2017-09-11 05:40:23 +00:00
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.\" Copyright (c) 2017 by Michael Kerrisk <mtk.manpages@gmail.com>
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.\"
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.\" %%%LICENSE_START(VERBATIM)
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execve.2, fallocate.2, getrlimit.2, io_submit.2, membarrier.2, mmap.2, msgget.2, open.2, ptrace.2, readv.2, semget.2, shmget.2, shutdown.2, syscall.2, wait.2, wait4.2, crypt.3, encrypt.3, fseek.3, getcwd.3, makedev.3, pthread_create.3, puts.3, tsearch.3, elf.5, filesystems.5, group.5, passwd.5, sysfs.5, mount_namespaces.7, posixoptions.7, time.7, unix.7, vdso.7, xattr.7, ld.so.8: tstamp
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
2018-04-30 15:41:31 +00:00
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.TH SYSFS 5 2018-04-30 "Linux" "Linux Programmer's Manual"
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2017-09-11 05:40:23 +00:00
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.SH NAME
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sysfs \- a filesystem for exporting kernel objects
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.SH DESCRIPTION
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The
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.B sysfs
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filesystem is a pseudo-filesystem which provides an interface to
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kernel data structures.
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(More precisely, the files and directories in
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.B sysfs
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provide a view of the
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.IR kobject
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structures defined internally within the kernel.)
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The files under
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.B sysfs
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provide information about devices, kernel modules, filesystems,
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and other kernel components.
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.PP
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The
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.B sysfs
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filesystem is commonly mounted at
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.IR /sys .
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Typically, it is mounted automatically by the system,
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but it can also be mounted manually using a command such as:
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.PP
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.in +4n
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.EX
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mount \-t sysfs sysfs /sys
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.EE
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.in
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.PP
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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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2017-09-11 10:14:44 +00:00
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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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2017-09-11 05:40:23 +00:00
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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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.I /sys
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hierarchy.
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.TP
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.IR /sys/block
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2017-09-11 10:14:44 +00:00
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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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2017-09-11 05:40:23 +00:00
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.TP
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.IR /sys/bus
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2017-09-11 10:14:44 +00:00
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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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2017-09-11 05:40:23 +00:00
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.TP
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.IR /sys/class
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2017-09-11 10:14:44 +00:00
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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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2017-09-11 05:40:23 +00:00
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.TP
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2017-09-22 08:08:54 +00:00
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.IR /sys/class/net
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Each of the entries in this directory is a symbolic link
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2017-12-10 22:15:08 +00:00
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representing one of the real or virtual networking devices
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2017-09-22 08:08:54 +00:00
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that are visible in the network namespace of the process
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that is accessing the directory.
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Each of these symbolic links refers 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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2017-09-11 05:40:23 +00:00
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.IR /sys/dev
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2017-09-11 10:14:44 +00:00
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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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2017-09-15 10:50:14 +00:00
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.IR major-ID : minor-ID ,
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2017-09-11 10:14:44 +00:00
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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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locale.1, memusage.1, pldd.1, _syscall.2, add_key.2, bind.2, bpf.2, chown.2, clone.2, copy_file_range.2, eventfd.2, execve.2, futex.2, getdents.2, getrlimit.2, ioctl_fat.2, ioctl_ns.2, kcmp.2, kexec_load.2, keyctl.2, listxattr.2, lseek.2, membarrier.2, memfd_create.2, mmap.2, mprotect.2, msgop.2, open_by_handle_at.2, perf_event_open.2, pipe.2, readdir.2, readlink.2, readv.2, recvmmsg.2, request_key.2, sched_setaffinity.2, seccomp.2, select.2, select_tut.2, sendmmsg.2, setns.2, signalfd.2, spu_run.2, stat.2, sysctl.2, tee.2, timer_create.2, timerfd_create.2, truncate.2, uname.2, unshare.2, userfaultfd.2, ustat.2, wait.2, CPU_SET.3, __ppc_get_timebase.3, argz_add.3, asprintf.3, backtrace.3, basename.3, bswap.3, bzero.3, cacos.3, cacosh.3, catan.3, catanh.3, catgets.3, clock_getcpuclockid.3, confstr.3, ctime.3, dl_iterate_phdr.3, dlinfo.3, duplocale.3, encrypt.3, end.3, endian.3, fgetws.3, fmemopen.3, fopencookie.3, fputws.3, frexp.3, ftw.3, get_nprocs_conf.3, get_phys_pages.3, getaddrinfo.3, getaddrinfo_a.3, getdate.3, getgrouplist.3, getifaddrs.3, getline.3, getlogin.3, getopt.3, getpass.3, getprotoent_r.3, getpwnam.3, getservent_r.3, getsubopt.3, glob.3, gnu_get_libc_version.3, hsearch.3, if_nameindex.3, index.3, inet.3, inet_net_pton.3, inet_pton.3, insque.3, iswblank.3, iswspace.3, makecontext.3, mallinfo.3, malloc_hook.3, malloc_info.3, mallopt.3, matherr.3, mbrtowc.3, mbsnrtowcs.3, mbsrtowcs.3, mbstowcs.3, mbtowc.3, mcheck.3, memchr.3, mq_getattr.3, mq_notify.3, newlocale.3, nl_langinfo.3, offsetof.3, perror.3, posix_spawn.3, printf.3, pthread_attr_init.3, pthread_cancel.3, pthread_cleanup_push.3, pthread_create.3, pthread_getattr_default_np.3, pthread_getattr_np.3, pthread_getcpuclockid.3, pthread_mutexattr_setrobust.3, pthread_setaffinity_np.3, pthread_setname_np.3, pthread_setschedparam.3, pthread_sigmask.3, qsort.3, rand.3, readdir.3, regex.3, rpmatch.3, rtime.3, scanf.3, sem_wait.3, setaliasent.3, setbuf.3, stpcpy.3, stpncpy.3, strcat.3, strchr.3, strcpy.3, strdup.3, strerror.3, strfromd.3, strftime.3, strlen.3, strnlen.3, strsep.3, strstr.3, strtok.3, strtol.3, strtoul.3, strverscmp.3, strxfrm.3, termios.3, tsearch.3, wcpcpy.3, wcpncpy.3, wcrtomb.3, wcscat.3, wcscpy.3, wcslen.3, wcsncat.3, wcsncmp.3, wcsncpy.3, wcsnlen.3, wcsnrtombs.3, wcsrtombs.3, wcsstr.3, wcstok.3, wcstombs.3, wcwidth.3, wprintf.3, console_codes.4, dsp56k.4, full.4, initrd.4, loop.4, vcs.4, charmap.5, core.5, elf.5, locale.5, proc.5, repertoiremap.5, sysfs.5, termcap.5, aio.7, bpf-helpers.7, cgroups.7, charsets.7, complex.7, fanotify.7, feature_test_macros.7, inotify.7, locale.7, man-pages.7, man.7, pkeys.7, pthreads.7, rtld-audit.7, sock_diag.7, unix.7, user_namespaces.7, utf-8.7: Use '\e' rather than '\\' to get a backslash
Quoting Branden:
*roff escape sequences may sometimes look like C escapes, but that
is misleading. *roff is in part a macro language and that means
recursive expansion to arbitrary depths.
You can get away with "\\" in a context where no macro expansion
is taking place, but try to spell a literal backslash this way in
the argument to a macro and you will likely be unhappy with
results.
Try viewing the attached file with "man -l".
"\e" is the preferred and portable way to get a portable "escape
literal" going back to CSTR #54, the original Bell Labs troff
paper.
groff(7) discusses the issue:
\\ reduces to a single backslash; useful to delay its
interpretation as escape character in copy mode. For a
printable backslash, use \e, or even better \[rs], to be
independent from the current escape character.
As of groff 1.22.4, groff_man(7) does as well:
\e Widely used in man pages to represent a backslash output
glyph. It works reliably as long as the .ec request is
not used, which should never happen in man pages, and it
is slightly more portable than the more exact ‘\(rs’
(“reverse solidus”) escape sequence.
People not concerned with portability to extremely old troffs should
probably just use \(rs (or \[rs]), as it means "the backslash
glyph", not "the glyph corresponding to whatever the current escape
character is".
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
2019-02-27 11:57:17 +00:00
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$ \fBreadlink /sys/dev/char/1\e:3\fP
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2017-09-11 10:14:44 +00:00
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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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2017-09-11 05:40:23 +00:00
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.TP
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.IR /sys/devices
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2017-09-11 10:14:44 +00:00
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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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2017-09-11 05:40:23 +00:00
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.TP
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.IR /sys/firmware
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2017-09-11 10:14:44 +00:00
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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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2017-09-11 05:40:23 +00:00
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.TP
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.IR /sys/fs
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2017-09-11 10:14:44 +00:00
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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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2017-09-11 05:40:23 +00:00
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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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.BR tmpfs (5)
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filesystem containing mount points for
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.BR cgroups (7)
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filesystems.
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.TP
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2018-03-08 11:30:59 +00:00
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.IR /sys/fs/smackfs
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The directory contains configuration files for the SMACK LSM.
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See the kernel source file
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.IR Documentation/admin-guide/LSM/Smack.rst .
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.TP
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2017-09-11 05:40:23 +00:00
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.IR /sys/hypervisor
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2017-09-11 10:14:44 +00:00
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[To be documented]
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2017-09-11 05:40:23 +00:00
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.TP
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.IR /sys/kernel
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2017-09-21 12:38:59 +00:00
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This subdirectory contains various files and subdirectories that provide
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information about the running kernel.
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2017-09-11 05:40:23 +00:00
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.TP
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2018-01-08 20:19:14 +00:00
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.IR /sys/kernel/cgroup/
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For information about the files in this directory, see
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.BR cgroups (7).
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.TP
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2017-09-28 09:03:05 +00:00
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.IR /sys/kernel/debug/tracing
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Mount point for the
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.I tracefs
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filesystem used by the kernel's
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.I ftrace
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facility.
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(For information on
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.IR ftrace ,
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see the kernel source file
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.IR Documentation/trace/ftrace.txt .)
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.TP
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2017-09-21 12:48:48 +00:00
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.IR /sys/kernel/mm
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This subdirectory contains various files and subdirectories that provide
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information about the kernel's memory management subsystem.
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.TP
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2017-09-21 12:49:03 +00:00
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.IR /sys/kernel/mm/hugepages
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This subdirectory contains one subdirectory for each of the
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huge page sizes that the system supports.
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The subdirectory name indicates the huge page size (e.g.,
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.IR hugepages-2048kB ).
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2017-10-03 15:45:12 +00:00
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Within each of these subdirectories is a set of files
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2017-09-21 12:49:03 +00:00
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that can be used to view and (in some cases) change settings
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associated with that huge page size.
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For further information, see the kernel source file
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ioctl_userfaultfd.2, madvise.2, memfd_create.2, migrate_pages.2, mmap.2, shmget.2, subpage_prot.2, userfaultfd.2, malloc.3, proc.5, sysfs.5, tmpfs.5: Update paths for in-kernel memory management documentation files
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
2018-11-16 21:14:56 +00:00
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.IR Documentation/admin-guide/mm/hugetlbpage.rst .
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2017-09-21 12:49:03 +00:00
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.TP
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2017-09-11 05:40:23 +00:00
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.IR /sys/module
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2017-09-11 10:14:44 +00:00
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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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2017-09-11 10:14:44 +00:00
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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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2017-09-11 05:40:23 +00:00
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.TP
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.IR /sys/power
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2017-09-11 10:14:44 +00:00
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[To be documented]
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2017-09-11 05:40:23 +00:00
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.SH VERSIONS
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The
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.B sysfs
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filesystem first appeared in Linux 2.6.0.
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.SH CONFORMING TO
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The
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.B sysfs
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filesystem is Linux-specific.
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.SH NOTES
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This manual page is incomplete, possibly inaccurate, and is the kind
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of thing that needs to be updated very often.
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.SH SEE ALSO
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.BR proc (5),
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.BR udev (7)
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.PP
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adjtimex.2, futex.2, mremap.2, seccomp.2, getnameinfo.3, random.3, console_codes.4, sysfs.5, sched.7, unicode.7: Use zero‐width space in appropriate locations
Quoting Branden:
*roff systems will interpret the period in the unpatched
page as sentence-ending punctuation and put inter-sentence
spacing after it. (This might not be visible on
nroff/terminal devices, but it is more likely to be on
typesetter/PostScript/PDF output).
groff_man(7) in groff 1.22.4 attempts to throw man page
writers a bone here:
\& Zero‐width space. Append to an input line to prevent
an end‐of‐ sentence punctuation sequence from being
recognized as such, or insert at the beginning of an
input line to prevent a dot or apostrophe from being
interpreted as the beginning of a roff request.
Reported-by: Bjarni Ingi Gislason <bjarniig@rhi.hi.is>
Reported-by: G. Branden Robinson <g.branden.robinson@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
2019-02-27 11:23:42 +00:00
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P.\& Mochel. (2005).
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2017-09-11 10:14:44 +00:00
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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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2017-09-11 05:40:23 +00:00
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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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.IR Documentation/ABI
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and
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.IR Documentation/*/sysfs.txt
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