections.  This information is mainly
                     used for debugging.

              [To be documented]

              [To be documented]

STANDARDS         top


HISTORY         top

       Linux 2.6.0.

NOTES         top

       This manual page is incomplete, possibly inaccurate, and is the
       kind of thing that needs to be updated very often.

SEE ALSO         top

       proc(5), udev(7)

       P. Mochel. (2005).  The sysfs filesystem.  Proceedings of the
       2005 Ottawa Linux Symposium.

       The kernel source file Documentation/filesystems/sysfs.txt and
       various other files in Documentation/ABI and

Linux man-pages (unreleased)     (date)                         sysfs(5)

Pages that refer to this page: madvise(2)sysfs(2)filesystems(5)proc(5)network_namespaces(7)