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SYSFS(5)                   Linux Programmer's ManualSYSFS(5)NAME       sysfs - a filesystem for exporting kernel objectsDESCRIPTION       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  manu-       ally 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 redun-       dancy,  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 de-              vice 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 de-                     vice driver that is loaded on this bus.       /sys/class              This subdirectory contains a single layer of further subdirecto-              ries 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  repre-              senting  one  of the real or virtual networking devices that are              visible in the network namespace of the process that is  access-              ing  the  directory.  Each of these symbolic links refers to en-              tries 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  de-              vice.   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 tostat(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 struc-              tures within the kernel.       /sys/firmware              This subdirectory contains interfaces for viewing and manipulat-              ing 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 ex-              plicitly create the subdirectory.       /sys/fs/cgroup              This  directory  conventionally  is  used as a mount point for atmpfs(5)  filesystem  containing  mount  points  forcgroups(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,   seecgroups(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 subsys-              tem.       /sys/kernel/mm/hugepages              This subdirectory contains one subdirectory for each of the huge              page sizes that the system supports.  The subdirectory name  in-              dicates  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  subdirec-              tories:              drivers                     [To be documented]              holders                     [To be documented]              notes  [To be documented]              parameters                     This  directory contains one file for each module parame-                     ter, 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 de-                     bugging.              [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 ALSOproc(5),udev(7)       P.  Mochel. (2005).  The sysfs filesystem.  Proceedings of the 2005 Ot-       tawa Linux Symposium.       The kernel source file Documentation/filesystems/sysfs.txt and  various       other files in Documentation/ABI and Documentation/*/sysfs.txtCOLOPHON       This  page  is  part of release 5.05 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                             2018-04-30SYSFS(5)