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NAME | DESCRIPTION | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
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SYSFS(5) Linux Programmer's 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 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.
/sys/class/net
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.
/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 manipu‐
lating 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/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/vm/hugetlbpage.txt.
/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 subdi‐
rectories:
drivers
[To be documented]
holders
[To be documented]
notes [To be documented]
parameters
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
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]
The sysfs filesystem first appeared in Linux 2.6.0.
The sysfs filesystem is Linux-specific.
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 release 4.15 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 2017-11-26 SYSFS(5)
Pages that refer to this page: sysfs(2), proc(5), network_namespaces(7)
Copyright and license for this manual page
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