filesystem is a pseudo-filesystem which is used as an interface to
kernel data structures. It is commonly mounted at
Most of it is read-only, but some files allow kernel variables to be
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.
This holds the complete command line for the process, unless the whole
process 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.
This is a link to the current working directory of the process. To find
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 properly. In bash, you may use pwd -P.
This file contains the environment for the process.
The entries are separated 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
Under Linux 2.2 and 2.4
is a symbolic link containing the actual path name of the executed
symbolic link can be dereferenced normally - attempting to open
will open the executable. You can even type
to run another copy of the same process as [number].
Under Linux 2.0 and earlier
is a pointer to the binary which was executed,
and appears as a symbolic link. A
call on the
special file under Linux 2.0 returns a string in the format:
For example, :1502 would be inode 1502 on device major 03 (IDE,
MFM, etc. drives) minor 01 (first partition on the first drive).
with the -inum option can be used to locate the file.
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 output, can be effectively foiled this way, 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. 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.
A file containing the currently mapped memory regions and their access
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.
file one can access the pages of a process's memory through
Unix and Linux support the idea of a per-process root of the
filesystem, set by the
system call. Root points to the file system root, and behaves as exe,
fd/*, etc. do.
Status information about the process. This is used by
It is defined in
The fields, in order, with their proper
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.
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
- stime %lu
The number of jiffies that this process has been scheduled in kernel
- cutime %ld
The number of jiffies that this process's
waited-for children have been scheduled in user mode. (See also
- 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
- nice %ld
The nice value ranges from 19 (nicest) to -19 (not nice to others).
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.
Provides information about memory status in pages. The columns are:
size total program size
resident resident set size
share shared pages
trs text (code)
dt dirty pages
Provides much of the information in
in a format that's easier for humans to parse.
Advanced power management version and battery information
when CONFIG_APM is defined at kernel compilation time.
Contains subdirectories for installed busses.
Subdirectory for pcmcia devices when CONFIG_PCMCIA is set
at kernel compilation time.
Contains various bus subdirectories and pseudo-files containing
information about pci busses, installed devices, and device
drivers. Some of these files are not ASCII.
Information about pci devices. They may be accessed through
Arguments passed to the Linux kernel at boot time. Often done via
a boot manager such as
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
Text listing of major numbers and device groups. This can be used by
MAKEDEV scripts for consistency with the kernel.
This is a list of the registered ISA DMA (direct memory access)
channels in use.
List of the execution domains (ABI personalities).
Frame buffer information when CONFIG_FB is defined during kernel
A text listing of the filesystems which were compiled into the kernel.
Incidentally, this is used by
to cycle through different filesystems when none is specified.
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
utility provides access to this information in a friendly format.
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
I/O memory map in Linux 2.4.
This is a list of currently registered Input-Output port regions that
are in use.
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
This file can be used instead of the
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
system call facility to log kernel messages.
Information in this file is retrieved with the
This holds the kernel exported symbol definitions used by the
tools to dynamically link and bind loadable modules.
The load average numbers give the number of jobs in the run queue (state
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
and other programs.
This file shows current file locks
(flock(2) and fcntl(2))
This file is only present if CONFIGDEBUGMALLOC was defined during
This is used by
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
It is in the same format as
except in bytes rather than KB.
This is a list of all the file systems currently mounted on the system.
The format of this file is documented in
A text list of the modules that have been loaded by the system.
Memory Type Range Registers.
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
suite provides much cleaner access to these files.
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.
The dev pseudo-file contains network device status information. This gives
the number of received and sent packets, the number of errors and
and other basic statistics. These are used by the
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
indx ifterface_name dmi_u dmi_g dmi_address
2 eth0 1 0 01005e000001
3 eth1 1 0 01005e000001
4 eth2 1 0 01005e000001
Internet Group Management Protocol. Defined in
This file uses the same format as the
file and contains the current reverse mapping database used to provide
reverse address lookup services. If RARP is not configured into the
this file will not be present.
Holds a dump of the RAW socket table. Much of the information is not of
apart from debugging. The 'sl' value is the kernel hash slot for the
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.
This file holds the ASCII data needed for the IP, ICMP, TCP, and UDP
information bases for an snmp agent.
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 creator euid of the socket.
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
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.
Contains major and minor numbers of each partition as well as number
of blocks and partition name.
This is a listing of all PCI devices found during kernel initialization
and their configuration.
A directory with the scsi midlevel pseudo-file and various SCSI lowlevel
directories, which contain a file for each SCSI host in this system, all
which give the status of some part of the SCSI IO subsystem.
These files contain ASCII structures and are, therefore, readable with
You can also write to some of the files to reconfigure the subsystem or
certain features on or off.
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
root to add a hotplugged device to the list of known devices.
echo 'scsi add-single-device 1 0 5 0' > /proc/scsi/scsi
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.
[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
HBA. Every directory contains one file per registered host. Every
host-file is named after the number the host was assigned during
Reading these files will usually show driver and host configuration,
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.
This directory refers to the process accessing the /proc filesystem,
and is identical to the /proc directory named by the process ID of the
Information about kernel caches. The columns are:
kernel/system statistics. Varies with architecture. Common
- 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
second 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.
Swap areas in use. See also
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 file system, and the
system call. Presently, there are subdirectories
abi, debug, dev, fs, kernel, net, proc,
rxrpc, sunrpc and vm
that each contain more files and subdirectories.
This directory may contain files with application binary information.
On some systems, it is not present.
This directory may be empty.
This directory contains device specific information (eg dev/cdrom/info).
some systems, it may be empty.
This contains the subdirectory
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.
Documentation for files in this directory can in the kernel sources in
This file contains six numbers,
nr_dentry, nr_unused, age_limit (age in seconds),
(pages requested by system) and two dummy values.
nr_dentry 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.
This file can be used to disable or enable the
interface described in
on a system-wide basis.
A value of 0 in this file disables the interface,
and a value of 1 enables it.
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.
This file shows the number of allocated disk quota
entries and the number of free disk quota entries.
This file defines
a system-wide limit on the number of open files for all processes.
which can be used by a process to set the per-process limit,
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
imposes an upper limit on the value that may be placed in
If you increase
be sure to increase
to 3-4 times the new
or you will run out of inodes.
This (read-only) file
gives the number of files presently opened.
It contains three numbers: The number of allocated
file handles, the number of free file handles and the maximum
number of file handles. The kernel allocates file handles dynamically,
doesn't free them again. If the number 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.
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.
This file contains the first two values from inode-state.
contains seven numbers: nr_inodes, nr_free_inodes, preshrink and four
nr_inodes is the number of inodes the system has
allocated. 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
specifies the grace period that the kernel grants to a process
holding a file lease
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.
This file can be used to enable or disable file leases
on a system-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
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.
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.
contains the number of filesystems currently mounted.
This directory contains files
acct, cad_pid, cap-bound,
ctrl-alt-del, dentry-state, domainname,
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.
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.
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
(new in Linux 2.5) provides finer control over the form of
a core filename than the obsolete
file described below.
The name for a core file is controlled by defining a template in
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
does not include "%p" and
is non-zero, then .PID will be appended to the core filename.
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
If this file contains a non-zero value, then the core dump file includes
the process ID in a name of the form
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
program to handle a graceful restart.
When the value is > 0, 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.
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 "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
(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.
(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.
is described by the kernel source file Documentation/kmod.txt.
This file defines
a system-wide limit specifying the maximum number of bytes in
a single message written on a System V message queue.
This file defines the system-wide limit on the number of
message queue identifiers.
(This file is only present in Linux 2.4 onwards.)
This file defines a system-wide paramter used to initialise the
setting for subsequenly created message queues.
setting specifies the maximum number of bytes that may be written to the
- /proc/sys/kernel/ostype and /proc/sys/kernel/osrelease
give substrings of
- /proc/sys/kernel/overflowgid and /proc/sys/kernel/overflowuid
These files duplicate the files
gives read/write access to the kernel variable
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.
This file (new in Linux 2.5) controls the kernel's behaviour when an oops
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.
file is also non-zero then the machine will be rebooted.
(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)
contains a flag. If set, Linux-PPC will use the 'nap' mode of
otherwise the 'doze' mode will be used.
The four values in this file
are console_loglevel, default_message_loglevel, minimum_console_level and
These values influence printk() behavior when printing or
logging error messages. See
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.
minimum_console_loglevel is the minimum (highest) value to which
console_loglevel can be set.
default_console_loglevel is the default value for console_loglevel.
- /proc/sys/kernel/pty (since Linux 2.6.4)
contains two files relating to the number of Unix 98
on the system.
This file defines the maximum number of pseudo-terminals.
This read-only file
indicates how many pseudo-terminals are currently in use.
contains various parameters controlling the operation of the 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
This file can be used to tune the maximum number
of POSIX realtime (queued) signals that can be outstanding
in the system.
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:
The maximum semaphores per semaphore set.
A system-wide limit on the number of semaphores in all semaphore sets.
The maximum number of operations that may be specified in a
A system-wide limit on the maximum number of semaphore identifiers.
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
contains the system-wide limit on the total number of pages of
System V shared memory.
can be used to query and set the run time limit
on the maximum (System V IPC) shared memory segment size that can be
Shared memory segments up to 1Gb are now supported in the
kernel. This value defaults to SHMMAX.
(available in Linux 2.4 and onwards)
specifies the system-wide maximum number of System V shared memory
segments that can be created.
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)
contains a flag. When enabled (non-zero), Linux-PPC will pre-zero pages in
the idle loop, possibly speeding up get_free_pages.
This directory contains networking stuff.
This directory may be empty.
This directory supports Sun remote procedure call for network file system
(NFS). On some systems, it is not present.
This directory contains files for memory management tuning, buffer and
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
These files have headers and are formatted (one IPC object per line)
for easy understanding.
provides further background on the information shown by these files.
Subdirectory containing the psuedo-files and subdirectories for
tty drivers and line disciplines.
This file contains two numbers: the uptime of the system (seconds),
and the amount of time spent in idle process (seconds).
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
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
This manual page is incomplete, possibly inaccurate, and is the kind
of thing that needs to be updated very often.
The material on /proc/sys/fs and /proc/sys/kernel is closely based on
kernel source documentation files written by Rik van Riel.