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 interpret-
ing /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 following 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 as
having read 0 characters. This file is null-
terminated, but not newline-terminated.
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 this context.
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 a pointer to the binary which was executed, and
appears as a symbolic link. readlink(2) on the
exe special file 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).
Also, the 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].
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
00000000-0002f000 r-x-- 00000400 03:03 1401
0002f000-00032000 rwx-p 0002f400 03:03 1401
00032000-0005b000 rwx-p 00000000 00:00 0
60000000-60098000 rwx-p 00000400 03:03 215
60098000-600c7000 rwx-p 00000000 00:00 0
bfffa000-c0000000 rwx-p 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.
mem This is not the same as the mem (1,1) device,
despite the fact that it has the same device
numbers. The /dev/mem device is the physical
memory before any address translation is done, but
the mem file here is the memory of the process
that accesses it. This cannot be mmap(2)'ed
currently, and will not be until a general mmap(2)
is added to the kernel. (This might have happened
by the time you read this.)
mmap Directory of maps by mmap(2) which are symbolic
links like exe, fd/*, etc. Note that maps
includes a superset of this information, so
/proc/*/mmap should be considered obsolete.
"0" is usually libc.so.4.
/proc/*/mmap was removed in Linux kernel version
1.1.40. (It really was obsolete!)
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).
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 "RSDZT" where R
is running, S is sleeping in an interruptible
wait, D is sleeping in an uninterruptible
wait or swapping, Z is zombie, and T is
traced or stopped (on a signal).
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 %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 %u
The flags of the process. Currently, every
flag has the math bit set, because crt0.s
checks for math emulation, so this is not
included in the output. This is probably a
bug, as not every process is a compiled C
program. The math bit should be a decimal 4,
and the traced bit is decimal 10.
minflt %u
The number of minor faults the process has
made, those which have not required loading a
memory page from disk.
cminflt %u
The number of minor faults that the process
and its children have made.
majflt %u
The number of major faults the process has
made, those which have required loading a
memory page from disk.
cmajflt %u
The number of major faults that the process
and its children have made.
utime %d
The number of jiffies that this process has
been scheduled in user mode.
stime %d
The number of jiffies that this process has
been scheduled in kernel mode.
cutime %d
The number of jiffies that this process and
its children have been scheduled in user
mode.
cstime %d
The number of jiffies that this process and
its children have been scheduled in kernel
mode.
counter %d
The current maximum size in jiffies of the
process's next timeslice, or what is
currently left of its current timeslice, if
it is the currently running process.
priority %d
The standard nice value, plus fifteen. The
value is never negative in the kernel.
timeout %u
The time in jiffies of the process's next
timeout.
itrealvalue %u
The time (in jiffies) before the next SIGALRM
is sent to the process due to an interval
timer.
system
starttime %d Time the process started in jiffies after
boot.
vsize %u
Virtual memory size
rss %u
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 %u
Current limit in bytes on the rss of the
process (usually 2,147,483,647).
startcode %u
The address above which program text can run.
endcode %u
The address below which program text can run.
startstack %u
The address of the start of the stack.
kstkesp %u
The current value of esp (32-bit stack
pointer), as found in the kernel stack page
for the process.
kstkeip %u
The current EIP (32-bit instruction pointer).
signal %d
The bitmap of pending signals (usually 0).
blocked %d
The bitmap of blocked signals (usually 0, 2
for shells).
sigignore %d
The bitmap of ignored signals.
sigcatch %d
The bitmap of catched signals.
wchan %u
This is the "channel" in which the process is
waiting. This 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)
cpuinfo
This is a collection of CPU and system architecture
dependent items, for each supported architecture a
different list. The only two common entries are cpu
which is (guess what) the CPU currently in use and
BogoMIPS a system constant which is calculated during
kernel initialization.
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.
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.
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.
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 core file format. With this
pseudo-file, and an unstripped kernel
(/usr/src/linux/tools/zSystem) 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 log 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).
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 averaged over 1, 5 and 15 minutes. They are
the same as the load average numbers given by uptime(1)
and other programs.
malloc
This file is only present if CONFIGDEBUGMALLOC was
defined during 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.
modules
A text list of the modules that have been loaded by the
system.
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.
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
10.11.100.129 0x1 0x6 00:20:8A:00:0C:5A
10.11.100.5 0x1 0x2 00:C0:EA:00:00:4E
44.131.10.6 0x3 0x2 GW4PTS
Where 'IP address' is the IPv4 address of the machine,
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 physical layer mapping for
that IP address if it is known.
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 |packets errs drop fifo frame|packets errs drop fifo colls carrier
lo: 0 0 0 0 0 2353 0 0 0 0 0
eth0: 644324 1 0 0 1 563770 0 0 0 581 0
ipx No information.
ipx_route
No information.
rarp This file uses the same format as the arp file and
contains the current reverse mapping database used
to provide rarp(8) reverse address lookup
services. If RARP is not configured into the
kernel this file will not be present.
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.
route
No information, but looks similar to route(8)
snmp This file holds the ASCII data needed for the IP,
ICMP, TCP and UDP management information bases for
an snmp agent. As of writing the TCP mib is
incomplete. It is hoped to have it completed by
1.2.0.
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 creator euid of
the socket.
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
unix Lists the UNIX domain sockets present within the
system and their status. The format is:
9 Num RefCount Protocol Flags Type St Path
0: 00000002 00000000 00000000 0001 03
1: 00000001 00000000 00010000 0001 01 /dev/printer
9
Where '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. Type is
always '1' currently (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.
pci This is a listing of all PCI devices found during
kernel initialization 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 subsystem or switch certain features on or off.
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
singledevice command which allows root to add a
hotplugged device to the list of known devices.
An echo 'scsi singledevice 1 0 5 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
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
which registered at least one SCSI HBA. Every
directory contains one file per registered host.
Every host-file is named after the number the host
got assigned during initilization.
Reading these files will usually show driver and
host configuration, statistics 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.
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.
stat kernel/system statistics
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.
disk 0 0 0 0
The four disk entries are not implemented at this
time. I'm not even sure what this should be,
since kernel statistics on other machines usually
track both transfer rate and I/Os per second and
this only allows for one field per drive.
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.
The number of interrupts received from the system
boot.
ctxt 115315
The number of context switches that the system
underwent.
btime 769041601
boot time, in seconds since the epoch (January 1,
1970).
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 using the
sysctl(2) system call. Presently, there are
subdirectories kernel, net, vm that each contain more
files and subdirectories.
kernel
This contains files domainname, file-max, file-nr,
inode-max, inode-nr, osrelease, panic, real-root-
dev, securelevel, with function fairly clear from
the name.
The (read-only) file file-nr gives the number of files
presently opened.
The file file-max gives the maximum number of open
files the kernel is willing to handle. If 1024 is not
enough for you, try
echo 4096 > /proc/sys/kernel/file-max
Similarly, the files inode-nr and inode-max indicate
the present and the maximum number of inodes.
The files ostype, osrelease, version give substrings of
/proc/version.
The file panic gives r/w 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.
The file securelevel seems rather meaningless at
present - root is just too powerful.
uptime
This file contains two numbers: the uptime of the
system (seconds), and the amount of time spent in idle
process (seconds).
This strings identifies the kernel version that is
currently running. For instance:
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),
readlink(2), mmap(2), chroot(2), syslog(2), hier(7), arp(8),
dmesg(8), netstat(8), route(8), ifconfig(8), procinfo(8) and
much more
CONFORMS TO
This roughly conforms to a Linux 1.3.11 kernel. Please
update this as necessary!
Last updated for Linux 1.3.11.
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.
This manual page is incomplete, possibly inaccurate, and is
the kind of thing that needs to be updated very often.
BUGS
The /proc file system may introduce security holes into
processes running with chroot(2). For example, if /proc is
mounted in the chroot hierarchy, a chdir(2) to /proc/1/root
will return to the original root of the file system. This
may be considered a feature instead of a bug, since Linux
does not yet support the fchroot(2) call.