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PROC(5) Linux Programmer’s Manual PROC(5)
NAME
proc - process information pseudo-filesystem
DESCRIPTION
The proc filesystem is a pseudo-filesystem which is used as 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 outline gives a quick tour through the /proc hierarchy.
/proc/[number]
There is a numerical subdirectory for each running process; the subdirectory
is named by the process ID. Each contains the following pseudo-files and
directories.
/proc/[number]/cmdline
This holds the complete command line for the process, unless the whole pro-
cess has been swapped out, or unless the process is a zombie. In either of
these later cases, there is nothing in this file: i.e. a read on this file
will return 0 characters. The command line arguments appear in this file as
a set of null-separated strings, with a further null byte after the last
string.
/proc/[number]/cwd
This is a link to the current working directory of the process. To find out
the cwd of process 20, for instance, you can do this:
cd /proc/20/cwd; /bin/pwd
Note that the pwd command is often a shell builtin, and might not work prop-
erly. In bash, you may use pwd -P.
/proc/[number]/environ
This file contains the environment for the process. The entries are sepa-
rated by null characters, and there may be a null character at the end.
Thus, to print out the environment of process 1, you would do:
(cat /proc/1/environ; echo) | tr "\000" "\n"
(For a reason why one should want to do this, see lilo(8).)
/proc/[number]/exe
Under Linux 2.2 and 2.4 exe is a symbolic link containing the actual path
name of the executed command. The exe symbolic link can be dereferenced
normally - attempting to open exe will open the executable. You can even
type /proc/[number]/exe to run another copy of the same process as [number].
Under Linux 2.0 and earlier exe is a pointer to the binary which was exe-
cuted, and appears as a symbolic link. A readlink(2) call on the exe special
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/[number]/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 (as the exe entry does). Thus, 0 is standard input, 1 standard
output, 2 standard error, etc.
Programs that will take a filename, but will not take the standard input,
and which write to a file, but will not send their output to standard out-
put, can be effectively foiled this way, assuming that -i is the flag desig-
nating 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. Note that this will not work for programs
that seek on their files, as the files in the fd directory are not seekable.
/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.
/proc/[number]/maps
A file containing the currently mapped memory regions and their access per-
missions.
The format is:
address perms offset dev inode pathname
08048000-08056000 r-xp 00000000 03:0c 64593 /usr/sbin/gpm
08056000-08058000 rw-p 0000d000 03:0c 64593 /usr/sbin/gpm
08058000-0805b000 rwxp 00000000 00:00 0
40000000-40013000 r-xp 00000000 03:0c 4165 /lib/ld-2.2.4.so
40013000-40015000 rw-p 00012000 03:0c 4165 /lib/ld-2.2.4.so
4001f000-40135000 r-xp 00000000 03:0c 45494 /lib/libc-2.2.4.so
40135000-4013e000 rw-p 00115000 03:0c 45494 /lib/libc-2.2.4.so
4013e000-40142000 rw-p 00000000 00:00 0
bffff000-c0000000 rwxp 00000000 00:00 0
where address is the address space in the process that it occupies, perms is
a set of permissions:
r = read
w = write
x = execute
s = shared
p = private (copy on write)
offset is the offset into the file/whatever, dev is the device
(major:minor), and inode is the inode on that device. 0 indicates that no
inode is associated with the memory region, as the case would be with bss.
Under Linux 2.0 there is no field giving pathname.
/proc/[number]/mem
Via the mem file one can access the pages of a process’s memory through
open(2), read(2), and fseek(3).
/proc/[number]/root
Unix and Linux support the idea of a per-process root of the filesystem, set
by the chroot(2) system call. Root points to the file system root, and
behaves as exe, fd/*, etc. do.
/proc/[number]/stat
Status information about the process. This is used by ps(1). It is defined
in /usr/src/linux/fs/proc/array.c.
The fields, in order, with their proper scanf(3) format specifiers, are:
pid %d The process id.
comm %s
The filename of the executable, in parentheses. This is visible
whether or not the executable is swapped out.
state %c
One character from the string "RSDZTW" where R is running, S is
sleeping in an interruptible wait, D is waiting in uninterruptible
disk sleep, Z is zombie, T is traced or stopped (on a signal), and W
is paging.
ppid %d
The PID of the parent.
pgrp %d
The process group ID of the process.
session %d
The session ID of the process.
tty_nr %d
The tty the process uses.
tpgid %d
The process group ID of the process which currently owns the tty that
the process is connected to.
flags %lu
The flags of the process. The math bit is decimal 4, and the traced
bit is decimal 10.
minflt %lu
The number of minor faults the process has made which have not
required loading a memory page from disk.
cminflt %lu
The number of minor faults that the process’s waited-for children
have made.
majflt %lu
The number of major faults the process has made which have required
loading a memory page from disk.
cmajflt %lu
The number of major faults that the process’s waited-for children
have made.
utime %lu
The number of jiffies that this process has been scheduled in user
mode.
stime %lu
The number of jiffies that this process has been scheduled in kernel
mode.
cutime %ld
The number of jiffies that this process’s waited-for children have
been scheduled in user mode. (See also times(2).)
cstime %ld
The number of jiffies that this process’ waited-for children have
been scheduled in kernel mode.
priority %ld
The standard nice value, plus fifteen. The value is never negative
in the kernel.
nice %ld
The nice value ranges from 19 (nicest) to -19 (not nice to others).
0 %ld This value is hard coded to 0 as a placeholder for a removed field.
itrealvalue %ld
The time in jiffies before the next SIGALRM is sent to the process
due to an interval timer.
starttime %lu
The time in jiffies the process started after system boot.
vsize %lu
Virtual memory size in bytes.
rss %ld
Resident Set Size: number of pages the process has in real memory,
minus 3 for administrative purposes. This is just the pages which
count towards text, data, or stack space. This does not include
pages which have not been demand-loaded in, or which are swapped out.
rlim %lu
Current limit in bytes on the rss of the process (usually 4294967295
on i386).
startcode %lu
The address above which program text can run.
endcode %lu
The address below which program text can run.
startstack %lu
The address of the start of the stack.
kstkesp %lu
The current value of esp (stack pointer), as found in the kernel
stack page for the process.
kstkeip %lu
The current EIP (instruction pointer).
signal %lu
The bitmap of pending signals (usually 0).
blocked %lu
The bitmap of blocked signals (usually 0, 2 for shells).
sigignore %lu
The bitmap of ignored signals.
sigcatch %lu
The bitmap of catched signals.
wchan %lu
This is the "channel" in which the process is waiting. It is the
address of a system call, and can be looked up in a namelist if you
need a textual name. (If you have an up-to-date /etc/psdatabase,
then try ps -l to see the WCHAN field in action.)
nswap %lu
Number of pages swapped - not maintained.
cnswap %lu
Cumulative nswap for child processes.
exit_signal %d
Signal to be sent to parent when we die.
processor %d
CPU number last executed on.
/proc/[number]/statm
Provides information about memory status in pages. The columns are:
size total program size
resident resident set size
share shared pages
trs text (code)
drs data/stack
lrs library
dt dirty pages
/proc/[number]/status
Provides much of the information in /proc/[number]/stat and /proc/[num-
ber]/statm in a format that’s easier for humans to parse.
/proc/apm
Advanced power management version and battery information when CONFIG_APM is
defined at kernel compilation time.
/proc/bus
Contains subdirectories for installed busses.
/proc/bus/pccard
Subdirectory for pcmcia devices when CONFIG_PCMCIA is set at kernel compila-
tion time.
/proc/bus/pccard/drivers
/proc/bus/pci
Contains various bus subdirectories and pseudo-files containing information
about pci busses, installed devices, and device drivers. Some of these
files are not ASCII.
/proc/bus/pci/devices
Information about pci devices. They may be accessed through lspci(8) and
setpci(8).
/proc/cmdline
Arguments passed to the Linux kernel at boot time. Often done via a boot
manager such as lilo(1).
/proc/cpuinfo
This is a collection of CPU and system architecture dependent items, for
each supported architecture a different list. Two common entries are pro-
cessor which gives CPU number and bogomips; a system constant that is calcu-
lated during kernel initialization. SMP machines have information for each
CPU.
/proc/devices
Text listing of major numbers and device groups. This can be used by
MAKEDEV scripts for consistency with the kernel.
/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 compila-
tion.
/proc/filesystems
A text listing of the filesystems which were compiled into the kernel.
Incidentally, this is used by mount(1) to cycle through different filesys-
tems when none is specified.
/proc/fs
Empty subdirectory.
/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 hexidecimal
media media type
model manufacturer’s model number
settings drive settings
smart_thresholds in hexidecimal
smart_values in hexidecimal
The hdparm(8) utility provides access to this information in a friendly for-
mat.
/proc/interrupts
This is used to record the number of interrupts per each IRQ on (at least)
the i386 architechure. 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/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(8) program.
/proc/ksyms
This holds the kernel exported symbol definitions used by the modules(X)
tools to dynamically link and bind loadable modules.
/proc/loadavg
The load average numbers give 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 pro-
grams.
/proc/locks
This file shows current file locks (flock(2) and fcntl(2)) and leases
(fcntl(2)).
/proc/malloc
This file is only present if CONFIGDEBUGMALLOC was defined during compila-
tion.
/proc/meminfo
This 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.
It is in the same format as free(1), except in bytes rather than KB.
/proc/mounts
This is a list of all the file systems currently mounted on the system. The
format of this file is documented in fstab(5).
/proc/modules
A text list of the modules that have been loaded by the system. See also
lsmod(8).
/proc/mtrr
Memory Type Range Registers. See /usr/src/linux/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. 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 pre-programmed 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 ifterface_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 ser-
vices. 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 creator euid of the socket.
/proc/net/snmp
This file holds the ASCII data needed for the IP, ICMP, TCP, and UDP manage-
ment 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 "remote
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 cre-
ator euid 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 "remote
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 creator euid 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 ker-
nel). ’St’ is the internal state of the socket and Path is the bound path
(if any) of the socket.
/proc/partitions
Contains major and minor numbers of each partition as well as number of
blocks and partition name.
/proc/pci
This is a listing of all PCI devices found during kernel initialization and
their configuration.
/proc/scsi
A directory with the scsi midlevel pseudo-file and various SCSI lowlevel
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.
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.
An echo â€â€™scsi add-single-device 1 0 5 0â€â€™ > /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 con-
tains one file per registered host. Every host-file is named after the num-
ber the host was assigned during initialization.
Reading these files will usually show driver and host configuration, statis-
tics etc.
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 pro-
cess.
/proc/slabinfo
Information about kernel caches. The columns 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 number of jiffies (1/100ths of a second) that the system spent in
user mode, user mode with low priority (nice), system mode, and the
idle task, respectively. The last value should be 100 times the sec-
ond entry in the uptime pseudo-file.
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
The number of interrupts received from the system boot.
disk_io: (2,0):(31,30,5764,1,2) (3,0):...
(major,minor):(noinfo, read_io_ops, blks_read, write_io_ops,
blks_written)
ctxt 115315
The number of context switches that the system underwent.
btime 769041601
boot time, in seconds since the epoch (January 1, 1970).
processes 86031
Number of forks since boot.
/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 subdi-
rectories corresponding to kernel variables. These variables can be read
and sometimes modified using the proc file system, and the sysctl(2) system
call. Presently, there are subdirectories abi, debug, dev, fs, kernel, net,
proc, rxrpc, sunrpc and vm that each contain more files and subdirectories.
/proc/sys/abi
This directory may contain files with application binary information. On
some systems, it is not present.
/proc/sys/debug
This directory may be empty.
/proc/sys/dev
This directory contains device specific information (eg dev/cdrom/info). On
some systems, it may be empty.
/proc/sys/fs
This contains the subdirectory binfmt_misc and files dentry-state, dir-
notify-enable, dquot-nr, file-max, file-nr, inode-max, inode-nr, inode-
state, lease-break-time, leases-enable, overflowgid, overflowuid super-max
and super-nr with function fairly clear from the name.
/proc/sys/fs/binfmt_misc
Documentation for files in this directory can in the kernel sources in Docu-
mentation/binfmt_misc.txt.
/proc/sys/fs/dentry-state
This file contains six numbers, nr_dentry, nr_unused, age_limit (age in sec-
onds), want_pages (pages requested by system) and two dummy values. nr_den-
try seems to be 0 all the time. nr_unused seems to be the number of unused
dentries. age_limit is the age in seconds after which dcache entries can be
reclaimed when memory is short and 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 quotas
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/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 about running out of file handles, 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.
If you increase /proc/sys/fs/file-max, be sure to increase
/proc/sys/fs/inode-max to 3-4 times the new value of /proc/sys/fs/file-max,
or you will run out of inodes.
/proc/sys/fs/file-nr
This (read-only) file gives the number of files presently opened. It con-
tains three numbers: The number of allocated file handles, the number of
free file handles and the maximum number of file handles. The kernel allo-
cates file handles dynamically, but it doesn’t free them again. If the num-
ber of allocated files is close to the
maximum, you should consider increasing the maximum. When the number of
free file handles is large, you’ve encountered a peak in your usage of file
handles and you probably don’t need to increase the maximum.
/proc/sys/fs/inode-max
This file contains the maximum number of in-memory inodes. On some (2.4)
systems, it may not be present. 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.
/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. nr_inodes is the number of inodes the system has allo-
cated. This can be slightly more than inode-max because Linux allocates
them one pageful at a time. 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.
/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 sys-
tem-wide basis. If this file contains the value 0, leases are disabled. A
non-zero value enables leases.
/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 only support 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/super-max
This file controls the maximum number of superblocks, and thus the maximum
number of mounted filesystems the kernel can have. You only need to increase
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 acct, cad_pid, cap-bound, core_pattern,
core_uses_pid, ctrl-alt-del, dentry-state, domainname, hotplug, hostname,
htab-reclaim (PowerPC only), java-appletviewer (binfmt_java, obsolete),
java-interpreter (binfmt_java, obsolete), l2cr (PowerPC only), modprobe,
msgmax, msgmnb, msgmni, osrelease, ostype, overflowgid, overflowuid, panic,
panic_on_oops, pid_max, powersave-nap (PowerPC only), printk, pty, random,
real-root-dev, reboot-cmd (SPARC only), rtsig-max, rtsig-nr, sem, sg-big-
buff, shmall, shmmax, shmmni, sysrq, tainted, threads-max, version and zero-
paged (PowerPC only) with function fairly clear from the name.
/proc/sys/kernel/acct
This file contains three numbers: highwater, lowwater and frequency. If
BSD-style process accounting is enabled these values control its behaviour.
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% of space is free; resume it if >= 4% of space is
free; consider information about amount of free space valid for 30 seconds.
/proc/sys/kernel/cap-bound
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 exec.
/proc/sys/kernel/core_pattern
This file (new in Linux 2.5) provides finer control over the form of a core
filename than the obsolete /proc/sys/kernel/core_uses_pid file described
below. The name for a core file is controlled by defining a template in
/proc/sys/kernel/core_pattern. The template can contain % specifiers which
are substituted by the following values when a core file is created:
%% A single % character
%p PID of dumped process
%u real UID of dumped process
%g real GID of dumped process
%s number of signal causing dump
%t time of dump (secs since 0:00h, 1 Jan 1970)
%h hostname (same as the ’nodename’
returned by uname(2))
%e executable filename
A single % at the end of the template is dropped from the core filename, as
is the combination of a % followed by any character other than those listed
above. All other characters in the template become a literal part of the
core filename. The maximum size of the resulting core filename is 64 bytes.
The default value in this file is "core". For backward compatibility, if
/proc/sys/kernel/core_pattern does not include "%p" and /proc/sys/ker-
nel/core_uses_pid is non-zero, then .PID will be appended to the core file-
name.
/proc/sys/kernel/core_uses_pid
This file can be used control the naming of a core dump file on Linux 2.4.
If this file contains the value 0, then a core dump file is simply named
core. If this file contains a non-zero value, then the core dump file
includes the process ID in a name of the form core.PID.
/proc/sys/kernel/ctrl-alt-del
This file controls the handling of Ctrl-Alt-Del from the keyboard. When the
value in this file is 0, Ctrl-Alt-Del is trapped and sent to the init(1)
program to handle a graceful restart. When the value is > 0, Linux’s reac-
tion 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 key-
board 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/hotplug
This file contains the path for the hotplug policy agent. The default value
in this file "/sbin/hotplug".
/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 and hostname, i.e.:
# 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 "dark-
star" 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/htab-reclaim
(PowerPC only) If this file is set to a non-zero 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/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 is described by the kernel source file Documentation/kmod.txt.
/proc/sys/kernel/msgmax
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
This file defines the system-wide limit on the number of message queue iden-
tifiers. (This file is only present in Linux 2.4 onwards.)
/proc/sys/kernel/msgmnb
This file defines a system-wide paramter used to initialise the msg_qbytes
setting for subsequenly created message queues. The msg_qbytes setting
specifies the maximum number of bytes that may be written to the message
queue.
/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
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 ker-
nel should autoreboot after this number of seconds. When you use the soft-
ware watchdog device driver, the recommended setting is 60.
/proc/sys/kernel/panic_on_oops
This file (new in Linux 2.5) controls the kernel’s behaviour when an oops or
BUG is encountered. If this file contains 0, then the system tries to con-
tinue 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 non-zero then the machine will be
rebooted.
/proc/sys/kernel/pid_max
This file (new in Linux 2.5) specifies the value at which PIDs wrap around
(i.e., the value in this file is one greater than the maximum PID). The
default value for this file, 32768, results in the same range of PIDs as on
earlier kernels. The value in this file 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
The four values in this file are console_loglevel, default_message_loglevel,
minimum_console_level and default_console_loglevel. These values influence
printk() behavior when printing or logging error messages. See syslog(2) for
more info on the different loglevels. Messages with a higher priority than
console_loglevel will be printed to the console. Messages without an
explicit priority will be printed with priority default_message_level. min-
imum_console_loglevel is the minimum (highest) value to which con-
sole_loglevel can be set. default_console_loglevel is the default value for
console_loglevel.
/proc/sys/kernel/pty (since Linux 2.6.4)
This directory contains two files relating to the number of Unix 98 pseudo-
terminals (see pts(4)) on the system.
/proc/sys/kernel/pty/max
This file defines the maximum number of pseudo-terminals.
/proc/sys/kernel/pty/nr
This read-only file indicates how many pseudo-terminals are currently in
use.
/proc/sys/kernel/random
This directory contains various parameters controlling the operation of the
file /dev/random.
/proc/sys/kernel/real-root-dev
This file is documented in the 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
This file can be used to tune the maximum number of POSIX realtime (queued)
signals that can be outstanding in the system.
/proc/sys/kernel/rtsig-nr
This file shows the number POSIX realtime signals currently queued.
/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 on 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/shmall
This file contains the system-wide limit on the total number of pages of
System V shared memory.
/proc/sys/kernel/shmmax
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 mem-
ory segments up to 1Gb are now supported in the kernel. This value defaults
to SHMMAX.
/proc/sys/kernel/shmmni
(available in Linux 2.4 and onwards) This file specifies the system-wide
maximum number of System V shared memory segments that can be created.
/proc/sys/kernel/version
contains a string like:
#5 Wed Feb 25 21:49:24 MET 1998.TP
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/zero-paged (PowerPC only)
This file contains a flag. When enabled (non-zero), Linux-PPC will pre-zero
pages in the idle loop, possibly speeding up get_free_pages.
/proc/sys/net
This directory contains networking stuff.
/proc/sys/proc
This directory may be empty.
/proc/sys/sunrpc
This directory supports Sun remote procedure call for network file system
(NFS). On some systems, it is not present.
/proc/sys/vm
This directory contains files for memory management tuning, buffer and cache
management.
/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 under-
standing. ipc(5) provides further background on the information shown by
these files.
/proc/tty
Subdirectory containing the psuedo-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/ostype, /proc/sys/osrelease and
/proc/sys/version. For example:
Linux version 1.0.9 (quinlan@phaze) #1 Sat May 14 01:51:54 EDT 1994
SEE ALSO
cat(1), find(1), free(1), mount(1), ps(1), tr(1), uptime(1), chroot(2), mmap(2),
readlink(2), syslog(2), slabinfo(5), hier(7), arp(8), dmesg(8), hdparm(8), ifcon-
fig(8), lsmod(8), lspci(8), netstat(8), procinfo(8), route(8), /usr/src/linux/Docu-
mentation/filesystems/proc.txt
CAVEATS
Note that many strings (i.e., the environment and command line) are in the internal
format, with sub-fields terminated by NUL bytes, 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.
ACKNOWLEDGEMENTS
The material on /proc/sys/fs and /proc/sys/kernel is closely based on kernel source
documentation files written by Rik van Riel.
2003-05-27 PROC(5)
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