# SYSFS(5) - man - phpMan [SYSFS(5)](https://www.chedong.com/phpMan.php/man/SYSFS/5/markdown) Linux Programmer's Manual [SYSFS(5)](https://www.chedong.com/phpMan.php/man/SYSFS/5/markdown) ## NAME sysfs - a filesystem for exporting kernel objects ## DESCRIPTION The **sysfs** filesystem is a pseudo-filesystem which provides an interface to kernel data struc‐ tures. (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, allow‐ ing 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 dis‐ covered 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. In‐ side each of these directories are two subdirectories: _devices_ This subdirectory contains symbolic links to entries in _/sys/devices_ that cor‐ respond 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 de‐ vices, 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, respec‐ tively, to the block and character devices on the system. Inside each of these subdi‐ rectories 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)](https://www.chedong.com/phpMan.php/man/stat/2/markdown) (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)](https://www.chedong.com/phpMan.php/man/tmpfs/5/markdown) filesystem con‐ taining mount points for [**cgroups**(7)](https://www.chedong.com/phpMan.php/man/cgroups/7/markdown) 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)](https://www.chedong.com/phpMan.php/man/cgroups/7/markdown). _/sys/kernel/debug/tracing_ Mount point for the _tracefs_ filesystem used by the kernel's _ftrace_ facility. (For in‐ formation 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 subdi‐ rectories, 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 con‐ taining 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)](https://www.chedong.com/phpMan.php/man/proc/5/markdown), [**udev**(7)](https://www.chedong.com/phpMan.php/man/udev/7/markdown) 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 _Docu__‐ _mentation/ABI_ and _Documentation/*/sysfs.txt_ ## COLOPHON This page is part of release 5.10 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)](https://www.chedong.com/phpMan.php/man/SYSFS/5/markdown)