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NAME | DESCRIPTION | NOTES | SEE ALSO | COLOPHON |
PROC(5) Linux Programmer's Manual PROC(5)
proc - process information pseudo-filesystem
The proc filesystem is a pseudo-filesystem which provides an
interface to kernel data structures. It is commonly mounted at
/proc. Most of it is read-only, but some files allow 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
following 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.
However, as a security measure, the ownership is made
root:root if the process's "dumpable" attribute is set to a
value other than 1. 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
modules. For the purpose of explanation, examples of how
SELinux uses these files are provided below.
This directory is present only if the kernel was configured
with CONFIG_SECURITY.
/proc/[pid]/attr/current (since Linux 2.6.0)
The contents of this file represent the current security
attributes of the process.
In SELinux, this file is used to get the security context of a
process. Prior to Linux 2.6.11, this file could not be used
to set the security context (a write was always denied), since
SELinux limited process security transitions to execve(2) (see
the description of /proc/[pid]/attr/exec, below). Since Linux
2.6.11, SELinux lifted this restriction and began supporting
"set" operations via writes to this node if authorized by
policy, although use of this operation is only suitable for
applications that are trusted to maintain any desired
separation between the old and new security contexts. Prior
to Linux 2.6.28, SELinux did not allow threads within a 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" operations for threads within a multithreaded process if
the new security context is bounded by the old security
context, where the bounded relation is defined in policy and
guarantees that the new security context has a subset of the
permissions of the old security context. Other security
modules may choose to support "set" operations via writes to
this node.
/proc/[pid]/attr/exec (since Linux 2.6.0)
This file represents the attributes to assign to the process
upon a subsequent execve(2).
In SELinux, this is needed to support role/domain transitions,
and execve(2) is the preferred point to make such transitions
because it offers better control over the initialization of
the process in the new security label and the inheritance of
state. In SELinux, this attribute is reset on execve(2) so
that the new program reverts to the default behavior for any
execve(2) calls that it may make. In SELinux, a process can
set only its own /proc/[pid]/attr/exec attribute.
/proc/[pid]/attr/fscreate (since Linux 2.6.0)
This file represents the attributes to assign to files created
by subsequent calls to open(2), mkdir(2), symlink(2), and
mknod(2)
SELinux employs this file to support creation of a file (using
the aforementioned system calls) in a secure state, so that
there is no risk of inappropriate access being obtained
between the time of creation and the time that attributes are
set. In SELinux, this attribute is reset on execve(2), so
that the new program reverts to the default behavior for any
file creation calls it may make, but the attribute will
persist across multiple file creation calls within a program
unless it is explicitly reset. In SELinux, a process can set
only its own /proc/[pid]/attr/fscreate attribute.
/proc/[pid]/attr/keycreate (since Linux 2.6.18)
If a process writes a security context into this file, all
subsequently created keys (add_key(2)) will be labeled with
this context. For further information, see the kernel source
file Documentation/keys.txt.
/proc/[pid]/attr/prev (since Linux 2.6.0)
This file contains the security context of the process before
the last execve(2); that is, the previous value of
/proc/[pid]/attr/current.
/proc/[pid]/attr/socketcreate (since Linux 2.6.18)
If a process writes a security context into this file, all
subsequently created sockets will be labeled with this
context.
/proc/[pid]/autogroup (since Linux 2.6.38)
See sched(7).
/proc/[pid]/auxv (since 2.6.0-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_Referenced and ACCESSED/YOUNG bits and, after some measured
time interval, once again inspects the values in the
"Referenced" fields to get an idea of the change in memory
footprint of the process during the measured interval. If one
is interested only in inspecting the selected mapping types,
then the value 2 or 3 can be used instead of 1.
Further values can be written to affect different properties:
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
CONFIG_PROC_PAGE_MONITOR kernel configuration option is
enabled.
/proc/[pid]/cmdline
This read-only file holds the complete command line for the
process, unless the process is a zombie. In the latter case,
there is nothing in this file: that is, a read on this file
will return 0 characters. The command-line arguments appear
in this file as a set of strings separated by null bytes
('\0'), with a further null byte after the last string.
/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
containing the actual pathname of the executed command. This
symbolic link can be dereferenced normally; attempting to open
it will open the executable. You can even type
/proc/[pid]/exe to run another copy of the same executable
that is being run by process [pid]. If the pathname has been
unlinked, the symbolic link will contain the string
'(deleted)' appended to the original pathname. In a
multithreaded process, the contents of this symbolic link are
not available if the main thread has already terminated
(typically by calling pthread_exit(3)).
Permission to dereference or read (readlink(2)) this symbolic
link is governed by a ptrace access mode
PTRACE_MODE_READ_FSCREDS check; see ptrace(2).
Under Linux 2.0 and earlier, /proc/[pid]/exe is a pointer to
the binary which was executed, and appears as a symbolic link.
A readlink(2) call on this file under Linux 2.0 returns a
string in the format:
[device]:inode
For example, [0301]:1502 would be inode 1502 on device major
03 (IDE, MFM, etc. drives) minor 01 (first partition on the
first drive).
find(1) with the -inum option can be used to locate the file.
/proc/[pid]/fd/
This is a subdirectory containing one entry for each file
which the process has open, named by its file descriptor, and
which is a symbolic link to the actual file. Thus, 0 is
standard input, 1 standard output, 2 standard error, and so
on.
For file descriptors for pipes and sockets, the entries will
be symbolic links whose content is the file type with the
inode. A readlink(2) call on this file returns a string in
the format:
type:[inode]
For example, socket:[2248868] will be a socket and its inode
is 2248868. For sockets, that inode can be used to find more
information in one of the files under /proc/net/.
For file descriptors that have no corresponding inode (e.g.,
file descriptors produced by bpf(2), epoll_create(2),
eventfd(2), inotify_init(2), perf_event_open(2), signalfd(2),
timerfd_create(2), and userfaultfd(2)), the entry will be a
symbolic link with contents of the form
anon_inode:<file-type>
In many cases (but not all), the file-type is surrounded by
square brackets.
For example, an epoll file descriptor will have a symbolic
link whose content is the string anon_inode:[eventpoll].
In a multithreaded process, the contents of this directory are
not available if the main thread has already terminated
(typically by calling pthread_exit(3)).
Programs that take a filename as a command-line argument, but
don't take input from standard input if no argument is
supplied, and programs that write to a file named as a
command-line argument, but don't send their output to standard
output if no argument is supplied, can nevertheless be made to
use standard input or standard output by using /proc/[pid]/fd
files as command-line arguments. For example, assuming that
-i is the flag designating an input file and -o is the flag
designating an output file:
$ foobar -i /proc/self/fd/0 -o /proc/self/fd/1 ...
and you have a working filter.
/proc/self/fd/N is approximately the same as /dev/fd/N in some
UNIX and UNIX-like systems. Most Linux MAKEDEV scripts
symbolically link /dev/fd to /proc/self/fd, in fact.
Most systems provide symbolic links /dev/stdin, /dev/stdout,
and /dev/stderr, which respectively link to the files 0, 1,
and 2 in /proc/self/fd. Thus the example command above could
be written as:
$ foobar -i /dev/stdin -o /dev/stdout ...
Permission to dereference or read (readlink(2)) the symbolic
links in this directory is governed by a ptrace access mode
PTRACE_MODE_READ_FSCREDS check; see ptrace(2).
/proc/[pid]/fdinfo/ (since Linux 2.6.22)
This is a subdirectory containing one entry for each file
which the process has open, named by its file descriptor. The
files in this directory are readable only by the owner of the
process. The contents of each file can be read to obtain
information about the corresponding file descriptor. The
content depends on the type of file referred to by the
corresponding file descriptor.
For regular files and directories, we see something like:
$ cat /proc/12015/fdinfo/4
pos: 1000
flags: 01002002
mnt_id: 21
The fields are as follows:
pos This is a decimal number showing the file offset.
flags This is an octal number that displays the file access
mode and file status flags (see open(2)). If the
close-on-exec file descriptor flag is set, then flags
will also include the value O_CLOEXEC.
Before Linux 3.1, this field incorrectly displayed the
setting of O_CLOEXEC at the time the file was opened,
rather than the current setting of the close-on-exec
flag.
mnt_id This field, present since Linux 3.15, is the ID of the
mount point containing this file. See the description
of /proc/[pid]/mountinfo.
For eventfd file descriptors (see eventfd(2)), we see (since
Linux 3.8) the following fields:
pos: 0
flags: 02
mnt_id: 10
eventfd-count: 40
eventfd-count is the current value of the eventfd counter, in
hexadecimal.
For epoll file descriptors (see epoll(7)), we see (since Linux
3.8) the following fields:
pos: 0
flags: 02
mnt_id: 10
tfd: 9 events: 19 data: 74253d2500000009
tfd: 7 events: 19 data: 74253d2500000007
Each of the lines beginning tfd describes one of the file
descriptors being monitored via the epoll file descriptor (see
epoll_ctl(2) for some details). The tfd field is the number
of the file descriptor. The events field is a hexadecimal
mask of the events being monitored for this file descriptor.
The data field is the data value associated with this file
descriptor.
For signalfd file descriptors (see signalfd(2)), we see (since
Linux 3.8) the following fields:
pos: 0
flags: 02
mnt_id: 10
sigmask: 0000000000000006
sigmask is the hexadecimal mask of signals that are accepted
via this signalfd file descriptor. (In this example, bits 2
and 3 are set, corresponding to the signals SIGINT and
SIGQUIT; see signal(7).)
For inotify file descriptors (see inotify(7)), we see (since
Linux 3.8) the following fields:
pos: 0
flags: 00
mnt_id: 11
inotify wd:2 ino:7ef82a sdev:800001 mask:800afff ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:2af87e00220ffd73
inotify wd:1 ino:192627 sdev:800001 mask:800afff ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:27261900802dfd73
Each of the lines beginning with "inotify" displays
information about one file or directory that is being
monitored. The fields in this line are as follows:
wd A watch descriptor number (in decimal).
ino The inode number of the target file (in hexadecimal).
sdev The ID of the device where the target file resides (in
hexadecimal).
mask The mask of events being monitored for the target file
(in hexadecimal).
If the kernel was built with exportfs support, the path to the
target file is exposed as a file handle, via three hexadecimal
fields: fhandle-bytes, fhandle-type, and f_handle.
For fanotify file descriptors (see fanotify(7)), we see (since
Linux 3.8) the following fields:
pos: 0
flags: 02
mnt_id: 11
fanotify flags:0 event-flags:88002
fanotify ino:19264f sdev:800001 mflags:0 mask:1 ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:4f261900a82dfd73
The fourth line displays information defined when the fanotify
group was created via fanotify_init(2):
flags The flags argument given to fanotify_init(2) (expressed
in hexadecimal).
event-flags
The event_f_flags argument given to fanotify_init(2)
(expressed in hexadecimal).
Each additional line shown in the file contains information
about one of the marks in the fanotify group. Most of these
fields are as for inotify, except:
mflags The flags associated with the mark (expressed in
hexadecimal).
mask The events mask for this mark (expressed in
hexadecimal).
ignored_mask
The mask of events that are ignored for this mark
(expressed in hexadecimal).
For details on these fields, see fanotify_mark(2).
/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
measurement for each of the process's resource limits (see
getrlimit(2)). Up to and including Linux 2.6.35, this file is
protected to allow reading only by the real UID of the
process. Since Linux 2.6.36, this file is readable by all
users on the system.
/proc/[pid]/map_files/ (since kernel 3.3)
This subdirectory contains entries corresponding to memory-
mapped files (see mmap(2)). Entries are named by memory
region start and end address pair (expressed as hexadecimal
numbers), and are symbolic links to the mapped files
themselves. Here is an example, with the output wrapped and
reformatted to fit on an 80-column display:
# ls -l /proc/self/map_files/
lr--------. 1 root root 64 Apr 16 21:31
3252e00000-3252e20000 -> /usr/lib64/ld-2.15.so
...
Although these entries are present for memory regions that
were mapped with the MAP_FILE flag, the way anonymous shared
memory (regions created with the MAP_ANON | MAP_SHARED flags)
is implemented in Linux means that such regions also appear on
this directory. Here is an example where the target file is
the deleted /dev/zero one:
lrw-------. 1 root root 64 Apr 16 21:33
7fc075d2f000-7fc075e6f000 -> /dev/zero (deleted)
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
directory.
/proc/[pid]/maps
A file containing the currently mapped memory regions and
their access permissions. See mmap(2) for some further
information about memory mappings.
Permission to access this file is governed by a ptrace access
mode PTRACE_MODE_READ_FSCREDS check; see ptrace(2).
The format of the file is:
address perms offset dev inode pathname
00400000-00452000 r-xp 00000000 08:02 173521 /usr/bin/dbus-daemon
00651000-00652000 r--p 00051000 08:02 173521 /usr/bin/dbus-daemon
00652000-00655000 rw-p 00052000 08:02 173521 /usr/bin/dbus-daemon
00e03000-00e24000 rw-p 00000000 00:00 0 [heap]
00e24000-011f7000 rw-p 00000000 00:00 0 [heap]
...
35b1800000-35b1820000 r-xp 00000000 08:02 135522 /usr/lib64/ld-2.15.so
35b1a1f000-35b1a20000 r--p 0001f000 08:02 135522 /usr/lib64/ld-2.15.so
35b1a20000-35b1a21000 rw-p 00020000 08:02 135522 /usr/lib64/ld-2.15.so
35b1a21000-35b1a22000 rw-p 00000000 00:00 0
35b1c00000-35b1dac000 r-xp 00000000 08:02 135870 /usr/lib64/libc-2.15.so
35b1dac000-35b1fac000 ---p 001ac000 08:02 135870 /usr/lib64/libc-2.15.so
35b1fac000-35b1fb0000 r--p 001ac000 08:02 135870 /usr/lib64/libc-2.15.so
35b1fb0000-35b1fb2000 rw-p 001b0000 08:02 135870 /usr/lib64/libc-2.15.so
...
f2c6ff8c000-7f2c7078c000 rw-p 00000000 00:00 0 [stack:986]
...
7fffb2c0d000-7fffb2c2e000 rw-p 00000000 00:00 0 [stack]
7fffb2d48000-7fffb2d49000 r-xp 00000000 00:00 0 [vdso]
The address field is the address space in the process that the
mapping occupies. The perms field is a set of permissions:
r = read
w = write
x = execute
s = shared
p = private (copy on write)
The offset field is the offset into the file/whatever; dev is
the device (major:minor); inode is the inode on that device.
0 indicates that no inode is associated with the memory
region, as would be the case with BSS (uninitialized data).
The pathname field will usually be the file that is backing
the mapping. For ELF files, you can easily coordinate with
the offset field by looking at the Offset field in the ELF
program headers (readelf -l).
There are additional helpful pseudo-paths:
[stack]
The initial process's (also known as the main
thread's) stack.
[stack:<tid>] (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
supplies various information (e.g., propagation state, root of
mount for bind mounts, identifier for each mount and its
parent) that is missing from the (older) /proc/[pid]/mounts
file, and fixes various other problems with that file (e.g.,
nonextensibility, failure to distinguish per-mount versus per-
superblock options).
The file contains lines of the form:
36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
(1)(2)(3) (4) (5) (6) (7) (8) (9) (10) (11)
The numbers in parentheses are labels for the descriptions
below:
(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
top of the mount tree).
(3) major:minor: the value of st_dev for files on this
filesystem (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
unrecognized optional fields.
For more information on mount propagation see:
Documentation/filesystems/sharedsubtree.txt in the Linux
kernel source tree.
/proc/[pid]/mounts (since Linux 2.4.19)
This file lists all the filesystems currently mounted in the
process's mount namespace (see mount_namespaces(7)). The
format of this file is documented in fstab(5).
Since kernel version 2.6.15, this file is pollable: after
opening the file for reading, a change in this file (i.e., a
filesystem mount or unmount) causes select(2) to mark the file
descriptor as having an exceptional condition, and poll(2) and
epoll_wait(2) mark the file as having a priority event
(POLLPRI). (Before Linux 2.6.30, a change in this file was
indicated by the file descriptor being marked as readable for
select(2), and being marked as having an error condition for
poll(2) and epoll_wait(2).)
/proc/[pid]/mountstats (since Linux 2.6.17)
This file exports information (statistics, configuration
information) about the mount points in the process's mount
namespace (see mount_namespaces(7)). Lines in this file have
the form:
device /dev/sda7 mounted on /home with fstype ext3 [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.
Currently (as at Linux 2.6.26), only NFS filesystems
export information via this field.
This file is readable only by the owner of the process.
/proc/[pid]/net " (since Linux 2.6.25)"
See the description of /proc/net.
/proc/[pid]/ns/ (since Linux 3.0)
This is a subdirectory containing one entry for each namespace
that supports being manipulated by setns(2). For more
information, see namespaces(7).
/proc/[pid]/numa_maps (since Linux 2.6.14)
See numa(7).
/proc/[pid]/oom_adj (since Linux 2.6.11)
This file can be used to adjust the score used to select which
process should be killed in an out-of-memory (OOM) situation.
The kernel uses this value for a bit-shift operation of the
process's oom_score value: valid values are in the range -16
to +15, plus the special value -17, which disables OOM-killing
altogether for this process. A positive score increases the
likelihood of this process being killed by the OOM-killer; a
negative score decreases the likelihood.
The default value for this file is 0; a new process inherits
its parent's oom_adj setting. A process must be privileged
(CAP_SYS_RESOURCE) to update this file.
Since Linux 2.6.36, use of this file is deprecated in favor of
/proc/[pid]/oom_score_adj.
/proc/[pid]/oom_score (since Linux 2.6.11)
This file displays the current score that the kernel gives to
this process for the purpose of selecting a process for the
OOM-killer. A higher score means that the process is more
likely to be selected by the OOM-killer. The basis for this
score is the amount of memory used by the process, with
increases (+) or decreases (-) for factors including:
* whether the process 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) (+);
* whether the process is privileged (-); 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
follows:
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.
60-56 (since Linux 3.11)
Zero
55 (since Linux 3.11)
PTE is soft-dirty (see the kernel source file
Documentation/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
CONFIG_PROC_PAGE_MONITOR kernel configuration option is
enabled.
Permission to access this file is governed by a ptrace access
mode PTRACE_MODE_READ_FSCREDS check; see ptrace(2).
/proc/[pid]/personality (since Linux 2.6.28)
This read-only file exposes the process's execution domain, as
set by personality(2). The value is displayed in hexadecimal
notation.
Permission to access this file is governed by a ptrace access
mode PTRACE_MODE_ATTACH_FSCREDS check; see ptrace(2).
/proc/[pid]/root
UNIX and Linux support the idea of a per-process root of the
filesystem, set by the chroot(2) system call. This file is a
symbolic link that points to the process's root directory, and
behaves in the same way as exe, and fd/*.
Note however that this file is not merely a symbolic link. It
provides the same view of the filesystem (including namespaces
and the set of per-process mounts) as the process itself. An
example illustrates this point. In one terminal, we start a
shell in new user and mount namespaces, and in that shell we
create some new mount points:
$ PS1='sh1# ' unshare -Urnm
sh1# mount -t tmpfs tmpfs /etc # Mount empty tmpfs at /etc
sh1# mount --bind /usr /dev # Mount /usr at /dev
sh1# echo $$
27123
In a second terminal window, in the initial mount namespace,
we look at the contents of the corresponding mounts in the
initial and new namespaces:
$ PS1='sh2# ' sudo sh
sh2# ls /etc | wc -l # In initial NS
309
sh2# ls /proc/27123/root/etc | wc -l # /etc in other NS
0 # The empty tmpfs dir
sh2# ls /dev | wc -l # In initial NS
205
sh2# ls /proc/27123/root/dev | wc -l # /dev in other NS
11 # Actually bind
# mounted to /usr
sh2# ls /usr | wc -l # /usr in initial NS
11
In a multithreaded process, the contents of the
/proc/[pid]/root symbolic link are not available if the main
thread has already terminated (typically by calling
pthread_exit(3)).
Permission to dereference or read (readlink(2)) this symbolic
link is governed by a ptrace access mode
PTRACE_MODE_READ_FSCREDS check; see ptrace(2).
/proc/[pid]/seccomp (Linux 2.6.12 to 2.6.22)
This file can be used to read and change the process's secure
computing (seccomp) mode setting. It contains the value 0 if
the process is not in seccomp mode, and 1 if the process is in
strict seccomp mode (see seccomp(2)). Writing 1 to this file
places the process irreversibly in strict seccomp mode.
(Further attempts to write to the file fail with the EPERM
error.)
In Linux 2.6.23, this file went away, to be replaced by the
prctl(2) PR_GET_SECCOMP and PR_SET_SECCOMP operations (and
later by seccomp(2) and the Seccomp field in
/proc/[pid]/status).
/proc/[pid]/setgroups (since Linux 3.19)
See user_namespaces(7).
/proc/[pid]/smaps (since Linux 2.6.14)
This file shows memory consumption for each of the process's
mappings. (The pmap(1) command displays similar information,
in a form that may be easier for parsing.) For each mapping
there is a series of lines such as the following:
00400000-0048a000 r-xp 00000000 fd:03 960637 /bin/bash
Size: 552 kB
Rss: 460 kB
Pss: 100 kB
Shared_Clean: 452 kB
Shared_Dirty: 0 kB
Private_Clean: 8 kB
Private_Dirty: 0 kB
Referenced: 460 kB
Anonymous: 0 kB
AnonHugePages: 0 kB
ShmemHugePages: 0 kB
ShmemPmdMapped: 0 kB
Swap: 0 kB
KernelPageSize: 4 kB
MMUPageSize: 4 kB
KernelPageSize: 4 kB
MMUPageSize: 4 kB
Locked: 0 kB
ProtectionKey: 0
VmFlags: rd ex mr mw me dw
The first of these lines shows the same information as is
displayed for the mapping in /proc/[pid]/maps. The following
lines show the size of the mapping, the amount of the mapping
that is currently resident in RAM ("Rss"), the process's
proportional share of this mapping ("Pss"), the number of
clean and dirty shared pages in the mapping, and the number of
clean and dirty private pages in the mapping. "Referenced"
indicates the amount of memory currently marked as referenced
or accessed. "Anonymous" shows the amount of memory that does
not belong to any file. "Swap" shows how much would-be-
anonymous memory is also used, but out on swap.
The "KernelPageSize" line (available since Linux 2.6.29) is
the page size used by the kernel to back the virtual memory
area. This matches the size used by the MMU in the majority
of cases. However, one counter-example occurs on PPC64
kernels whereby a kernel using 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))
associated with the virtual memory area. This entry is
present only if the kernel was built with the
CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS configuration option.
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_PROTECTION_KEYS configuration option.
(since Linux 4.6)
The /proc/[pid]/smaps file is present only if the
CONFIG_PROC_PAGE_MONITOR kernel configuration option is
enabled.
/proc/[pid]/stack (since Linux 2.6.29)
This file provides a symbolic trace of the function calls in
this process's kernel stack. This file is provided only if
the kernel was built with the CONFIG_STACKTRACE configuration
option.
Permission to access this file is governed by a ptrace access
mode PTRACE_MODE_ATTACH_FSCREDS check; see ptrace(2).
/proc/[pid]/stat
Status information about the process. This is used by ps(1).
It is defined in the kernel source file fs/proc/array.c.
The fields, in order, with their proper scanf(3) format
specifiers, are listed below. Whether or not certain of these
fields display valid information is governed by a ptrace
access mode PTRACE_MODE_READ_FSCREDS | PTRACE_MODE_NOAUDIT
check (refer to ptrace(2)). If the check denies access, then
the field value is displayed as 0. The affected fields are
indicated with the marking [PT].
(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
controlling terminal of the process.
(9) flags %u
The kernel flags word of the process. For bit
meanings, see the PF_* defines in the Linux kernel
source file include/linux/sched.h. Details depend
on the kernel version.
The format for this field was %lu before Linux 2.6.
(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 calculations.
(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 (setpriority(2)) as represented in the
kernel. The kernel stores nice values as numbers in
the range 0 (high) to 39 (low), corresponding to the
user-visible nice range of -20 to 19.
Before Linux 2.6, this was a scaled value based on
the scheduler weighting given to this process.
(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 information 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 information 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 information 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
information 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
policy, 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
virtual 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
uninitialized (BSS) data are placed.
(46) end_data %lu (since Linux 3.3) [PT]
Address below which program initialized and
uninitialized (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
waitpid(2).
/proc/[pid]/statm
Provides information about memory usage, measured in pages.
The columns are:
size (1) total program size
(same as VmSize in /proc/[pid]/status)
resident (2) resident set size
(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
namespaces 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
NStgid. (Since Linux 4.1.)
* NSsid: descendant namespace session ID hierarchy Session ID
in each of the PID namespaces of which [pid] is a member.
The fields are ordered as for NStgid. (Since Linux 4.1.)
* VmPeak: Peak virtual memory size.
* VmSize: Virtual memory size.
* VmLck: Locked memory size (see mlock(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
capabilities(7)).
* CapBnd: Capability Bounding set (since Linux 2.6.26, see
capabilities(7)).
* CapAmb: Ambient capability set (since Linux 4.3, see
capabilities(7)).
* NoNewPrivs: Value of the no_new_privs bit (since Linux 4.10,
see prctl(2)).
* Seccomp: Seccomp mode of the process (since Linux 3.8, see
seccomp(2)). 0 means SECCOMP_MODE_DISABLED; 1 means
SECCOMP_MODE_STRICT; 2 means SECCOMP_MODE_FILTER. This
field is provided only if the kernel was built with the
CONFIG_SECCOMP kernel configuration option enabled.
* 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
CONFIG_HAVE_ARCH_TRACEHOOK.
Permission to access this file is governed by a ptrace access
mode PTRACE_MODE_ATTACH_FSCREDS check; see ptrace(2).
/proc/[pid]/task (since Linux 2.6.0-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]
directories. For attributes that are shared by all threads,
the contents for each of the files under the task/[tid]
subdirectories will be the same as in the corresponding file
in the parent /proc/[pid] directory (e.g., in a multithreaded
process, all of the task/[tid]/cwd files will have the same
value as the /proc/[pid]/cwd file in the parent directory,
since all of the threads in a process share a working
directory). For attributes that are distinct for each thread,
the corresponding files under task/[tid] may have different
values (e.g., various fields in each of the task/[tid]/status
files may be different for each thread), or they might not
exist in /proc/[pid] at all. In a multithreaded process, the
contents of the /proc/[pid]/task directory are not available
if the main thread has already terminated (typically by
calling pthread_exit(3)).
/proc/[pid]/task/[tid]/children (since Linux 3.5)
A space-separated list of child tasks of this task. Each
child task is represented by its TID.
This option is intended for use by the checkpoint-restore
(CRIU) system, and reliably provides a list of children only
if all of the child processes are stopped or frozen. It does
not work properly if children of the target task exit while
the file is being read! Exiting children may cause non-
exiting children to be omitted from the list. This makes this
interface even more unreliable than classic PID-based
approaches if the inspected task and its children aren't
frozen, and most code should probably not use this interface.
Until Linux 4.2, the presence of this file was governed by the
CONFIG_CHECKPOINT_RESTORE kernel configuration option. Since
Linux 4.2, it is governed by the CONFIG_PROC_CHILDREN option.
/proc/[pid]/timers (since Linux 3.10)
A list of the POSIX timers for this process. Each timer is
listed with a line that starts with the string "ID:". For
example:
ID: 1
signal: 60/00007fff86e452a8
notify: signal/pid.2634
ClockID: 0
ID: 0
signal: 60/00007fff86e452a8
notify: signal/pid.2634
ClockID: 1
The lines shown for each timer have the following meanings:
ID The ID for this timer. This is not the same as the
timer ID returned by timer_create(2); rather, it is the
same kernel-internal ID that is available via the
si_timerid field of the siginfo_t structure (see
sigaction(2)).
signal This is the signal number that this timer uses to
deliver notifications followed by a slash, and then the
sigev_value value supplied to the signal handler.
Valid only for timers that notify via a signal.
notify The part before the slash specifies the mechanism that
this timer uses to deliver notifications, and is one of
"thread", "signal", or "none". Immediately following
the slash is either the string "tid" for timers with
SIGEV_THREAD_ID notification, or "pid" for timers that
notify by other mechanisms. Following the "." is the
PID of the process (or the kernel thread ID of the
thread) that will be delivered a signal if the timer
delivers notifications via a signal.
ClockID
This field identifies the clock that the timer uses for
measuring time. For most clocks, this is a number that
matches one of the user-space CLOCK_* constants exposed
via <time.h>. CLOCK_PROCESS_CPUTIME_ID timers display
with a value of -6 in this field.
CLOCK_THREAD_CPUTIME_ID timers display with a value of
-2 in this field.
This file is available only when the kernel was configured
with CONFIG_CHECKPOINT_RESTORE.
/proc/[pid]/timerslack_ns (since Linux 4.6)
This file exposes the process's "current" timer slack value,
expressed in nanoseconds. The file is writable, allowing the
process's timer slack value to be changed. Writing 0 to this
file resets the "current" timer slack to the "default" timer
slack value. For further details, see the discussion of
PR_SET_TIMERSLACK in prctl(2).
Permission to access this file is governed by a ptrace access
mode PTRACE_MODE_ATTACH_FSCREDS check; see ptrace(2).
/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
memory fragmentation issues. Each line starts with the
identification of the node and the name of the zone which
together identify a memory region This is then followed by the
count of available chunks of a certain order in which these
zones are split. The size in bytes of a certain order is
given by the formula:
(2^order) * PAGE_SIZE
The binary buddy allocator algorithm inside the kernel will
split one chunk into two chunks of a smaller order (thus with
half the size) or combine two contiguous chunks into one
larger chunk of a higher order (thus with double the size) to
satisfy allocation requests and to counter memory
fragmentation. The order matches the column number, when
starting to count at zero.
For example on a x86_64 system:
Node 0, zone DMA 1 1 1 0 2 1 1 0 1 1 3
Node 0, zone DMA32 65 47 4 81 52 28 13 10 5 1 404
Node 0, zone Normal 216 55 189 101 84 38 37 27 5 3 587
In this example, there is one node containing three zones and
there are 11 different chunk sizes. If the page size is 4
kilobytes, then the first zone called DMA (on x86 the first 16
megabyte of memory) has 1 chunk of 4 kilobytes (order 0)
available and has 3 chunks of 4 megabytes (order 10)
available.
If the memory is heavily fragmented, the counters for higher
order chunks will be zero and allocation of large contiguous
areas will fail.
Further information about the zones can be found in
/proc/zoneinfo.
/proc/bus
Contains subdirectories for installed busses.
/proc/bus/pccard
Subdirectory for PCMCIA devices when CONFIG_PCMCIA is set at
kernel compilation time.
/proc/bus/pccard/drivers
/proc/bus/pci
Contains various bus subdirectories and pseudo-files
containing information about PCI busses, installed devices,
and device drivers. Some of these files are not ASCII.
/proc/bus/pci/devices
Information about PCI devices. They may be accessed through
lspci(8) and setpci(8).
/proc/cgroups (since Linux 2.6.24)
See cgroups(7).
/proc/cmdline
Arguments passed to the Linux kernel at boot time. Often done
via a boot manager such as lilo(8) or grub(8).
/proc/config.gz (since Linux 2.6)
This file exposes the configuration options that were used to
build the currently running kernel, in the same format as they
would be shown in the .config file that resulted when
configuring the kernel (using make xconfig, make config, or
similar). The file contents are compressed; view or search
them using zcat(1) and zgrep(1). As long as no changes have
been made to the following file, the contents of
/proc/config.gz are the same as those provided by :
cat /lib/modules/$(uname -r)/build/.config
/proc/config.gz is provided only if the kernel is configured
with CONFIG_IKCONFIG_PROC.
/proc/crypto
A list of the ciphers provided by the kernel crypto API. For
details, see the kernel Linux Kernel Crypto API documentation
available under the kernel source directory
Documentation/DocBook. (That documentation can be built using
a command such as make htmldocs in the root directory of the
kernel source tree.)
/proc/cpuinfo
This is a collection of CPU and system architecture dependent
items, for each supported architecture a different list. Two
common entries are processor which gives CPU number and
bogomips; a system constant that is calculated during kernel
initialization. SMP machines have information for each CPU.
The lscpu(1) command gathers its information from this file.
/proc/devices
Text listing of major numbers and device groups. This can be
used by MAKEDEV scripts for consistency with the kernel.
/proc/diskstats (since Linux 2.5.69)
This file contains disk I/O statistics for each disk device.
See the Linux kernel source file Documentation/iostats.txt for
further information.
/proc/dma
This is a list of the registered ISA DMA (direct memory
access) channels in use.
/proc/driver
Empty subdirectory.
/proc/execdomains
List of the execution domains (ABI personalities).
/proc/fb
Frame buffer information when CONFIG_FB is defined during
kernel compilation.
/proc/filesystems
A text listing of the filesystems which are supported by the
kernel, namely filesystems which were compiled into the kernel
or whose kernel modules are currently loaded. (See also
filesystems(5).) If a filesystem is marked with "nodev", this
means that it does not require a block device to be mounted
(e.g., virtual filesystem, network filesystem).
Incidentally, this file may be used by mount(8) when no
filesystem is specified and it didn't manage to determine the
filesystem type. Then filesystems contained in this file are
tried (excepted those that are marked with "nodev").
/proc/fs
Contains subdirectories that in turn contain files with
information about (certain) mounted filesystems.
/proc/ide
This directory exists on systems with the IDE bus. There are
directories for each IDE channel and attached device. Files
include:
cache buffer size in KB
capacity number of sectors
driver driver version
geometry physical and logical geometry
identify in hexadecimal
media media type
model manufacturer's model number
settings drive settings
smart_thresholds 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
architectures, at least, this also includes interrupts
internal to the system (that is, not associated with a device
as such), such as NMI (nonmaskable interrupt), LOC (local
timer interrupt), and for SMP systems, TLB (TLB flush
interrupt), RES (rescheduling interrupt), CAL (remote function
call interrupt), and possibly others. Very easy to read
formatting, done in ASCII.
/proc/iomem
I/O memory map in Linux 2.4.
/proc/ioports
This is a list of currently registered Input-Output port
regions that are in use.
/proc/kallsyms (since Linux 2.5.71)
This holds the kernel exported symbol definitions used by the
modules(X) tools to dynamically link and bind loadable
modules. In Linux 2.5.47 and earlier, a similar file with
slightly different syntax was named ksyms.
/proc/kcore
This file represents the physical memory of the system and is
stored in the ELF core file format. With this pseudo-file,
and an unstripped kernel (/usr/src/linux/vmlinux) binary, GDB
can be used to examine the current state of any kernel data
structures.
The total length of the file is the size of physical memory
(RAM) plus 4KB.
/proc/keys (since Linux 2.6.10)
See keyrings(7).
/proc/key-users (since Linux 2.6.10)
See keyrings(7).
/proc/kmsg
This file can be used instead of the syslog(2) system call to
read kernel messages. A process must have superuser
privileges to read this file, and only one process should read
this file. This file should not be read if a syslog process
is running which uses the syslog(2) system call facility to
log kernel messages.
Information in this file is retrieved with the dmesg(1)
program.
/proc/kpagecount (since Linux 2.6.25)
This file contains a 64-bit count of the number of times each
physical page frame is mapped, indexed by page frame number
(see the discussion of /proc/[pid]/pagemap).
The /proc/kpagecount file is present only if the
CONFIG_PROC_PAGE_MONITOR kernel configuration option is
enabled.
/proc/kpageflags (since Linux 2.6.25)
This file contains 64-bit masks corresponding to each physical
page frame; it is indexed by page frame number (see the
discussion of /proc/[pid]/pagemap). The bits are as follows:
0 - KPF_LOCKED
1 - KPF_ERROR
2 - KPF_REFERENCED
3 - KPF_UPTODATE
4 - KPF_DIRTY
5 - KPF_LRU
6 - KPF_ACTIVE
7 - KPF_SLAB
8 - KPF_WRITEBACK
9 - KPF_RECLAIM
10 - KPF_BUDDY
11 - KPF_MMAP (since Linux 2.6.31)
12 - KPF_ANON (since Linux 2.6.31)
13 - KPF_SWAPCACHE (since Linux 2.6.31)
14 - KPF_SWAPBACKED (since Linux 2.6.31)
15 - KPF_COMPOUND_HEAD (since Linux 2.6.31)
16 - KPF_COMPOUND_TAIL (since Linux 2.6.31)
16 - 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)
For further details on the meanings of these bits, see the
kernel 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
CONFIG_PROC_PAGE_MONITOR kernel configuration option is
enabled.
/proc/ksyms (Linux 1.1.23-2.5.47)
See /proc/kallsyms.
/proc/loadavg
The first three fields in this file are load average figures
giving the number of jobs in the run queue (state R) or
waiting for disk I/O (state D) averaged over 1, 5, and 15
minutes. They are the same as the load average numbers given
by uptime(1) and other programs. The fourth field consists of
two numbers separated by a slash (/). The first of these is
the number of currently runnable kernel scheduling entities
(processes, threads). The value after the slash is the number
of kernel scheduling entities that currently exist on the
system. The fifth field is the PID of the process that was
most recently created on the system.
/proc/locks
This file shows current file locks (flock(2) and fcntl(2)) and
leases (fcntl(2)). The lslocks(8) command provides a bit more
information about each lock.
/proc/malloc (only up to and including Linux 2.2)
This file is present only if CONFIG_DEBUG_MALLOC was defined
during compilation.
/proc/meminfo
This file reports statistics about memory usage on the system.
It is used by free(1) to report the amount of free and used
memory (both physical and swap) on the system as well as the
shared memory and buffers used by the kernel. Each line of
the file consists of a parameter name, followed by a colon,
the value of the parameter, and an option unit of measurement
(e.g., "kB"). The list below describes the parameter names
and the format specifier required to read the field value.
Except as noted below, all of the fields have been present
since at least Linux 2.6.0. Some fields are displayed only if
the kernel was configured with various options; those
dependencies are noted in the list.
MemTotal %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 everything from Slab is allocated. Bad
things happen when you're out of lowmem.
LowFree %lu
(Starting with Linux 2.6.19, CONFIG_HIGHMEM is
required.) Amount of free lowmem.
MmapCopy %lu (since Linux 2.6.29)
(CONFIG_MMU is required.) [To be documented.]
SwapTotal %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
pressure.
KernelStack %lu (since Linux 2.6.32)
Amount of memory allocated to kernel stacks.
PageTables %lu (since Linux 2.6.18)
Amount of memory dedicated to the lowest level of page
tables.
Quicklists %lu (since Linux 2.6.27)
(CONFIG_QUICKLIST is required.) [To be documented.]
NFS_Unstable %lu (since Linux 2.6.18)
NFS pages sent to the server, but not yet committed to
stable storage.
Bounce %lu (since Linux 2.6.18)
Memory used for block device "bounce buffers".
WritebackTmp %lu (since Linux 2.6.26)
Memory used by FUSE for temporary writeback buffers.
CommitLimit %lu (since Linux 2.6.10)
This is the total amount of memory currently available
to be allocated on the system, expressed in kilobytes.
This limit is adhered to only if strict overcommit
accounting is enabled (mode 2 in
/proc/sys/vm/overcommit_memory). The limit is
calculated according to the formula described under
/proc/sys/vm/overcommit_memory. For further details,
see the kernel source file Documentation/vm/overcommit-
accounting.
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
application. With strict overcommit enabled on the
system (mode 2 in /proc/sys/vm/overcommit_memory),
allocations which would exceed the CommitLimit will not
be permitted. This is useful if one needs to guarantee
that processes will not fail due to lack of memory once
that memory has been successfully allocated.
VmallocTotal %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.
(CONFIG_CMA is required.)
CmaFree %lu (since Linux 3.1)
Free CMA (Contiguous Memory Allocator) pages.
(CONFIG_CMA is required.)
HugePages_Total %lu
(CONFIG_HUGETLB_PAGE is required.) The size of the
pool of huge pages.
HugePages_Free %lu
(CONFIG_HUGETLB_PAGE is required.) The number of huge
pages in the pool that are not yet allocated.
HugePages_Rsvd %lu (since Linux 2.6.17)
(CONFIG_HUGETLB_PAGE is required.) This is the number
of huge pages for which a commitment to allocate from
the pool has been made, but no allocation has yet been
made. These reserved huge pages guarantee that an
application will be able to allocate a huge page from
the pool of huge pages at fault time.
HugePages_Surp %lu (since Linux 2.6.24)
(CONFIG_HUGETLB_PAGE is required.) This is the number
of huge pages in the pool above the value in
/proc/sys/vm/nr_hugepages. The maximum number of
surplus huge pages is controlled by
/proc/sys/vm/nr_overcommit_hugepages.
Hugepagesize %lu
(CONFIG_HUGETLB_PAGE is required.) The size of huge
pages.
DirectMap4k %lu (since Linux 2.6.27)
Number of bytes of RAM linearly mapped by kernel in 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
CONFIG_X86_PAE enabled.)
DirectMap1G %lu (since Linux 2.6.27)
(x86 with CONFIG_X86_64 and CONFIG_X86_DIRECT_GBPAGES
enabled.)
/proc/modules
A text list of the modules that have been loaded by the
system. See also lsmod(8).
/proc/mounts
Before kernel 2.4.19, this file was a list of all the
filesystems currently mounted on the system. With the
introduction of per-process mount namespaces in Linux 2.4.19
(see mount_namespaces(7)), this file became a link to
/proc/self/mounts, which lists the mount points of the
process's own mount namespace. The format of this file is
documented in fstab(5).
/proc/mtrr
Memory Type Range Registers. See the Linux kernel source file
Documentation/mtrr.txt for details.
/proc/net
This directory contains various files and subdirectories
containing information about the networking layer. The files
contain ASCII structures and are, therefore, readable with
cat(1). However, the standard netstat(8) suite provides much
cleaner access to these files.
With the advent of network namespaces, various information
relating to the network stack is virtualized (see
namespaces(7)). Thus, since Linux 2.6.25, /proc/net is a
symbolic link to the directory /proc/self/net, which contains
the same files and directories as listed below. However,
these files and directories now expose information for the
network namespace of which the process is a member.
/proc/net/arp
This holds an ASCII readable dump of the kernel ARP table used
for address resolutions. It will show both dynamically
learned and preprogrammed ARP entries. The format is:
IP address HW type Flags HW address Mask Device
192.168.0.50 0x1 0x2 00:50:BF:25:68:F3 * eth0
192.168.0.250 0x1 0xc 00:00:00:00:00:00 * eth0
Here "IP address" is the IPv4 address of the machine and the
"HW type" is the hardware type of the address from RFC 826.
The flags are the internal flags of the ARP structure (as
defined in /usr/include/linux/if_arp.h) and the "HW address"
is the data link layer mapping for that IP address if it is
known.
/proc/net/dev
The dev pseudo-file contains network device status
information. This gives the number of received and sent
packets, the number of errors and collisions and other basic
statistics. These are used by the ifconfig(8) program to
report device status. The format is:
Inter-| Receive | Transmit
face |bytes packets errs drop fifo frame compressed multicast|bytes packets errs drop fifo colls carrier compressed
lo: 2776770 11307 0 0 0 0 0 0 2776770 11307 0 0 0 0 0 0
eth0: 1215645 2751 0 0 0 0 0 0 1782404 4324 0 0 0 427 0 0
ppp0: 1622270 5552 1 0 0 0 0 0 354130 5669 0 0 0 0 0 0
tap0: 7714 81 0 0 0 0 0 0 7714 81 0 0 0 0 0 0
/proc/net/dev_mcast
Defined in /usr/src/linux/net/core/dev_mcast.c:
indx interface_name dmi_u dmi_g dmi_address
2 eth0 1 0 01005e000001
3 eth1 1 0 01005e000001
4 eth2 1 0 01005e000001
/proc/net/igmp
Internet Group Management Protocol. Defined in
/usr/src/linux/net/core/igmp.c.
/proc/net/rarp
This file uses the same format as the arp file and contains
the current reverse mapping database used to provide rarp(8)
reverse address lookup services. If RARP is not configured
into the kernel, this file will not be present.
/proc/net/raw
Holds a dump of the RAW socket table. Much of the information
is not of use apart from debugging. The "sl" value is the
kernel hash slot for the socket, the "local_address" is the
local address and protocol number pair. "St" is the internal
status of the socket. The "tx_queue" and "rx_queue" are the
outgoing and incoming data queue in terms of kernel memory
usage. The "tr", "tm->when", and "rexmits" fields are not
used by RAW. The "uid" field holds the effective UID of the
creator of the socket.
/proc/net/snmp
This file holds the ASCII data needed for the IP, ICMP, TCP,
and UDP management information bases for an SNMP agent.
/proc/net/tcp
Holds a dump of the TCP socket table. Much of the information
is not of use apart from debugging. The "sl" value is the
kernel hash slot for the socket, the "local_address" is the
local address and port number pair. The "rem_address" is the
remote address and port number pair (if connected). "St" is
the internal status of the socket. The "tx_queue" and
"rx_queue" are the outgoing and incoming data queue in terms
of kernel memory usage. The "tr", "tm->when", and "rexmits"
fields hold internal information of the kernel socket state
and are useful only for debugging. The "uid" field holds the
effective UID of the creator of the socket.
/proc/net/udp
Holds a dump of the UDP socket table. Much of the information
is not of use apart from debugging. The "sl" value is the
kernel hash slot for the socket, the "local_address" is the
local address and port number pair. The "rem_address" is the
remote address and port number pair (if connected). "St" is
the internal status of the socket. The "tx_queue" and
"rx_queue" are the outgoing and incoming data queue in terms
of kernel memory usage. The "tr", "tm->when", and "rexmits"
fields are not used by UDP. The "uid" field holds the
effective UID of the creator of the socket. The format is:
sl local_address rem_address st tx_queue rx_queue tr rexmits tm->when uid
1: 01642C89:0201 0C642C89:03FF 01 00000000:00000001 01:000071BA 00000000 0
1: 00000000:0801 00000000:0000 0A 00000000:00000000 00:00000000 6F000100 0
1: 00000000:0201 00000000:0000 0A 00000000:00000000 00:00000000 00000000 0
/proc/net/unix
Lists the UNIX domain sockets present within the system and
their status. The format is:
Num RefCount Protocol Flags Type St 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
queueing, if used. Each line represents a queue. Queues that
have not been subscribed to by user space are not shown.
1 4207 0 2 65535 0 0 0 1
(1) (2) (3)(4) (5) (6) (7) (8)
The fields in each line are:
(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 information.
(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
initialization and their configuration.
This file has been deprecated in favor of a new /proc
interface for PCI (/proc/bus/pci). It became optional in
Linux 2.2 (available with CONFIG_PCI_OLD_PROC set at kernel
compilation). It became once more nonoptionally enabled in
Linux 2.4. Next, it was deprecated in Linux 2.6 (still
available with CONFIG_PCI_LEGACY_PROC set), and finally
removed altogether since Linux 2.6.17.
/proc/profile (since Linux 2.4)
This file is present only if the kernel was booted with the
profile=1 command-line option. It exposes kernel profiling
information in a binary format for use by readprofile(1).
Writing (e.g., an empty string) to this file resets the
profiling counters; on some architectures, writing a binary
integer "profiling multiplier" of size sizeof(int) sets the
profiling interrupt frequency.
/proc/scsi
A directory with the scsi mid-level pseudo-file and various
SCSI low-level driver directories, which contain a file for
each SCSI host in this system, all of which give the status of
some part of the SCSI IO subsystem. These files contain ASCII
structures and are, therefore, readable with cat(1).
You can also write to some of the files to reconfigure the
subsystem or switch certain features on or off.
/proc/scsi/scsi
This is a listing of all SCSI devices known to the kernel.
The listing is similar to the one seen during bootup. scsi
currently supports only the add-single-device command which
allows root to add a hotplugged device to the list of known
devices.
The command
echo 'scsi add-single-device 1 0 5 0' > /proc/scsi/scsi
will cause host scsi1 to scan on SCSI channel 0 for a device
on ID 5 LUN 0. If there is already a device known on this
address or the address is invalid, an error will be returned.
/proc/scsi/[drivername]
[drivername] can currently be NCR53c7xx, aha152x, aha1542,
aha1740, aic7xxx, buslogic, eata_dma, eata_pio, fdomain,
in2000, pas16, qlogic, scsi_debug, seagate, t128, u15-24f,
ultrastore, or wd7000. These directories show up for all
drivers that registered at least one SCSI HBA. Every
directory contains one file per registered host. Every host-
file is named after the number the host was assigned during
initialization.
Reading these files will usually show driver and host
configuration, statistics, and so on.
Writing to these files allows different things on different
hosts. For example, with the latency and nolatency commands,
root can switch on and off command latency measurement code in
the eata_dma driver. With the lockup and unlock commands,
root can control bus lockups simulated by the scsi_debug
driver.
/proc/self
This directory refers to the process accessing the /proc
filesystem, and is identical to the /proc directory named by
the process ID of the same process.
/proc/slabinfo
Information about kernel caches. See slabinfo(5) for details.
/proc/stat
kernel/system statistics. Varies with architecture. Common
entries include:
cpu 3357 0 4313 1362393
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 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.)
/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 integer or long values, these may be
separated by any of the following whitespace
characters: ' ', '\t', or '\n'. Using other separators
leads to the error EINVAL.
/proc/sys/abi (since Linux 2.4.10)
This directory may contain files with application
binary information. See the Linux kernel source file
Documentation/sysctl/abi.txt for more information.
/proc/sys/debug
This directory may be empty.
/proc/sys/dev
This directory contains device-specific information
(e.g., dev/cdrom/info). On some systems, it may be
empty.
/proc/sys/fs
This directory contains the files and subdirectories
for kernel variables related to filesystems.
/proc/sys/fs/binfmt_misc
Documentation for files in this directory can be found
in the Linux kernel sources in
Documentation/binfmt_misc.txt.
/proc/sys/fs/dentry-state (since Linux 2.2)
This file contains information about the status of the
directory cache (dcache). The file contains six
numbers, nr_dentry, nr_unused, age_limit (age in
seconds), want_pages (pages requested by system) and
two dummy values.
* nr_dentry is the number of allocated dentries (dcache
entries). This field is unused in Linux 2.2.
* nr_unused is the number of unused dentries.
* age_limit is the age in seconds after which dcache
entries can be reclaimed when memory is short.
* want_pages is nonzero when the kernel has called
shrink_dcache_pages() and the dcache isn't pruned
yet.
/proc/sys/fs/dir-notify-enable
This file can be used to disable or enable the dnotify
interface described in fcntl(2) on a system-wide basis.
A value of 0 in this file disables the interface, and a
value of 1 enables it.
/proc/sys/fs/dquot-max
This file shows the maximum number of cached disk quota
entries. On some (2.4) systems, it is not present. If
the number of free cached disk quota entries is very
low and you have some awesome number of simultaneous
system users, you might want to raise the limit.
/proc/sys/fs/dquot-nr
This file shows the number of allocated disk quota
entries and the number of free disk quota entries.
/proc/sys/fs/epoll (since Linux 2.6.28)
This directory contains the file max_user_watches,
which can be used to limit the amount of kernel memory
consumed by the epoll interface. For further details,
see epoll(7).
/proc/sys/fs/file-max
This file defines a system-wide limit on the number of
open files for all processes. System calls that fail
when encountering this limit fail with the error
ENFILE. (See also setrlimit(2), which can be used by a
process to set the per-process limit, RLIMIT_NOFILE, on
the number of files it may open.) If you get lots of
error messages in the kernel log about running out of
file handles (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 system needs to prune the inode list instead of
allocating more; since Linux 2.4, this field is a dummy
value (always zero).
/proc/sys/fs/inotify (since Linux 2.6.13)
This directory contains files max_queued_events,
max_user_instances, and max_user_watches, that can be
used to limit the amount of kernel memory consumed by
the inotify interface. For further details, see
inotify(7).
/proc/sys/fs/lease-break-time
This file specifies the grace period that the kernel
grants to a process holding a file lease (fcntl(2))
after it has sent a signal to that process notifying it
that another process is waiting to open the file. If
the lease holder does not remove or downgrade the lease
within this grace period, the kernel forcibly breaks
the lease.
/proc/sys/fs/leases-enable
This file can be used to enable or disable file leases
(fcntl(2)) on a system-wide basis. If this file
contains the value 0, leases are disabled. A nonzero
value enables leases.
/proc/sys/fs/mount-max (since Linux 4.9)
The value in this file specifies the maximum number of
mounts that may exist in a mount namespace. The
default value in this file is 100,000.
/proc/sys/fs/mqueue (since Linux 2.6.6)
This directory contains files msg_max, msgsize_max, and
queues_max, controlling the resources used by POSIX
message queues. See mq_overview(7) for details.
/proc/sys/fs/nr_open (since Linux 2.6.25)
This file imposes 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 behavior before Linux 3.6). When the value
in this file is 1, a hard link can be created to a
target file only if one of the following conditions is
true:
* The calling process has the CAP_FOWNER capability in
its user namespace and the file UID has a mapping in
the namespace.
* The filesystem UID of the process creating the link
matches the owner (UID) of the target file (as
described in credentials(7), a process's filesystem
UID is normally the same as its effective UID).
* All of the following conditions are true:
· the target is a regular file;
· the target file does not have its set-user-ID
mode bit enabled;
· the target file does not have both its set-
group-ID and group-executable mode bits enabled;
and
· the caller has permission to read and write the
target file (either via the file's permissions
mask or because it has suitable capabilities).
The default value in this file is 0. Setting the value
to 1 prevents a longstanding class of security issues
caused by hard-link-based time-of-check, time-of-use
races, most commonly seen in world-writable directories
such as /tmp. The common method of exploiting this
flaw is to cross privilege boundaries when following a
given hard link (i.e., a root process follows a hard
link created by another user). Additionally, on
systems without separated partitions, this stops
unauthorized users from "pinning" vulnerable set-user-
ID and set-group-ID files against being upgraded by the
administrator, or linking to special files.
/proc/sys/fs/protected_symlinks (since Linux 3.6)
When the value in this file is 0, no restrictions are
placed on following symbolic links (i.e., this is the
historical behavior before Linux 3.6). When the value
in this file is 1, symbolic links are followed only in
the following circumstances:
* the filesystem UID of the process following the link
matches the owner (UID) of the symbolic link (as
described in credentials(7), a process's filesystem
UID is normally the same as its effective UID);
* the link is not in a sticky world-writable
directory; or
* the symbolic link and its parent directory have the
same owner (UID)
A system call that fails to follow a symbolic link
because of the above restrictions returns the error
EACCES in errno.
The default value in this file is 0. Setting the value
to 1 avoids a longstanding class of security issues
based on time-of-check, time-of-use races when
accessing symbolic links.
/proc/sys/fs/suid_dumpable (since Linux 2.6.13)
The value in this file is assigned to a process's
"dumpable" flag in the circumstances described in
prctl(2). In effect, the value in this file determines
whether core dump files are produced for set-user-ID or
otherwise protected/tainted binaries. The "dumpable"
setting also affects the ownership of files in a
process's /proc/[pid] directory, as described above.
Three different integer values can be specified:
0 (default)
This provides the traditional (pre-Linux 2.6.13)
behavior. A core dump will not be produced for
a process which has changed credentials (by
calling seteuid(2), setgid(2), or similar, or by
executing a set-user-ID or set-group-ID program)
or whose binary does not have read permission
enabled.
1 ("debug")
All processes dump core when possible. (Reasons
why a process might nevertheless not dump core
are described in core(5).) The core dump is
owned by the filesystem user ID of the dumping
process and no security is applied. This is
intended for system debugging situations only:
this mode is insecure because it allows
unprivileged users to examine the memory
contents of privileged processes.
2 ("suidsafe")
Any binary which normally would not be dumped
(see "0" above) is dumped readable by root only.
This allows the user to remove the core dump
file but not to read it. For security reasons
core dumps in this mode will not overwrite one
another or other files. This mode is
appropriate when administrators are attempting
to debug problems in a normal environment.
Additionally, since Linux 3.6,
/proc/sys/kernel/core_pattern must either be an
absolute pathname or a pipe command, as detailed
in core(5). Warnings will be written to the
kernel log if core_pattern does not follow these
rules, and no core dump will be produced.
For details of the effect of a process's "dumpable"
setting on ptrace access mode checking, see ptrace(2).
/proc/sys/fs/super-max
This file controls the maximum number of superblocks,
and thus the maximum number of mounted filesystems the
kernel can have. You need increase only super-max if
you need to mount more filesystems than the current
value in super-max allows you to.
/proc/sys/fs/super-nr
This file contains the number of filesystems currently
mounted.
/proc/sys/kernel
This directory contains files controlling a range of
kernel parameters, as described below.
/proc/sys/kernel/acct
This file contains three numbers: highwater, lowwater,
and frequency. If BSD-style process accounting is
enabled, these values control its behavior. If free
space on filesystem where the log lives goes below
lowwater percent, accounting suspends. If free space
gets above highwater percent, accounting resumes.
frequency determines how often the kernel checks the
amount of free space (value is in seconds). Default
values are 4, 2 and 30. That is, suspend accounting if
2% or less space is free; resume it if 4% or more space
is free; consider information about amount of free
space valid for 30 seconds.
/proc/sys/kernel/auto_msgmni (Linux 2.6.27 to 3.18)
From Linux 2.6.27 to 3.18, this file was used to
control recomputing of the value in
/proc/sys/kernel/msgmni upon the addition or removal of
memory or upon IPC namespace creation/removal. Echoing
"1" into this file enabled msgmni automatic recomputing
(and triggered a recomputation of msgmni based on the
current amount of available memory and number of IPC
namespaces). Echoing "0" disabled automatic
recomputing. (Automatic recomputing was also disabled
if a value was explicitly assigned to
/proc/sys/kernel/msgmni.) The default value in
auto_msgmni was 1.
Since Linux 3.19, the content of this file has no
effect (because msgmni defaults to near the maximum
value possible), and reads from this file always return
the value "0".
/proc/sys/kernel/cap_last_cap (since Linux 3.2)
See capabilities(7).
/proc/sys/kernel/cap-bound (from Linux 2.2 to 2.6.24)
This file holds the value of the kernel capability
bounding set (expressed as a signed decimal number).
This set is ANDed against the capabilities permitted to
a process during execve(2). Starting with Linux
2.6.25, the system-wide capability bounding set
disappeared, and was replaced by a per-thread bounding
set; see capabilities(7).
/proc/sys/kernel/core_pattern
See core(5).
/proc/sys/kernel/core_pipe_limit
See core(5).
/proc/sys/kernel/core_uses_pid
See core(5).
/proc/sys/kernel/ctrl-alt-del
This file controls the handling of Ctrl-Alt-Del from
the keyboard. When the value in this file is 0, Ctrl-
Alt-Del is trapped and sent to the init(1) program to
handle a graceful restart. When the value is greater
than zero, Linux's reaction to a Vulcan Nerve Pinch
(tm) will be an immediate reboot, without even syncing
its dirty buffers. Note: when a program (like dosemu)
has the keyboard in "raw" mode, the ctrl-alt-del is
intercepted by the program before it ever reaches the
kernel tty layer, and it's up to the program to decide
what to do with it.
/proc/sys/kernel/dmesg_restrict (since Linux 2.6.37)
The value in this file determines who can see kernel
syslog contents. A value of 0 in this file imposes no
restrictions. If the value is 1, only privileged users
can read the kernel syslog. (See syslog(2) for more
details.) Since Linux 3.4, only users with the
CAP_SYS_ADMIN capability may change the value in this
file.
/proc/sys/kernel/domainname and /proc/sys/kernel/hostname
can be used to set the NIS/YP domainname and the
hostname of your box in exactly the same way as the
commands domainname(1) and hostname(1), that is:
# echo 'darkstar' > /proc/sys/kernel/hostname
# echo 'mydomain' > /proc/sys/kernel/domainname
has the same effect as
# hostname 'darkstar'
# domainname 'mydomain'
Note, however, that the classic darkstar.frop.org has
the hostname "darkstar" and DNS (Internet Domain Name
Server) domainname "frop.org", not to be confused with
the NIS (Network Information Service) or YP (Yellow
Pages) domainname. These two domain names are in
general different. For a detailed discussion see the
hostname(1) man page.
/proc/sys/kernel/hotplug
This file contains the path for the hotplug policy
agent. The default value in this file is
/sbin/hotplug.
/proc/sys/kernel/htab-reclaim
(PowerPC only) If this file is set to a nonzero value,
the PowerPC htab (see kernel file
Documentation/powerpc/ppc_htab.txt) is pruned each time
the system hits the idle loop.
/proc/sys/kernel/keys/*
This directory contains various files that define
parameters and limits for the key-management facility.
These files are described in keyrings(7).
/proc/sys/kernel/kptr_restrict (since Linux 2.6.38)
The value in this file determines whether kernel
addresses are exposed via /proc files and other
interfaces. A value of 0 in this file imposes no
restrictions. If the value is 1, kernel pointers
printed using the %pK format specifier will be replaced
with zeros unless the user has the CAP_SYSLOG
capability. If the value is 2, kernel pointers printed
using the %pK format specifier will be replaced with
zeros regardless of the user's capabilities. The
initial default value for this file was 1, but the
default was changed to 0 in Linux 2.6.39. Since Linux
3.4, only users with the CAP_SYS_ADMIN capability can
change the value in this file.
/proc/sys/kernel/l2cr
(PowerPC only) This file contains a flag that controls
the L2 cache of G3 processor boards. If 0, the cache
is disabled. Enabled if nonzero.
/proc/sys/kernel/modprobe
This file contains the 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
CONFIG_MODULES option enabled.
/proc/sys/kernel/msgmax (since Linux 2.2)
This file defines a system-wide limit specifying the
maximum number of bytes in a single message written on
a System V message queue.
/proc/sys/kernel/msgmni (since Linux 2.4)
This file defines the system-wide limit on the number
of message queue identifiers. See also
/proc/sys/kernel/auto_msgmni.
/proc/sys/kernel/msgmnb (since Linux 2.2)
This file defines a system-wide parameter used to
initialize the msg_qbytes setting for subsequently
created message queues. The msg_qbytes setting
specifies the maximum number of bytes that may be
written to the message queue.
/proc/sys/kernel/ngroups_max (since Linux 2.6.4)
This is a read-only file that displays the upper limit
on the number of a process's group memberships.
/proc/sys/kernel/ostype and /proc/sys/kernel/osrelease
These files give substrings of /proc/version.
/proc/sys/kernel/overflowgid and /proc/sys/kernel/overflowuid
These files duplicate the files
/proc/sys/fs/overflowgid and /proc/sys/fs/overflowuid.
/proc/sys/kernel/panic
This file gives read/write access to the kernel
variable panic_timeout. If this is zero, the kernel
will loop on a panic; if nonzero, it indicates that the
kernel should autoreboot after this number of seconds.
When you use the software watchdog device driver, the
recommended setting is 60.
/proc/sys/kernel/panic_on_oops (since Linux 2.5.68)
This file controls the kernel's behavior when an oops
or BUG is encountered. If this file contains 0, then
the system tries to continue operation. If it contains
1, then the system delays a few seconds (to give klogd
time to record the oops output) and then panics. If
the /proc/sys/kernel/panic file is also nonzero, then
the machine will be rebooted.
/proc/sys/kernel/pid_max (since Linux 2.5.34)
This file specifies the value at which PIDs wrap around
(i.e., the value in this file is one greater than the
maximum PID). PIDs greater than this value are not
allocated; thus, the value in this file also acts as a
system-wide limit on the total number of processes and
threads. The default value for this file, 32768,
results in the same range of PIDs as on earlier
kernels. On 32-bit platforms, 32768 is the maximum
value for pid_max. On 64-bit systems, pid_max can be
set to any value up to 2^22 (PID_MAX_LIMIT,
approximately 4 million).
/proc/sys/kernel/powersave-nap (PowerPC only)
This file contains a flag. If set, Linux-PPC will use
the "nap" mode of powersaving, otherwise the "doze"
mode will be used.
/proc/sys/kernel/printk
See syslog(2).
/proc/sys/kernel/pty (since Linux 2.6.4)
This directory contains two files relating to the
number of UNIX 98 pseudoterminals (see pts(4)) on the
system.
/proc/sys/kernel/pty/max
This file defines the maximum number of
pseudoterminals.
/proc/sys/kernel/pty/nr
This read-only file indicates how many pseudoterminals
are currently in use.
/proc/sys/kernel/random
This directory contains various parameters controlling
the operation of the file /dev/random. See random(4)
for further information.
/proc/sys/kernel/random/uuid (since Linux 2.4)
Each read from this read-only file returns a randomly
generated 128-bit UUID, as a string in the standard
UUID format.
/proc/sys/kernel/randomize_va_space (since Linux 2.6.12)
Select the address space layout randomization (ASLR)
policy for the system (on architectures that support
ASLR). Three values are supported for this file:
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
Documentation/initrd.txt.
/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/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 possible to create shared memory
segments that exist independently of any attached
process.
The effect is as though a shmctl(2) IPC_RMID is
performed on all existing segments as well as all
segments created in the future (until this file is
reset to 0). Note that existing segments that are
attached to no process will be immediately destroyed
when this file is set to 1. Setting this option will
also destroy segments that were created, but never
attached, upon termination of the process that created
the segment with shmget(2).
Setting this file to 1 provides a way of ensuring that
all System V shared memory segments are counted against
the resource usage and resource limits (see the
description of RLIMIT_AS in getrlimit(2)) of at least
one process.
Because setting this file to 1 produces behavior that
is nonstandard and could also break existing
applications, the default value in this file is 0. Set
this file to 1 only if you have a good understanding of
the semantics of the applications using System V shared
memory on your system.
/proc/sys/kernel/shmall (since Linux 2.2)
This file contains the system-wide limit on the total
number of pages of System V shared memory.
/proc/sys/kernel/shmmax (since Linux 2.2)
This file can be used to query and set the run-time
limit on the maximum (System V IPC) shared memory
segment size that can be created. Shared memory
segments up to 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 overwrite 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 buffer will be ignored.
Writes to numeric /proc/sys entries must always be
at file offset 0 and the value must be fully
contained in the buffer provided to write(2).
/proc/sys/kernel/sysrq
This file controls the functions allowed to be invoked
by the SysRq key. By default, the file contains 1
meaning that every possible SysRq request is allowed
(in older kernel versions, SysRq was disabled by
default, and you were required to specifically enable
it at run-time, but this is not the case any more).
Possible values in this file are:
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 configuration option is enabled. For further
details see the Linux kernel source file
Documentation/sysrq.txt.
/proc/sys/kernel/version
This file contains a string such as:
#5 Wed Feb 25 21:49:24 MET 1998
The "#5" means that this is the fifth kernel built from
this source base and the date following it indicates
the time the kernel was built.
/proc/sys/kernel/threads-max (since Linux 2.3.11)
This file specifies the system-wide limit on the number
of threads (tasks) that can be created on the system.
Since Linux 4.1, the value that can be written to
threads-max is bounded. The minimum value that can be
written is 20. The maximum value that can be written
is given by the constant FUTEX_TID_MASK (0x3fffffff).
If a value outside of this range is written to threads-
max, the error EINVAL occurs.
The value written is checked against the available RAM
pages. If the thread structures would occupy too much
(more than 1/8th) of the available RAM pages, threads-
max is reduced accordingly.
/proc/sys/kernel/yama/ptrace_scope (since Linux 3.5)
See ptrace(2).
/proc/sys/kernel/zero-paged (PowerPC only)
This file contains a flag. When enabled (nonzero),
Linux-PPC will pre-zero pages in the idle loop,
possibly speeding up get_free_pages.
/proc/sys/net
This directory contains networking stuff. Explanations
for some of the files under this directory can be found
in tcp(7) and ip(7).
/proc/sys/net/core/bpf_jit_enable
See bpf(2).
/proc/sys/net/core/somaxconn
This file defines a ceiling value for the backlog
argument of listen(2); see the listen(2) manual page
for details.
/proc/sys/proc
This directory may be empty.
/proc/sys/sunrpc
This directory supports Sun remote procedure call for
network filesystem (NFS). On some systems, it is not
present.
/proc/sys/user (since Linux 4.9)
See namespaces(7).
/proc/sys/vm
This directory contains files for memory management
tuning, buffer and cache management.
/proc/sys/vm/admin_reserve_kbytes (since Linux 3.10)
This file defines the amount of free memory (in KiB) on
the system that that should be reserved for users with
the capability CAP_SYS_ADMIN.
The default value in this file is the minimum of [3% of
free pages, 8MiB] expressed as KiB. The default is
intended to provide enough for the superuser to log in
and kill a process, if necessary, under the default
overcommit 'guess' mode (i.e., 0 in
/proc/sys/vm/overcommit_memory).
Systems running in "overcommit never" mode (i.e., 2 in
/proc/sys/vm/overcommit_memory) should increase the
value in this file to account for the full virtual
memory size of the programs used to recover (e.g.,
login(1) ssh(1), and top(1)) Otherwise, the superuser
may not be able to log in to recover the system. For
example, on x86_64 a suitable value is 131072 (128MiB
reserved).
Changing the value in this file takes effect whenever
an application requests memory.
/proc/sys/vm/compact_memory (since Linux 2.6.35)
When 1 is written to this file, all zones are compacted
such that free memory is available in contiguous blocks
where possible. The effect of this action can be seen
by examining /proc/buddyinfo.
Present only if the kernel was configured with
CONFIG_COMPACTION.
/proc/sys/vm/drop_caches (since Linux 2.6.16)
Writing to this file causes the kernel to drop clean
caches, dentries, and inodes from memory, causing that
memory to become free. This can be useful for memory
management testing and performing reproducible
filesystem benchmarks. Because writing to this file
causes the benefits of caching to be lost, it can
degrade overall system performance.
To free pagecache, use:
echo 1 > /proc/sys/vm/drop_caches
To free dentries and inodes, use:
echo 2 > /proc/sys/vm/drop_caches
To free pagecache, dentries and inodes, use:
echo 3 > /proc/sys/vm/drop_caches
Because writing to this file is a nondestructive
operation and dirty objects are not freeable, the user
should run sync(1) first.
/proc/sys/vm/legacy_va_layout (since Linux 2.6.9)
If nonzero, this disables the new 32-bit memory-mapping
layout; the kernel will use the legacy (2.4) layout for
all processes.
/proc/sys/vm/memory_failure_early_kill (since Linux 2.6.32)
Control how to kill processes when an uncorrected
memory error (typically a 2-bit error in a memory
module) that cannot be handled by the kernel is
detected in the background by hardware. In some cases
(like the page still having a valid copy on disk), the
kernel will handle the failure transparently without
affecting any applications. But if there is no other
up-to-date copy of the data, it will kill processes to
prevent any data corruptions from propagating.
The file has one of the following values:
1: Kill all processes that have the corrupted-and-not-
reloadable page mapped as soon as the corruption is
detected. Note that this is not supported for a
few types of pages, such as kernel internally
allocated data or the swap cache, but works for the
majority of user pages.
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_MEMORY_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_MEMORY_FAILURE.
/proc/sys/vm/oom_dump_tasks (since Linux 2.6.25)
Enables a system-wide task dump (excluding kernel
threads) to be produced when the kernel performs an
OOM-killing. The dump includes the following
information for each task (thread, process): thread ID,
real user ID, thread group ID (process ID), virtual
memory size, resident set size, the CPU that the task
is scheduled on, oom_adj score (see the description of
/proc/[pid]/oom_adj), and command name. This is
helpful to determine why the OOM-killer was invoked and
to identify the rogue task that caused it.
If this contains the value zero, this information is
suppressed. On very large systems with thousands of
tasks, it may not be feasible to dump the memory state
information for each one. Such systems should not be
forced to incur a performance penalty in OOM situations
when the information may not be desired.
If this is set to nonzero, this information is shown
whenever the OOM-killer actually kills a memory-hogging
task.
The default value is 0.
/proc/sys/vm/oom_kill_allocating_task (since Linux 2.6.24)
This enables or disables killing the OOM-triggering
task in out-of-memory situations.
If this is set to zero, the OOM-killer will scan
through the entire tasklist and select a task based on
heuristics to kill. This normally selects a rogue
memory-hogging task that frees up a large amount of
memory when killed.
If this is set to nonzero, the OOM-killer simply kills
the task that triggered the out-of-memory condition.
This avoids a possibly expensive tasklist scan.
If /proc/sys/vm/panic_on_oom is nonzero, it takes
precedence over whatever value is used in
/proc/sys/vm/oom_kill_allocating_task.
The default value is 0.
/proc/sys/vm/overcommit_kbytes (since Linux 3.14)
This writable file provides an alternative to
/proc/sys/vm/overcommit_ratio for controlling the
CommitLimit when /proc/sys/vm/overcommit_memory has the
value 2. It allows the amount of memory overcommitting
to be specified as an absolute value (in kB), rather
than as a percentage, as is done with overcommit_ratio.
This allows for finer-grained control of CommitLimit on
systems with extremely large memory sizes.
Only one of overcommit_kbytes or overcommit_ratio can
have an effect: if overcommit_kbytes has a nonzero
value, then it is used to calculate CommitLimit,
otherwise overcommit_ratio is used. Writing a value to
either of these files causes the value in the other
file to be set to zero.
/proc/sys/vm/overcommit_memory
This file contains the kernel virtual memory accounting
mode. Values are:
0: heuristic overcommit (this is the default)
1: always overcommit, never check
2: always check, never overcommit
In mode 0, calls of mmap(2) with MAP_NORESERVE are not
checked, and the default check is very weak, leading to
the risk of getting a process "OOM-killed".
In mode 1, the kernel pretends there is always enough
memory, until memory actually runs out. One use case
for this mode is scientific computing applications that
employ large sparse arrays. In Linux kernel versions
before 2.6.0, any nonzero value implies mode 1.
In mode 2 (available since Linux 2.6), the total
virtual address space that can be allocated
(CommitLimit in /proc/meminfo) is calculated as
CommitLimit = (total_RAM - total_huge_TLB) *
overcommit_ratio / 100 + total_swap
where:
* total_RAM is the total amount of RAM on the
system;
* total_huge_TLB is the amount of memory set
aside for huge pages;
* overcommit_ratio is the value in
/proc/sys/vm/overcommit_ratio; and
* total_swap is the amount of swap space.
For example, on a system with 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 situation.
If this file is set to the value 0, the kernel's OOM-
killer will kill some rogue process. Usually, the OOM-
killer is able to kill a rogue process and the system
will survive.
If this file is set to the value 1, then the kernel
normally panics when out-of-memory happens. However,
if a process limits allocations to certain nodes using
memory policies (mbind(2) MPOL_BIND) or cpusets
(cpuset(7)) and those nodes reach memory exhaustion
status, one process may be killed by the OOM-killer.
No panic occurs in this case: because other nodes'
memory may be free, this means the system as a whole
may not have reached an out-of-memory situation yet.
If this file is set to the value 2, the kernel always
panics when an out-of-memory condition occurs.
The default value is 0. 1 and 2 are for failover of
clustering. Select either according to your policy of
failover.
/proc/sys/vm/swappiness
The value in this file controls how aggressively the
kernel will swap memory pages. Higher values increase
aggressiveness, lower values decrease aggressiveness.
The default value is 60.
/proc/sys/vm/user_reserve_kbytes (since Linux 3.10)
Specifies an amount of memory (in KiB) to reserve for
user processes, This is intended to prevent a user from
starting a single memory hogging process, such that
they cannot recover (kill the hog). The value in this
file has an effect only when
/proc/sys/vm/overcommit_memory is set to 2 ("overcommit
never" mode). In this case, the system reserves an
amount of memory that is the minimum of [3% of current
process size, user_reserve_kbytes].
The default value in this file is the minimum of [3% of
free pages, 128MiB] expressed as KiB.
If the value in this file is set to zero, then a user
will be allowed to allocate all free memory with a
single process (minus the amount reserved by
/proc/sys/vm/admin_reserve_kbytes). Any subsequent
attempts to execute a command will result in "fork:
Cannot allocate memory".
Changing the value in this file takes effect whenever
an application requests memory.
/proc/sysrq-trigger (since Linux 2.4.21)
Writing a character to this file triggers the same
SysRq function as typing ALT-SysRq-<character> (see the
description of /proc/sys/kernel/sysrq). This file is
normally writable only by root. For further details
see the Linux kernel source file
Documentation/sysrq.txt.
/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
filesystem, and is identical to the
/proc/self/task/[tid] directory named by the process
thread ID ([tid]) of the same thread.
/proc/timer_list (since Linux 2.6.21)
This read-only file exposes a list of all currently
pending (high-resolution) timers, all clock-event
sources, and their parameters in a human-readable form.
/proc/timer_stats (since Linux 2.6.21)
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.
/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 (seconds), and the amount of time spent in idle
process (seconds).
/proc/version
This string identifies the kernel version that is
currently running. It includes the contents of
/proc/sys/kernel/ostype, /proc/sys/kernel/osrelease and
/proc/sys/kernel/version. For example:
Linux version 1.0.9 (quinlan@phaze) #1 Sat May 14 01:51:54 EDT 1994
/proc/vmstat (since Linux 2.6.0)
This file displays various virtual memory statistics.
Each line of this file contains a single name-value
pair, delimited by white space. Some files are present
only if the kernel was configured with suitable
options. (In some cases, the options required for
particular files have changed across kernel versions,
so they are not listed here. Details can be found by
consulting the kernel source code.) The following
fields may be present:
nr_free_pages (since Linux 2.6.31)
nr_alloc_batch (since Linux 3.12)
nr_inactive_anon (since Linux 2.6.28)
nr_active_anon (since Linux 2.6.28)
nr_inactive_file (since Linux 2.6.28)
nr_active_file (since Linux 2.6.28)
nr_unevictable (since Linux 2.6.28)
nr_mlock (since Linux 2.6.28)
nr_anon_pages (since Linux 2.6.18)
nr_mapped (since Linux 2.6.0)
nr_file_pages (since Linux 2.6.18)
nr_dirty (since Linux 2.6.0)
nr_writeback (since Linux 2.6.0)
nr_slab_reclaimable (since Linux 2.6.19)
nr_slab_unreclaimable (since Linux 2.6.19)
nr_page_table_pages (since Linux 2.6.0)
nr_kernel_stack (since Linux 2.6.32)
Amount of memory allocated to kernel stacks.
nr_unstable (since Linux 2.6.0)
nr_bounce (since Linux 2.6.12)
nr_vmscan_write (since Linux 2.6.19)
nr_vmscan_immediate_reclaim (since Linux 3.2)
nr_writeback_temp (since Linux 2.6.26)
nr_isolated_anon (since Linux 2.6.32)
nr_isolated_file (since Linux 2.6.32)
nr_shmem (since Linux 2.6.32)
Pages used by shmem and tmpfs(5).
nr_dirtied (since Linux 2.6.37)
nr_written (since Linux 2.6.37)
nr_pages_scanned (since Linux 3.17)
numa_hit (since Linux 2.6.18)
numa_miss (since Linux 2.6.18)
numa_foreign (since Linux 2.6.18)
numa_interleave (since Linux 2.6.18)
numa_local (since Linux 2.6.18)
numa_other (since Linux 2.6.18)
workingset_refault (since Linux 3.15)
workingset_activate (since Linux 3.15)
workingset_nodereclaim (since Linux 3.15)
nr_anon_transparent_hugepages (since Linux 2.6.38)
nr_free_cma (since Linux 3.7)
Number of free CMA (Contiguous Memory Allocator)
pages.
nr_dirty_threshold (since Linux 2.6.37)
nr_dirty_background_threshold (since Linux 2.6.37)
pgpgin (since Linux 2.6.0)
pgpgout (since Linux 2.6.0)
pswpin (since Linux 2.6.0)
pswpout (since Linux 2.6.0)
pgalloc_dma (since Linux 2.6.5)
pgalloc_dma32 (since Linux 2.6.16)
pgalloc_normal (since Linux 2.6.5)
pgalloc_high (since Linux 2.6.5)
pgalloc_movable (since Linux 2.6.23)
pgfree (since Linux 2.6.0)
pgactivate (since Linux 2.6.0)
pgdeactivate (since Linux 2.6.0)
pgfault (since Linux 2.6.0)
pgmajfault (since Linux 2.6.0)
pgrefill_dma (since Linux 2.6.5)
pgrefill_dma32 (since Linux 2.6.16)
pgrefill_normal (since Linux 2.6.5)
pgrefill_high (since Linux 2.6.5)
pgrefill_movable (since Linux 2.6.23)
pgsteal_kswapd_dma (since Linux 3.4)
pgsteal_kswapd_dma32 (since Linux 3.4)
pgsteal_kswapd_normal (since Linux 3.4)
pgsteal_kswapd_high (since Linux 3.4)
pgsteal_kswapd_movable (since Linux 3.4)
pgsteal_direct_dma
pgsteal_direct_dma32 (since Linux 3.4)
pgsteal_direct_normal (since Linux 3.4)
pgsteal_direct_high (since Linux 3.4)
pgsteal_direct_movable (since Linux 2.6.23)
pgscan_kswapd_dma
pgscan_kswapd_dma32 (since Linux 2.6.16)
pgscan_kswapd_normal (since Linux 2.6.5)
pgscan_kswapd_high
pgscan_kswapd_movable (since Linux 2.6.23)
pgscan_direct_dma
pgscan_direct_dma32 (since Linux 2.6.16)
pgscan_direct_normal
pgscan_direct_high
pgscan_direct_movable (since Linux 2.6.23)
pgscan_direct_throttle (since Linux 3.6)
zone_reclaim_failed (since linux 2.6.31)
pginodesteal (since linux 2.6.0)
slabs_scanned (since linux 2.6.5)
kswapd_inodesteal (since linux 2.6.0)
kswapd_low_wmark_hit_quickly (since 2.6.33)
kswapd_high_wmark_hit_quickly (since 2.6.33)
pageoutrun (since Linux 2.6.0)
allocstall (since Linux 2.6.0)
pgrotated (since Linux 2.6.0)
drop_pagecache (since Linux 3.15)
drop_slab (since Linux 3.15)
numa_pte_updates (since Linux 3.8)
numa_huge_pte_updates (since Linux 3.13)
numa_hint_faults (since Linux 3.8)
numa_hint_faults_local (since Linux 3.8)
numa_pages_migrated (since Linux 3.8)
pgmigrate_success (since Linux 3.8)
pgmigrate_fail (since Linux 3.8)
compact_migrate_scanned (since Linux 3.8)
compact_free_scanned (since Linux 3.8)
compact_isolated (since Linux 3.8)
compact_stall (since Linux 2.6.35)
See the kernel source file
Documentation/vm/transhuge.txt.
compact_fail (since Linux 2.6.35)
See the kernel source file
Documentation/vm/transhuge.txt.
compact_success (since Linux 2.6.35)
See the kernel source file
Documentation/vm/transhuge.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/transhuge.txt.
thp_fault_fallback (since Linux 2.6.39)
See the kernel source file
Documentation/vm/transhuge.txt.
thp_collapse_alloc (since Linux 2.6.39)
See the kernel source file
Documentation/vm/transhuge.txt.
thp_collapse_alloc_failed (since Linux 2.6.39)
See the kernel source file
Documentation/vm/transhuge.txt.
thp_split (since Linux 2.6.39)
See the kernel source file
Documentation/vm/transhuge.txt.
thp_zero_page_alloc (since Linux 3.8)
See the kernel source file
Documentation/vm/transhuge.txt.
thp_zero_page_alloc_failed (since Linux 3.8)
See the kernel source file
Documentation/vm/transhuge.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 useful for analyzing virtual memory behavior.
Many strings (i.e., the environment and command line) are in the
internal 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.
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), hier(7),
namespaces(7), time(7), arp(8), hdparm(8), ifconfig(8), lsmod(8),
lspci(8), mount(8), netstat(8), procinfo(8), route(8), sysctl(8)
The Linux kernel source files: Documentation/filesystems/proc.txt
Documentation/sysctl/fs.txt, Documentation/sysctl/kernel.txt,
Documentation/sysctl/net.txt, and Documentation/sysctl/vm.txt.
This page is part of release 4.12 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/.
Linux 2017-05-03 PROC(5)
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