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diff --git a/man5/sysfs.5 b/man5/sysfs.5 new file mode 100644 index 0000000..2edd582 --- /dev/null +++ b/man5/sysfs.5 @@ -0,0 +1,275 @@ +.\" Copyright (c) 2017 by Michael Kerrisk <mtk.manpages@gmail.com> +.\" +.\" SPDX-License-Identifier: Linux-man-pages-copyleft +.\" +.TH sysfs 5 2023-03-30 "Linux man-pages 6.05.01" +.SH NAME +sysfs \- a filesystem for exporting kernel objects +.SH DESCRIPTION +The +.B sysfs +filesystem is a pseudo-filesystem which provides an interface to +kernel data structures. +(More precisely, the files and directories in +.B sysfs +provide a view of the +.I kobject +structures defined internally within the kernel.) +The files under +.B sysfs +provide information about devices, kernel modules, filesystems, +and other kernel components. +.PP +The +.B sysfs +filesystem is commonly mounted at +.IR /sys . +Typically, it is mounted automatically by the system, +but it can also be mounted manually using a command such as: +.PP +.in +4n +.EX +mount \-t sysfs sysfs /sys +.EE +.in +.PP +Many of the files in the +.B 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. +.\" +.SS Files and directories +The following list describes some of the files and directories under the +.I /sys +hierarchy. +.TP +.I /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 +.IR /sys/devices . +.TP +.I /sys/bus +This directory contains one subdirectory for each of the bus types +in the kernel. +Inside each of these directories are two subdirectories: +.RS +.TP +.I devices +This subdirectory contains symbolic links to entries in +.I /sys/devices +that correspond to the devices discovered on this bus. +.TP +.I drivers +This subdirectory contains one subdirectory for each device driver +that is loaded on this bus. +.RE +.TP +.I /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 +.I /sys/devices +directory. +.TP +.I /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 +.I /sys/devices +directory. +.TP +.I /sys/dev +This directory contains two subdirectories +.I block/ +and +.IR 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 +.IR 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 +.B sysfs +directory for a device. +The symbolic links inside +.I /sys/dev +thus provide an easy way to look up the +.B sysfs +interface using the device IDs returned by a call to +.BR stat (2) +(or similar). +.IP +The following shell session shows an example from +.IR /sys/dev : +.IP +.in +4n +.EX +$ \fBstat \-c "%t %T" /dev/null\fP +1 3 +$ \fBreadlink /sys/dev/char/1\e:3\fP +\&../../devices/virtual/mem/null +$ \fBls \-Fd /sys/devices/virtual/mem/null\fP +/sys/devices/virtual/mem/null/ +$ \fBls \-d1 /sys/devices/virtual/mem/null/*\fP +/sys/devices/virtual/mem/null/dev +/sys/devices/virtual/mem/null/power/ +/sys/devices/virtual/mem/null/subsystem@ +/sys/devices/virtual/mem/null/uevent +.EE +.in +.TP +.I /sys/devices +This is a directory that contains a filesystem representation of +the kernel device tree, +which is a hierarchy of +.I device +structures within the kernel. +.TP +.I /sys/firmware +This subdirectory contains interfaces for viewing and manipulating +firmware-specific objects and attributes. +.TP +.I /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. +.TP +.I /sys/fs/cgroup +This directory conventionally is used as a mount point for a +.BR tmpfs (5) +filesystem containing mount points for +.BR cgroups (7) +filesystems. +.TP +.I /sys/fs/smackfs +The directory contains configuration files for the SMACK LSM. +See the kernel source file +.IR Documentation/admin\-guide/LSM/Smack.rst . +.TP +.I /sys/hypervisor +[To be documented] +.TP +.I /sys/kernel +This subdirectory contains various files and subdirectories that provide +information about the running kernel. +.TP +.I /sys/kernel/cgroup/ +For information about the files in this directory, see +.BR cgroups (7). +.TP +.I /sys/kernel/debug/tracing +Mount point for the +.I tracefs +filesystem used by the kernel's +.I ftrace +facility. +(For information on +.IR ftrace , +see the kernel source file +.IR Documentation/trace/ftrace.txt .) +.TP +.I /sys/kernel/mm +This subdirectory contains various files and subdirectories that provide +information about the kernel's memory management subsystem. +.TP +.I /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., +.IR 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 +.IR Documentation/admin\-guide/mm/hugetlbpage.rst . +.TP +.I /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: +.RS +.TP +.I coresize +[to be documented] +.TP +.I initsize +[to be documented] +.TP +.I initstate +[to be documented] +.TP +.I refcnt +[to be documented] +.TP +.I srcversion +[to be documented] +.TP +.I taint +[to be documented] +.TP +.I uevent +[to be documented] +.TP +.I version +[to be documented] +.RE +.IP +In each of the subdirectories, there may be following subdirectories: +.RS +.TP +.I drivers +[To be documented] +.TP +.I holders +[To be documented] +.TP +.I notes +[To be documented] +.TP +.I 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 +.TP +.I sections +This subdirectories contains files with information about module sections. +This information is mainly used for debugging. +.TP +.I +[To be documented] +.RE +.TP +.I /sys/power +[To be documented] +.SH STANDARDS +Linux. +.SH HISTORY +Linux 2.6.0. +.SH NOTES +This manual page is incomplete, possibly inaccurate, and is the kind +of thing that needs to be updated very often. +.SH SEE ALSO +.BR proc (5), +.BR udev (7) +.PP +P.\& Mochel. (2005). +.IR "The sysfs filesystem" . +Proceedings of the 2005 Ottawa Linux Symposium. +.\" https://www.kernel.org/pub/linux/kernel/people/mochel/doc/papers/ols-2005/mochel.pdf +.PP +The kernel source file +.I Documentation/filesystems/sysfs.txt +and various other files in +.I Documentation/ABI +and +.I Documentation/*/sysfs.txt |