PROC(5) Linux Programmer's Manual PROC(5)
NAME
proc - process information pseudo-filesystem
DESCRIPTION
/proc is a pseudo-filesystem which is used as an interface to kernel
data structures rather than reading and interpreting /dev/kmem. 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.
[number]
There is a numerical subdirectory for each running process; the
subdirectory is named by the process ID. Each contains the fol-
lowing pseudo-files and directories.
cmdline
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.
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 properly. In bash, you may use pwd -P.
environ
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
lilo(8).)
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 pro-
cess as [number].
Under Linux 2.0 and earlier exe is a pointer to the
binary which was executed, 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 parti-
tion on the first drive).
find(1) with the -inum option can be used to locate the
file.
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 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.
maps A file containing the currently mapped memory regions and
their access permissions.
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.
mem Via the mem file one can access the pages of a process's
memory through open(2), read(2), and fseek(3).
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.
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 cur-
rently owns the tty that the process is connected
to.
flags %lu
The flags of the process. The math bit is deci-
mal 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 and
its 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 and
its 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 and its
children have been scheduled in user mode.
cstime %ld
The number of jiffies that this process and its
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 tex-
tual 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.
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
status Provides much of the information in stat and statm in an
format that's easier for humans to parse.
apm Advanced power management version and battery information when
CONFIG_APM is defined at kernel compilation time.
bus Contains subdirectories for installed busses.
pccard Subdirectory for pcmcia devices when CONFIG_PCMCIA is set
at kernel compilation time.
drivers
pci Contains various bus subdirectories and pseudo-files con-
taining information about pci busses, installed devices,
and device drivers. Some of these files are not ASCII.
devices
Information about pci devices. They may be
accessed through lspci(8) and setpci(8).
cmdline
Arguments passed to the Linux kernel at boot time. Often done
via a boot manager such as lilo(1).
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.
devices
Text listing of major numbers and device groups. This can be
used by MAKEDEV scripts for consistency with the kernel.
dma This is a list of the registered ISA DMA (direct memory access)
channels in use.
driver Empty subdirectory.
execdomains
List of the execution domains (ABI personalities).
fb Frame buffer information when CONFIG_FB is defined during kernel
compilation.
filesystems
A text listing of the filesystems which were compiled into the
kernel. Incidentally, this is used by mount(1) to cycle through
different filesystems when none is specified.
fs Empty subdirectory.
ide ide 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 format.
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.
iomem I/O memory map in Linux 2.4.
ioports
This is a list of currently registered Input-Output port regions
that are in use.
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.
kmsg This file can be used instead of the syslog(2) system call to
read kernel messages. A process must have superuser privileges
to read this file, and only one process should read this file.
This file should not be read if a syslog process is running
which uses the syslog(2) system call facility to log kernel mes-
sages.
Information in this file is retrieved with the dmesg(8) program.
ksyms This holds the kernel exported symbol definitions used by the
modules(X) tools to dynamically link and bind loadable modules.
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 programs.
locks This file shows current file locks (flock(2) and fcntl(2)) and
leases (fcntl(2)).
malloc This file is only present if CONFIGDEBUGMALLOC was defined dur-
ing compilation.
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.
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).
modules
A text list of the modules that have been loaded by the system.
See also lsmod(8).
mtrr Memory Type Range Registers. See /usr/src/linux/Documenta-
tion/mtrr.txt for details.
net various net pseudo-files, all of which give the status of some
part of the networking layer. These files contain ASCII struc-
tures and are, therefore, readable with cat. However, the stan-
dard netstat(8) suite provides much cleaner access to these
files.
arp This holds an ASCII readable dump of the kernel ARP table
used for address resolutions. It will show both dynami-
cally 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 physi-
cal layer mapping for that IP address if it is known.
dev The dev pseudo-file contains network device status infor-
mation. This gives the number of received and sent pack-
ets, 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
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
igmp Internet Group Management Protocol. Defined in
/usr/src/linux/net/core/igmp.c.
rarp This file uses the same format as the arp file and con-
tains the current reverse mapping database used to pro-
vide rarp(8) reverse address lookup services. If RARP is
not configured into the kernel, this file will not be
present.
raw Holds a dump of the RAW socket table. Much of the infor-
mation 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.
snmp This file holds the ASCII data needed for the IP, ICMP,
TCP, and UDP management information bases for an snmp
agent.
tcp Holds a dump of the TCP socket table. Much of the infor-
mation 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 use-
ful for debugging. The uid field holds the creator euid
of the socket.
udp Holds a dump of the UDP socket table. Much of the infor-
mation 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
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 data-
gram 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.
partitions
Contains major and minor numbers of each partition as well as
number of blocks and partition name.
pci This is a listing of all PCI devices found during kernel ini-
tialization and their configuration.
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 sub-
system or switch certain features on or off.
scsi This is a listing of all SCSI devices known to the ker-
nel. 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'scsiadd-single-device1050'>
/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.
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 etc.
Writing to these files allows different things on differ-
ent hosts. For example, with the latency and nolatency
commands, root can switch on and off command latency mea-
surement code in the eata_dma driver. With the lockup and
unlock commands, root can control bus lockups simulated
by the scsi_debug driver.
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.
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.
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 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.
swaps Swap areas in use. See also swapon(8).
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 file
system, and the sysctl(2) system call. Presently, there are sub-
directories abi, debug, dev, fs, kernel, net, proc, rxrpc, sun-
rpc and vm that each contain more files and subdirectories.
abi This directory may contain files with application binary
information. On some systems, it is not present.
debug This directory may be empty.
dev This directory contains device specific information (eg
dev/cdrom/info). On some systems, it may be empty.
fs This contains the subdirectory binfmt_misc and files den-
try-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 the files in /proc/sys/binfmt_misc can be
found in the kernel sources in Documentation/binfmt_misc.txt.
The file dentry-state contains six numbers, nr_dentry,
nr_unused, age_limit (age in seconds), want_pages (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.
The file dir-notify-enable 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.
The file dquot-max shows the maximum number of cached disk quota
entries. On some (2.4) systems, it is not present. If the num-
ber 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.
The file dquot-nr shows the number of allocated disk quota
entries and the number of free disk quota entries.
The file file-max is 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 file-max, be sure to increase inode-max to 3-4
times the new value of file-max, or you will run out of inodes.
The (read-only) file file-nr 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,
but it 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.
The file inode-max 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.
The file inode-nr contains the first two values from inode-
state.
The file inode-state contains seven numbers: nr_inodes,
nr_free_inodes, preshrink and four dummy values. 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
more.
The file lease-break-time 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.
The file leases-enable 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 non-zero value enables
leases.
The files overflowgid and 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.
The file super-max 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. The file super-nr contains the number of
filesystems currently mounted.
kernel This directory contains files acct, cad_pid, cap-bound,
core_uses_pid, ctrl-alt-del, dentry-state, domainname,
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, powersave-nap (PowerPC only), printk, 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.
The file acct 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.
The file cap-bound 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.
The file core_uses_pid 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.
The file ctrl-alt-del 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 reaction to a Vulcan
Nerve Pinch (tm) will be an immediate reboot, without even sync-
ing 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.
The files domainname and 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 host-
name "darkstar" and DNS (Internet Domain Name Server) domainname
"frop.org", not to be confused with the NIS (Network Information
Service) or YP (Yellow Pages) domainname. These two domain names
are in general different. For a detailed discussion see the
hostname(1) man page.
If the file htab-reclaim (PowerPC only) is set to a non-zero
value, the PowerPC htab (see kernel file Documentation/pow-
erpc/ppc_htab.txt) is pruned each time the system hits the idle
loop.
The file l2cr (PowerPC only) contains a flag that controls the
L2 cache of G3 processor boards. If 0, the cache is disabled.
Enabled if nonzero.
The file modprobe is described by the kernel source file
Documentation/kmod.txt.
The file msgmax is a system-wide limit specifying the maximum
number of bytes in a single message written on a System V mes-
sage queue.
The file msgmni defines the system-wide limit on the number of
message queue identifiers. (This file is only present in Linux
2.4 onwards.)
The file msgmnb is 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.
The files ostype and osrelease give substrings of /proc/version.
The files overflowgid and overflowuid duplicate the files
/proc/sys/fs/overflowgid and /proc/sys/fs/overflowuid.
The file 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 kernel should autoreboot
after this number of seconds. When you use the software watch-
dog device driver, the recommended setting is 60.
The file powersave-nap (PowerPC only) contains a flag. If set,
Linux-PPC will use the 'nap' mode of powersaving, otherwise the
'doze' mode will be used.
The four values in the file printk are console_loglevel,
default_message_loglevel, minimum_console_level and default_con-
sole_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. minimum_console_loglevel is the minimum
(highest) value to which console_loglevel can be set.
default_console_loglevel is the default value for con-
sole_loglevel.
The directory random contains various parameters controlling the
operation of the file /dev/random.
The file real-root-dev is documented in the kernel source file
Documentation/initrd.txt.
The file reboot-cmd (Sparc only) 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?
The file rtsig-max can be used to tune the maximum number of
POSIX realtime (queued) signals that can be outstanding in the
system.
The file rtsig-nr shows the number POSIX realtime signals cur-
rently queued.
The file sem (available in Linux 2.4 onwards) 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.
The file sg-big-buff 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.
The file shmall contains the system-wide limit on the total num-
ber of pages of System V shared memory.
The file shmmax 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 sup-
ported in the kernel. This value defaults to SHMMAX.
The file shmmni (available in Linux 2.4 and onwards) specifies
the system-wide maximum number of System V shared memory seg-
ments that can be created.
The file 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.
The file zero-paged (PowerPC only) contains a flag. When enabled
(non-zero), Linux-PPC will pre-zero pages in the idle loop, pos-
sibly speeding up get_free_pages.
The net This directory contains networking stuff.
proc This directory may be empty.
sunrpc This directory supports Sun remote procedure call for
network file system (NFS). On some systems, it is not
present.
vm This directory contains files for memory management tun-
ing, buffer and cache management.
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. ipc(5) provides further background on the infor-
mation shown by these files.
tty Subdirectory containing the psuedo-files and subdirectories for
tty drivers and line disciplines.
uptime This file contains two numbers: the uptime of the system (sec-
onds), and the amount of time spent in idle process (seconds).
version
This string identifies the kernel version that is currently run-
ning. 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
SEEALSO
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), ifconfig(8), lsmod(8), lspci(8), netstat(8),
procinfo(8), route(8) /usr/src/linux/Documentation/filesystems/proc.txt
CONFORMSTO
This roughly conforms to a Linux 2.4.17 kernel. Please update this as
necessary!
Last updated for Linux 2.4.17.
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.
2002-07-13 PROC(5)
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