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NAME | DESCRIPTION | STANDARDS | HISTORY | NOTES | SEE ALSO | COLOPHON |
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sysfs(5) File Formats Manual sysfs(5)
sysfs - a filesystem for exporting kernel objects
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]
Linux.
Linux 2.6.0.
This manual page is incomplete, possibly inaccurate, and is the
kind of thing that needs to be updated very often.
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
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
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
[email protected]
Linux man-pages 6.15 2025-05-17 sysfs(5)
Pages that refer to this page: madvise(2), sysfs(2), filesystems(5), proc(5), network_namespaces(7)
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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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