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sysfs.5: Various additions and improvements
Drawn from Documentation/filesystems/sysfs.txt, P. Mochel's OLS paper, and some naive investigation. Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
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man5/sysfs.5
140
man5/sysfs.5
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@ -57,6 +57,8 @@ Many of the files in the
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.B sysfs
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filesystem are read-only,
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but some files are writable, allowing kernel variables to be changed.
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To avoid redundancy,
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symbolic links are heavily used to connect entries across the filesystem tree.
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.\"
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.SS Files and directories
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The following list describes some of the files and directories under the
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@ -64,18 +66,93 @@ The following list describes some of the files and directories under the
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hierarchy.
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.TP
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.IR /sys/block
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This subdirectory contains one symbolic link for each block device
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that has been discovered on the system.
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The symbolic links point to corresponding directories under
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.IR /sys/devices .
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.TP
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.IR /sys/bus
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This directory contains one subdirectory for each of the bus types
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in the kernel.
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Inside each of these directories are two subdirectories:
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.RS
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.TP
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.IR devices
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This subdirectory contains symbolic links to entries in
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.IR /sys/devices
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that correspond to the devices discovered on this bus.
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.TP
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.IR drivers
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This subdirectory contains one subdirectory for each device driver
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that is loaded on this bus.
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.RE
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.TP
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.IR /sys/class
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This subdirectory contains a single layer of further subdirectories
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for each of the device classes that have been registered on the system
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(e.g., terminals, network devices, block devices, graphics devices,
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sound devices, and so on).
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Inside each of these subdirectories are symbolic links for each of the
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devices in this class.
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These symbolic links refer to entries in the
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.IR /sys/devices
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directory.
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.TP
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.IR /sys/dev
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This directory contains two subdirectories
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.IR block /
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and
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.IR char/ ,
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corresponding, respectively,
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to the block and character devices on the system.
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Inside each of these subdirectories are symbolic links with names of the form
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.IR major-ID : minor-ID ,
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where the ID values correspond to the major and minor ID of a specific device.
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Each symbolic link points to the
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.B sysfs
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directory for a device.
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The symbolic links inside
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.IR /sys/dev
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thus provide an easy way to look up the
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.B sysfs
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interface using the device IDs returned by a call to
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.BR stat (2)
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(or similar).
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.IP
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The following shell session shows an example from
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.IR /sys/dev :
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.IP
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.in +4n
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.EX
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$ \fBstat \-c "%t %T" /dev/null\fP
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1 3
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$ \fBreadlink /sys/dev/char/1\\:3\fP
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\&../../devices/virtual/mem/null
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$ \fBls \-Fd /sys/devices/virtual/mem/null\fP
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/sys/devices/virtual/mem/null/
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$ \fBls \-d1 /sys/devices/virtual/mem/null/*\fP
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/sys/devices/virtual/mem/null/dev
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/sys/devices/virtual/mem/null/power/
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/sys/devices/virtual/mem/null/subsystem@
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/sys/devices/virtual/mem/null/uevent
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.EE
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.in
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.TP
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.IR /sys/devices
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This is a directory that contains a filesystem representation of
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the kernel device tree,
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which is a hierarchy of
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.I device
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structures within the kernel.
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.TP
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.IR /sys/firmware
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This subdirectory contains interfaces for viewing and manipulating
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firmware-specific objects and attributes.
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.TP
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.IR /sys/fs
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This directory contains subdirectories for some filesystems.
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A filesystem will have a subdirectory here only if it chose
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to explicitly create the subdirectory.
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.TP
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.IR /sys/fs/cgroup
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This directory conventionally is used as a mount point for a
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@ -85,12 +162,70 @@ filesystem containing mount points for
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filesystems.
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.TP
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.IR /sys/hypervisor
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[To be documented]
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.TP
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.IR /sys/kernel
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[To be documented]
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.TP
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.IR /sys/module
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This subdirectory contains one subdirectory
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for each module that is loaded into the kernel.
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The name of each directory is the name of the module.
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In each of the subdirectories, there may be following files:
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.RS
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.TP
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.I coresize
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[to be documented]
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.TP
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.I initsize
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[to be documented]
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.TP
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.I initstate
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[to be documented]
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.TP
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.I refcnt
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[to be documented]
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.TP
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.I srcversion
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[to be documented]
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.TP
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.I taint
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[to be documented]
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.TP
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.I uevent
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[to be documented]
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.TP
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.I version
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[to be documented]
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.RE
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.IP
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In each of the subdirectories, there may be following subdirectories:
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.RS
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.TP
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.I drivers
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[To be documented]
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.TP
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.I holders
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[To be documented]
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.TP
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.I notes
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[To be documented]
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.TP
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.I parameters
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This directory contains one file for each module parameter,
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with each file containing the value of the corresponding parameter.
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Some of these files are writable, allowing the
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.TP
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.I sections
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This subdirectories contains files with information about module sections.
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This information is mainly used for debugging.
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.TP
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.I
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[To be documented]
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.RE
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.TP
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.IR /sys/power
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[To be documented]
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.SH VERSIONS
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The
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.B sysfs
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@ -106,6 +241,11 @@ of thing that needs to be updated very often.
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.BR proc (5),
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.BR udev (7)
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.PP
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P. Mochel. (2005).
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.IR "The sysfs filesystem" .
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Proceedings of the 2005 Ottawa Linux Symposium.
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.\" https://www.kernel.org/pub/linux/kernel/people/mochel/doc/papers/ols-2005/mochel.pdf
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.PP
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The kernel source file
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.I Documentation/filesystems/sysfs.txt
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and various other files in
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