NAME¶
proc - process information pseudo-filesystem
DESCRIPTION¶
The
proc filesystem is a pseudo-filesystem which provides an interface to
kernel data structures. It is commonly mounted at
/proc. Most of it is
read-only, but some files allow kernel variables to be changed.
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 such subdirectory contains
the following pseudo-files and directories.
- /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).
- /proc/[pid]/cgroup (since Linux 2.6.24)
- This file describes control groups to which the process/task belongs. For
each cgroup hierarchy there is one entry containing colon-separated fields
of the form:
5:cpuacct,cpu,cpuset:/daemons
- The colon-separated fields are, from left to right:
- 1.
- hierarchy ID number
- 2.
- set of subsystems bound to the hierarchy
- 3.
- control group in the hierarchy to which the process belongs
- This file is present only if the CONFIG_CGROUPS kernel
configuration option is enabled.
- /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.
A further value can be written to affect a different bit:
- 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.
- 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)).
- /proc/[pid]/environ
- This file contains the environment for the process. 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
- /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 as is being run by process [pid]. 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)).
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 epoll_create(2), eventfd(2),
inotify_init(2), signalfd(2), and timerfd(2)), the
entry will be a symbolic link with contents of the form
anon_inode:<file-type>
In some cases, 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 will take a filename as a command-line argument, but will not
take input from standard input if no argument is supplied, or that write
to a file named as a command-line argument, but will not send their output
to standard output if no argument is supplied, can nevertheless be made to
use standard input or standard out using /proc/[pid]/fd. 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 ...
- /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 contents of each file
can be read to obtain information about the corresponding file descriptor,
for example:
$ cat /proc/12015/fdinfo/4
pos: 1000
flags: 01002002
The pos field is a decimal number showing the current file offset.
The flags field is an octal number that displays the file access
mode and file status flags (see open(2)).
The files in this directory are readable only by the owner of the
process.
- /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.
- /proc/[pid]/gid_map (since Linux 3.5)
- See the description of /proc/[pid]/uid_map.
- /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.
- /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.
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.
- [heap]
- The process's heap.
- If the pathname field is blank, this is an anonymous mapping as
obtained via the mmap(2) function. 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).
- /proc/[pid]/mountinfo (since Linux 2.6.26)
- This file contains information about mount points. It 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: unique identifier of the mount (may be reused after
umount(2)).
- (2)
- parent ID: ID of parent mount (or of self for the top of the mount
tree).
- (3)
- major:minor: value of st_dev for files on filesystem (see
stat(2)).
- (4)
- root: root of the mount within the filesystem.
- (5)
- mount point: mount point relative to the process's root.
- (6)
- mount options: per-mount options.
- (7)
- optional fields: zero or more fields of the form
"tag[:value]".
- (8)
- separator: marks the end of the optional fields.
- (9)
- filesystem type: name of filesystem in the form
"type[.subtype]".
- (10)
- mount source: filesystem-specific information or "none".
- (11)
- super options: per-superblock options.
- Parsers should ignore all unrecognized optional fields. Currently the
possible optional fields are:
- shared:X
- mount is shared in peer group X
- master:X
- mount is slave to peer group X
- propagate_from:X
- mount is slave and receives propagation from peer group X (*)
- unbindable
- mount is unbindable
- (*) X is the closest dominant peer group under the process's root. If X is
the immediate master of the mount, or if there is no dominant peer group
under the same root, then only the "master:X" field is present
and not the "propagate_from:X" field.
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 is a list of all the filesystems currently mounted in the process's
mount namespace. 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 readable, and
poll(2) and epoll_wait(2) mark the file as having an error
condition. See namespaces(7) for more information.
- /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. 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.
See namespaces(7) for more information.
- /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 a 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.
- /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.
- /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/*.
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)).
- /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
Swap: 0 kB
KernelPageSize: 4 kB
MMUPageSize: 4 kB
Locked: 0 kB
The first of these lines shows the same information as is displayed for the
mapping in /proc/[pid]/maps. The remaining lines show the size of
the mapping, the amount of the mapping that is currently resident in RAM
("Rss"), the process' 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" entry is the page size used by the kernel to
back a VMA. 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 64K as a base page size may still use 4K pages for the MMU on
older processors. To distinguish, this patch reports
"MMUPageSize" as the page size used by the MMU.
The "Locked" indicates whether the mapping is locked in memory or
not.
"VmFlags" field represents the kernel flags associated with the
particular virtual memory area in two letter encoded manner. The codes are
the following:
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
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.
- /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:
- (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.
- (1) 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
- The address above which program text can run.
- (27) endcode %lu
- The address below which program text can run.
- (28) startstack %lu
- The address of the start (i.e., bottom) of the stack.
- (29) kstkesp %lu
- The current value of ESP (stack pointer), as found in the kernel stack
page for the process.
- (30) kstkeip %lu
- 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
- 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)
- Address above which program initialized and uninitialized (BSS) data are
placed.
- (46) end_data %lu (since Linux 3.3)
- Address below which program initialized and uninitialized (BSS) data are
placed.
- (47) start_brk %lu (since Linux 3.3)
- Address above which program heap can be expanded with brk(2).
- (48) arg_start %lu (since Linux 3.5)
- Address above which program command-line arguments (argv) are
placed.
- (49) arg_end %lu (since Linux 3.5)
- Address below program command-line arguments (argv) are
placed.
- (50) env_start %lu (since Linux 3.5)
- Address above which program environment is placed.
- (51) env_end %lu (since Linux 3.5)
- Address below which program environment is placed.
- (52) exit_code %d (since Linux 3.5)
- 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)
share (3) shared pages (i.e., backed by a file)
text (4) text (code)
lib (5) library (unused in Linux 2.6)
data (6) data + stack
dt (7) dirty pages (unused in Linux 2.6)
- /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
State: S (sleeping)
Tgid: 3515
Pid: 3515
PPid: 3452
TracerPid: 0
Uid: 1000 1000 1000 1000
Gid: 100 100 100 100
FDSize: 256
Groups: 16 33 100
VmPeak: 9136 kB
VmSize: 7896 kB
VmLck: 0 kB
VmHWM: 7572 kB
VmRSS: 6316 kB
VmData: 5224 kB
VmStk: 88 kB
VmExe: 572 kB
VmLib: 1708 kB
VmPTE: 20 kB
Threads: 1
SigQ: 0/3067
SigPnd: 0000000000000000
ShdPnd: 0000000000000000
SigBlk: 0000000000010000
SigIgn: 0000000000384004
SigCgt: 000000004b813efb
CapInh: 0000000000000000
CapPrm: 0000000000000000
CapEff: 0000000000000000
CapBnd: ffffffffffffffff
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.
- *
- 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).
- *
- 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.
- *
- VmPeak: Peak virtual memory size.
- *
- VmSize: Virtual memory size.
- *
- VmLck: Locked memory size (see mlock(3)).
- *
- VmHWM: Peak resident set size ("high water mark").
- *
- VmRSS: Resident set size.
- *
- 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).
- *
- 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)).
- *
- 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 file
contains just the string "running".
This file is present only if the kernel was configured with
CONFIG_HAVE_ARCH_TRACEHOOK.
- /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).
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]/uid_map, /proc/[pid]/gid_map (since Linux
3.5)
- These files expose the mappings for user and group IDs inside the user
namespace for the process pid. The description here explains the
details for uid_map; gid_map is exactly the same, but each
instance of "user ID" is replaced by "group ID".
The uid_map file exposes the mapping of user IDs from the user
namespace of the process pid to the user namespace of the process
that opened uid_map (but see a qualification to this point below).
In other words, processes that are in different user namespaces will
potentially see different values when reading from a particular
uid_map file, depending on the user ID mappings for the user
namespaces of the reading processes.
Each line in the file specifies a 1-to-1 mapping of a range of contiguous
between two user namespaces. The specification in each line takes the form
of three numbers delimited by white space. The first two numbers specify
the starting user ID in each user namespace. The third number specifies
the length of the mapped range. In detail, the fields are interpreted as
follows:
- (1)
- The start of the range of user IDs in the user namespace of the process
pid.
- (2)
- The start of the range of user IDs to which the user IDs specified by
field one map. How field two is interpreted depends on whether the process
that opened uid_map and the process pid are in the same user
namespace, as follows:
- a)
- If the two processes are in different user namespaces: field two is the
start of a range of user IDs in the user namespace of the process that
opened uid_map.
- b)
- If the two processes are in the same user namespace: field two is the
start of the range of user IDs in the parent user namespace of the process
pid. (The "parent user namespace" is the user namespace
of the process that created a user namespace via a call to
unshare(2) or clone(2) with the CLONE_NEWUSER flag.)
This case enables the opener of uid_map (the common case here is
opening /proc/self/uid_map) to see the mapping of user IDs into the
user namespace of the process that created this user namespace.
- (3)
- The length of the range of user IDs that is mapped between the two user
namespaces.
- After the creation of a new user namespace, the uid_map file may be
written to exactly once to specify the mapping of user IDs in the new user
namespace. (An attempt to write more than once to the file fails with the
error EPERM.)
- The lines written to uid_map must conform to the following
rules:
- *
- The three fields must be valid numbers, and the last field must be greater
than 0.
- *
- Lines are terminated by newline characters.
- *
- There is an (arbitrary) limit on the number of lines in the file. As at
Linux 3.8, the limit is five lines.
- *
- The range of user IDs specified in each line cannot overlap with the
ranges in any other lines. In the current implementation (Linux 3.8), this
requirement is satisfied by a simplistic implementation that imposes the
further requirement that the values in both field 1 and field 2 of
successive lines must be in ascending numerical order.
- Writes that violate the above rules fail with the error EINVAL.
In order for a process to write to the /proc/[pid]/uid_map
(/proc/[pid]/gid_map) file, the following requirements must be
met:
- *
- The process must have the CAP_SETUID (CAP_SETGID) capability
in the user namespace of the process pid.
- *
- The process must have the CAP_SETUID (CAP_SETGID) capability
in the parent user namespace.
- *
- The process must be in either the user namespace of the process pid
or inside the parent user namespace of the process pid.
For further details, see
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.
- /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 formual:
(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 kilobyteis, 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 fragmentated, 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/[pid]/timers (since Linux 3.10)
- A list of the POSIX timers for this process. Each timer is listed with a
line that started 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.sival_ptr 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 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.
- /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/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/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/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)).
- /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.
- 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)
- [To be documented.]
- Slab %lu
- In-kernel data structures cache.
- 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 IR /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.
- 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.
- /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, 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
- various net pseudo-files, all of which give the status of some part of the
networking layer. These files contain ASCII structures and are, therefore,
readable with cat(1). However, the standard netstat(8) suite
provides much cleaner access to these files.
- /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 only useful
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
Here "Num" is the kernel table slot number, "RefCount"
is the number of users of the socket, "Protocol" is currently
always 0, "Flags" represent the internal kernel flags holding
the status of the socket. Currently, type is always "1" (UNIX
domain datagram sockets are not yet supported in the kernel).
"St" is the internal state of the socket and Path is the bound
path (if any) of the socket.
- /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. Since Linux 2.6.16 this file is present
only if the CONFIG_SLAB kernel configuration option is enabled. The
columns in /proc/slabinfo are:
cache-name
num-active-objs
total-objs
object-size
num-active-slabs
total-slabs
num-pages-per-slab
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.
- 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.
- /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. (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
The kernel constant NR_OPEN imposes an upper limit on the value that
may be placed in 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/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/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)
- The value in this file defines an upper limit for raising the capacity of
a pipe using the fcntl(2) F_SETPIPE_SZ operation. This limit
applies only to unprivileged processes. The default value for this file is
1,048,576. The value assigned to this file may be rounded upward, to
reflect the value actually employed for a convenient implementation. To
determine the rounded-up value, display the contents of this file after
assigning a value to it. The minimum value that can be assigned to this
file is the system page size.
- /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 caller has the CAP_FOWNER capability.
- *
- 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 permission bit enabled;
- •
- the target file does not have both its set-group-ID and group-executable
permission 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 determines whether core dump files are produced for
set-user-ID or otherwise protected/tainted binaries. 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. 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. Ptrace is
unchecked.
- 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.
- /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/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_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(8) 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/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.
- /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/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
POSIX real-time signals currently queued.
- /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. Only set this file to 1 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/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 like:
#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 behind 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.
- /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/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/vm
- This directory contains files for memory management tuning, buffer and
cache management.
- /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 this is not supported for a
few types of pages, like kernel internally allocated data or the swap
cache, but works for the majority of user pages.
- 0:
- Only unmap the corrupted page from all processes and kill only a process
that tries to access it.
- 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.
- Only present 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.
- Only present 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". Under Linux 2.4, 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
- /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/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/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)
- This file displays various virtual memory statistics.
- /proc/zoneinfo (since Linux 2.6.13)
- This file display information about memory zones. This is useful for
analyzing virtual memory behavior.
NOTES¶
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.
SEE ALSO¶
cat(1),
dmesg(1),
find(1),
free(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),
init(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.
COLOPHON¶
This page is part of release 3.74 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
http://www.kernel.org/doc/man-pages/.