NAME
proc - process information pseudo-filesystem
DESCRIPTION
The proc filesystem is a pseudo-filesystem which provides an interface to kernel data structures. It is commonly mounted at /proc. Typi‐ cally, 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.
Mount options The proc filesystem supports the following mount options:
hidepid=n (since Linux 3.3) This option controls who can access the information in /proc/[pid] directories. The argument, n, is one of the follow‐ ing values:
0 Everybody may access all /proc/[pid] directories. This is
the traditional behavior, and the default if this mount
option is not specified.
1 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).
2 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=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.
Files and directories The following list describes 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. These files are normally owned by
the effective user and effective group ID of the process. How‐
ever, as a security measure, the ownership is made root:root if
the process's "dumpable" attribute is set to a value other than
1. This 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 real UID and real 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 mod‐ ules. 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 pol‐
icy, although use of this operation is only suitable for appli‐
cations 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 multi-threaded
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" oper‐
ations 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 sup‐
port "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 multi‐
ple 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 sub‐ sequently 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 Documenta‐ tion/security/keys.txt on Linux between 3.0 and 4.13, or Docu‐ mentation/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 sub‐ sequently 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-test7) 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:
1 (since Linux 2.6.22)
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.)
2 (since Linux 2.6.32)
Reset the PG_Referenced and ACCESSED/YOUNG bits for all
anonymous pages associated with the process.
3 (since Linux 2.6.32)
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_Refer‐
enced 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:
4 (since Linux 3.11)
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.
5 (since Linux 4.0)
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 CON‐
FIG_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.
/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 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.
/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; /bin/pwd
Note that the pwd command is often a shell built-in, and might
not work properly. In bash(1), you may use 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:
$ strings /proc/1/environ
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 contain‐ ing 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 sym‐ bolic link are not available if the main thread has already ter‐ minated (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 sym‐
bolic 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 (typi‐
cally 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 argu‐
ment, but don't send their output to standard output if no argu‐
ment 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 designat‐
ing 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 symboli‐
cally 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 descrip‐ tor.
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 hexadec‐
imal).
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).
/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 read
The 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 written
The 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 syscalls
Attempt to count the number of read I/O operations—that
is, system calls such as read(2) and pread(2).
syscw: write syscalls
Attempt to count the number of write I/O operations—that
is, system calls such as write(2) and pwrite(2).
read_bytes: bytes read
Attempt 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 written
Attempt 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
1MB to a file and then deletes the file, it will in fact
perform no writeout. But it will have been accounted as
having caused 1MB 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 mea‐ surement for each of the process’s resource limits (see getr‐ limit(2)). Up to and including Linux 2.6.35, this file is pro‐ tected 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 imple‐
mented 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)
This directory appears only if the CONFIG_CHECKPOINT_RESTORE
kernel configuration option is enabled. Privilege
(CAP_SYS_ADMIN) is required to view the contents of this direc‐
tory.
/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 off‐
set 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>] (since Linux 3.4)
A thread's stack (where the <tid> is a thread ID).
It corresponds to the /proc/[pid]/task/[tid]/ path.
[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.
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 sup‐ plies 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., nonextensi‐ bility, 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:
(1) mount ID: a unique ID for the mount (may be reused after
umount(2)).
(2) parent ID: the ID of the parent mount (or of self for the
root of this mount namespace's mount tree).
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.
(3) major:minor: the value of st_dev for files on this filesys‐
tem (see stat(2)).
(4) root: the pathname of the directory in the filesystem which
forms the root of this mount.
(5) mount point: the pathname of the mount point relative to
the process's root directory.
(6) mount options: per-mount options.
(7) optional fields: zero or more fields of the form
"tag[:value]"; see below.
(8) separator: the end of the optional fields is marked by a
single hyphen.
(9) filesystem type: the filesystem type in the form
"type[.subtype]".
(10) mount source: filesystem-specific information or "none".
(11) super options: per-superblock options.
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 unrecog‐
nized optional fields.
For more information on mount propagation see: Documenta‐
tion/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 open‐
ing 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 (POLL‐
PRI). (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 infor‐
mation) 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 [statistics]
( 1 ) ( 2 ) (3 ) (4)
The fields in each line are:
(1) The name of the mounted device (or "nodevice" if there is
no corresponding device).
(2) The mount point within the filesystem tree.
(3) The filesystem type.
(4) Optional statistics and configuration information. Cur‐
rently (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 informa‐
tion, 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.
/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 fol‐
lows:
63 If set, the page is present in RAM.
62 If set, the page is in swap space
61 (since Linux 3.5)
The page is a file-mapped page or a shared anonymous
page.
60–57 (since Linux 3.11)
Zero
56 (since Linux 4.2)
The page is exclusively mapped.
55 (since Linux 3.11)
PTE is soft-dirty (see the kernel source file Docu‐
mentation/vm/soft-dirty.txt).
54–0 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 CON‐
FIG_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. (Fur‐
ther 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 dis‐
played 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. "Anony‐
mous" 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 64kB as a base page size may still use 4kB 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)) associ‐
ated with the virtual memory area. This entry is present only
if the kernel was built with the CONFIG_X86_INTEL_MEMORY_PROTEC‐
TION_KEYS configuration option.
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
nl - non-linear mapping
ar - architecture specific flag
dd - do not include area into core dump
sd - soft-dirty flag
mm - mixed map area
hg - huge page advise flag
nh - no-huge page advise flag
mg - mergeable advise flag
"ProtectionKey" field contains the memory protection key (see
pkeys(5)) associated with the virtual memory area. Present only
if the kernel was built with the CONFIG_X86_INTEL_MEMORY_PROTEC‐
TION_KEYS configuration option. (since Linux 4.6)
The /proc/[pid]/smaps file is present only if the CON‐
FIG_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 speci‐
fiers, 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].
(1) pid %d
The process ID.
(2) comm %s
The filename of the executable, in parentheses. This
is visible whether or not the executable is swapped
out.
(3) state %c
One of the following characters, indicating process
state:
R Running
S Sleeping in an interruptible wait
D Waiting in uninterruptible disk sleep
Z Zombie
T Stopped (on a signal) or (before Linux 2.6.33)
trace stopped
t Tracing stop (Linux 2.6.33 onward)
W Paging (only before Linux 2.6.0)
X Dead (from Linux 2.6.0 onward)
x Dead (Linux 2.6.33 to 3.13 only)
K Wakekill (Linux 2.6.33 to 3.13 only)
W Waking (Linux 2.6.33 to 3.13 only)
P Parked (Linux 3.9 to 3.13 only)
(4) ppid %d
The PID of the parent of this process.
(5) pgrp %d
The process group ID of the process.
(6) session %d
The session ID of the process.
(7) tty_nr %d
The 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.)
(8) tpgid %d
The ID of the foreground process group of the control‐
ling terminal of the process.
(9) flags %u
The kernel flags word of the process. For bit mean‐
ings, 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.
(10) minflt %lu
The number of minor faults the process has made which
have not required loading a memory page from disk.
(11) cminflt %lu
The number of minor faults that the process's waited-
for children have made.
(12) majflt %lu
The number of major faults the process has made which
have required loading a memory page from disk.
(13) cmajflt %lu
The number of major faults that the process's waited-
for children have made.
(14) utime %lu
Amount 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 cal‐
culations.
(15) stime %lu
Amount of time that this process has been scheduled in
kernel mode, measured in clock ticks (divide by
sysconf(_SC_CLK_TCK)).
(16) cutime %ld
Amount 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).
(17) cstime %ld
Amount 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)).
(18) 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 (setpri‐
ority(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.
(19) nice %ld
The nice value (see setpriority(2)), a value in the
range 19 (low priority) to -20 (high priority).
(20) num_threads %ld
Number 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.
(21) itrealvalue %ld
The 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.
(22) starttime %llu
The 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.
(23) vsize %lu
Virtual memory size in bytes.
(24) rss %ld
Resident 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.
(25) rsslim %lu
Current soft limit in bytes on the rss of the process;
see the description of RLIMIT_RSS in getrlimit(2).
(26) startcode %lu [PT]
The address above which program text can run.
(27) endcode %lu [PT]
The address below which program text can run.
(28) startstack %lu [PT]
The address of the start (i.e., bottom) of the stack.
(29) kstkesp %lu [PT]
The current value of ESP (stack pointer), as found in
the kernel stack page for the process.
(30) kstkeip %lu [PT]
The current EIP (instruction pointer).
(31) signal %lu
The bitmap of pending signals, displayed as a decimal
number. Obsolete, because it does not provide infor‐
mation on real-time signals; use /proc/[pid]/status
instead.
(32) blocked %lu
The bitmap of blocked signals, displayed as a decimal
number. Obsolete, because it does not provide infor‐
mation on real-time signals; use /proc/[pid]/status
instead.
(33) sigignore %lu
The bitmap of ignored signals, displayed as a decimal
number. Obsolete, because it does not provide infor‐
mation on real-time signals; use /proc/[pid]/status
instead.
(34) sigcatch %lu
The bitmap of caught signals, displayed as a decimal
number. Obsolete, because it does not provide infor‐
mation on real-time signals; use /proc/[pid]/status
instead.
(35) 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.
(36) nswap %lu
Number of pages swapped (not maintained).
(37) cnswap %lu
Cumulative nswap for child processes (not maintained).
(38) exit_signal %d (since Linux 2.1.22)
Signal to be sent to parent when we die.
(39) processor %d (since Linux 2.2.8)
CPU number last executed on.
(40) 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 pol‐
icy, or 0, for non-real-time processes (see
sched_setscheduler(2)).
(41) 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.
(42) delayacct_blkio_ticks %llu (since Linux 2.6.18)
Aggregated block I/O delays, measured in clock ticks
(centiseconds).
(43) guest_time %lu (since Linux 2.6.24)
Guest time of the process (time spent running a vir‐
tual CPU for a guest operating system), measured in
clock ticks (divide by sysconf(_SC_CLK_TCK)).
(44) 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)).
(45) start_data %lu (since Linux 3.3) [PT]
Address above which program initialized and uninitial‐
ized (BSS) data are placed.
(46) end_data %lu (since Linux 3.3) [PT]
Address below which program initialized and uninitial‐
ized (BSS) data are placed.
(47) start_brk %lu (since Linux 3.3) [PT]
Address above which program heap can be expanded with
brk(2).
(48) arg_start %lu (since Linux 3.5) [PT]
Address above which program command-line arguments
(argv) are placed.
(49) arg_end %lu (since Linux 3.5) [PT]
Address below program command-line arguments (argv)
are placed.
(50) env_start %lu (since Linux 3.5) [PT]
Address above which program environment is placed.
(51) env_end %lu (since Linux 3.5) [PT]
Address below which program environment is placed.
(52) exit_code %d (since Linux 3.5) [PT]
The thread's exit status in the form reported by wait‐
pid(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
(same as VmRSS in /proc/[pid]/status)
shared (3) number of resident shared pages (i.e., backed by a file)
(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)
/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
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
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.
* 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 names‐
paces of which [pid] is a member. The leftmost entry shows
the value with respect to the PID namespace of the reading
process, 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 NSt‐
gid. (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(3)).
* 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").
* VmRSS: Resident set size. Note that the value here is the sum
of RssAnon, RssFile, and RssShmem.
* RssAnon: Size of resident anonymous memory. (since Linux
4.5).
* RssFile: Size of resident file mappings. (since Linux 4.5).
* 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.
* VmLib: Shared library code size.
* VmPTE: Page table entries size (since Linux 2.6.10).
* VmPMD: Size of second-level page tables (since Linux 4.0).
* VmSwap: Swapped-out virtual memory size by anonymous private
pages; shmem swap usage is not included (since Linux 2.6.34).
* HugetlbPages: Size of hugetlb memory portions. (since Linux
4.4).
* 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: Number of signals pending for thread and for
process as a whole (see pthreads(7) and signal(7)).
* SigBlk, SigIgn, SigCgt: Masks indicating signals being
blocked, ignored, and caught (see signal(7)).
* CapInh, CapPrm, CapEff: Masks of capabilities enabled in
inheritable, permitted, and effective sets (see capabili‐
ties(7)).
* CapBnd: Capability Bounding set (since Linux 2.6.26, see capa‐
bilities(7)).
* CapAmb: Ambient capability set (since Linux 4.3, see capabili‐
ties(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 SEC‐
COMP_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.
* Cpus_allowed: 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 CON‐
FIG_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-test6)
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] direc‐
tories. For attributes that are shared by all threads, the con‐
tents 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 ter‐
minated (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 proba‐
bly 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 exam‐
ple:
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/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 mem‐
ory fragmentation issues. Each line starts with the identifica‐
tion of the node and the name of the zone which together iden‐
tify 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 kilo‐
bytes, then the first zone called DMA (on x86 the first 16
megabyte of memory) has 1 chunk of 4 kilobytes (order 0) avail‐
able 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/zone‐
info.
/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 configur‐
ing 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 Documenta‐
tion/crypto/ (or Documentation/DocBook before 4.10; the documen‐
tation 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 filesys‐
tem is specified and it didn't manage to determine the filesys‐
tem 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 informa‐
tion 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 in hexadecimal
smart_values in hexadecimal
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 architec‐
tures, 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 dif‐
ferent 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 mes‐
sages.
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 CON‐
FIG_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 discus‐
sion 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 ker‐
nel source file Documentation/vm/pagemap.txt. 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 CON‐
FIG_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 sepa‐
rated by a slash (/). The first of these is the number of cur‐
rently 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:
(1) The ordinal position of the lock in the list.
(2) The lock type. Values that may appear here include:
FLOCK This is a BSD file lock created using flock(2).
OFDLCK This is an open file description (OFD) lock created
using fcntl(2).
POSIX This is a POSIX byte-range lock created using
fcntl(2).
(3) Among the strings that can appear here are the following:
ADVISORY
This is an advisory lock.
MANDATORY
This is a mandatory lock.
(4) The type of lock. Values that can appear here are:
READ This is a POSIX or OFD read lock, or a BSD shared
lock.
WRITE This is a POSIX or OFD write lock, or a BSD exclusive
lock.
(5) 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.)
(6) 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.
(7) The byte offset of the first byte of the lock. For BSD
locks, this value is always 0.
(8) 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 fil‐
tered to show just the locks for the processes in the PID names‐
pace (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 mem‐
ory (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 config‐
ured with various options; those dependencies are noted in the
list.
MemTotal %lu
Total usable RAM (i.e., physical RAM minus a few reserved
bits and the kernel binary code).
MemFree %lu
The 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 %lu
Relatively temporary storage for raw disk blocks that
shouldn't get tremendously large (20MB or so).
Cached %lu
In-memory cache for files read from the disk (the page
cache). Doesn't include SwapCached.
SwapCached %lu
Memory 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 %lu
Memory that has been used more recently and usually not
reclaimed unless absolutely necessary.
Inactive %lu
Memory 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
~860MB 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 every‐
thing 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 %lu
Total amount of swap space available.
SwapFree %lu
Amount of swap space that is currently unused.
Dirty %lu
Memory which is waiting to get written back to the disk.
Writeback %lu
Memory 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 %lu
Files 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.
Slab %lu
In-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 pres‐
sure.
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 fur‐
ther details, see the kernel source file Documenta‐
tion/vm/overcommit-accounting.
Committed_AS %lu
The 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 1GB
of memory (using malloc(3) or similar), but touches only
300MB of that memory will show up as using only 300MB of
memory even if it has the address space allocated for the
entire 1GB.
This 1GB is memory which has been "committed" to by the
VM and can be used at any time by the allocating applica‐
tion. 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 %lu
Total size of vmalloc memory area.
VmallocUsed %lu
Amount of vmalloc area which is used.
VmallocChunk %lu
Largest contiguous block of vmalloc area which is free.
HardwareCorrupted %lu (since Linux 2.6.32)
(CONFIG_MEMORY_FAILURE is required.) [To be documented.]
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. (CON‐
FIG_CMA is required.)
CmaFree %lu (since Linux 3.1)
Free CMA (Contiguous Memory Allocator) pages. (CON‐
FIG_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_overcom‐
mit_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 4kB
pages. (x86.)
DirectMap4M %lu (since Linux 2.6.27)
Number of bytes of RAM linearly mapped by kernel in 4MB
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 2MB
pages. (x86 with neither CONFIG_X86_64 nor CON‐
FIG_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 filesys‐
tems currently mounted on the system. With the introduction of
per-process mount namespaces in Linux 2.4.19 (see mount_names‐
paces(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 con‐
taining information about the networking layer. The files con‐
tain 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 names‐
paces(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 ker‐
nel 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 ker‐
nel 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 inter‐
nal 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 cre‐
ator 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 ker‐
nel 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 inter‐
nal 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 Path
0: 00000002 00000000 00000000 0001 03
1: 00000001 00000000 00010000 0001 01 /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.
Path: the bound path (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 queue‐
ing, 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:
(1) 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 infor‐
mation.
(2) The netlink port ID subscribed to the queue.
(3) The number of packets currently queued and waiting to be
processed by the application.
(4) The copy mode of the queue. It is either 1 (metadata only)
or 2 (also copy payload data to user space).
(5) Copy range; that is, how many bytes of packet payload
should be copied to user space at most.
(6) 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.
(7) 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.
(8) 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 ini‐
tialization 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 CON‐
FIG_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 pro‐
file=1 command-line option. It exposes kernel profiling infor‐
mation in a binary format for use by readprofile(1). Writing
(e.g., an empty string) to this file resets the profiling coun‐
ters; 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 sub‐
system 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 cur‐
rently 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 reg‐
istered 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 configura‐
tion, 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:
cpu 10132153 290696 3084719 46828483 16683 0 25195 0 175628 0
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:
1. 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.
2. 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.
3. The value in this field may decrease in certain
conditions.
irq (since Linux 2.6.0-test4)
(6) Time servicing interrupts.
softirq (since Linux 2.6.0-test4)
(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.)
softirq 229245889 94 60001584 13619 5175704 2471304 28 51212741
59130143 0 51240672
This line shows the number of softirq for all CPUs. The
first column is the total of all softirqs and each subse‐
quent 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 sometimes 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 inte‐
ger or long values, these may be separated by any of the follow‐
ing whitespace characters: ' ', '\t', or '\n'. Using other sep‐
arators leads to the error EINVAL.
/proc/sys/abi (since Linux 2.4.10)
This directory may contain files with application binary infor‐
mation. See the Linux kernel source file Documenta‐
tion/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/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 encounter‐
ing this limit fail with the error ENFILE. (See also setr‐
limit(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 (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 files presently
opened); 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 sys‐
tem 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 inter‐
face. 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 sig‐
nal to that process notifying it that another process is waiting
to open the file. If the lease holder does not remove or down‐
grade 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 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_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 behav‐
ior 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 follow‐
ing 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 creden‐
tials(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 "pin‐
ning" vulnerable set-user-ID and set-group-ID files against
being upgraded by the administrator, or linking to special
files.
/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 creden‐
tials(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 pro‐
duced 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) behav‐
ior. 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 pro‐
cesses.
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_pat‐
tern must either be an absolute pathname or a pipe com‐
mand, 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 fre‐
quency. If BSD-style process accounting is enabled, these val‐
ues 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 recom‐
puting 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). Echo‐
ing "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 capabil‐
ity 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 key‐
board. 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, with‐
out 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 con‐
tents. A value of 0 in this file imposes no restrictions. If
the value is 1, only privileged users can read the kernel sys‐
log. (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 host‐
name "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 path 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 Pow‐
erPC 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 path 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 CON‐
FIG_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 mes‐
sage 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 autore‐
boot 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 num‐
ber 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 cur‐
rently in use.
/proc/sys/kernel/random
This directory contains various parameters controlling the oper‐
ation of the file /dev/random. See random(4) for further infor‐
mation.
/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:
0 Turn ASLR off. This is the default for architectures that
don't support ASLR, and when the kernel is booted with the
norandmaps parameter.
1 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.
2 (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 Documen‐
tation/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 con‐
figuration. 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:
SEMMSL The maximum semaphores per semaphore set.
SEMMNS A system-wide limit on the number of semaphores in all
semaphore sets.
SEMOPM The maximum number of operations that may be specified
in a semop(2) call.
SEMMNI 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 possi‐
ble 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 Sys‐
tem 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 non‐
standard 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 1GB 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:
-1 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 over‐
write the entire value, regardless of the file position.
0 (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.
1 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 buf‐
fer 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 specifi‐
cally enable it at run-time, but this is not the case any more).
Possible values in this file are:
0 Disable sysrq completely
1 Enable all functions of sysrq
> 1 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 con‐
figuration option is enabled. For further details see the Linux
kernel source file Documentation/admin-guide/sysrq.rst (or Docu‐
mentation/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 max‐
imum 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, buf‐
fer 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 sys‐
tem 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 pro‐
vide 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 appli‐
cation 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 possi‐
ble. The effect of this action can be seen by examining
/proc/buddyinfo.
Present only if the kernel was configured with CONFIG_COM‐
PACTION.
/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 per‐
forming 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 han‐
dled 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 affect‐
ing any applications. But if there is no other up-to-date copy
of the data, it will kill processes to prevent any data corrup‐
tions from propagating.
The file has one of the following values:
1: Kill all processes that have the corrupted-and-not-reload‐
able 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.
0: 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_MEM‐
ORY_FAILURE.
/proc/sys/vm/memory_failure_recovery (since Linux 2.6.32)
Enable memory failure recovery (when supported by the platform)
1: Attempt recovery.
0: Always panic on a memory failure.
Present only if the kernel was configured with CONFIG_MEM‐
ORY_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 pos‐
sibly 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_allocat‐
ing_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/over‐
commit_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 Com‐
mitLimit 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 get‐
ting 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/overcom‐
mit_ratio; and
* total_swap is the amount of swap space.
For example, on a system with 16GB of physical RAM, 16GB of
swap, no space dedicated to huge pages, and an overcommit_ratio
of 50, this formula yields a CommitLimit of 24GB.
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/admiin_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 sit‐
uation.
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 pro‐
cesses, This is intended to prevent a user from starting a sin‐
gle 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 appli‐
cation requests memory.
/proc/sysrq-trigger (since Linux 2.4.21)
Writing a character to this file triggers the same SysRq func‐
tion 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 Doc‐
umentation/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. svipc(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 filesys‐
tem, 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 runtime overhead and a relatively small data-
structure overhead. Even if collection is enabled at runtime,
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: the uptime of the system (sec‐
onds), and the amount of time spent in idle process (seconds).
/proc/version
This string identifies the kernel version that is currently run‐
ning. 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 con‐
figured with suitable options. (In some cases, the options
required for particular files have changed across kernel ver‐
sions, 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/vm/tran‐
shuge.txt.
compact_fail (since Linux 2.6.35)
See the kernel source file Documentation/vm/tran‐
shuge.txt.
compact_success (since Linux 2.6.35)
See the kernel source file Documentation/vm/tran‐
shuge.txt.
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/vm/tran‐
shuge.txt.
thp_fault_fallback (since Linux 2.6.39)
See the kernel source file Documentation/vm/tran‐
shuge.txt.
thp_collapse_alloc (since Linux 2.6.39)
See the kernel source file Documentation/vm/tran‐
shuge.txt.
thp_collapse_alloc_failed (since Linux 2.6.39)
See the kernel source file Documentation/vm/tran‐
shuge.txt.
thp_split (since Linux 2.6.39)
See the kernel source file Documentation/vm/tran‐
shuge.txt.
thp_zero_page_alloc (since Linux 3.8)
See the kernel source file Documentation/vm/tran‐
shuge.txt.
thp_zero_page_alloc_failed (since Linux 3.8)
See the kernel source file Documentation/vm/tran‐
shuge.txt.
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 display information about memory zones. This is use‐
ful for analyzing virtual memory behavior.
NOTES
Many strings (i.e., the environment and command line) are in the inter‐
nal format, with subfields terminated by null bytes ('\0'), so you may
find that things are more readable if you use od -c or tr "\000" "\n"
to read them. Alternatively, echo `cat <file>` works well.
This manual page is incomplete, possibly inaccurate, and is the kind of
thing that needs to be updated very often.
SEE ALSO
cat(1), dmesg(1), find(1), free(1), init(1), ps(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 Docu‐ mentation/sysctl/fs.txt, Documentation/sysctl/kernel.txt, Documenta‐ tion/sysctl/net.txt, and Documentation/sysctl/vm.txt.
COLOPHON
This page is part of release 4.15 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/.