sysfs

SYSFS(5)                   Linux Programmer's Manual                  SYSFS(5)



NAME
       sysfs - a filesystem for exporting kernel objects

DESCRIPTION
       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.

       /sys/block
              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 /sys/devices.

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

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

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

       /sys/class
              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 directory.

       /sys/class/net
              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.

       /sys/dev
              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 /sys/dev:

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

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

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

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

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

       /sys/fs/smackfs
              The directory contains configuration files for the SMACK LSM.
              See the kernel source file Documentation/admin-
              guide/LSM/Smack.rst.

       /sys/hypervisor
              [To be documented]

       /sys/kernel
              This subdirectory contains various files and subdirectories that
              provide information about the running kernel.

       /sys/kernel/cgroup/
              For information about the files in this directory, see
              cgroups(7).

       /sys/kernel/debug/tracing
              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.)

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

       /sys/kernel/mm/hugepages
              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 Documentation/admin-guide/mm/hugetlbpage.rst.

       /sys/module
              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:

              coresize
                     [to be documented]

              initsize
                     [to be documented]

              initstate
                     [to be documented]

              refcnt [to be documented]

              srcversion
                     [to be documented]

              taint  [to be documented]

              uevent [to be documented]

              version
                     [to be documented]

              In each of the subdirectories, there may be following
              subdirectories:

              drivers
                     [To be documented]

              holders
                     [To be documented]

              notes  [To be documented]

              parameters
                     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

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

              [To be documented]

       /sys/power
              [To be documented]

VERSIONS
       The sysfs filesystem first appeared in Linux 2.6.0.

CONFORMING TO
       The sysfs filesystem is Linux-specific.

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

SEE ALSO
       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 Documentation/*/sysfs.txt

COLOPHON
       This page is part of release 5.03 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.



Linux                             2018-04-30                          SYSFS(5)