proc - process information pseudo-filesystem
The proc filesystem is a pseudo-filesystem which
provides an interface to kernel data structures. It is commonly mounted
at /proc
. Typically, it is mounted automatically by the system,
but it can also be mounted manually using a command such as:
mount -t proc proc /proc
Most of the files in the proc filesystem are read-only, but some files are writable, allowing kernel variables to be changed.
The proc filesystem supports the following mount options:
n
(since Linux 3.3)This option controls who can access the information in
/proc/[pid]
directories. The argument, n
, is one of
the following values:
Everybody may access all /proc/[pid]
directories. This is
the traditional behavior, and the default if this mount option is not
specified.
Users may not access files and subdirectories inside any
/proc/[pid]
directories but their own (the /proc/[pid]
directories themselves remain visible). Sensitive files such as
/proc/[pid]/cmdline
and /proc/[pid]/status
are now
protected against other users. This makes it impossible to learn whether
any user is running a specific program (so long as the program doesn't
otherwise reveal itself by its behavior).
As for mode 1, but in addition the /proc/[pid]
directories
belonging to other users become invisible. This means that
/proc/[pid]
entries can no longer be used to discover the PIDs
on the system. This doesn't hide the fact that a process with a specific
PID value exists (it can be learned by other means, for example, by
"kill -0 $PID"), but it hides a process's UID and GID, which could
otherwise be learned by employing stat(2) on a
/proc/[pid]
directory. This greatly complicates an attacker's
task of gathering information about running processes (e.g., discovering
whether some daemon is running with elevated privileges, whether another
user is running some sensitive program, whether other users are running
any program at all, and so on).
gid
(since Linux 3.3)Specifies the ID of a group whose members are authorized to learn
process information otherwise prohibited by hidepid
(i.e., users in this group behave as though /proc
was mounted
with hidepid=0
). This group should be used instead of
approaches such as putting nonroot users into the
sudoers(5) file.
Underneath /proc
, there are the following general groups of
files and subdirectories:
/proc/[pid]
subdirectoriesEach one of these subdirectories contains files and subdirectories exposing information about the process with the corresponding process ID.
Underneath each of the /proc/[pid]
directories, a
task
subdirectory contains subdirectories of the form
task/[tid]
, which contain corresponding information about each
of the threads in the process, where tid
is the kernel thread
ID of the thread.
The /proc/[pid]
subdirectories are visible when iterating
through /proc
with getdents(2) (and thus are
visible when one uses ls(1) to view the contents of
/proc
).
/proc/[tid]
subdirectoriesEach one of these subdirectories contains files and subdirectories
exposing information about the thread with the corresponding thread ID.
The contents of these directories are the same as the corresponding
/proc/[pid]/task/[tid]
directories.
The /proc/[tid]
subdirectories are not
visible when
iterating through /proc
with getdents(2) (and
thus are not
visible when one uses ls(1) to
view the contents of /proc
).
/proc/self
When a process accesses this magic symbolic link, it resolves to the
process's own /proc/[pid]
directory.
/proc/thread-self
When a thread accesses this magic symbolic link, it resolves to the
process's own /proc/self/task/[tid]
directory.
/proc/[a-z]*
Various other files and subdirectories under /proc
expose
system-wide information.
All of the above are described in more detail below.
The following list provides details of many of the files and
directories under the /proc
hierarchy.
/proc/[pid]
There is a numerical subdirectory for each running process; the
subdirectory is named by the process ID. Each /proc/[pid]
subdirectory contains the pseudo-files and directories described
below.
The files inside each /proc/[pid]
directory are normally
owned by the effective user and effective group ID of the process.
However, as a security measure, the ownership is made root:root
if the process's "dumpable" attribute is set to a value other than
1.
Before Linux 4.11, root:root
meant the "global" root user ID
and group ID (i.e., UID 0 and GID 0 in the initial user namespace).
Since Linux 4.11, if the process is in a noninitial user namespace that
has a valid mapping for user (group) ID 0 inside the namespace, then the
user (group) ownership of the files under /proc/[pid]
is
instead made the same as the root user (group) ID of the namespace. This
means that inside a container, things work as expected for the container
"root" user.
The process's "dumpable" attribute may change for the following reasons:
The attribute was explicitly set via the prctl(2) PR_SET_DUMPABLE operation.
The attribute was reset to the value in the file
/proc/sys/fs/suid_dumpable
(described below), for the reasons
described in prctl(2).
Resetting the "dumpable" attribute to 1 reverts the ownership of the
/proc/[pid]/*
files to the process's effective UID and GID.
Note, however, that if the effective UID or GID is subsequently
modified, then the "dumpable" attribute may be reset, as described in
prctl(2). Therefore, it may be desirable to reset the
"dumpable" attribute after
making any desired changes to the
process's effective UID or GID.
/proc/[pid]/attr
The files in this directory provide an API for security modules. The contents of this directory are files that can be read and written in order to set security-related attributes. This directory was added to support SELinux, but the intention was that the API be general enough to support other security modules. For the purpose of explanation, examples of how SELinux uses these files are provided below.
This directory is present only if the kernel was configured with CONFIG_SECURITY.
/proc/[pid]/attr/current
(since Linux 2.6.0)The contents of this file represent the current security attributes of the process.
In SELinux, this file is used to get the security context of a
process. Prior to Linux 2.6.11, this file could not be used to set the
security context (a write was always denied), since SELinux limited
process security transitions to execve(2) (see the
description of /proc/[pid]/attr/exec
, below). Since Linux
2.6.11, SELinux lifted this restriction and began supporting "set"
operations via writes to this node if authorized by policy, although use
of this operation is only suitable for applications that are trusted to
maintain any desired separation between the old and new security
contexts.
Prior to Linux 2.6.28, SELinux did not allow threads within a multithreaded process to set their security context via this node as it would yield an inconsistency among the security contexts of the threads sharing the same memory space. Since Linux 2.6.28, SELinux lifted this restriction and began supporting "set" operations for threads within a multithreaded process if the new security context is bounded by the old security context, where the bounded relation is defined in policy and guarantees that the new security context has a subset of the permissions of the old security context.
Other security modules may choose to support "set" operations via writes to this node.
/proc/[pid]/attr/exec
(since Linux 2.6.0)This file represents the attributes to assign to the process upon a subsequent execve(2).
In SELinux, this is needed to support role/domain transitions, and
execve(2) is the preferred point to make such
transitions because it offers better control over the initialization of
the process in the new security label and the inheritance of state. In
SELinux, this attribute is reset on execve(2) so that
the new program reverts to the default behavior for any
execve(2) calls that it may make. In SELinux, a process
can set only its own /proc/[pid]/attr/exec
attribute.
/proc/[pid]/attr/fscreate
(since Linux 2.6.0)This file represents the attributes to assign to files created by subsequent calls to open(2), mkdir(2), symlink(2), and mknod(2)
SELinux employs this file to support creation of a file (using the
aforementioned system calls) in a secure state, so that there is no risk
of inappropriate access being obtained between the time of creation and
the time that attributes are set. In SELinux, this attribute is reset on
execve(2), so that the new program reverts to the
default behavior for any file creation calls it may make, but the
attribute will persist across multiple file creation calls within a
program unless it is explicitly reset. In SELinux, a process can set
only its own /proc/[pid]/attr/fscreate
attribute.
/proc/[pid]/attr/keycreate
(since Linux 2.6.18)If a process writes a security context into this file, all
subsequently created keys (add_key(2)) will be labeled
with this context. For further information, see the kernel source file
Documentation/security/keys/core.rst
(or file
Documentation/security/keys.txt
on Linux between 3.0 and 4.13,
or Documentation/keys.txt
before Linux 3.0).
/proc/[pid]/attr/prev
(since Linux 2.6.0)This file contains the security context of the process before the
last execve(2); that is, the previous value of
/proc/[pid]/attr/current
.
/proc/[pid]/attr/socketcreate
(since Linux 2.6.18)If a process writes a security context into this file, all subsequently created sockets will be labeled with this context.
/proc/[pid]/autogroup
(since Linux 2.6.38)See sched(7).
/proc/[pid]/auxv
(since 2.6.0)This contains the contents of the ELF interpreter information passed
to the process at exec time. The format is one unsigned long
ID
plus one unsigned long
value for each entry. The last entry
contains two zeros. See also getauxval(3).
Permission to access this file is governed by a ptrace access mode PTRACE_MODE_READ_FSCREDS check; see ptrace(2).
/proc/[pid]/cgroup
(since Linux 2.6.24)See cgroups(7).
/proc/[pid]/clear_refs
(since Linux 2.6.22)This is a write-only file, writable only by owner of the process.
The following values may be written to the file:
Reset the PG_Referenced and ACCESSED/YOUNG bits for all the pages associated with the process. (Before kernel 2.6.32, writing any nonzero value to this file had this effect.)
Reset the PG_Referenced and ACCESSED/YOUNG bits for all anonymous pages associated with the process.
Reset the PG_Referenced and ACCESSED/YOUNG bits for all file-mapped pages associated with the process.
Clearing the PG_Referenced and ACCESSED/YOUNG bits provides a method
to measure approximately how much memory a process is using. One first
inspects the values in the "Referenced" fields for the VMAs shown in
/proc/[pid]/smaps
to get an idea of the memory footprint of the
process. One then clears the PG_Referenced and ACCESSED/YOUNG bits and,
after some measured time interval, once again inspects the values in the
"Referenced" fields to get an idea of the change in memory footprint of
the process during the measured interval. If one is interested only in
inspecting the selected mapping types, then the value 2 or 3 can be used
instead of 1.
Further values can be written to affect different properties:
Clear the soft-dirty bit for all the pages associated with the
process. This is used (in conjunction with /proc/[pid]/pagemap
)
by the check-point restore system to discover which pages of a process
have been dirtied since the file /proc/[pid]/clear_refs
was
written to.
Reset the peak resident set size ("high water mark") to the process's current resident set size value.
Writing any value to /proc/[pid]/clear_refs
other than those
listed above has no effect.
The /proc/[pid]/clear_refs
file is present only if the
CONFIG_PROC_PAGE_MONITOR kernel configuration option is
enabled.
/proc/[pid]/cmdline
This read-only file holds the complete command line for the process, unless the process is a zombie. In the latter case, there is nothing in this file: that is, a read on this file will return 0 characters. The command-line arguments appear in this file as a set of strings separated by null bytes ('\0'), with a further null byte after the last string.
If, after an execve(2), the process modifies its
argv
strings, those changes will show up here. This is not the
same thing as modifying the argv
array.
Furthermore, a process may change the memory location that this file refers via prctl(2) operations such as PR_SET_MM_ARG_START.
Think of this file as the command line that the process wants you to see.
/proc/[pid]/comm
(since Linux 2.6.33)This file exposes the process's comm
value—that is, the
command name associated with the process. Different threads in the same
process may have different comm
values, accessible via
/proc/[pid]/task/[tid]/comm
. A thread may modify its
comm
value, or that of any of other thread in the same thread
group (see the discussion of CLONE_THREAD in
clone(2)), by writing to the file
/proc/self/task/[tid]/comm
. Strings longer than
TASK_COMM_LEN (16) characters (including the
terminating null byte) are silently truncated.
This file provides a superset of the prctl(2)
PR_SET_NAME and PR_GET_NAME
operations, and is employed by pthread_setname_np(3)
when used to rename threads other than the caller. The value in this
file is used for the %e
specifier in
/proc/sys/kernel/core_pattern
; see
core(5).
/proc/[pid]/coredump_filter
(since Linux 2.6.23)See core(5).
/proc/[pid]/cpuset
(since Linux 2.6.12)See cpuset(7).
/proc/[pid]/cwd
This is a symbolic link to the current working directory of the process. To find out the current working directory of process 20, for instance, you can do this:
$ cd /proc/20/cwd; pwd -P
In a multithreaded process, the contents of this symbolic link are not available if the main thread has already terminated (typically by calling pthread_exit(3)).
Permission to dereference or read (readlink(2)) this symbolic link is governed by a ptrace access mode PTRACE_MODE_READ_FSCREDS check; see ptrace(2).
/proc/[pid]/environ
This file contains the initial environment that was set when the currently executing program was started via execve(2). The entries are separated by null bytes ('\0'), and there may be a null byte at the end. Thus, to print out the environment of process 1, you would do:
$ cat /proc/1/environ | tr '\000' '\n'
If, after an execve(2), the process modifies its
environment (e.g., by calling functions such as
putenv(3) or modifying the environ(7)
variable directly), this file will not
reflect those
changes.
Furthermore, a process may change the memory location that this file refers via prctl(2) operations such as PR_SET_MM_ENV_START.
Permission to access this file is governed by a ptrace access mode PTRACE_MODE_READ_FSCREDS check; see ptrace(2).
/proc/[pid]/exe
Under Linux 2.2 and later, this file is a symbolic link containing
the actual pathname of the executed command. This symbolic link can be
dereferenced normally; attempting to open it will open the executable.
You can even type /proc/[pid]/exe
to run another copy of the
same executable that is being run by process [pid]. If the pathname has
been unlinked, the symbolic link will contain the string '(deleted)'
appended to the original pathname. In a multithreaded process, the
contents of this symbolic link are not available if the main thread has
already terminated (typically by calling
pthread_exit(3)).
Permission to dereference or read (readlink(2)) this symbolic link is governed by a ptrace access mode PTRACE_MODE_READ_FSCREDS check; see ptrace(2).
Under Linux 2.0 and earlier, /proc/[pid]/exe
is a pointer to
the binary which was executed, and appears as a symbolic link. A
readlink(2) call on this file under Linux 2.0 returns a
string in the format:
[device]:inode
For example, [0301]:1502 would be inode 1502 on device major 03 (IDE, MFM, etc. drives) minor 01 (first partition on the first drive).
find(1) with the -inum
option can be used
to locate the file.
/proc/[pid]/fd/
This is a subdirectory containing one entry for each file which the process has open, named by its file descriptor, and which is a symbolic link to the actual file. Thus, 0 is standard input, 1 standard output, 2 standard error, and so on.
For file descriptors for pipes and sockets, the entries will be symbolic links whose content is the file type with the inode. A readlink(2) call on this file returns a string in the format:
type:[inode]
For example, socket:[2248868]
will be a socket and its inode
is 2248868. For sockets, that inode can be used to find more information
in one of the files under /proc/net/
.
For file descriptors that have no corresponding inode (e.g., file descriptors produced by bpf(2), epoll_create(2), eventfd(2), inotify_init(2), perf_event_open(2), signalfd(2), timerfd_create(2), and userfaultfd(2)), the entry will be a symbolic link with contents of the form
anon_inode:<file-type>
In many cases (but not all), the file-type
is surrounded by
square brackets.
For example, an epoll file descriptor will have a symbolic link whose
content is the string anon_inode:[eventpoll]
.
In a multithreaded process, the contents of this directory are not available if the main thread has already terminated (typically by calling pthread_exit(3)).
Programs that take a filename as a command-line argument, but don't
take input from standard input if no argument is supplied, and programs
that write to a file named as a command-line argument, but don't send
their output to standard output if no argument is supplied, can
nevertheless be made to use standard input or standard output by using
/proc/[pid]/fd
files as command-line arguments. For example,
assuming that -i
is the flag designating an input file and
-o
is the flag designating an output file:
$ foobar -i /proc/self/fd/0 -o /proc/self/fd/1 ...
and you have a working filter.
/proc/self/fd/N
is approximately the same as
/dev/fd/N
in some UNIX and UNIX-like systems. Most Linux
MAKEDEV scripts symbolically link /dev/fd
to
/proc/self/fd
, in fact.
Most systems provide symbolic links /dev/stdin
,
/dev/stdout
, and /dev/stderr
, which respectively link
to the files 0
, 1
, and 2
in
/proc/self/fd
. Thus the example command above could be written
as:
$ foobar -i /dev/stdin -o /dev/stdout ...
Permission to dereference or read (readlink(2)) the symbolic links in this directory is governed by a ptrace access mode PTRACE_MODE_READ_FSCREDS check; see ptrace(2).
Note that for file descriptors referring to inodes (pipes and
sockets, see above), those inodes still have permission bits and
ownership information distinct from those of the /proc/[pid]/fd
entry, and that the owner may differ from the user and group IDs of the
process. An unprivileged process may lack permissions to open them, as
in this example:
$ echo test | sudo -u nobody cat
test
$ echo test | sudo -u nobody cat /proc/self/fd/0
cat: /proc/self/fd/0: Permission denied
File descriptor 0 refers to the pipe created by the shell and owned
by that shell's user, which is not nobody
, so
cat does not have permission to create a new file
descriptor to read from that inode, even though it can still read from
its existing file descriptor 0.
/proc/[pid]/fdinfo/
(since Linux 2.6.22)This is a subdirectory containing one entry for each file which the process has open, named by its file descriptor. The files in this directory are readable only by the owner of the process. The contents of each file can be read to obtain information about the corresponding file descriptor. The content depends on the type of file referred to by the corresponding file descriptor.
For regular files and directories, we see something like:
$ cat /proc/12015/fdinfo/4
pos: 1000
flags: 01002002
mnt_id: 21
The fields are as follows:
pos
This is a decimal number showing the file offset.
flags
This is an octal number that displays the file access mode and file
status flags (see open(2)). If the close-on-exec file
descriptor flag is set, then flags
will also include the value
O_CLOEXEC.
Before Linux 3.1, this field incorrectly displayed the setting of O_CLOEXEC at the time the file was opened, rather than the current setting of the close-on-exec flag.
mnt_id
This field, present since Linux 3.15, is the ID of
the mount point containing this file. See the description of
/proc/[pid]/mountinfo
.
For eventfd file descriptors (see eventfd(2)), we see (since Linux 3.8) the following fields:
pos: 0
flags: 02
mnt_id: 10
eventfd-count: 40
eventfd-count
is the current value of the eventfd counter,
in hexadecimal.
For epoll file descriptors (see epoll(7)), we see (since Linux 3.8) the following fields:
pos: 0
flags: 02
mnt_id: 10
tfd: 9 events: 19 data: 74253d2500000009
tfd: 7 events: 19 data: 74253d2500000007
Each of the lines beginning tfd
describes one of the file
descriptors being monitored via the epoll file descriptor (see
epoll_ctl(2) for some details). The tfd
field
is the number of the file descriptor. The events
field is a
hexadecimal mask of the events being monitored for this file descriptor.
The data
field is the data value associated with this file
descriptor.
For signalfd file descriptors (see signalfd(2)), we see (since Linux 3.8) the following fields:
pos: 0
flags: 02
mnt_id: 10
sigmask: 0000000000000006
sigmask
is the hexadecimal mask of signals that are accepted
via this signalfd file descriptor. (In this example, bits 2 and 3 are
set, corresponding to the signals SIGINT and
SIGQUIT; see signal(7).)
For inotify file descriptors (see inotify(7)), we see (since Linux 3.8) the following fields:
pos: 0
flags: 00
mnt_id: 11
inotify wd:2 ino:7ef82a sdev:800001 mask:800afff ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:2af87e00220ffd73
inotify wd:1 ino:192627 sdev:800001 mask:800afff ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:27261900802dfd73
Each of the lines beginning with "inotify" displays information about one file or directory that is being monitored. The fields in this line are as follows:
wd
A watch descriptor number (in decimal).
ino
The inode number of the target file (in hexadecimal).
sdev
The ID of the device where the target file resides (in hexadecimal).
mask
The mask of events being monitored for the target file (in hexadecimal).
If the kernel was built with exportfs support, the path to the target
file is exposed as a file handle, via three hexadecimal fields:
fhandle-bytes
, fhandle-type
, and
f_handle
.
For fanotify file descriptors (see fanotify(7)), we see (since Linux 3.8) the following fields:
pos: 0
flags: 02
mnt_id: 11
fanotify flags:0 event-flags:88002
fanotify ino:19264f sdev:800001 mflags:0 mask:1 ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:4f261900a82dfd73
The fourth line displays information defined when the fanotify group was created via fanotify_init(2):
flags
The flags
argument given to
fanotify_init(2) (expressed in hexadecimal).
event-flags
The event_f_flags
argument given to
fanotify_init(2) (expressed in hexadecimal).
Each additional line shown in the file contains information about one of the marks in the fanotify group. Most of these fields are as for inotify, except:
mflags
The flags associated with the mark (expressed in hexadecimal).
mask
The events mask for this mark (expressed in hexadecimal).
ignored_mask
The mask of events that are ignored for this mark (expressed in hexadecimal).
For details on these fields, see fanotify_mark(2).
For timerfd file descriptors (see timerfd(2)), we see (since Linux 3.17) the following fields:
pos: 0
flags: 02004002
mnt_id: 13
clockid: 0
ticks: 0
settime flags: 03
it_value: (7695568592, 640020877)
it_interval: (0, 0)
clockid
This is the numeric value of the clock ID (corresponding to one of
the CLOCK_* constants defined via
<time.h>
) that is used to mark the progress of the timer
(in this example, 0 is CLOCK_REALTIME).
ticks
This is the number of timer expirations that have occurred, (i.e., the value that read(2) on it would return).
settime flags
This field lists the flags with which the timerfd was last armed (see timerfd_settime(2)), in octal (in this example, both TFD_TIMER_ABSTIME and TFD_TIMER_CANCEL_ON_SET are set).
it_value
This field contains the amount of time until the timer will next expire, expressed in seconds and nanoseconds. This is always expressed as a relative value, regardless of whether the timer was created using the TFD_TIMER_ABSTIME flag.
it_interval
This field contains the interval of the timer, in seconds and
nanoseconds. (The it_value
and it_interval
fields
contain the values that timerfd_gettime(2) on this file
descriptor would return.)
/proc/[pid]/gid_map
(since Linux 3.5)See user_namespaces(7).
/proc/[pid]/io
(since kernel 2.6.20)This file contains I/O statistics for the process, for example:
# cat /proc/3828/io
rchar: 323934931
wchar: 323929600
syscr: 632687
syscw: 632675
read_bytes: 0
write_bytes: 323932160
cancelled_write_bytes: 0
The fields are as follows:
rchar
: characters readThe number of bytes which this task has caused to be read from storage. This is simply the sum of bytes which this process passed to read(2) and similar system calls. It includes things such as terminal I/O and is unaffected by whether or not actual physical disk I/O was required (the read might have been satisfied from pagecache).
wchar
: characters writtenThe number of bytes which this task has caused, or shall cause to be
written to disk. Similar caveats apply here as with rchar
.
syscr
: read syscallsAttempt to count the number of read I/O operations—that is, system calls such as read(2) and pread(2).
syscw
: write syscallsAttempt to count the number of write I/O operations—that is, system calls such as write(2) and pwrite(2).
read_bytes
: bytes readAttempt to count the number of bytes which this process really did cause to be fetched from the storage layer. This is accurate for block-backed filesystems.
write_bytes
: bytes writtenAttempt to count the number of bytes which this process caused to be sent to the storage layer.
cancelled_write_bytes
:The big inaccuracy here is truncate. If a process writes 1 MB to a
file and then deletes the file, it will in fact perform no writeout. But
it will have been accounted as having caused 1 MB of write. In other
words: this field represents the number of bytes which this process
caused to not happen, by truncating pagecache. A task can cause
"negative" I/O too. If this task truncates some dirty pagecache, some
I/O which another task has been accounted for (in its
write_bytes
) will not be happening.
Note
: In the current implementation, things are a bit racy
on 32-bit systems: if process A reads process B's
/proc/[pid]/io
while process B is updating one of these 64-bit
counters, process A could see an intermediate result.
Permission to access this file is governed by a ptrace access mode PTRACE_MODE_READ_FSCREDS check; see ptrace(2).
/proc/[pid]/limits
(since Linux 2.6.24)This file displays the soft limit, hard limit, and units of measurement for each of the process's resource limits (see getrlimit(2)). Up to and including Linux 2.6.35, this file is protected to allow reading only by the real UID of the process. Since Linux 2.6.36, this file is readable by all users on the system.
/proc/[pid]/map_files/
(since kernel 3.3)This subdirectory contains entries corresponding to memory-mapped files (see mmap(2)). Entries are named by memory region start and end address pair (expressed as hexadecimal numbers), and are symbolic links to the mapped files themselves. Here is an example, with the output wrapped and reformatted to fit on an 80-column display:
# ls -l /proc/self/map_files/
lr--------. 1 root root 64 Apr 16 21:31
3252e00000-3252e20000 -> /usr/lib64/ld-2.15.so
...
Although these entries are present for memory regions that were
mapped with the MAP_FILE flag, the way anonymous shared
memory (regions created with the MAP_ANON | MAP_SHARED
flags) is implemented in Linux means that such regions also appear on
this directory. Here is an example where the target file is the deleted
/dev/zero
one:
lrw-------. 1 root root 64 Apr 16 21:33
7fc075d2f000-7fc075e6f000 -> /dev/zero (deleted)
Permission to access this file is governed by a ptrace access mode PTRACE_MODE_READ_FSCREDS check; see ptrace(2).
Until kernel version 4.3, this directory appeared only if the CONFIG_CHECKPOINT_RESTORE kernel configuration option was enabled.
Capabilities are required to read the contents of the symbolic links in this directory: before Linux 5.9, the reading process requires CAP_SYS_ADMIN in the initial user namespace; since Linux 5.9, the reading process must have either CAP_SYS_ADMIN or CAP_CHECKPOINT_RESTORE in the user namespace where it resides.
/proc/[pid]/maps
A file containing the currently mapped memory regions and their access permissions. See mmap(2) for some further information about memory mappings.
Permission to access this file is governed by a ptrace access mode PTRACE_MODE_READ_FSCREDS check; see ptrace(2).
The format of the file is:
address perms offset dev inode pathname
00400000-00452000 r-xp 00000000 08:02 173521 /usr/bin/dbus-daemon
00651000-00652000 r--p 00051000 08:02 173521 /usr/bin/dbus-daemon
00652000-00655000 rw-p 00052000 08:02 173521 /usr/bin/dbus-daemon
00e03000-00e24000 rw-p 00000000 00:00 0 [heap]
00e24000-011f7000 rw-p 00000000 00:00 0 [heap]
...
35b1800000-35b1820000 r-xp 00000000 08:02 135522 /usr/lib64/ld-2.15.so
35b1a1f000-35b1a20000 r--p 0001f000 08:02 135522 /usr/lib64/ld-2.15.so
35b1a20000-35b1a21000 rw-p 00020000 08:02 135522 /usr/lib64/ld-2.15.so
35b1a21000-35b1a22000 rw-p 00000000 00:00 0
35b1c00000-35b1dac000 r-xp 00000000 08:02 135870 /usr/lib64/libc-2.15.so
35b1dac000-35b1fac000 ---p 001ac000 08:02 135870 /usr/lib64/libc-2.15.so
35b1fac000-35b1fb0000 r--p 001ac000 08:02 135870 /usr/lib64/libc-2.15.so
35b1fb0000-35b1fb2000 rw-p 001b0000 08:02 135870 /usr/lib64/libc-2.15.so
...
f2c6ff8c000-7f2c7078c000 rw-p 00000000 00:00 0 [stack:986]
...
7fffb2c0d000-7fffb2c2e000 rw-p 00000000 00:00 0 [stack]
7fffb2d48000-7fffb2d49000 r-xp 00000000 00:00 0 [vdso]
The address
field is the address space in the process that
the mapping occupies. The perms
field is a set of
permissions:
r = read
w = write
x = execute
s = shared
p = private (copy on write)
The offset
field is the offset into the file/whatever;
dev
is the device (major:minor); inode
is the inode on
that device. 0 indicates that no inode is associated with the memory
region, as would be the case with BSS (uninitialized data).
The pathname
field will usually be the file that is backing
the mapping. For ELF files, you can easily coordinate with the
offset
field by looking at the Offset field in the ELF program
headers (readelf -l
).
There are additional helpful pseudo-paths:
[stack]
The initial process's (also known as the main thread's) stack.
[stack:<tid>]
(from Linux 3.4 to 4.4)A thread's stack (where the <tid>
is a thread ID). It
corresponds to the /proc/[pid]/task/[tid]/
path. This field was
removed in Linux 4.5, since providing this information for a process
with large numbers of threads is expensive.
[vdso]
The virtual dynamically linked shared object. See vdso(7).
[heap]
The process's heap.
If the pathname
field is blank, this is an anonymous mapping
as obtained via mmap(2). There is no easy way to
coordinate this back to a process's source, short of running it through
gdb(1), strace(1), or similar.
pathname
is shown unescaped except for newline characters,
which are replaced with an octal escape sequence. As a result, it is not
possible to determine whether the original pathname contained a newline
character or the literal \012
character sequence.
If the mapping is file-backed and the file has been deleted, the string " (deleted)" is appended to the pathname. Note that this is ambiguous too.
Under Linux 2.0, there is no field giving pathname.
/proc/[pid]/mem
This file can be used to access the pages of a process's memory through open(2), read(2), and lseek(2).
Permission to access this file is governed by a ptrace access mode PTRACE_MODE_ATTACH_FSCREDS check; see ptrace(2).
/proc/[pid]/mountinfo
(since Linux 2.6.26)This file contains information about mount points in the process's
mount namespace (see mount_namespaces(7)). It supplies
various information (e.g., propagation state, root of mount for bind
mounts, identifier for each mount and its parent) that is missing from
the (older) /proc/[pid]/mounts
file, and fixes various other
problems with that file (e.g., nonextensibility, failure to distinguish
per-mount versus per-superblock options).
The file contains lines of the form:
36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
(1)(2)(3) (4) (5) (6) (7) (8) (9) (10) (11)
The numbers in parentheses are labels for the descriptions below:
mount ID: a unique ID for the mount (may be reused after umount(2)).
parent ID: the ID of the parent mount (or of self for the root of this mount namespace's mount tree).
If a new mount is stacked on top of a previous existing mount (so that it hides the existing mount) at pathname P, then the parent of the new mount is the previous mount at that location. Thus, when looking at all the mounts stacked at a particular location, the top-most mount is the one that is not the parent of any other mount at the same location. (Note, however, that this top-most mount will be accessible only if the longest path subprefix of P that is a mount point is not itself hidden by a stacked mount.)
If the parent mount point lies outside the process's root directory
(see chroot(2)), the ID shown here won't have a
corresponding record in mountinfo
whose mount ID (field 1)
matches this parent mount ID (because mount points that lie outside the
process's root directory are not shown in mountinfo
). As a
special case of this point, the process's root mount point may have a
parent mount (for the initramfs filesystem) that lies outside the
process's root directory, and an entry for that mount point will not
appear in mountinfo
.
major:minor: the value of st_dev
for files on this
filesystem (see stat(2)).
root: the pathname of the directory in the filesystem which forms the root of this mount.
mount point: the pathname of the mount point relative to the process's root directory.
mount options: per-mount options (see mount(2)).
optional fields: zero or more fields of the form "tag[:value]"; see below.
separator: the end of the optional fields is marked by a single hyphen.
filesystem type: the filesystem type in the form "type[.subtype]".
mount source: filesystem-specific information or "none".
super options: per-superblock options (see mount(2)).
Currently, the possible optional fields are shared
,
master
, propagate_from
, and unbindable
. See
mount_namespaces(7) for a description of these fields.
Parsers should ignore all unrecognized optional fields.
For more information on mount propagation see:
Documentation/filesystems/sharedsubtree.txt
in the Linux kernel
source tree.
/proc/[pid]/mounts
(since Linux 2.4.19)This file lists all the filesystems currently mounted in the process's mount namespace (see mount_namespaces(7)). The format of this file is documented in fstab(5).
Since kernel version 2.6.15, this file is pollable: after opening the file for reading, a change in this file (i.e., a filesystem mount or unmount) causes select(2) to mark the file descriptor as having an exceptional condition, and poll(2) and epoll_wait(2) mark the file as having a priority event (POLLPRI). (Before Linux 2.6.30, a change in this file was indicated by the file descriptor being marked as readable for select(2), and being marked as having an error condition for poll(2) and epoll_wait(2).)
/proc/[pid]/mountstats
(since Linux 2.6.17)This file exports information (statistics, configuration information) about the mount points in the process's mount namespace (see mount_namespaces(7)). Lines in this file have the form:
device /dev/sda7 mounted on /home with fstype ext3 [stats]
( 1 ) ( 2 ) (3 ) ( 4 )
The fields in each line are:
The name of the mounted device (or "nodevice" if there is no corresponding device).
The mount point within the filesystem tree.
The filesystem type.
Optional statistics and configuration information. Currently (as at Linux 2.6.26), only NFS filesystems export information via this field.
This file is readable only by the owner of the process.
/proc/[pid]/net
(since Linux 2.6.25)See the description of /proc/net
.
/proc/[pid]/ns/
(since Linux 3.0)This is a subdirectory containing one entry for each namespace that supports being manipulated by setns(2). For more information, see namespaces(7).
/proc/[pid]/numa_maps
(since Linux 2.6.14)See numa(7).
/proc/[pid]/oom_adj
(since Linux 2.6.11)This file can be used to adjust the score used to select which
process should be killed in an out-of-memory (OOM) situation. The kernel
uses this value for a bit-shift operation of the process's
oom_score
value: valid values are in the range -16 to +15, plus
the special value -17, which disables OOM-killing altogether for this
process. A positive score increases the likelihood of this process being
killed by the OOM-killer; a negative score decreases the likelihood.
The default value for this file is 0; a new process inherits its
parent's oom_adj
setting. A process must be privileged
(CAP_SYS_RESOURCE) to update this file.
Since Linux 2.6.36, use of this file is deprecated in favor of
/proc/[pid]/oom_score_adj
.
/proc/[pid]/oom_score
(since Linux 2.6.11)This file displays the current score that the kernel gives to this process for the purpose of selecting a process for the OOM-killer. A higher score means that the process is more likely to be selected by the OOM-killer. The basis for this score is the amount of memory used by the process, with increases (+) or decreases (-) for factors including:
whether the process is privileged (-).
Before kernel 2.6.36 the following factors were also used in the calculation of oom_score:
whether the process creates a lot of children using fork(2) (+);
whether the process has been running a long time, or has used a lot of CPU time (-);
whether the process has a low nice value (i.e., > 0) (+); and
whether the process is making direct hardware access (-).
The oom_score
also reflects the adjustment specified by the
oom_score_adj
or oom_adj
setting for the process.
/proc/[pid]/oom_score_adj
(since Linux 2.6.36)This file can be used to adjust the badness heuristic used to select which process gets killed in out-of-memory conditions.
The badness heuristic assigns a value to each candidate task ranging from 0 (never kill) to 1000 (always kill) to determine which process is targeted. The units are roughly a proportion along that range of allowed memory the process may allocate from, based on an estimation of its current memory and swap use. For example, if a task is using all allowed memory, its badness score will be 1000. If it is using half of its allowed memory, its score will be 500.
There is an additional factor included in the badness score: root processes are given 3% extra memory over other tasks.
The amount of "allowed" memory depends on the context in which the OOM-killer was called. If it is due to the memory assigned to the allocating task's cpuset being exhausted, the allowed memory represents the set of mems assigned to that cpuset (see cpuset(7)). If it is due to a mempolicy's node(s) being exhausted, the allowed memory represents the set of mempolicy nodes. If it is due to a memory limit (or swap limit) being reached, the allowed memory is that configured limit. Finally, if it is due to the entire system being out of memory, the allowed memory represents all allocatable resources.
The value of oom_score_adj
is added to the badness score
before it is used to determine which task to kill. Acceptable values
range from -1000 (OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX). This
allows user space to control the preference for OOM-killing, ranging
from always preferring a certain task or completely disabling it from
OOM killing. The lowest possible value, -1000, is equivalent to
disabling OOM-killing entirely for that task, since it will always
report a badness score of 0.
Consequently, it is very simple for user space to define the amount
of memory to consider for each task. Setting an oom_score_adj
value of +500, for example, is roughly equivalent to allowing the
remainder of tasks sharing the same system, cpuset, mempolicy, or memory
controller resources to use at least 50% more memory. A value of -500,
on the other hand, would be roughly equivalent to discounting 50% of the
task's allowed memory from being considered as scoring against the
task.
For backward compatibility with previous kernels,
/proc/[pid]/oom_adj
can still be used to tune the badness
score. Its value is scaled linearly with oom_score_adj
.
Writing to /proc/[pid]/oom_score_adj
or
/proc/[pid]/oom_adj
will change the other with its scaled
value.
The choom(1) program provides a command-line
interface for adjusting the oom_score_adj
value of a running
process or a newly executed command.
/proc/[pid]/pagemap
(since Linux 2.6.25)This file shows the mapping of each of the process's virtual pages into physical page frames or swap area. It contains one 64-bit value for each virtual page, with the bits set as follows:
If set, the page is present in RAM.
If set, the page is in swap space
The page is a file-mapped page or a shared anonymous page.
Zero
The page is exclusively mapped.
PTE is soft-dirty (see the kernel source file
Documentation/admin-guide/mm/soft-dirty.rst
).
If the page is present in RAM (bit 63), then these bits provide the
page frame number, which can be used to index /proc/kpageflags
and /proc/kpagecount
. If the page is present in swap (bit 62),
then bits 4–0 give the swap type, and bits 54–5 encode the swap
offset.
Before Linux 3.11, bits 60–55 were used to encode the base-2 log of the page size.
To employ /proc/[pid]/pagemap
efficiently, use
/proc/[pid]/maps
to determine which areas of memory are
actually mapped and seek to skip over unmapped regions.
The /proc/[pid]/pagemap
file is present only if the
CONFIG_PROC_PAGE_MONITOR kernel configuration option is
enabled.
Permission to access this file is governed by a ptrace access mode PTRACE_MODE_READ_FSCREDS check; see ptrace(2).
/proc/[pid]/personality
(since Linux 2.6.28)This read-only file exposes the process's execution domain, as set by personality(2). The value is displayed in hexadecimal notation.
Permission to access this file is governed by a ptrace access mode PTRACE_MODE_ATTACH_FSCREDS check; see ptrace(2).
/proc/[pid]/root
UNIX and Linux support the idea of a per-process root of the
filesystem, set by the chroot(2) system call. This file
is a symbolic link that points to the process's root directory, and
behaves in the same way as exe
, and fd/*
.
Note however that this file is not merely a symbolic link. It provides the same view of the filesystem (including namespaces and the set of per-process mounts) as the process itself. An example illustrates this point. In one terminal, we start a shell in new user and mount namespaces, and in that shell we create some new mount points:
$ PS1='sh1# ' unshare -Urnm
sh1# mount -t tmpfs tmpfs /etc # Mount empty tmpfs at /etc
sh1# mount --bind /usr /dev # Mount /usr at /dev
sh1# echo $$
27123
In a second terminal window, in the initial mount namespace, we look at the contents of the corresponding mounts in the initial and new namespaces:
$ PS1='sh2# ' sudo sh
sh2# ls /etc | wc -l # In initial NS
309
sh2# ls /proc/27123/root/etc | wc -l # /etc in other NS
0 # The empty tmpfs dir
sh2# ls /dev | wc -l # In initial NS
205
sh2# ls /proc/27123/root/dev | wc -l # /dev in other NS
11 # Actually bind
# mounted to /usr
sh2# ls /usr | wc -l # /usr in initial NS
11
In a multithreaded process, the contents of the
/proc/[pid]/root
symbolic link are not available if the main
thread has already terminated (typically by calling
pthread_exit(3)).
Permission to dereference or read (readlink(2)) this symbolic link is governed by a ptrace access mode PTRACE_MODE_READ_FSCREDS check; see ptrace(2).
/proc/[pid]/seccomp
(Linux 2.6.12 to 2.6.22)This file can be used to read and change the process's secure computing (seccomp) mode setting. It contains the value 0 if the process is not in seccomp mode, and 1 if the process is in strict seccomp mode (see seccomp(2)). Writing 1 to this file places the process irreversibly in strict seccomp mode. (Further attempts to write to the file fail with the EPERM error.)
In Linux 2.6.23, this file went away, to be replaced by the
prctl(2) PR_GET_SECCOMP and
PR_SET_SECCOMP operations (and later by
seccomp(2) and the Seccomp
field in
/proc/[pid]/status
).
/proc/[pid]/setgroups
(since Linux 3.19)See user_namespaces(7).
/proc/[pid]/smaps
(since Linux 2.6.14)This file shows memory consumption for each of the process's mappings. (The pmap(1) command displays similar information, in a form that may be easier for parsing.) For each mapping there is a series of lines such as the following:
00400000-0048a000 r-xp 00000000 fd:03 960637 /bin/bash
Size: 552 kB
Rss: 460 kB
Pss: 100 kB
Shared_Clean: 452 kB
Shared_Dirty: 0 kB
Private_Clean: 8 kB
Private_Dirty: 0 kB
Referenced: 460 kB
Anonymous: 0 kB
AnonHugePages: 0 kB
ShmemHugePages: 0 kB
ShmemPmdMapped: 0 kB
Swap: 0 kB
KernelPageSize: 4 kB
MMUPageSize: 4 kB
KernelPageSize: 4 kB
MMUPageSize: 4 kB
Locked: 0 kB
ProtectionKey: 0
VmFlags: rd ex mr mw me dw
The first of these lines shows the same information as is displayed
for the mapping in /proc/[pid]/maps
. The following lines show
the size of the mapping, the amount of the mapping that is currently
resident in RAM ("Rss"), the process's proportional share of this
mapping ("Pss"), the number of clean and dirty shared pages in the
mapping, and the number of clean and dirty private pages in the mapping.
"Referenced" indicates the amount of memory currently marked as
referenced or accessed. "Anonymous" shows the amount of memory that does
not belong to any file. "Swap" shows how much would-be-anonymous memory
is also used, but out on swap.
The "KernelPageSize" line (available since Linux 2.6.29) is the page size used by the kernel to back the virtual memory area. This matches the size used by the MMU in the majority of cases. However, one counter-example occurs on PPC64 kernels whereby a kernel using 64 kB as a base page size may still use 4 kB pages for the MMU on older processors. To distinguish the two attributes, the "MMUPageSize" line (also available since Linux 2.6.29) reports the page size used by the MMU.
The "Locked" indicates whether the mapping is locked in memory or not.
The "ProtectionKey" line (available since Linux 4.9, on x86 only) contains the memory protection key (see pkeys(7)) associated with the virtual memory area. This entry is present only if the kernel was built with the CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS configuration option (since Linux 4.6).
The "VmFlags" line (available since Linux 3.8) represents the kernel flags associated with the virtual memory area, encoded using the following two-letter codes:
rd - readable wr - writable ex - executable sh - shared mr - may read mw - may write me - may execute ms - may share gd - stack segment grows down pf - pure PFN range dw - disabled write to the mapped file lo - pages are locked in memory io - memory mapped I/O area sr - sequential read advise provided rr - random read advise provided dc - do not copy area on fork de - do not expand area on remapping ac - area is accountable nr - swap space is not reserved for the area ht - area uses huge tlb pages sf - perform synchronous page faults (since Linux 4.15) nl - non-linear mapping (removed in Linux 4.0) ar - architecture specific flag wf - wipe on fork (since Linux 4.14) dd - do not include area into core dump sd - soft-dirty flag (since Linux 3.13) mm - mixed map area hg - huge page advise flag nh - no-huge page advise flag mg - mergeable advise flag um - userfaultfd missing pages tracking (since Linux 4.3) uw - userfaultfd wprotect pages tracking (since Linux 4.3)
The /proc/[pid]/smaps
file is present only if the
CONFIG_PROC_PAGE_MONITOR kernel configuration option is
enabled.
/proc/[pid]/stack
(since Linux 2.6.29)This file provides a symbolic trace of the function calls in this process's kernel stack. This file is provided only if the kernel was built with the CONFIG_STACKTRACE configuration option.
Permission to access this file is governed by a ptrace access mode PTRACE_MODE_ATTACH_FSCREDS check; see ptrace(2).
/proc/[pid]/stat
Status information about the process. This is used by
ps(1). It is defined in the kernel source file
fs/proc/array.c
.
The fields, in order, with their proper scanf(3) format specifiers, are listed below. Whether or not certain of these fields display valid information is governed by a ptrace access mode PTRACE_MODE_READ_FSCREDS | PTRACE_MODE_NOAUDIT check (refer to ptrace(2)). If the check denies access, then the field value is displayed as 0. The affected fields are indicated with the marking [PT].
pid
%d
The process ID.
comm
%sThe filename of the executable, in parentheses. Strings longer than TASK_COMM_LEN (16) characters (including the terminating null byte) are silently truncated. This is visible whether or not the executable is swapped out.
state
%cOne of the following characters, indicating process state:
Running
Sleeping in an interruptible wait
Waiting in uninterruptible disk sleep
Zombie
Stopped (on a signal) or (before Linux 2.6.33) trace stopped
Tracing stop (Linux 2.6.33 onward)
Paging (only before Linux 2.6.0)
Dead (from Linux 2.6.0 onward)
Dead (Linux 2.6.33 to 3.13 only)
Wakekill (Linux 2.6.33 to 3.13 only)
Waking (Linux 2.6.33 to 3.13 only)
Parked (Linux 3.9 to 3.13 only)
ppid
%dThe PID of the parent of this process.
pgrp
%dThe process group ID of the process.
session
%dThe session ID of the process.
tty_nr
%dThe controlling terminal of the process. (The minor device number is contained in the combination of bits 31 to 20 and 7 to 0; the major device number is in bits 15 to 8.)
tpgid
%dThe ID of the foreground process group of the controlling terminal of the process.
flags
%uThe kernel flags word of the process. For bit meanings, see the PF_*
defines in the Linux kernel source file include/linux/sched.h
.
Details depend on the kernel version.
The format for this field was %lu before Linux 2.6.
minflt
%luThe number of minor faults the process has made which have not required loading a memory page from disk.
cminflt
%luThe number of minor faults that the process's waited-for children have made.
majflt
%luThe number of major faults the process has made which have required loading a memory page from disk.
cmajflt
%luThe number of major faults that the process's waited-for children have made.
utime
%luAmount of time that this process has been scheduled in user mode,
measured in clock ticks (divide by sysconf(_SC_CLK_TCK)
). This
includes guest time, guest_time
(time spent running a virtual
CPU, see below), so that applications that are not aware of the guest
time field do not lose that time from their calculations.
stime
%luAmount of time that this process has been scheduled in kernel mode,
measured in clock ticks (divide by sysconf(_SC_CLK_TCK)
).
cutime
%ldAmount of time that this process's waited-for children have been
scheduled in user mode, measured in clock ticks (divide by
sysconf(_SC_CLK_TCK)
). (See also times(2).)
This includes guest time, cguest_time
(time spent running a
virtual CPU, see below).
cstime
%ldAmount of time that this process's waited-for children have been
scheduled in kernel mode, measured in clock ticks (divide by
sysconf(_SC_CLK_TCK)
).
priority
%ld(Explanation for Linux 2.6) For processes running a real-time
scheduling policy (policy
below; see
sched_setscheduler(2)), this is the negated scheduling
priority, minus one; that is, a number in the range -2 to -100,
corresponding to real-time priorities 1 to 99. For processes running
under a non-real-time scheduling policy, this is the raw nice value
(setpriority(2)) as represented in the kernel. The
kernel stores nice values as numbers in the range 0 (high) to 39 (low),
corresponding to the user-visible nice range of -20 to 19.
Before Linux 2.6, this was a scaled value based on the scheduler weighting given to this process.
nice
%ldThe nice value (see setpriority(2)), a value in the range 19 (low priority) to -20 (high priority).
num_threads
%ldNumber of threads in this process (since Linux 2.6). Before kernel 2.6, this field was hard coded to 0 as a placeholder for an earlier removed field.
itrealvalue
%ldThe time in jiffies before the next SIGALRM is sent to the process due to an interval timer. Since kernel 2.6.17, this field is no longer maintained, and is hard coded as 0.
starttime
%lluThe time the process started after system boot. In kernels before
Linux 2.6, this value was expressed in jiffies. Since Linux 2.6, the
value is expressed in clock ticks (divide by
sysconf(_SC_CLK_TCK)
).
The format for this field was %lu before Linux 2.6.
vsize
%luVirtual memory size in bytes.
rss
%ldResident Set Size: number of pages the process has in real memory.
This is just the pages which count toward text, data, or stack space.
This does not include pages which have not been demand-loaded in, or
which are swapped out. This value is inaccurate; see
/proc/[pid]/statm
below.
rsslim
%luCurrent soft limit in bytes on the rss of the process; see the description of RLIMIT_RSS in getrlimit(2).
startcode
%lu [PT]The address above which program text can run.
endcode
%lu [PT]The address below which program text can run.
startstack
%lu [PT]The address of the start (i.e., bottom) of the stack.
kstkesp
%lu [PT]The current value of ESP (stack pointer), as found in the kernel stack page for the process.
kstkeip
%lu [PT]The current EIP (instruction pointer).
signal
%luThe bitmap of pending signals, displayed as a decimal number.
Obsolete, because it does not provide information on real-time signals;
use /proc/[pid]/status
instead.
blocked
%luThe bitmap of blocked signals, displayed as a decimal number.
Obsolete, because it does not provide information on real-time signals;
use /proc/[pid]/status
instead.
sigignore
%luThe bitmap of ignored signals, displayed as a decimal number.
Obsolete, because it does not provide information on real-time signals;
use /proc/[pid]/status
instead.
sigcatch
%luThe bitmap of caught signals, displayed as a decimal number.
Obsolete, because it does not provide information on real-time signals;
use /proc/[pid]/status
instead.
wchan
%lu [PT]This is the "channel" in which the process is waiting. It is the
address of a location in the kernel where the process is sleeping. The
corresponding symbolic name can be found in
/proc/[pid]/wchan
.
nswap
%luNumber of pages swapped (not maintained).
cnswap
%luCumulative nswap
for child processes (not maintained).
exit_signal
%d (since Linux 2.1.22)Signal to be sent to parent when we die.
processor
%d (since Linux 2.2.8)CPU number last executed on.
rt_priority
%u (since Linux 2.5.19)Real-time scheduling priority, a number in the range 1 to 99 for processes scheduled under a real-time policy, or 0, for non-real-time processes (see sched_setscheduler(2)).
policy
%u (since Linux 2.5.19)Scheduling policy (see sched_setscheduler(2)).
Decode using the SCHED_* constants in linux/sched.h
.
The format for this field was %lu before Linux 2.6.22.
delayacct_blkio_ticks
%llu (since Linux 2.6.18)Aggregated block I/O delays, measured in clock ticks (centiseconds).
guest_time
%lu (since Linux 2.6.24)Guest time of the process (time spent running a virtual CPU for a
guest operating system), measured in clock ticks (divide by
sysconf(_SC_CLK_TCK)
).
cguest_time
%ld (since Linux 2.6.24)Guest time of the process's children, measured in clock ticks (divide
by sysconf(_SC_CLK_TCK)
).
start_data
%lu (since Linux 3.3) [PT]Address above which program initialized and uninitialized (BSS) data are placed.
end_data
%lu (since Linux 3.3) [PT]Address below which program initialized and uninitialized (BSS) data are placed.
start_brk
%lu (since Linux 3.3) [PT]Address above which program heap can be expanded with brk(2).
arg_start
%lu (since Linux 3.5) [PT]Address above which program command-line arguments (argv
)
are placed.
arg_end
%lu (since Linux 3.5) [PT]Address below program command-line arguments (argv
) are
placed.
env_start
%lu (since Linux 3.5) [PT]Address above which program environment is placed.
env_end
%lu (since Linux 3.5) [PT]Address below which program environment is placed.
exit_code
%d (since Linux 3.5) [PT]The thread's exit status in the form reported by waitpid(2).
/proc/[pid]/statm
Provides information about memory usage, measured in pages. The columns are:
size (1) total program size
(same as VmSize in /proc/[pid]/status)
resident (2) resident set size
(inaccurate; same as VmRSS in /proc/[pid]/status)
shared (3) number of resident shared pages
(i.e., backed by a file)
(inaccurate; same as RssFile+RssShmem in
/proc/[pid]/status)
text (4) text (code)
lib (5) library (unused since Linux 2.6; always 0)
data (6) data + stack
dt (7) dirty pages (unused since Linux 2.6; always 0)
Some of these values are inaccurate because of a kernel-internal
scalability optimization. If accurate values are required, use
/proc/[pid]/smaps
or /proc/[pid]/smaps_rollup
instead,
which are much slower but provide accurate, detailed information.
/proc/[pid]/status
Provides much of the information in /proc/[pid]/stat
and
/proc/[pid]/statm
in a format that's easier for humans to
parse. Here's an example:
$ cat /proc/$$/status
Name: bash
Umask: 0022
State: S (sleeping)
Tgid: 17248
Ngid: 0
Pid: 17248
PPid: 17200
TracerPid: 0
Uid: 1000 1000 1000 1000
Gid: 100 100 100 100
FDSize: 256
Groups: 16 33 100
NStgid: 17248
NSpid: 17248
NSpgid: 17248
NSsid: 17200
VmPeak: 131168 kB
VmSize: 131168 kB
VmLck: 0 kB
VmPin: 0 kB
VmHWM: 13484 kB
VmRSS: 13484 kB
RssAnon: 10264 kB
RssFile: 3220 kB
RssShmem: 0 kB
VmData: 10332 kB
VmStk: 136 kB
VmExe: 992 kB
VmLib: 2104 kB
VmPTE: 76 kB
VmPMD: 12 kB
VmSwap: 0 kB
HugetlbPages: 0 kB # 4.4
CoreDumping: 0 # 4.15
Threads: 1
SigQ: 0/3067
SigPnd: 0000000000000000
ShdPnd: 0000000000000000
SigBlk: 0000000000010000
SigIgn: 0000000000384004
SigCgt: 000000004b813efb
CapInh: 0000000000000000
CapPrm: 0000000000000000
CapEff: 0000000000000000
CapBnd: ffffffffffffffff
CapAmb: 0000000000000000
NoNewPrivs: 0
Seccomp: 0
Speculation_Store_Bypass: vulnerable
Cpus_allowed: 00000001
Cpus_allowed_list: 0
Mems_allowed: 1
Mems_allowed_list: 0
voluntary_ctxt_switches: 150
nonvoluntary_ctxt_switches: 545
The fields are as follows:
Name
Command run by this process. Strings longer than TASK_COMM_LEN (16) characters (including the terminating null byte) are silently truncated.
Umask
Process umask, expressed in octal with a leading zero; see umask(2). (Since Linux 4.7.)
State
Current state of the process. One of "R (running)", "S (sleeping)", "D (disk sleep)", "T (stopped)", "t (tracing stop)", "Z (zombie)", or "X (dead)".
Tgid
Thread group ID (i.e., Process ID).
Ngid
NUMA group ID (0 if none; since Linux 3.13).
Pid
Thread ID (see gettid(2)).
PPid
PID of parent process.
TracerPid
PID of process tracing this process (0 if not being traced).
Uid
, Gid
Real, effective, saved set, and filesystem UIDs (GIDs).
FDSize
Number of file descriptor slots currently allocated.
Groups
Supplementary group list.
NStgid
Thread group ID (i.e., PID) in each of the PID namespaces of which
[pid]
is a member. The leftmost entry shows the value with
respect to the PID namespace of the process that mounted this procfs (or
the root namespace if mounted by the kernel), followed by the value in
successively nested inner namespaces. (Since Linux 4.1.)
NSpid
Thread ID in each of the PID namespaces of which [pid]
is a
member. The fields are ordered as for NStgid
. (Since Linux
4.1.)
NSpgid
Process group ID in each of the PID namespaces of which
[pid]
is a member. The fields are ordered as for
NStgid
. (Since Linux 4.1.)
NSsid
descendant namespace session ID hierarchy Session ID in each of the
PID namespaces of which [pid]
is a member. The fields are
ordered as for NStgid
. (Since Linux 4.1.)
VmPeak
Peak virtual memory size.
VmSize
Virtual memory size.
VmLck
Locked memory size (see mlock(2)).
VmPin
Pinned memory size (since Linux 3.2). These are pages that can't be moved because something needs to directly access physical memory.
VmHWM
Peak resident set size ("high water mark"). This value is inaccurate;
see /proc/[pid]/statm
above.
VmRSS
Resident set size. Note that the value here is the sum of
RssAnon
, RssFile
, and RssShmem
. This value is
inaccurate; see /proc/[pid]/statm
above.
RssAnon
Size of resident anonymous memory. (since Linux 4.5). This value is
inaccurate; see /proc/[pid]/statm
above.
RssFile
Size of resident file mappings. (since Linux 4.5). This value is
inaccurate; see /proc/[pid]/statm
above.
RssShmem
Size of resident shared memory (includes System V shared memory, mappings from tmpfs(5), and shared anonymous mappings). (since Linux 4.5).
VmData
, VmStk
, VmExe
Size of data, stack, and text segments. This value is inaccurate; see
/proc/[pid]/statm
above.
VmLib
Shared library code size.
VmPTE
Page table entries size (since Linux 2.6.10).
VmPMD
Size of second-level page tables (added in Linux 4.0; removed in Linux 4.15).
VmSwap
Swapped-out virtual memory size by anonymous private pages; shmem
swap usage is not included (since Linux 2.6.34). This value is
inaccurate; see /proc/[pid]/statm
above.
HugetlbPages
Size of hugetlb memory portions (since Linux 4.4).
CoreDumping
Contains the value 1 if the process is currently dumping core, and 0 if it is not (since Linux 4.15). This information can be used by a monitoring process to avoid killing a process that is currently dumping core, which could result in a corrupted core dump file.
Threads
Number of threads in process containing this thread.
SigQ
This field contains two slash-separated numbers that relate to queued signals for the real user ID of this process. The first of these is the number of currently queued signals for this real user ID, and the second is the resource limit on the number of queued signals for this process (see the description of RLIMIT_SIGPENDING in getrlimit(2)).
SigPnd
, ShdPnd
Mask (expressed in hexadecimal) of signals pending for thread and for process as a whole (see pthreads(7) and signal(7)).
SigBlk
, SigIgn
, SigCgt
Masks (expressed in hexadecimal) indicating signals being blocked, ignored, and caught (see signal(7)).
CapInh
, CapPrm
, CapEff
Masks (expressed in hexadecimal) of capabilities enabled in inheritable, permitted, and effective sets (see capabilities(7)).
CapBnd
Capability bounding set, expressed in hexadecimal (since Linux 2.6.26, see capabilities(7)).
CapAmb
Ambient capability set, expressed in hexadecimal (since Linux 4.3, see capabilities(7)).
NoNewPrivs
Value of the no_new_privs
bit (since Linux 4.10, see
prctl(2)).
Seccomp
Seccomp mode of the process (since Linux 3.8, see seccomp(2)). 0 means SECCOMP_MODE_DISABLED; 1 means SECCOMP_MODE_STRICT; 2 means SECCOMP_MODE_FILTER. This field is provided only if the kernel was built with the CONFIG_SECCOMP kernel configuration option enabled.
Speculation_Store_Bypass
Speculation flaw mitigation state (since Linux 4.17, see prctl(2)).
Cpus_allowed
Hexadecimal mask of CPUs on which this process may run (since Linux 2.6.24, see cpuset(7)).
Cpus_allowed_list
Same as previous, but in "list format" (since Linux 2.6.26, see cpuset(7)).
Mems_allowed
Mask of memory nodes allowed to this process (since Linux 2.6.24, see cpuset(7)).
Mems_allowed_list
Same as previous, but in "list format" (since Linux 2.6.26, see cpuset(7)).
voluntary_ctxt_switches
,
nonvoluntary_ctxt_switches
Number of voluntary and involuntary context switches (since Linux 2.6.23).
/proc/[pid]/syscall
(since Linux 2.6.27)This file exposes the system call number and argument registers for the system call currently being executed by the process, followed by the values of the stack pointer and program counter registers. The values of all six argument registers are exposed, although most system calls use fewer registers.
If the process is blocked, but not in a system call, then the file displays -1 in place of the system call number, followed by just the values of the stack pointer and program counter. If process is not blocked, then the file contains just the string "running".
This file is present only if the kernel was configured with CONFIG_HAVE_ARCH_TRACEHOOK.
Permission to access this file is governed by a ptrace access mode PTRACE_MODE_ATTACH_FSCREDS check; see ptrace(2).
/proc/[pid]/task
(since Linux 2.6.0)This is a directory that contains one subdirectory for each thread in
the process. The name of each subdirectory is the numerical thread ID
([tid]
) of the thread (see gettid(2)).
Within each of these subdirectories, there is a set of files with the
same names and contents as under the /proc/[pid]
directories.
For attributes that are shared by all threads, the contents for each of
the files under the task/[tid]
subdirectories will be the same
as in the corresponding file in the parent /proc/[pid]
directory (e.g., in a multithreaded process, all of the
task/[tid]/cwd
files will have the same value as the
/proc/[pid]/cwd
file in the parent directory, since all of the
threads in a process share a working directory). For attributes that are
distinct for each thread, the corresponding files under
task/[tid]
may have different values (e.g., various fields in
each of the task/[tid]/status
files may be different for each
thread), or they might not exist in /proc/[pid]
at all.
In a multithreaded process, the contents of the
/proc/[pid]/task
directory are not available if the main thread
has already terminated (typically by calling
pthread_exit(3)).
/proc/[pid]/task/[tid]/children
(since Linux 3.5)A space-separated list of child tasks of this task. Each child task is represented by its TID.
This option is intended for use by the checkpoint-restore (CRIU) system, and reliably provides a list of children only if all of the child processes are stopped or frozen. It does not work properly if children of the target task exit while the file is being read! Exiting children may cause non-exiting children to be omitted from the list. This makes this interface even more unreliable than classic PID-based approaches if the inspected task and its children aren't frozen, and most code should probably not use this interface.
Until Linux 4.2, the presence of this file was governed by the CONFIG_CHECKPOINT_RESTORE kernel configuration option. Since Linux 4.2, it is governed by the CONFIG_PROC_CHILDREN option.
/proc/[pid]/timers
(since Linux 3.10)A list of the POSIX timers for this process. Each timer is listed with a line that starts with the string "ID:". For example:
ID: 1
signal: 60/00007fff86e452a8
notify: signal/pid.2634
ClockID: 0
ID: 0
signal: 60/00007fff86e452a8
notify: signal/pid.2634
ClockID: 1
The lines shown for each timer have the following meanings:
ID
The ID for this timer. This is not the same as the timer ID returned
by timer_create(2); rather, it is the same
kernel-internal ID that is available via the si_timerid
field
of the siginfo_t
structure (see
sigaction(2)).
signal
This is the signal number that this timer uses to deliver
notifications followed by a slash, and then the sigev_value
value supplied to the signal handler. Valid only for timers that notify
via a signal.
notify
The part before the slash specifies the mechanism that this timer uses to deliver notifications, and is one of "thread", "signal", or "none". Immediately following the slash is either the string "tid" for timers with SIGEV_THREAD_ID notification, or "pid" for timers that notify by other mechanisms. Following the "." is the PID of the process (or the kernel thread ID of the thread) that will be delivered a signal if the timer delivers notifications via a signal.
ClockID
This field identifies the clock that the timer uses for measuring
time. For most clocks, this is a number that matches one of the
user-space CLOCK_* constants exposed via
<time.h>
. CLOCK_PROCESS_CPUTIME_ID
timers display with a value of -6 in this field.
CLOCK_THREAD_CPUTIME_ID timers display with a value of
-2 in this field.
This file is available only when the kernel was configured with CONFIG_CHECKPOINT_RESTORE.
/proc/[pid]/timerslack_ns
(since Linux 4.6)This file exposes the process's "current" timer slack value, expressed in nanoseconds. The file is writable, allowing the process's timer slack value to be changed. Writing 0 to this file resets the "current" timer slack to the "default" timer slack value. For further details, see the discussion of PR_SET_TIMERSLACK in prctl(2).
Initially, permission to access this file was governed by a ptrace access mode PTRACE_MODE_ATTACH_FSCREDS check (see ptrace(2)). However, this was subsequently deemed too strict a requirement (and had the side effect that requiring a process to have the CAP_SYS_PTRACE capability would also allow it to view and change any process's memory). Therefore, since Linux 4.9, only the (weaker) CAP_SYS_NICE capability is required to access this file.
/proc/[pid]/uid_map
, /proc/[pid]/gid_map
(since
Linux 3.5)See user_namespaces(7).
/proc/[pid]/wchan
(since Linux 2.6.0)The symbolic name corresponding to the location in the kernel where the process is sleeping.
Permission to access this file is governed by a ptrace access mode PTRACE_MODE_READ_FSCREDS check; see ptrace(2).
/proc/[tid]
There is a numerical subdirectory for each running thread that is not
a thread group leader (i.e., a thread whose thread ID is not the same as
its process ID); the subdirectory is named by the thread ID. Each one of
these subdirectories contains files and subdirectories exposing
information about the thread with the thread ID tid
. The
contents of these directories are the same as the corresponding
/proc/[pid]/task/[tid]
directories.
The /proc/[tid]
subdirectories are not
visible when
iterating through /proc
with getdents(2) (and
thus are not
visible when one uses ls(1) to
view the contents of /proc
). However, the pathnames of these
directories are visible to (i.e., usable as arguments in) system calls
that operate on pathnames.
/proc/apm
Advanced power management version and battery information when CONFIG_APM is defined at kernel compilation time.
/proc/buddyinfo
This file contains information which is used for diagnosing memory fragmentation issues. Each line starts with the identification of the node and the name of the zone which together identify a memory region. This is then followed by the count of available chunks of a certain order in which these zones are split. The size in bytes of a certain order is given by the formula:
(2^order) * PAGE_SIZE
The binary buddy allocator algorithm inside the kernel will split one chunk into two chunks of a smaller order (thus with half the size) or combine two contiguous chunks into one larger chunk of a higher order (thus with double the size) to satisfy allocation requests and to counter memory fragmentation. The order matches the column number, when starting to count at zero.
For example on an x86-64 system:
Node 0, zone DMA 1 1 1 0 2 1 1 0 1 1 3
Node 0, zone DMA32 65 47 4 81 52 28 13 10 5 1 404
Node 0, zone Normal 216 55 189 101 84 38 37 27 5 3 587
In this example, there is one node containing three zones and there
are 11 different chunk sizes. If the page size is 4 kilobytes, then the
first zone called DMA
(on x86 the first 16 megabyte of memory)
has 1 chunk of 4 kilobytes (order 0) available and has 3 chunks of 4
megabytes (order 10) available.
If the memory is heavily fragmented, the counters for higher order chunks will be zero and allocation of large contiguous areas will fail.
Further information about the zones can be found in
/proc/zoneinfo
.
/proc/bus
Contains subdirectories for installed busses.
/proc/bus/pccard
Subdirectory for PCMCIA devices when CONFIG_PCMCIA is set at kernel compilation time.
/proc/bus/pccard/drivers
/proc/bus/pci
Contains various bus subdirectories and pseudo-files containing information about PCI busses, installed devices, and device drivers. Some of these files are not ASCII.
/proc/bus/pci/devices
Information about PCI devices. They may be accessed through lspci(8) and setpci(8).
/proc/cgroups
(since Linux 2.6.24)See cgroups(7).
/proc/cmdline
Arguments passed to the Linux kernel at boot time. Often done via a boot manager such as lilo(8) or grub(8).
/proc/config.gz
(since Linux 2.6)This file exposes the configuration options that were used to build
the currently running kernel, in the same format as they would be shown
in the .config
file that resulted when configuring the kernel
(using make xconfig
, make config
, or similar). The
file contents are compressed; view or search them using
zcat(1) and zgrep(1). As long as no
changes have been made to the following file, the contents of
/proc/config.gz
are the same as those provided by:
cat /lib/modules/$(uname -r)/build/.config
/proc/config.gz
is provided only if the kernel is configured
with CONFIG_IKCONFIG_PROC.
/proc/crypto
A list of the ciphers provided by the kernel crypto API. For details,
see the kernel Linux Kernel Crypto API
documentation available
under the kernel source directory Documentation/crypto/
(or
Documentation/DocBook
before 4.10; the documentation can be
built using a command such as make htmldocs
in the root
directory of the kernel source tree).
/proc/cpuinfo
This is a collection of CPU and system architecture dependent items,
for each supported architecture a different list. Two common entries are
processor
which gives CPU number and bogomips
; a
system constant that is calculated during kernel initialization. SMP
machines have information for each CPU. The lscpu(1)
command gathers its information from this file.
/proc/devices
Text listing of major numbers and device groups. This can be used by MAKEDEV scripts for consistency with the kernel.
/proc/diskstats
(since Linux 2.5.69)This file contains disk I/O statistics for each disk device. See the
Linux kernel source file Documentation/iostats.txt
for further
information.
/proc/dma
This is a list of the registered ISA
DMA (direct memory
access) channels in use.
/proc/driver
Empty subdirectory.
/proc/execdomains
List of the execution domains (ABI personalities).
/proc/fb
Frame buffer information when CONFIG_FB is defined during kernel compilation.
/proc/filesystems
A text listing of the filesystems which are supported by the kernel, namely filesystems which were compiled into the kernel or whose kernel modules are currently loaded. (See also filesystems(5).) If a filesystem is marked with "nodev", this means that it does not require a block device to be mounted (e.g., virtual filesystem, network filesystem).
Incidentally, this file may be used by mount(8) when no filesystem is specified and it didn't manage to determine the filesystem type. Then filesystems contained in this file are tried (excepted those that are marked with "nodev").
/proc/fs
Contains subdirectories that in turn contain files with information about (certain) mounted filesystems.
/proc/ide
This directory exists on systems with the IDE bus. There are directories for each IDE channel and attached device. Files include:
cache buffer size in KB
capacity number of sectors
driver driver version
geometry physical and logical geometry
identify in hexadecimal
media media type
model manufacturer's model number
settings drive settings
smart_thresholds IDE disk management thresholds (in hex)
smart_values IDE disk management values (in hex)
The hdparm(8) utility provides access to this information in a friendly format.
/proc/interrupts
This is used to record the number of interrupts per CPU per IO device. Since Linux 2.6.24, for the i386 and x86-64 architectures, at least, this also includes interrupts internal to the system (that is, not associated with a device as such), such as NMI (nonmaskable interrupt), LOC (local timer interrupt), and for SMP systems, TLB (TLB flush interrupt), RES (rescheduling interrupt), CAL (remote function call interrupt), and possibly others. Very easy to read formatting, done in ASCII.
/proc/iomem
I/O memory map in Linux 2.4.
/proc/ioports
This is a list of currently registered Input-Output port regions that are in use.
/proc/kallsyms
(since Linux 2.5.71)This holds the kernel exported symbol definitions used by the
modules(X) tools to dynamically link and bind loadable
modules. In Linux 2.5.47 and earlier, a similar file with slightly
different syntax was named ksyms
.
/proc/kcore
This file represents the physical memory of the system and is stored
in the ELF core file format. With this pseudo-file, and an unstripped
kernel (/usr/src/linux/vmlinux
) binary, GDB can be used to
examine the current state of any kernel data structures.
The total length of the file is the size of physical memory (RAM) plus 4 KiB.
/proc/keys
(since Linux 2.6.10)See keyrings(7).
/proc/key-users
(since Linux 2.6.10)See keyrings(7).
/proc/kmsg
This file can be used instead of the syslog(2) system call to read kernel messages. A process must have superuser privileges to read this file, and only one process should read this file. This file should not be read if a syslog process is running which uses the syslog(2) system call facility to log kernel messages.
Information in this file is retrieved with the dmesg(1) program.
/proc/kpagecgroup
(since Linux 4.3)This file contains a 64-bit inode number of the memory cgroup each
page is charged to, indexed by page frame number (see the discussion of
/proc/[pid]/pagemap
).
The /proc/kpagecgroup
file is present only if the
CONFIG_MEMCG kernel configuration option is
enabled.
/proc/kpagecount
(since Linux 2.6.25)This file contains a 64-bit count of the number of times each
physical page frame is mapped, indexed by page frame number (see the
discussion of /proc/[pid]/pagemap
).
The /proc/kpagecount
file is present only if the
CONFIG_PROC_PAGE_MONITOR kernel configuration option is
enabled.
/proc/kpageflags
(since Linux 2.6.25)This file contains 64-bit masks corresponding to each physical page
frame; it is indexed by page frame number (see the discussion of
/proc/[pid]/pagemap
). The bits are as follows:
0 - KPF_LOCKED 1 - KPF_ERROR 2 - KPF_REFERENCED 3 - KPF_UPTODATE 4 - KPF_DIRTY 5 - KPF_LRU 6 - KPF_ACTIVE 7 - KPF_SLAB 8 - KPF_WRITEBACK 9 - KPF_RECLAIM 10 - KPF_BUDDY 11 - KPF_MMAP (since Linux 2.6.31) 12 - KPF_ANON (since Linux 2.6.31) 13 - KPF_SWAPCACHE (since Linux 2.6.31) 14 - KPF_SWAPBACKED (since Linux 2.6.31) 15 - KPF_COMPOUND_HEAD (since Linux 2.6.31) 16 - KPF_COMPOUND_TAIL (since Linux 2.6.31) 17 - KPF_HUGE (since Linux 2.6.31) 18 - KPF_UNEVICTABLE (since Linux 2.6.31) 19 - KPF_HWPOISON (since Linux 2.6.31) 20 - KPF_NOPAGE (since Linux 2.6.31) 21 - KPF_KSM (since Linux 2.6.32) 22 - KPF_THP (since Linux 3.4) 23 - KPF_BALLOON (since Linux 3.18) 24 - KPF_ZERO_PAGE (since Linux 4.0) 25 - KPF_IDLE (since Linux 4.3)
For further details on the meanings of these bits, see the kernel
source file Documentation/admin-guide/mm/pagemap.rst
. Before
kernel 2.6.29, KPF_WRITEBACK,
KPF_RECLAIM, KPF_BUDDY, and
KPF_LOCKED did not report correctly.
The /proc/kpageflags
file is present only if the
CONFIG_PROC_PAGE_MONITOR kernel configuration option is
enabled.
/proc/ksyms
(Linux 1.1.23–2.5.47)See /proc/kallsyms
.
/proc/loadavg
The first three fields in this file are load average figures giving the number of jobs in the run queue (state R) or waiting for disk I/O (state D) averaged over 1, 5, and 15 minutes. They are the same as the load average numbers given by uptime(1) and other programs. The fourth field consists of two numbers separated by a slash (/). The first of these is the number of currently runnable kernel scheduling entities (processes, threads). The value after the slash is the number of kernel scheduling entities that currently exist on the system. The fifth field is the PID of the process that was most recently created on the system.
/proc/locks
This file shows current file locks (flock(2) and fcntl(2)) and leases (fcntl(2)).
An example of the content shown in this file is the following:
1: POSIX ADVISORY READ 5433 08:01:7864448 128 128
2: FLOCK ADVISORY WRITE 2001 08:01:7864554 0 EOF
3: FLOCK ADVISORY WRITE 1568 00:2f:32388 0 EOF
4: POSIX ADVISORY WRITE 699 00:16:28457 0 EOF
5: POSIX ADVISORY WRITE 764 00:16:21448 0 0
6: POSIX ADVISORY READ 3548 08:01:7867240 1 1
7: POSIX ADVISORY READ 3548 08:01:7865567 1826 2335
8: OFDLCK ADVISORY WRITE -1 08:01:8713209 128 191
The fields shown in each line are as follows:
The ordinal position of the lock in the list.
The lock type. Values that may appear here include:
Among the strings that can appear here are the following:
This is an advisory lock.
This is a mandatory lock.
The type of lock. Values that can appear here are:
This is a POSIX or OFD read lock, or a BSD shared lock.
This is a POSIX or OFD write lock, or a BSD exclusive lock.
The PID of the process that owns the lock.
Because OFD locks are not owned by a single process (since multiple processes may have file descriptors that refer to the same open file description), the value -1 is displayed in this field for OFD locks. (Before kernel 4.14, a bug meant that the PID of the process that initially acquired the lock was displayed instead of the value -1.)
Three colon-separated subfields that identify the major and minor device ID of the device containing the filesystem where the locked file resides, followed by the inode number of the locked file.
The byte offset of the first byte of the lock. For BSD locks, this value is always 0.
The byte offset of the last byte of the lock.
EOF in this field means that the lock extends to the
end of the file. For BSD locks, the value shown is always
EOF
.
Since Linux 4.9, the list of locks shown in /proc/locks
is
filtered to show just the locks for the processes in the PID namespace
(see pid_namespaces(7)) for which the /proc
filesystem was mounted. (In the initial PID namespace, there is no
filtering of the records shown in this file.)
The lslocks(8) command provides a bit more information about each lock.
/proc/malloc
(only up to and including Linux 2.2)This file is present only if CONFIG_DEBUG_MALLOC was defined during compilation.
/proc/meminfo
This file reports statistics about memory usage on the system. It is used by free(1) to report the amount of free and used memory (both physical and swap) on the system as well as the shared memory and buffers used by the kernel. Each line of the file consists of a parameter name, followed by a colon, the value of the parameter, and an option unit of measurement (e.g., "kB"). The list below describes the parameter names and the format specifier required to read the field value. Except as noted below, all of the fields have been present since at least Linux 2.6.0. Some fields are displayed only if the kernel was configured with various options; those dependencies are noted in the list.
MemTotal
%luTotal usable RAM (i.e., physical RAM minus a few reserved bits and the kernel binary code).
MemFree
%luThe sum of LowFree
+HighFree
.
MemAvailable
%lu (since Linux 3.14)An estimate of how much memory is available for starting new applications, without swapping.
Buffers
%luRelatively temporary storage for raw disk blocks that shouldn't get tremendously large (20 MB or so).
Cached
%luIn-memory cache for files read from the disk (the page cache).
Doesn't include SwapCached
.
SwapCached
%luMemory that once was swapped out, is swapped back in but still also is in the swap file. (If memory pressure is high, these pages don't need to be swapped out again because they are already in the swap file. This saves I/O.)
Active
%luMemory that has been used more recently and usually not reclaimed unless absolutely necessary.
Inactive
%luMemory which has been less recently used. It is more eligible to be reclaimed for other purposes.
Active(anon)
%lu (since Linux 2.6.28)[To be documented.]
Inactive(anon)
%lu (since Linux 2.6.28)[To be documented.]
Active(file)
%lu (since Linux 2.6.28)[To be documented.]
Inactive(file)
%lu (since Linux 2.6.28)[To be documented.]
Unevictable
%lu (since Linux 2.6.28)(From Linux 2.6.28 to 2.6.30, CONFIG_UNEVICTABLE_LRU was required.) [To be documented.]
Mlocked
%lu (since Linux 2.6.28)(From Linux 2.6.28 to 2.6.30, CONFIG_UNEVICTABLE_LRU was required.) [To be documented.]
HighTotal
%lu(Starting with Linux 2.6.19, CONFIG_HIGHMEM is required.) Total amount of highmem. Highmem is all memory above ~860 MB of physical memory. Highmem areas are for use by user-space programs, or for the page cache. The kernel must use tricks to access this memory, making it slower to access than lowmem.
HighFree
%lu(Starting with Linux 2.6.19, CONFIG_HIGHMEM is required.) Amount of free highmem.
LowTotal
%lu(Starting with Linux 2.6.19, CONFIG_HIGHMEM is
required.) Total amount of lowmem. Lowmem is memory which can be used
for everything that highmem can be used for, but it is also available
for the kernel's use for its own data structures. Among many other
things, it is where everything from Slab
is allocated. Bad
things happen when you're out of lowmem.
LowFree
%lu(Starting with Linux 2.6.19, CONFIG_HIGHMEM is required.) Amount of free lowmem.
MmapCopy
%lu (since Linux 2.6.29)(CONFIG_MMU is required.) [To be documented.]
SwapTotal
%luTotal amount of swap space available.
SwapFree
%luAmount of swap space that is currently unused.
Dirty
%luMemory which is waiting to get written back to the disk.
Writeback
%luMemory which is actively being written back to the disk.
AnonPages
%lu (since Linux 2.6.18)Non-file backed pages mapped into user-space page tables.
Mapped
%luFiles which have been mapped into memory (with mmap(2)), such as libraries.
Shmem
%lu (since Linux 2.6.32)Amount of memory consumed in tmpfs(5) filesystems.
KReclaimable
%lu (since Linux 4.20)Kernel allocations that the kernel will attempt to reclaim under
memory pressure. Includes SReclaimable
(below), and other
direct allocations with a shrinker.
Slab
%luIn-kernel data structures cache. (See slabinfo(5).)
SReclaimable
%lu (since Linux 2.6.19)Part of Slab
, that might be reclaimed, such as caches.
SUnreclaim
%lu (since Linux 2.6.19)Part of Slab
, that cannot be reclaimed on memory
pressure.
KernelStack
%lu (since Linux 2.6.32)Amount of memory allocated to kernel stacks.
PageTables
%lu (since Linux 2.6.18)Amount of memory dedicated to the lowest level of page tables.
Quicklists
%lu (since Linux 2.6.27)(CONFIG_QUICKLIST is required.) [To be documented.]
NFS_Unstable
%lu (since Linux 2.6.18)NFS pages sent to the server, but not yet committed to stable storage.
Bounce
%lu (since Linux 2.6.18)Memory used for block device "bounce buffers".
WritebackTmp
%lu (since Linux 2.6.26)Memory used by FUSE for temporary writeback buffers.
CommitLimit
%lu (since Linux 2.6.10)This is the total amount of memory currently available to be
allocated on the system, expressed in kilobytes. This limit is adhered
to only if strict overcommit accounting is enabled (mode 2 in
/proc/sys/vm/overcommit_memory
). The limit is calculated
according to the formula described under
/proc/sys/vm/overcommit_memory
. For further details, see the
kernel source file
Documentation/vm/overcommit-accounting.rst
.
Committed_AS
%luThe amount of memory presently allocated on the system. The committed memory is a sum of all of the memory which has been allocated by processes, even if it has not been "used" by them as of yet. A process which allocates 1 GB of memory (using malloc(3) or similar), but touches only 300 MB of that memory will show up as using only 300 MB of memory even if it has the address space allocated for the entire 1 GB.
This 1 GB is memory which has been "committed" to by the VM and can
be used at any time by the allocating application. With strict
overcommit enabled on the system (mode 2 in
/proc/sys/vm/overcommit_memory
), allocations which would exceed
the CommitLimit
will not be permitted. This is useful if one
needs to guarantee that processes will not fail due to lack of memory
once that memory has been successfully allocated.
VmallocTotal
%luTotal size of vmalloc memory area.
VmallocUsed
%luAmount of vmalloc area which is used. Since Linux 4.4, this field is
no longer calculated, and is hard coded as 0. See
/proc/vmallocinfo
.
VmallocChunk
%luLargest contiguous block of vmalloc area which is free. Since Linux
4.4, this field is no longer calculated and is hard coded as 0. See
/proc/vmallocinfo
.
HardwareCorrupted
%lu (since Linux 2.6.32)(CONFIG_MEMORY_FAILURE is required.) [To be documented.]
LazyFree
%lu (since Linux 4.12)Shows the amount of memory marked by madvise(2) MADV_FREE.
AnonHugePages
%lu (since Linux 2.6.38)(CONFIG_TRANSPARENT_HUGEPAGE is required.) Non-file backed huge pages mapped into user-space page tables.
ShmemHugePages
%lu (since Linux 4.8)(CONFIG_TRANSPARENT_HUGEPAGE is required.) Memory used by shared memory (shmem) and tmpfs(5) allocated with huge pages.
ShmemPmdMapped
%lu (since Linux 4.8)(CONFIG_TRANSPARENT_HUGEPAGE is required.) Shared memory mapped into user space with huge pages.
CmaTotal
%lu (since Linux 3.1)Total CMA (Contiguous Memory Allocator) pages. (CONFIG_CMA is required.)
CmaFree
%lu (since Linux 3.1)Free CMA (Contiguous Memory Allocator) pages. (CONFIG_CMA is required.)
HugePages_Total
%lu(CONFIG_HUGETLB_PAGE is required.) The size of the pool of huge pages.
HugePages_Free
%lu(CONFIG_HUGETLB_PAGE is required.) The number of huge pages in the pool that are not yet allocated.
HugePages_Rsvd
%lu (since Linux 2.6.17)(CONFIG_HUGETLB_PAGE is required.) This is the number of huge pages for which a commitment to allocate from the pool has been made, but no allocation has yet been made. These reserved huge pages guarantee that an application will be able to allocate a huge page from the pool of huge pages at fault time.
HugePages_Surp
%lu (since Linux 2.6.24)(CONFIG_HUGETLB_PAGE is required.) This is the
number of huge pages in the pool above the value in
/proc/sys/vm/nr_hugepages
. The maximum number of surplus huge
pages is controlled by
/proc/sys/vm/nr_overcommit_hugepages
.
Hugepagesize
%lu(CONFIG_HUGETLB_PAGE is required.) The size of huge pages.
DirectMap4k
%lu (since Linux 2.6.27)Number of bytes of RAM linearly mapped by kernel in 4 kB pages. (x86.)
DirectMap4M
%lu (since Linux 2.6.27)Number of bytes of RAM linearly mapped by kernel in 4 MB pages. (x86 with CONFIG_X86_64 or CONFIG_X86_PAE enabled.)
DirectMap2M
%lu (since Linux 2.6.27)Number of bytes of RAM linearly mapped by kernel in 2 MB pages. (x86 with neither CONFIG_X86_64 nor CONFIG_X86_PAE enabled.)
DirectMap1G
%lu (since Linux 2.6.27)(x86 with CONFIG_X86_64 and CONFIG_X86_DIRECT_GBPAGES enabled.)
/proc/modules
A text list of the modules that have been loaded by the system. See also lsmod(8).
/proc/mounts
Before kernel 2.4.19, this file was a list of all the filesystems
currently mounted on the system. With the introduction of per-process
mount namespaces in Linux 2.4.19 (see
mount_namespaces(7)), this file became a link to
/proc/self/mounts
, which lists the mount points of the
process's own mount namespace. The format of this file is documented in
fstab(5).
/proc/mtrr
Memory Type Range Registers. See the Linux kernel source file
Documentation/x86/mtrr.txt
(or Documentation/mtrr.txt
before Linux 2.6.28) for details.
/proc/net
This directory contains various files and subdirectories containing information about the networking layer. The files contain ASCII structures and are, therefore, readable with cat(1). However, the standard netstat(8) suite provides much cleaner access to these files.
With the advent of network namespaces, various information relating
to the network stack is virtualized (see
network_namespaces(7)). Thus, since Linux 2.6.25,
/proc/net
is a symbolic link to the directory
/proc/self/net
, which contains the same files and directories
as listed below. However, these files and directories now expose
information for the network namespace of which the process is a
member.
/proc/net/arp
This holds an ASCII readable dump of the kernel ARP table used for address resolutions. It will show both dynamically learned and preprogrammed ARP entries. The format is:
IP address HW type Flags HW address Mask Device
192.168.0.50 0x1 0x2 00:50:BF:25:68:F3 * eth0
192.168.0.250 0x1 0xc 00:00:00:00:00:00 * eth0
Here "IP address" is the IPv4 address of the machine and the "HW
type" is the hardware type of the address from RFC 826. The flags are
the internal flags of the ARP structure (as defined in
/usr/include/linux/if_arp.h
) and the "HW address" is the data
link layer mapping for that IP address if it is known.
/proc/net/dev
The dev pseudo-file contains network device status information. This gives the number of received and sent packets, the number of errors and collisions and other basic statistics. These are used by the ifconfig(8) program to report device status. The format is:
Inter-| Receive | Transmit
face |bytes packets errs drop fifo frame compressed multicast|bytes packets errs drop fifo colls carrier compressed
lo: 2776770 11307 0 0 0 0 0 0 2776770 11307 0 0 0 0 0 0
eth0: 1215645 2751 0 0 0 0 0 0 1782404 4324 0 0 0 427 0 0
ppp0: 1622270 5552 1 0 0 0 0 0 354130 5669 0 0 0 0 0 0
tap0: 7714 81 0 0 0 0 0 0 7714 81 0 0 0 0 0 0
/proc/net/dev_mcast
Defined in /usr/src/linux/net/core/dev_mcast.c
:
indx interface_name dmi_u dmi_g dmi_address
2 eth0 1 0 01005e000001
3 eth1 1 0 01005e000001
4 eth2 1 0 01005e000001
/proc/net/igmp
Internet Group Management Protocol. Defined in
/usr/src/linux/net/core/igmp.c
.
/proc/net/rarp
This file uses the same format as the arp
file and contains
the current reverse mapping database used to provide
rarp(8) reverse address lookup services. If RARP is not
configured into the kernel, this file will not be present.
/proc/net/raw
Holds a dump of the RAW socket table. Much of the information is not of use apart from debugging. The "sl" value is the kernel hash slot for the socket, the "local_address" is the local address and protocol number pair. "St" is the internal status of the socket. The "tx_queue" and "rx_queue" are the outgoing and incoming data queue in terms of kernel memory usage. The "tr", "tm->when", and "rexmits" fields are not used by RAW. The "uid" field holds the effective UID of the creator of the socket.
/proc/net/snmp
This file holds the ASCII data needed for the IP, ICMP, TCP, and UDP management information bases for an SNMP agent.
/proc/net/tcp
Holds a dump of the TCP socket table. Much of the information is not of use apart from debugging. The "sl" value is the kernel hash slot for the socket, the "local_address" is the local address and port number pair. The "rem_address" is the remote address and port number pair (if connected). "St" is the internal status of the socket. The "tx_queue" and "rx_queue" are the outgoing and incoming data queue in terms of kernel memory usage. The "tr", "tm->when", and "rexmits" fields hold internal information of the kernel socket state and are useful only for debugging. The "uid" field holds the effective UID of the creator of the socket.
/proc/net/udp
Holds a dump of the UDP socket table. Much of the information is not of use apart from debugging. The "sl" value is the kernel hash slot for the socket, the "local_address" is the local address and port number pair. The "rem_address" is the remote address and port number pair (if connected). "St" is the internal status of the socket. The "tx_queue" and "rx_queue" are the outgoing and incoming data queue in terms of kernel memory usage. The "tr", "tm->when", and "rexmits" fields are not used by UDP. The "uid" field holds the effective UID of the creator of the socket. The format is:
sl local_address rem_address st tx_queue rx_queue tr rexmits tm->when uid
1: 01642C89:0201 0C642C89:03FF 01 00000000:00000001 01:000071BA 00000000 0
1: 00000000:0801 00000000:0000 0A 00000000:00000000 00:00000000 6F000100 0
1: 00000000:0201 00000000:0000 0A 00000000:00000000 00:00000000 00000000 0
/proc/net/unix
Lists the UNIX domain sockets present within the system and their status. The format is:
Num RefCount Protocol Flags Type St Inode Path
0: 00000002 00000000 00000000 0001 03 42
1: 00000001 00000000 00010000 0001 01 1948 /dev/printer
The fields are as follows:
Num
:the kernel table slot number.
RefCount
:the number of users of the socket.
Protocol
:currently always 0.
Flags
:the internal kernel flags holding the status of the socket.
Type
:the socket type. For SOCK_STREAM sockets, this is 0001; for SOCK_DGRAM sockets, it is 0002; and for SOCK_SEQPACKET sockets, it is 0005.
St
:the internal state of the socket.
Inode
:the inode number of the socket.
Path
:the bound pathname (if any) of the socket. Sockets in the abstract
namespace are included in the list, and are shown with a Path
that commences with the character '@'.
/proc/net/netfilter/nfnetlink_queue
This file contains information about netfilter user-space queueing, if used. Each line represents a queue. Queues that have not been subscribed to by user space are not shown.
1 4207 0 2 65535 0 0 0 1
(1) (2) (3)(4) (5) (6) (7) (8)
The fields in each line are:
The ID of the queue. This matches what is specified in the --queue-num or --queue-balance options to the iptables(8) NFQUEUE target. See iptables-extensions(8) for more information.
The netlink port ID subscribed to the queue.
The number of packets currently queued and waiting to be processed by the application.
The copy mode of the queue. It is either 1 (metadata only) or 2 (also copy payload data to user space).
Copy range; that is, how many bytes of packet payload should be copied to user space at most.
queue dropped. Number of packets that had to be dropped by the kernel because too many packets are already waiting for user space to send back the mandatory accept/drop verdicts.
queue user dropped. Number of packets that were dropped within the netlink subsystem. Such drops usually happen when the corresponding socket buffer is full; that is, user space is not able to read messages fast enough.
sequence number. Every queued packet is associated with a (32-bit) monotonically increasing sequence number. This shows the ID of the most recent packet queued.
The last number exists only for compatibility reasons and is always 1.
/proc/partitions
Contains the major and minor numbers of each partition as well as the number of 1024-byte blocks and the partition name.
/proc/pci
This is a listing of all PCI devices found during kernel initialization and their configuration.
This file has been deprecated in favor of a new /proc
interface for PCI (/proc/bus/pci
). It became optional in Linux
2.2 (available with CONFIG_PCI_OLD_PROC set at kernel
compilation). It became once more nonoptionally enabled in Linux 2.4.
Next, it was deprecated in Linux 2.6 (still available with
CONFIG_PCI_LEGACY_PROC set), and finally removed
altogether since Linux 2.6.17.
/proc/profile
(since Linux 2.4)This file is present only if the kernel was booted with the
profile=1
command-line option. It exposes kernel profiling
information in a binary format for use by
readprofile(1). Writing (e.g., an empty string) to this
file resets the profiling counters; on some architectures, writing a
binary integer "profiling multiplier" of size sizeof(int)
sets
the profiling interrupt frequency.
/proc/scsi
A directory with the scsi
mid-level pseudo-file and various
SCSI low-level driver directories, which contain a file for each SCSI
host in this system, all of which give the status of some part of the
SCSI IO subsystem. These files contain ASCII structures and are,
therefore, readable with cat(1).
You can also write to some of the files to reconfigure the subsystem or switch certain features on or off.
/proc/scsi/scsi
This is a listing of all SCSI devices known to the kernel. The
listing is similar to the one seen during bootup. scsi currently
supports only the add-single-device
command which allows root
to add a hotplugged device to the list of known devices.
The command
echo 'scsi add-single-device 1 0 5 0' > /proc/scsi/scsi
will cause host scsi1 to scan on SCSI channel 0 for a device on ID 5 LUN 0. If there is already a device known on this address or the address is invalid, an error will be returned.
/proc/scsi/[drivername]
[drivername]
can currently be NCR53c7xx, aha152x, aha1542,
aha1740, aic7xxx, buslogic, eata_dma, eata_pio, fdomain, in2000, pas16,
qlogic, scsi_debug, seagate, t128, u15-24f, ultrastore, or wd7000. These
directories show up for all drivers that registered at least one SCSI
HBA. Every directory contains one file per registered host. Every
host-file is named after the number the host was assigned during
initialization.
Reading these files will usually show driver and host configuration, statistics, and so on.
Writing to these files allows different things on different hosts.
For example, with the latency
and nolatency
commands,
root can switch on and off command latency measurement code in the
eata_dma driver. With the lockup
and unlock
commands,
root can control bus lockups simulated by the scsi_debug driver.
/proc/self
This directory refers to the process accessing the /proc
filesystem, and is identical to the /proc
directory named by
the process ID of the same process.
/proc/slabinfo
Information about kernel caches. See slabinfo(5) for details.
/proc/stat
kernel/system statistics. Varies with architecture. Common entries include:
cpu0 1393280 32966 572056 13343292 6130 0 17875 0 23933 0
The amount of time, measured in units of USER_HZ (1/100ths of a
second on most architectures, use sysconf(_SC_CLK_TCK)
to
obtain the right value), that the system ("cpu" line) or the specific
CPU ("cpuN
" line) spent in various states:
user
(1) Time spent in user mode.
nice
(2) Time spent in user mode with low priority (nice).
system
(3) Time spent in system mode.
idle
(4) Time spent in the idle task. This value should be USER_HZ times
the second entry in the /proc/uptime
pseudo-file.
iowait
(since Linux 2.5.41)(5) Time waiting for I/O to complete. This value is not reliable, for the following reasons:
The CPU will not wait for I/O to complete; iowait is the time that a task is waiting for I/O to complete. When a CPU goes into idle state for outstanding task I/O, another task will be scheduled on this CPU.
On a multi-core CPU, the task waiting for I/O to complete is not running on any CPU, so the iowait of each CPU is difficult to calculate.
The value in this field may decrease
in certain
conditions.
irq
(since Linux 2.6.0)(6) Time servicing interrupts.
softirq
(since Linux 2.6.0)(7) Time servicing softirqs.
steal
(since Linux 2.6.11)(8) Stolen time, which is the time spent in other operating systems when running in a virtualized environment
guest
(since Linux 2.6.24)(9) Time spent running a virtual CPU for guest operating systems under the control of the Linux kernel.
guest_nice
(since Linux 2.6.33)(10) Time spent running a niced guest (virtual CPU for guest operating systems under the control of the Linux kernel).
page 5741 1808
The number of pages the system paged in and the number that were paged out (from disk).
swap 1 0
The number of swap pages that have been brought in and out.
intr 1462898
This line shows counts of interrupts serviced since boot time, for each of the possible system interrupts. The first column is the total of all interrupts serviced including unnumbered architecture specific interrupts; each subsequent column is the total for that particular numbered interrupt. Unnumbered interrupts are not shown, only summed into the total.
disk_io: (2,0):(31,30,5764,1,2) (3,0):
...(major,disk_idx):(noinfo, read_io_ops, blks_read, write_io_ops,
blks_written)
(Linux 2.4 only)
ctxt 115315
The number of context switches that the system underwent.
btime 769041601
boot time, in seconds since the Epoch, 1970-01-01 00:00:00 +0000 (UTC).
processes 86031
Number of forks since boot.
procs_running 6
Number of processes in runnable state. (Linux 2.5.45 onward.)
procs_blocked 2
Number of processes blocked waiting for I/O to complete. (Linux 2.5.45 onward.)
This line shows the number of softirq for all CPUs. The first column is the total of all softirqs and each subsequent column is the total for particular softirq. (Linux 2.6.31 onward.)
/proc/swaps
Swap areas in use. See also swapon(8).
/proc/sys
This directory (present since 1.3.57) contains a number of files and
subdirectories corresponding to kernel variables. These variables can be
read and in some cases modified using the /proc
filesystem, and
the (deprecated) sysctl(2) system call.
String values may be terminated by either '\0' or '\n'.
Integer and long values may be written either in decimal or in hexadecimal notation (e.g., 0x3FFF). When writing multiple integer or long values, these may be separated by any of the following whitespace characters: ' ', '\t', or '\n'. Using other separators leads to the error EINVAL.
/proc/sys/abi
(since Linux 2.4.10)This directory may contain files with application binary information.
See the Linux kernel source file Documentation/sysctl/abi.txt
for more information.
/proc/sys/debug
This directory may be empty.
/proc/sys/dev
This directory contains device-specific information (e.g.,
dev/cdrom/info
). On some systems, it may be empty.
/proc/sys/fs
This directory contains the files and subdirectories for kernel variables related to filesystems.
/proc/sys/fs/aio-max-nr
and /proc/sys/fs/aio-nr
(since Linux 2.6.4)aio-nr
is the running total of the number of events
specified by io_setup(2) calls for all currently active
AIO contexts. If aio-nr
reaches aio-max-nr
, then
io_setup(2) will fail with the error
EAGAIN. Raising aio-max-nr
does not result in
the preallocation or resizing of any kernel data structures.
/proc/sys/fs/binfmt_misc
Documentation for files in this directory can be found in the Linux
kernel source in the file
Documentation/admin-guide/binfmt-misc.rst
(or in
Documentation/binfmt_misc.txt
on older kernels).
/proc/sys/fs/dentry-state
(since Linux 2.2)This file contains information about the status of the directory
cache (dcache). The file contains six numbers, nr_dentry
,
nr_unused
, age_limit
(age in seconds),
want_pages
(pages requested by system) and two dummy
values.
nr_dentry
is the number of allocated dentries (dcache
entries). This field is unused in Linux 2.2.
nr_unused
is the number of unused dentries.
age_limit
is the age in seconds after which dcache
entries can be reclaimed when memory is short.
want_pages
is nonzero when the kernel has called
shrink_dcache_pages() and the dcache isn't pruned yet.
/proc/sys/fs/dir-notify-enable
This file can be used to disable or enable the dnotify
interface described in fcntl(2) on a system-wide basis.
A value of 0 in this file disables the interface, and a value of 1
enables it.
/proc/sys/fs/dquot-max
This file shows the maximum number of cached disk quota entries. On some (2.4) systems, it is not present. If the number of free cached disk quota entries is very low and you have some awesome number of simultaneous system users, you might want to raise the limit.
/proc/sys/fs/dquot-nr
This file shows the number of allocated disk quota entries and the number of free disk quota entries.
/proc/sys/fs/epoll
(since Linux 2.6.28)This directory contains the file max_user_watches
, which can
be used to limit the amount of kernel memory consumed by the
epoll
interface. For further details, see
epoll(7).
/proc/sys/fs/file-max
This file defines a system-wide limit on the number of open files for all processes. System calls that fail when encountering this limit fail with the error ENFILE. (See also setrlimit(2), which can be used by a process to set the per-process limit, RLIMIT_NOFILE, on the number of files it may open.) If you get lots of error messages in the kernel log about running out of file handles (open file descriptions) (look for "VFS: file-max limit <number> reached"), try increasing this value:
echo 100000 > /proc/sys/fs/file-max
Privileged processes (CAP_SYS_ADMIN) can override
the file-max
limit.
/proc/sys/fs/file-nr
This (read-only) file contains three numbers: the number of allocated
file handles (i.e., the number of open file descriptions; see
open(2)); the number of free file handles; and the
maximum number of file handles (i.e., the same value as
/proc/sys/fs/file-max
). If the number of allocated file handles
is close to the maximum, you should consider increasing the maximum.
Before Linux 2.6, the kernel allocated file handles dynamically, but it
didn't free them again. Instead the free file handles were kept in a
list for reallocation; the "free file handles" value indicates the size
of that list. A large number of free file handles indicates that there
was a past peak in the usage of open file handles. Since Linux 2.6, the
kernel does deallocate freed file handles, and the "free file handles"
value is always zero.
/proc/sys/fs/inode-max
(only present until Linux 2.2)This file contains the maximum number of in-memory inodes. This value
should be 3–4 times larger than the value in file-max
, since
stdin
, stdout
and network sockets also need an inode
to handle them. When you regularly run out of inodes, you need to
increase this value.
Starting with Linux 2.4, there is no longer a static limit on the number of inodes, and this file is removed.
/proc/sys/fs/inode-nr
This file contains the first two values from
inode-state
.
/proc/sys/fs/inode-state
This file contains seven numbers: nr_inodes
,
nr_free_inodes
, preshrink
, and four dummy values
(always zero).
nr_inodes
is the number of inodes the system has allocated.
nr_free_inodes
represents the number of free inodes.
preshrink
is nonzero when the nr_inodes
>
inode-max
and the system needs to prune the inode list instead
of allocating more; since Linux 2.4, this field is a dummy value (always
zero).
/proc/sys/fs/inotify
(since Linux 2.6.13)This directory contains files max_queued_events
,
max_user_instances
, and max_user_watches
, that can be
used to limit the amount of kernel memory consumed by the
inotify
interface. For further details, see
inotify(7).
/proc/sys/fs/lease-break-time
This file specifies the grace period that the kernel grants to a process holding a file lease (fcntl(2)) after it has sent a signal to that process notifying it that another process is waiting to open the file. If the lease holder does not remove or downgrade the lease within this grace period, the kernel forcibly breaks the lease.
/proc/sys/fs/leases-enable
This file can be used to enable or disable file leases (fcntl(2)) on a system-wide basis. If this file contains the value 0, leases are disabled. A nonzero value enables leases.
/proc/sys/fs/mount-max
(since Linux 4.9)The value in this file specifies the maximum number of mounts that may exist in a mount namespace. The default value in this file is 100,000.
/proc/sys/fs/mqueue
(since Linux 2.6.6)This directory contains files msg_max
, msgsize_max
,
and queues_max
, controlling the resources used by POSIX message
queues. See mq_overview(7) for details.
/proc/sys/fs/nr_open
(since Linux 2.6.25)This file imposes a ceiling on the value to which the RLIMIT_NOFILE resource limit can be raised (see getrlimit(2)). This ceiling is enforced for both unprivileged and privileged process. The default value in this file is 1048576. (Before Linux 2.6.25, the ceiling for RLIMIT_NOFILE was hard-coded to the same value.)
/proc/sys/fs/overflowgid
and
/proc/sys/fs/overflowuid
These files allow you to change the value of the fixed UID and GID. The default is 65534. Some filesystems support only 16-bit UIDs and GIDs, although in Linux UIDs and GIDs are 32 bits. When one of these filesystems is mounted with writes enabled, any UID or GID that would exceed 65535 is translated to the overflow value before being written to disk.
/proc/sys/fs/pipe-max-size
(since Linux 2.6.35)See pipe(7).
/proc/sys/fs/pipe-user-pages-hard
(since Linux 4.5)See pipe(7).
/proc/sys/fs/pipe-user-pages-soft
(since Linux 4.5)See pipe(7).
/proc/sys/fs/protected_fifos
(since Linux 4.19)The value in this file is/can be set to one of the following:
Writing to FIFOs is unrestricted.
Don't allow O_CREAT open(2) on FIFOs that the caller doesn't own in world-writable sticky directories, unless the FIFO is owned by the owner of the directory.
As for the value 1, but the restriction also applies to group-writable sticky directories.
The intent of the above protections is to avoid unintentional writes to an attacker-controlled FIFO when a program expected to create a regular file.
/proc/sys/fs/protected_hardlinks
(since Linux 3.6)When the value in this file is 0, no restrictions are placed on the creation of hard links (i.e., this is the historical behavior before Linux 3.6). When the value in this file is 1, a hard link can be created to a target file only if one of the following conditions is true:
The calling process has the CAP_FOWNER capability in its user namespace and the file UID has a mapping in the namespace.
The filesystem UID of the process creating the link matches the owner (UID) of the target file (as described in credentials(7), a process's filesystem UID is normally the same as its effective UID).
All of the following conditions are true:
the target is a regular file;
the target file does not have its set-user-ID mode bit enabled;
the target file does not have both its set-group-ID and group-executable mode bits enabled; and
the caller has permission to read and write the target file (either via the file's permissions mask or because it has suitable capabilities).
The default value in this file is 0. Setting the value to 1 prevents
a longstanding class of security issues caused by hard-link-based
time-of-check, time-of-use races, most commonly seen in world-writable
directories such as /tmp
. The common method of exploiting this
flaw is to cross privilege boundaries when following a given hard link
(i.e., a root process follows a hard link created by another user).
Additionally, on systems without separated partitions, this stops
unauthorized users from "pinning" vulnerable set-user-ID and
set-group-ID files against being upgraded by the administrator, or
linking to special files.
/proc/sys/fs/protected_regular
(since Linux 4.19)The value in this file is/can be set to one of the following:
Writing to regular files is unrestricted.
Don't allow O_CREAT open(2) on regular files that the caller doesn't own in world-writable sticky directories, unless the regular file is owned by the owner of the directory.
As for the value 1, but the restriction also applies to group-writable sticky directories.
The intent of the above protections is similar to
protected_fifos
, but allows an application to avoid writes to
an attacker-controlled regular file, where the application expected to
create one.
/proc/sys/fs/protected_symlinks
(since Linux 3.6)When the value in this file is 0, no restrictions are placed on following symbolic links (i.e., this is the historical behavior before Linux 3.6). When the value in this file is 1, symbolic links are followed only in the following circumstances:
the filesystem UID of the process following the link matches the owner (UID) of the symbolic link (as described in credentials(7), a process's filesystem UID is normally the same as its effective UID);
the link is not in a sticky world-writable directory; or
the symbolic link and its parent directory have the same owner (UID)
A system call that fails to follow a symbolic link because of the
above restrictions returns the error EACCES in
errno
.
The default value in this file is 0. Setting the value to 1 avoids a longstanding class of security issues based on time-of-check, time-of-use races when accessing symbolic links.
/proc/sys/fs/suid_dumpable
(since Linux 2.6.13)The value in this file is assigned to a process's "dumpable" flag in
the circumstances described in prctl(2). In effect, the
value in this file determines whether core dump files are produced for
set-user-ID or otherwise protected/tainted binaries. The "dumpable"
setting also affects the ownership of files in a process's
/proc/[pid]
directory, as described above.
Three different integer values can be specified:
0 (default)
This provides the traditional (pre-Linux 2.6.13) behavior. A core dump will not be produced for a process which has changed credentials (by calling seteuid(2), setgid(2), or similar, or by executing a set-user-ID or set-group-ID program) or whose binary does not have read permission enabled.
1 ("debug")
All processes dump core when possible. (Reasons why a process might nevertheless not dump core are described in core(5).) The core dump is owned by the filesystem user ID of the dumping process and no security is applied. This is intended for system debugging situations only: this mode is insecure because it allows unprivileged users to examine the memory contents of privileged processes.
2 ("suidsafe")
Any binary which normally would not be dumped (see "0" above) is dumped readable by root only. This allows the user to remove the core dump file but not to read it. For security reasons core dumps in this mode will not overwrite one another or other files. This mode is appropriate when administrators are attempting to debug problems in a normal environment.
Additionally, since Linux 3.6, /proc/sys/kernel/core_pattern
must either be an absolute pathname or a pipe command, as detailed in
core(5). Warnings will be written to the kernel log if
core_pattern
does not follow these rules, and no core dump will
be produced.
For details of the effect of a process's "dumpable" setting on ptrace access mode checking, see ptrace(2).
/proc/sys/fs/super-max
This file controls the maximum number of superblocks, and thus the
maximum number of mounted filesystems the kernel can have. You need
increase only super-max
if you need to mount more filesystems
than the current value in super-max
allows you to.
/proc/sys/fs/super-nr
This file contains the number of filesystems currently mounted.
/proc/sys/kernel
This directory contains files controlling a range of kernel parameters, as described below.
/proc/sys/kernel/acct
This file contains three numbers: highwater
,
lowwater
, and frequency
. If BSD-style process
accounting is enabled, these values control its behavior. If free space
on filesystem where the log lives goes below lowwater
percent,
accounting suspends. If free space gets above highwater
percent, accounting resumes. frequency
determines how often the
kernel checks the amount of free space (value is in seconds). Default
values are 4, 2 and 30. That is, suspend accounting if 2% or less space
is free; resume it if 4% or more space is free; consider information
about amount of free space valid for 30 seconds.
/proc/sys/kernel/auto_msgmni
(Linux 2.6.27 to 3.18)From Linux 2.6.27 to 3.18, this file was used to control recomputing
of the value in /proc/sys/kernel/msgmni
upon the addition or
removal of memory or upon IPC namespace creation/removal. Echoing "1"
into this file enabled msgmni
automatic recomputing (and
triggered a recomputation of msgmni
based on the current amount
of available memory and number of IPC namespaces). Echoing "0" disabled
automatic recomputing. (Automatic recomputing was also disabled if a
value was explicitly assigned to /proc/sys/kernel/msgmni
.) The
default value in auto_msgmni
was 1.
Since Linux 3.19, the content of this file has no effect (because
msgmni
defaults to near the maximum value possible), and reads
from this file always return the value "0".
/proc/sys/kernel/cap_last_cap
(since Linux 3.2)See capabilities(7).
/proc/sys/kernel/cap-bound
(from Linux 2.2 to 2.6.24)This file holds the value of the kernel capability bounding set (expressed as a signed decimal number). This set is ANDed against the capabilities permitted to a process during execve(2). Starting with Linux 2.6.25, the system-wide capability bounding set disappeared, and was replaced by a per-thread bounding set; see capabilities(7).
/proc/sys/kernel/core_pattern
See core(5).
/proc/sys/kernel/core_pipe_limit
See core(5).
/proc/sys/kernel/core_uses_pid
See core(5).
/proc/sys/kernel/ctrl-alt-del
This file controls the handling of Ctrl-Alt-Del from the keyboard. When the value in this file is 0, Ctrl-Alt-Del is trapped and sent to the init(1) program to handle a graceful restart. When the value is greater than zero, Linux's reaction to a Vulcan Nerve Pinch (tm) will be an immediate reboot, without even syncing its dirty buffers. Note: when a program (like dosemu) has the keyboard in "raw" mode, the ctrl-alt-del is intercepted by the program before it ever reaches the kernel tty layer, and it's up to the program to decide what to do with it.
/proc/sys/kernel/dmesg_restrict
(since Linux 2.6.37)The value in this file determines who can see kernel syslog contents. A value of 0 in this file imposes no restrictions. If the value is 1, only privileged users can read the kernel syslog. (See syslog(2) for more details.) Since Linux 3.4, only users with the CAP_SYS_ADMIN capability may change the value in this file.
/proc/sys/kernel/domainname
and
/proc/sys/kernel/hostname
can be used to set the NIS/YP domainname and the hostname of your box in exactly the same way as the commands domainname(1) and hostname(1), that is:
# echo 'darkstar' > /proc/sys/kernel/hostname
# echo 'mydomain' > /proc/sys/kernel/domainname
has the same effect as
# hostname 'darkstar'
# domainname 'mydomain'
Note, however, that the classic darkstar.frop.org has the hostname "darkstar" and DNS (Internet Domain Name Server) domainname "frop.org", not to be confused with the NIS (Network Information Service) or YP (Yellow Pages) domainname. These two domain names are in general different. For a detailed discussion see the hostname(1) man page.
/proc/sys/kernel/hotplug
This file contains the pathname for the hotplug policy agent. The
default value in this file is /sbin/hotplug
.
/proc/sys/kernel/htab-reclaim
(before Linux 2.4.9.2)(PowerPC only) If this file is set to a nonzero value, the PowerPC
htab (see kernel file Documentation/powerpc/ppc_htab.txt
) is
pruned each time the system hits the idle loop.
/proc/sys/kernel/keys/*
This directory contains various files that define parameters and limits for the key-management facility. These files are described in keyrings(7).
/proc/sys/kernel/kptr_restrict
(since Linux 2.6.38)The value in this file determines whether kernel addresses are
exposed via /proc
files and other interfaces. A value of 0 in
this file imposes no restrictions. If the value is 1, kernel pointers
printed using the %pK
format specifier will be replaced with
zeros unless the user has the CAP_SYSLOG capability. If
the value is 2, kernel pointers printed using the %pK
format
specifier will be replaced with zeros regardless of the user's
capabilities. The initial default value for this file was 1, but the
default was changed to 0 in Linux 2.6.39. Since Linux 3.4, only users
with the CAP_SYS_ADMIN capability can change the value
in this file.
/proc/sys/kernel/l2cr
(PowerPC only) This file contains a flag that controls the L2 cache of G3 processor boards. If 0, the cache is disabled. Enabled if nonzero.
/proc/sys/kernel/modprobe
This file contains the pathname for the kernel module loader. The
default value is /sbin/modprobe
. The file is present only if
the kernel is built with the CONFIG_MODULES
(CONFIG_KMOD in Linux 2.6.26 and earlier) option
enabled. It is described by the Linux kernel source file
Documentation/kmod.txt
(present only in kernel 2.4 and
earlier).
/proc/sys/kernel/modules_disabled
(since Linux 2.6.31)A toggle value indicating if modules are allowed to be loaded in an otherwise modular kernel. This toggle defaults to off (0), but can be set true (1). Once true, modules can be neither loaded nor unloaded, and the toggle cannot be set back to false. The file is present only if the kernel is built with the CONFIG_MODULES option enabled.
/proc/sys/kernel/msgmax
(since Linux 2.2)This file defines a system-wide limit specifying the maximum number of bytes in a single message written on a System V message queue.
/proc/sys/kernel/msgmni
(since Linux 2.4)This file defines the system-wide limit on the number of message
queue identifiers. See also /proc/sys/kernel/auto_msgmni
.
/proc/sys/kernel/msgmnb
(since Linux 2.2)This file defines a system-wide parameter used to initialize the
msg_qbytes
setting for subsequently created message queues. The
msg_qbytes
setting specifies the maximum number of bytes that
may be written to the message queue.
/proc/sys/kernel/ngroups_max
(since Linux 2.6.4)This is a read-only file that displays the upper limit on the number of a process's group memberships.
/proc/sys/kernel/ns_last_pid
(since Linux 3.3)See pid_namespaces(7).
/proc/sys/kernel/ostype
and
/proc/sys/kernel/osrelease
These files give substrings of /proc/version
.
/proc/sys/kernel/overflowgid
and
/proc/sys/kernel/overflowuid
These files duplicate the files /proc/sys/fs/overflowgid
and
/proc/sys/fs/overflowuid
.
/proc/sys/kernel/panic
This file gives read/write access to the kernel variable
panic_timeout
. If this is zero, the kernel will loop on a
panic; if nonzero, it indicates that the kernel should autoreboot after
this number of seconds. When you use the software watchdog device
driver, the recommended setting is 60.
/proc/sys/kernel/panic_on_oops
(since Linux 2.5.68)This file controls the kernel's behavior when an oops or BUG is
encountered. If this file contains 0, then the system tries to continue
operation. If it contains 1, then the system delays a few seconds (to
give klogd time to record the oops output) and then panics. If the
/proc/sys/kernel/panic
file is also nonzero, then the machine
will be rebooted.
/proc/sys/kernel/pid_max
(since Linux 2.5.34)This file specifies the value at which PIDs wrap around (i.e., the
value in this file is one greater than the maximum PID). PIDs greater
than this value are not allocated; thus, the value in this file also
acts as a system-wide limit on the total number of processes and
threads. The default value for this file, 32768, results in the same
range of PIDs as on earlier kernels. On 32-bit platforms, 32768 is the
maximum value for pid_max
. On 64-bit systems, pid_max
can be set to any value up to 2^22 (PID_MAX_LIMIT,
approximately 4 million).
/proc/sys/kernel/powersave-nap
(PowerPC only)This file contains a flag. If set, Linux-PPC will use the "nap" mode of powersaving, otherwise the "doze" mode will be used.
/proc/sys/kernel/printk
See syslog(2).
/proc/sys/kernel/pty
(since Linux 2.6.4)This directory contains two files relating to the number of UNIX 98 pseudoterminals (see pts(4)) on the system.
/proc/sys/kernel/pty/max
This file defines the maximum number of pseudoterminals.
/proc/sys/kernel/pty/nr
This read-only file indicates how many pseudoterminals are currently in use.
/proc/sys/kernel/random
This directory contains various parameters controlling the operation
of the file /dev/random
. See random(4) for
further information.
/proc/sys/kernel/random/uuid
(since Linux 2.4)Each read from this read-only file returns a randomly generated 128-bit UUID, as a string in the standard UUID format.
/proc/sys/kernel/randomize_va_space
(since Linux
2.6.12)Select the address space layout randomization (ASLR) policy for the system (on architectures that support ASLR). Three values are supported for this file:
Turn ASLR off. This is the default for architectures that don't
support ASLR, and when the kernel is booted with the norandmaps
parameter.
Make the addresses of mmap(2) allocations, the stack, and the VDSO page randomized. Among other things, this means that shared libraries will be loaded at randomized addresses. The text segment of PIE-linked binaries will also be loaded at a randomized address. This value is the default if the kernel was configured with CONFIG_COMPAT_BRK.
(Since Linux 2.6.25) Also support heap randomization. This value is the default if the kernel was not configured with CONFIG_COMPAT_BRK.
/proc/sys/kernel/real-root-dev
This file is documented in the Linux kernel source file
Documentation/admin-guide/initrd.rst
(or
Documentation/initrd.txt
before Linux 4.10).
/proc/sys/kernel/reboot-cmd
(Sparc only)This file seems to be a way to give an argument to the SPARC ROM/Flash boot loader. Maybe to tell it what to do after rebooting?
/proc/sys/kernel/rtsig-max
(Only in kernels up to and including 2.6.7; see setrlimit(2)) This file can be used to tune the maximum number of POSIX real-time (queued) signals that can be outstanding in the system.
/proc/sys/kernel/rtsig-nr
(Only in kernels up to and including 2.6.7.) This file shows the number of POSIX real-time signals currently queued.
/proc/[pid]/sched_autogroup_enabled
(since Linux
2.6.38)See sched(7).
/proc/sys/kernel/sched_child_runs_first
(since Linux
2.6.23)If this file contains the value zero, then, after a fork(2), the parent is first scheduled on the CPU. If the file contains a nonzero value, then the child is scheduled first on the CPU. (Of course, on a multiprocessor system, the parent and the child might both immediately be scheduled on a CPU.)
/proc/sys/kernel/sched_rr_timeslice_ms
(since Linux
3.9)See sched_rr_get_interval(2).
/proc/sys/kernel/sched_rt_period_us
(since Linux
2.6.25)See sched(7).
/proc/sys/kernel/sched_rt_runtime_us
(since Linux
2.6.25)See sched(7).
/proc/sys/kernel/seccomp
(since Linux 4.14)This directory provides additional seccomp information and configuration. See seccomp(2) for further details.
/proc/sys/kernel/sem
(since Linux 2.4)This file contains 4 numbers defining limits for System V IPC semaphores. These fields are, in order:
The maximum semaphores per semaphore set.
A system-wide limit on the number of semaphores in all semaphore sets.
The maximum number of operations that may be specified in a semop(2) call.
A system-wide limit on the maximum number of semaphore identifiers.
/proc/sys/kernel/sg-big-buff
This file shows the size of the generic SCSI device (sg) buffer. You
can't tune it just yet, but you could change it at compile time by
editing include/scsi/sg.h
and changing the value of
SG_BIG_BUFF. However, there shouldn't be any reason to
change this value.
/proc/sys/kernel/shm_rmid_forced
(since Linux 3.1)If this file is set to 1, all System V shared memory segments will be marked for destruction as soon as the number of attached processes falls to zero; in other words, it is no longer possible to create shared memory segments that exist independently of any attached process.
The effect is as though a shmctl(2) IPC_RMID is performed on all existing segments as well as all segments created in the future (until this file is reset to 0). Note that existing segments that are attached to no process will be immediately destroyed when this file is set to 1. Setting this option will also destroy segments that were created, but never attached, upon termination of the process that created the segment with shmget(2).
Setting this file to 1 provides a way of ensuring that all System V shared memory segments are counted against the resource usage and resource limits (see the description of RLIMIT_AS in getrlimit(2)) of at least one process.
Because setting this file to 1 produces behavior that is nonstandard and could also break existing applications, the default value in this file is 0. Set this file to 1 only if you have a good understanding of the semantics of the applications using System V shared memory on your system.
/proc/sys/kernel/shmall
(since Linux 2.2)This file contains the system-wide limit on the total number of pages of System V shared memory.
/proc/sys/kernel/shmmax
(since Linux 2.2)This file can be used to query and set the run-time limit on the maximum (System V IPC) shared memory segment size that can be created. Shared memory segments up to 1 GB are now supported in the kernel. This value defaults to SHMMAX.
/proc/sys/kernel/shmmni
(since Linux 2.4)This file specifies the system-wide maximum number of System V shared memory segments that can be created.
/proc/sys/kernel/sysctl_writes_strict
(since Linux
3.16)The value in this file determines how the file offset affects the
behavior of updating entries in files under /proc/sys
. The file
has three possible values:
This provides legacy handling, with no printk warnings. Each write(2) must fully contain the value to be written, and multiple writes on the same file descriptor will overwrite the entire value, regardless of the file position.
(default) This provides the same behavior as for -1, but printk warnings are written for processes that perform writes when the file offset is not 0.
Respect the file offset when writing strings into /proc/sys
files. Multiple writes will append
to the value buffer.
Anything written beyond the maximum length of the value buffer will be
ignored. Writes to numeric /proc/sys
entries must always be at
file offset 0 and the value must be fully contained in the buffer
provided to write(2).
/proc/sys/kernel/sysrq
This file controls the functions allowed to be invoked by the SysRq key. By default, the file contains 1 meaning that every possible SysRq request is allowed (in older kernel versions, SysRq was disabled by default, and you were required to specifically enable it at run-time, but this is not the case any more). Possible values in this file are:
Disable sysrq completely
Enable all functions of sysrq
Bit mask of allowed sysrq functions, as follows:
- 2
Enable control of console logging level
- 4
Enable control of keyboard (SAK, unraw)
- 8
Enable debugging dumps of processes etc.
- 16
Enable sync command
- 32
Enable remount read-only
- 64
Enable signaling of processes (term, kill, oom-kill)
- 128
Allow reboot/poweroff
- 256
Allow nicing of all real-time tasks
This file is present only if the CONFIG_MAGIC_SYSRQ
kernel configuration option is enabled. For further details see the
Linux kernel source file Documentation/admin-guide/sysrq.rst
(or Documentation/sysrq.txt
before Linux 4.10).
/proc/sys/kernel/version
This file contains a string such as:
#5 Wed Feb 25 21:49:24 MET 1998
The "#5" means that this is the fifth kernel built from this source base and the date following it indicates the time the kernel was built.
/proc/sys/kernel/threads-max
(since Linux 2.3.11)This file specifies the system-wide limit on the number of threads (tasks) that can be created on the system.
Since Linux 4.1, the value that can be written to
threads-max
is bounded. The minimum value that can be written
is 20. The maximum value that can be written is given by the constant
FUTEX_TID_MASK (0x3fffffff). If a value outside of this
range is written to threads-max
, the error
EINVAL occurs.
The value written is checked against the available RAM pages. If the
thread structures would occupy too much (more than 1/8th) of the
available RAM pages, threads-max
is reduced accordingly.
/proc/sys/kernel/yama/ptrace_scope
(since Linux 3.5)See ptrace(2).
/proc/sys/kernel/zero-paged
(PowerPC only)This file contains a flag. When enabled (nonzero), Linux-PPC will pre-zero pages in the idle loop, possibly speeding up get_free_pages.
/proc/sys/net
This directory contains networking stuff. Explanations for some of the files under this directory can be found in tcp(7) and ip(7).
/proc/sys/net/core/bpf_jit_enable
See bpf(2).
/proc/sys/net/core/somaxconn
This file defines a ceiling value for the backlog
argument
of listen(2); see the listen(2) manual
page for details.
/proc/sys/proc
This directory may be empty.
/proc/sys/sunrpc
This directory supports Sun remote procedure call for network filesystem (NFS). On some systems, it is not present.
/proc/sys/user
(since Linux 4.9)See namespaces(7).
/proc/sys/vm
This directory contains files for memory management tuning, buffer and cache management.
/proc/sys/vm/admin_reserve_kbytes
(since Linux 3.10)This file defines the amount of free memory (in KiB) on the system that should be reserved for users with the capability CAP_SYS_ADMIN.
The default value in this file is the minimum of [3% of free pages,
8MiB] expressed as KiB. The default is intended to provide enough for
the superuser to log in and kill a process, if necessary, under the
default overcommit 'guess' mode (i.e., 0 in
/proc/sys/vm/overcommit_memory
).
Systems running in "overcommit never" mode (i.e., 2 in
/proc/sys/vm/overcommit_memory
) should increase the value in
this file to account for the full virtual memory size of the programs
used to recover (e.g., login(1)
ssh(1), and top(1)) Otherwise, the
superuser may not be able to log in to recover the system. For example,
on x86-64 a suitable value is 131072 (128MiB reserved).
Changing the value in this file takes effect whenever an application requests memory.
/proc/sys/vm/compact_memory
(since Linux 2.6.35)When 1 is written to this file, all zones are compacted such that
free memory is available in contiguous blocks where possible. The effect
of this action can be seen by examining /proc/buddyinfo
.
Present only if the kernel was configured with CONFIG_COMPACTION.
/proc/sys/vm/drop_caches
(since Linux 2.6.16)Writing to this file causes the kernel to drop clean caches, dentries, and inodes from memory, causing that memory to become free. This can be useful for memory management testing and performing reproducible filesystem benchmarks. Because writing to this file causes the benefits of caching to be lost, it can degrade overall system performance.
To free pagecache, use:
echo 1 > /proc/sys/vm/drop_caches
To free dentries and inodes, use:
echo 2 > /proc/sys/vm/drop_caches
To free pagecache, dentries and inodes, use:
echo 3 > /proc/sys/vm/drop_caches
Because writing to this file is a nondestructive operation and dirty objects are not freeable, the user should run sync(1) first.
/proc/sys/vm/legacy_va_layout
(since Linux 2.6.9)If nonzero, this disables the new 32-bit memory-mapping layout; the kernel will use the legacy (2.4) layout for all processes.
/proc/sys/vm/memory_failure_early_kill
(since Linux
2.6.32)Control how to kill processes when an uncorrected memory error (typically a 2-bit error in a memory module) that cannot be handled by the kernel is detected in the background by hardware. In some cases (like the page still having a valid copy on disk), the kernel will handle the failure transparently without affecting any applications. But if there is no other up-to-date copy of the data, it will kill processes to prevent any data corruptions from propagating.
The file has one of the following values:
Kill all processes that have the corrupted-and-not-reloadable page mapped as soon as the corruption is detected. Note that this is not supported for a few types of pages, such as kernel internally allocated data or the swap cache, but works for the majority of user pages.
Unmap the corrupted page from all processes and kill a process only if it tries to access the page.
The kill is performed using a SIGBUS signal with
si_code
set to BUS_MCEERR_AO. Processes can
handle this if they want to; see sigaction(2) for more
details.
This feature is active only on architectures/platforms with advanced machine check handling and depends on the hardware capabilities.
Applications can override the memory_failure_early_kill
setting individually with the prctl(2)
PR_MCE_KILL operation.
Present only if the kernel was configured with CONFIG_MEMORY_FAILURE.
/proc/sys/vm/memory_failure_recovery
(since Linux
2.6.32)Enable memory failure recovery (when supported by the platform).
Attempt recovery.
Always panic on a memory failure.
Present only if the kernel was configured with CONFIG_MEMORY_FAILURE.
/proc/sys/vm/oom_dump_tasks
(since Linux 2.6.25)Enables a system-wide task dump (excluding kernel threads) to be
produced when the kernel performs an OOM-killing. The dump includes the
following information for each task (thread, process): thread ID, real
user ID, thread group ID (process ID), virtual memory size, resident set
size, the CPU that the task is scheduled on, oom_adj score (see the
description of /proc/[pid]/oom_adj
), and command name. This is
helpful to determine why the OOM-killer was invoked and to identify the
rogue task that caused it.
If this contains the value zero, this information is suppressed. On very large systems with thousands of tasks, it may not be feasible to dump the memory state information for each one. Such systems should not be forced to incur a performance penalty in OOM situations when the information may not be desired.
If this is set to nonzero, this information is shown whenever the OOM-killer actually kills a memory-hogging task.
The default value is 0.
/proc/sys/vm/oom_kill_allocating_task
(since Linux
2.6.24)This enables or disables killing the OOM-triggering task in out-of-memory situations.
If this is set to zero, the OOM-killer will scan through the entire tasklist and select a task based on heuristics to kill. This normally selects a rogue memory-hogging task that frees up a large amount of memory when killed.
If this is set to nonzero, the OOM-killer simply kills the task that triggered the out-of-memory condition. This avoids a possibly expensive tasklist scan.
If /proc/sys/vm/panic_on_oom
is nonzero, it takes precedence
over whatever value is used in
/proc/sys/vm/oom_kill_allocating_task
.
The default value is 0.
/proc/sys/vm/overcommit_kbytes
(since Linux 3.14)This writable file provides an alternative to
/proc/sys/vm/overcommit_ratio
for controlling the
CommitLimit
when /proc/sys/vm/overcommit_memory
has
the value 2. It allows the amount of memory overcommitting to be
specified as an absolute value (in kB), rather than as a percentage, as
is done with overcommit_ratio
. This allows for finer-grained
control of CommitLimit
on systems with extremely large memory
sizes.
Only one of overcommit_kbytes
or overcommit_ratio
can have an effect: if overcommit_kbytes
has a nonzero value,
then it is used to calculate CommitLimit
, otherwise
overcommit_ratio
is used. Writing a value to either of these
files causes the value in the other file to be set to zero.
/proc/sys/vm/overcommit_memory
This file contains the kernel virtual memory accounting mode. Values are:
0: heuristic overcommit (this is the default)
1: always overcommit, never check
2: always check, never overcommit
In mode 0, calls of mmap(2) with MAP_NORESERVE are not checked, and the default check is very weak, leading to the risk of getting a process "OOM-killed".
In mode 1, the kernel pretends there is always enough memory, until memory actually runs out. One use case for this mode is scientific computing applications that employ large sparse arrays. In Linux kernel versions before 2.6.0, any nonzero value implies mode 1.
In mode 2 (available since Linux 2.6), the total virtual address
space that can be allocated (CommitLimit
in
/proc/meminfo
) is calculated as
CommitLimit = (total_RAM - total_huge_TLB) * overcommit_ratio / 100 + total_swap
where:
total_RAM
is the total amount of RAM on the
system;
total_huge_TLB
is the amount of memory set aside for
huge pages;
overcommit_ratio
is the value in
/proc/sys/vm/overcommit_ratio
; and
total_swap
is the amount of swap space.
For example, on a system with 16 GB of physical RAM, 16 GB of swap,
no space dedicated to huge pages, and an overcommit_ratio
of
50, this formula yields a CommitLimit
of 24 GB.
Since Linux 3.14, if the value in
/proc/sys/vm/overcommit_kbytes
is nonzero, then
CommitLimit
is instead calculated as:
CommitLimit = overcommit_kbytes + total_swap
See also the description of
/proc/sys/vm/admin_reserve_kbytes
and
/proc/sys/vm/user_reserve_kbytes
.
/proc/sys/vm/overcommit_ratio
(since Linux 2.6.0)This writable file defines a percentage by which memory can be
overcommitted. The default value in the file is 50. See the description
of /proc/sys/vm/overcommit_memory
.
/proc/sys/vm/panic_on_oom
(since Linux 2.6.18)This enables or disables a kernel panic in an out-of-memory situation.
If this file is set to the value 0, the kernel's OOM-killer will kill some rogue process. Usually, the OOM-killer is able to kill a rogue process and the system will survive.
If this file is set to the value 1, then the kernel normally panics when out-of-memory happens. However, if a process limits allocations to certain nodes using memory policies (mbind(2) MPOL_BIND) or cpusets (cpuset(7)) and those nodes reach memory exhaustion status, one process may be killed by the OOM-killer. No panic occurs in this case: because other nodes' memory may be free, this means the system as a whole may not have reached an out-of-memory situation yet.
If this file is set to the value 2, the kernel always panics when an out-of-memory condition occurs.
The default value is 0. 1 and 2 are for failover of clustering. Select either according to your policy of failover.
/proc/sys/vm/swappiness
The value in this file controls how aggressively the kernel will swap memory pages. Higher values increase aggressiveness, lower values decrease aggressiveness. The default value is 60.
/proc/sys/vm/user_reserve_kbytes
(since Linux 3.10)Specifies an amount of memory (in KiB) to reserve for user processes.
This is intended to prevent a user from starting a single memory hogging
process, such that they cannot recover (kill the hog). The value in this
file has an effect only when /proc/sys/vm/overcommit_memory
is
set to 2 ("overcommit never" mode). In this case, the system reserves an
amount of memory that is the minimum of [3% of current process size,
user_reserve_kbytes
].
The default value in this file is the minimum of [3% of free pages, 128MiB] expressed as KiB.
If the value in this file is set to zero, then a user will be allowed
to allocate all free memory with a single process (minus the amount
reserved by /proc/sys/vm/admin_reserve_kbytes
). Any subsequent
attempts to execute a command will result in "fork: Cannot allocate
memory".
Changing the value in this file takes effect whenever an application requests memory.
/proc/sys/vm/unprivileged_userfaultfd
(since Linux
5.2)This (writable) file exposes a flag that controls whether unprivileged processes are allowed to employ userfaultfd(2). If this file has the value 1, then unprivileged processes may use userfaultfd(2). If this file has the value 0, then only processes that have the CAP_SYS_PTRACE capability may employ userfaultfd(2). The default value in this file is 1.
/proc/sysrq-trigger
(since Linux 2.4.21)Writing a character to this file triggers the same SysRq function as
typing ALT-SysRq-<character> (see the description of
/proc/sys/kernel/sysrq
). This file is normally writable only by
root
. For further details see the Linux kernel source file
Documentation/admin-guide/sysrq.rst
(or
Documentation/sysrq.txt
before Linux 4.10).
/proc/sysvipc
Subdirectory containing the pseudo-files msg
, sem
and shm
. These files list the System V Interprocess
Communication (IPC) objects (respectively: message queues, semaphores,
and shared memory) that currently exist on the system, providing similar
information to that available via ipcs(1). These files
have headers and are formatted (one IPC object per line) for easy
understanding. sysvipc(7) provides further background
on the information shown by these files.
/proc/thread-self
(since Linux 3.17)This directory refers to the thread accessing the /proc
filesystem, and is identical to the /proc/self/task/[tid]
directory named by the process thread ID ([tid]
) of the same
thread.
/proc/timer_list
(since Linux 2.6.21)This read-only file exposes a list of all currently pending (high-resolution) timers, all clock-event sources, and their parameters in a human-readable form.
/proc/timer_stats
(from Linux 2.6.21 until Linux 4.10)This is a debugging facility to make timer (ab)use in a Linux system visible to kernel and user-space developers. It can be used by kernel and user-space developers to verify that their code does not make undue use of timers. The goal is to avoid unnecessary wakeups, thereby optimizing power consumption.
If enabled in the kernel (CONFIG_TIMER_STATS), but not used, it has almost zero run-time overhead and a relatively small data-structure overhead. Even if collection is enabled at run time, overhead is low: all the locking is per-CPU and lookup is hashed.
The /proc/timer_stats
file is used both to control sampling
facility and to read out the sampled information.
The timer_stats
functionality is inactive on bootup. A
sampling period can be started using the following command:
# echo 1 > /proc/timer_stats
The following command stops a sampling period:
# echo 0 > /proc/timer_stats
The statistics can be retrieved by:
$ cat /proc/timer_stats
While sampling is enabled, each readout from
/proc/timer_stats
will see newly updated statistics. Once
sampling is disabled, the sampled information is kept until a new sample
period is started. This allows multiple readouts.
Sample output from /proc/timer_stats
:
$ cat /proc/timer_stats
Timer Stats Version: v0.3
Sample period: 1.764 s
Collection: active
255, 0 swapper/3 hrtimer_start_range_ns (tick_sched_timer)
71, 0 swapper/1 hrtimer_start_range_ns (tick_sched_timer)
58, 0 swapper/0 hrtimer_start_range_ns (tick_sched_timer)
4, 1694 gnome-shell mod_delayed_work_on (delayed_work_timer_fn)
17, 7 rcu_sched rcu_gp_kthread (process_timeout)
...
1, 4911 kworker/u16:0 mod_delayed_work_on (delayed_work_timer_fn)
1D, 2522 kworker/0:0 queue_delayed_work_on (delayed_work_timer_fn)
1029 total events, 583.333 events/sec
The output columns are:
a count of the number of events, optionally (since Linux 2.6.23) followed by the letter 'D' if this is a deferrable timer;
the PID of the process that initialized the timer;
the name of the process that initialized the timer;
the function where the timer was initialized; and
(in parentheses) the callback function that is associated with the timer.
During the Linux 4.11 development cycle, this file was removed because of security concerns, as it exposes information across namespaces. Furthermore, it is possible to obtain the same information via in-kernel tracing facilities such as ftrace.
/proc/tty
Subdirectory containing the pseudo-files and subdirectories for tty drivers and line disciplines.
/proc/uptime
This file contains two numbers (values in seconds): the uptime of the system (including time spent in suspend) and the amount of time spent in the idle process.
/proc/version
This string identifies the kernel version that is currently running.
It includes the contents of /proc/sys/kernel/ostype
,
/proc/sys/kernel/osrelease
, and
/proc/sys/kernel/version
. For example:
Linux version 1.0.9 (quinlan@phaze) #1 Sat May 14 01:51:54 EDT 1994
/proc/vmstat
(since Linux 2.6.0)This file displays various virtual memory statistics. Each line of this file contains a single name-value pair, delimited by white space. Some lines are present only if the kernel was configured with suitable options. (In some cases, the options required for particular files have changed across kernel versions, so they are not listed here. Details can be found by consulting the kernel source code.) The following fields may be present:
nr_free_pages
(since Linux 2.6.31)nr_alloc_batch
(since Linux 3.12)nr_inactive_anon
(since Linux 2.6.28)nr_active_anon
(since Linux 2.6.28)nr_inactive_file
(since Linux 2.6.28)nr_active_file
(since Linux 2.6.28)nr_unevictable
(since Linux 2.6.28)nr_mlock
(since Linux 2.6.28)nr_anon_pages
(since Linux 2.6.18)nr_mapped
(since Linux 2.6.0)nr_file_pages
(since Linux 2.6.18)nr_dirty
(since Linux 2.6.0)nr_writeback
(since Linux 2.6.0)nr_slab_reclaimable
(since Linux 2.6.19)nr_slab_unreclaimable
(since Linux 2.6.19)nr_page_table_pages
(since Linux 2.6.0)nr_kernel_stack
(since Linux 2.6.32)Amount of memory allocated to kernel stacks.
nr_unstable
(since Linux 2.6.0)nr_bounce
(since Linux 2.6.12)nr_vmscan_write
(since Linux 2.6.19)nr_vmscan_immediate_reclaim
(since Linux 3.2)nr_writeback_temp
(since Linux 2.6.26)nr_isolated_anon
(since Linux 2.6.32)nr_isolated_file
(since Linux 2.6.32)nr_shmem
(since Linux 2.6.32)Pages used by shmem and tmpfs(5).
nr_dirtied
(since Linux 2.6.37)nr_written
(since Linux 2.6.37)nr_pages_scanned
(since Linux 3.17)numa_hit
(since Linux 2.6.18)numa_miss
(since Linux 2.6.18)numa_foreign
(since Linux 2.6.18)numa_interleave
(since Linux 2.6.18)numa_local
(since Linux 2.6.18)numa_other
(since Linux 2.6.18)workingset_refault
(since Linux 3.15)workingset_activate
(since Linux 3.15)workingset_nodereclaim
(since Linux 3.15)nr_anon_transparent_hugepages
(since Linux 2.6.38)nr_free_cma
(since Linux 3.7)Number of free CMA (Contiguous Memory Allocator) pages.
nr_dirty_threshold
(since Linux 2.6.37)nr_dirty_background_threshold
(since Linux 2.6.37)pgpgin
(since Linux 2.6.0)pgpgout
(since Linux 2.6.0)pswpin
(since Linux 2.6.0)pswpout
(since Linux 2.6.0)pgalloc_dma
(since Linux 2.6.5)pgalloc_dma32
(since Linux 2.6.16)pgalloc_normal
(since Linux 2.6.5)pgalloc_high
(since Linux 2.6.5)pgalloc_movable
(since Linux 2.6.23)pgfree
(since Linux 2.6.0)pgactivate
(since Linux 2.6.0)pgdeactivate
(since Linux 2.6.0)pgfault
(since Linux 2.6.0)pgmajfault
(since Linux 2.6.0)pgrefill_dma
(since Linux 2.6.5)pgrefill_dma32
(since Linux 2.6.16)pgrefill_normal
(since Linux 2.6.5)pgrefill_high
(since Linux 2.6.5)pgrefill_movable
(since Linux 2.6.23)pgsteal_kswapd_dma
(since Linux 3.4)pgsteal_kswapd_dma32
(since Linux 3.4)pgsteal_kswapd_normal
(since Linux 3.4)pgsteal_kswapd_high
(since Linux 3.4)pgsteal_kswapd_movable
(since Linux 3.4)pgsteal_direct_dma
pgsteal_direct_dma32
(since Linux 3.4)pgsteal_direct_normal
(since Linux 3.4)pgsteal_direct_high
(since Linux 3.4)pgsteal_direct_movable
(since Linux 2.6.23)pgscan_kswapd_dma
pgscan_kswapd_dma32
(since Linux 2.6.16)pgscan_kswapd_normal
(since Linux 2.6.5)pgscan_kswapd_high
pgscan_kswapd_movable
(since Linux 2.6.23)pgscan_direct_dma
pgscan_direct_dma32
(since Linux 2.6.16)pgscan_direct_normal
pgscan_direct_high
pgscan_direct_movable
(since Linux 2.6.23)pgscan_direct_throttle
(since Linux 3.6)zone_reclaim_failed
(since linux 2.6.31)pginodesteal
(since linux 2.6.0)slabs_scanned
(since linux 2.6.5)kswapd_inodesteal
(since linux 2.6.0)kswapd_low_wmark_hit_quickly
(since 2.6.33)kswapd_high_wmark_hit_quickly
(since 2.6.33)pageoutrun
(since Linux 2.6.0)allocstall
(since Linux 2.6.0)pgrotated
(since Linux 2.6.0)drop_pagecache
(since Linux 3.15)drop_slab
(since Linux 3.15)numa_pte_updates
(since Linux 3.8)numa_huge_pte_updates
(since Linux 3.13)numa_hint_faults
(since Linux 3.8)numa_hint_faults_local
(since Linux 3.8)numa_pages_migrated
(since Linux 3.8)pgmigrate_success
(since Linux 3.8)pgmigrate_fail
(since Linux 3.8)compact_migrate_scanned
(since Linux 3.8)compact_free_scanned
(since Linux 3.8)compact_isolated
(since Linux 3.8)compact_stall
(since Linux 2.6.35)See the kernel source file
Documentation/admin-guide/mm/transhuge.rst
.
compact_fail
(since Linux 2.6.35)See the kernel source file
Documentation/admin-guide/mm/transhuge.rst
.
compact_success
(since Linux 2.6.35)See the kernel source file
Documentation/admin-guide/mm/transhuge.rst
.
htlb_buddy_alloc_success
(since Linux 2.6.26)htlb_buddy_alloc_fail
(since Linux 2.6.26)unevictable_pgs_culled
(since Linux 2.6.28)unevictable_pgs_scanned
(since Linux 2.6.28)unevictable_pgs_rescued
(since Linux 2.6.28)unevictable_pgs_mlocked
(since Linux 2.6.28)unevictable_pgs_munlocked
(since Linux 2.6.28)unevictable_pgs_cleared
(since Linux 2.6.28)unevictable_pgs_stranded
(since Linux 2.6.28)thp_fault_alloc
(since Linux 2.6.39)See the kernel source file
Documentation/admin-guide/mm/transhuge.rst
.
thp_fault_fallback
(since Linux 2.6.39)See the kernel source file
Documentation/admin-guide/mm/transhuge.rst
.
thp_collapse_alloc
(since Linux 2.6.39)See the kernel source file
Documentation/admin-guide/mm/transhuge.rst
.
thp_collapse_alloc_failed
(since Linux 2.6.39)See the kernel source file
Documentation/admin-guide/mm/transhuge.rst
.
thp_split
(since Linux 2.6.39)See the kernel source file
Documentation/admin-guide/mm/transhuge.rst
.
thp_zero_page_alloc
(since Linux 3.8)See the kernel source file
Documentation/admin-guide/mm/transhuge.rst
.
thp_zero_page_alloc_failed
(since Linux 3.8)See the kernel source file
Documentation/admin-guide/mm/transhuge.rst
.
balloon_inflate
(since Linux 3.18)balloon_deflate
(since Linux 3.18)balloon_migrate
(since Linux 3.18)nr_tlb_remote_flush
(since Linux 3.12)nr_tlb_remote_flush_received
(since Linux 3.12)nr_tlb_local_flush_all
(since Linux 3.12)nr_tlb_local_flush_one
(since Linux 3.12)vmacache_find_calls
(since Linux 3.16)vmacache_find_hits
(since Linux 3.16)vmacache_full_flushes
(since Linux 3.19)/proc/zoneinfo
(since Linux 2.6.13)This file displays information about memory zones. This is useful for analyzing virtual memory behavior.
Many files contain strings (e.g., the environment and command line) that are in the internal format, with subfields terminated by null bytes ('\0'). When inspecting such files, you may find that the results are more readable if you use a command of the following form to display them:
$ cat file | tr '\000' '\n'
This manual page is incomplete, possibly inaccurate, and is the kind of thing that needs to be updated very often.
cat(1), dmesg(1), find(1), free(1), htop(1), init(1), ps(1), pstree(1), tr(1), uptime(1), chroot(2), mmap(2), readlink(2), syslog(2), slabinfo(5), sysfs(5), hier(7), namespaces(7), time(7), arp(8), hdparm(8), ifconfig(8), lsmod(8), lspci(8), mount(8), netstat(8), procinfo(8), route(8), sysctl(8)
The Linux kernel source files:
Documentation/filesystems/proc.txt
,
Documentation/sysctl/fs.txt
,
Documentation/sysctl/kernel.txt
,
Documentation/sysctl/net.txt
, and
Documentation/sysctl/vm.txt
.
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
https://www.kernel.org/doc/man-pages/.