sysfs(5) — Linux manual page


SYSFS(5)                  Linux Programmer's 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 /sys/devices.

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

                     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 subdirec‐
              tories for each of the device classes that have been regis‐
              tered 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.

              Each of the entries in this directory is a symbolic link rep‐
              resenting 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 /sys/dev:

                  $ 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 manipu‐
              lating 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)

              The directory contains configuration files for the SMACK LSM.
              See the kernel source file Documentation/admin-

              [To be documented]

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

              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

              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/hugetlb‐

              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 subdi‐

                     [To be documented]

                     [To be documented]

              notes  [To be documented]

                     This directory contains one file for each module param‐
                     eter, with each file containing the value of the corre‐
                     sponding 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]

VERSIONS         top

       The sysfs filesystem first appeared in Linux 2.6.0.

CONFORMING TO         top

       The sysfs filesystem is Linux-specific.

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

COLOPHON         top

       This page is part of release 5.08 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

Linux                            2018-04-30                         SYSFS(5)

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