cpuid \- x86 CPUID access device

.SH DESCRIPTION

CPUID provides an interface for querying information about the x86 CPU.

This device is accessed by

.BR lseek (2)

or

.BR pread (2)

to the appropriate CPUID level and reading in chunks of 16 bytes.

A larger read size means multiple reads of consecutive levels.

The lower 32 bits of the file position is used as the incoming

.IR %eax ,

and the upper 32 bits of the file position as the incoming

.I eax

levels like

.IR eax=4 .

This driver uses

.IR /dev/cpu/CPUNUM/cpuid ,

where

.I CPUNUM

as listed in

.IR /proc/cpuinfo .

This file is protected so that it can be read only by the user

.IR root ,

or members of the group

using inline assembler.

However this device allows convenient

access to all CPUs without changing process affinity.

Most of the information in

.I cpuid

is reported by the kernel in cooked form either in

.IR /sys/devices/system/cpu .

Direct CPUID access through this device should only

be used in exceptional cases.

The

.I cpuid

driver is not auto-loaded.

.PP

There is no support for CPUID functions that require additional

input registers.

Very old x86 CPUs don't support CPUID.

.SH SEE ALSO

Intel Corporation, Intel 64 and IA-32 Architectures

Software Developer's Manual Volume 2A:

Instruction Set Reference, A-M, 3-180 CPUID reference.

Intel Corporation, Intel Processor Identification and

the CPUID Instruction, Application note 485.

performance may drop,

to the point of needing a few seconds to access an entire track.

To prevent this, use interleaved formats.

It is not possible to

read floppies which are formatted using GCR (group code recording),

which is used by Apple II and Macintosh computers (800k disks).

Reading floppies which are hard sectored (one hole per sector, with

the index hole being a little skewed) is not supported.

This used to be common with older 8-inch floppies.

.B ENOSPC

error.

This can be used to test how a program handles disk-full errors.

Reads from the

.I /dev/full

device will return \\0 characters.

Seeks on

.I /dev/full

will always succeed.

>/proc/sys/kernel/nfs-root-addrs

echo 255 >/proc/sys/kernel/real-root-dev

.fi

.BR Note :

The use of

.I /proc/sys/kernel/real-root-dev

.BR ram (4),

.BR freeramdisk (8),

.BR rdev (8)

.I Documentation/initrd.txt

in the Linux kernel source tree, the LILO documentation,

the LOADLIN documentation, the SYSLINUX documentation

describes the pulse width as a percentage of the total cycle.

Currently, no special meaning is defined for 0 or 100, but the values

are reserved for future use.

.TP

.BR LIRC_GET_MIN_TIMEOUT " (\fIvoid\fP)", " "\

LIRC_GET_MAX_TIMEOUT " (\fIvoid\fP)"

.I CPUNUM

is the number of the CPU to access as listed in

.IR /proc/cpuinfo .

The register access is done by opening the file and seeking

to the MSR number as offset in the file, and then

reading or writing in chunks of 8 bytes.

An I/O transfer of more than 8 bytes means multiple reads or writes

of the same register.

This file is protected so that it can be read and written only by the user

.IR root ,

or members of the group

.SH NOTES

If these devices are not writable and readable for all users, many

programs will act strangely.

Since Linux 2.6.31,

.\" commit 2b83868723d090078ac0e2120e06a1cc94dbaef0

reads from

=

.I y

= 0 at the top left corner of the screen.)

When a 512-character font is loaded,

the 9th bit position can be fetched by applying the

.BR ioctl (2)

administrator can control access using filesystem permissions.

.PP

The devices for the first eight virtual consoles may be created by:

.nf

for x in 0 1 2 3 4 5 6 7 8; do

mknod \-m 644 /dev/vcs$x c 7 $x;

done

chown root:tty /dev/vcs*

.fi

No

.BR ioctl (2)

requests are supported.

Introduced with version 1.1.92 of the Linux kernel.

.SH EXAMPLE

You may do a screendump on vt3 by switching to vt1 and typing

cat /dev/vcs3 >foo

Note that the output does not contain

newline characters, so some processing may be required, like

in

fold \-w 81 /dev/vcs3 | lpr

or (horrors)

xetterm \-dump 3 \-file /proc/self/fd/1

The

.I /dev/vcsa0

device is used for Braille support.

This program displays the character and screen attributes under the

cursor of the second virtual console, then changes the background color

there:

.nf

#include <unistd.h>

#include <stdlib.h>

The character set definition section starts with the keyword

.I CHARMAP

in the first column.

The following lines may have one of the two following forms to

define the character set:

.TP

The width section for individual characters starts with the keyword

.I WIDTH

in the first column.

The following lines may have one of the two following forms to

define the widths of the characters:

.TP

to inspect the state of the program at the time that it terminated.

A list of the signals which cause a process to dump core can be found in

.BR signal (7).

A process can set its soft

.B RLIMIT_CORE

resource limit to place an upper limit on the size of the core dump file

that will be produced if it receives a "core dump" signal; see

.BR getrlimit (2)

for details.

There are various circumstances in which a core dump file is

not produced:

.IP * 3

.I /proc/sys/kernel/core_uses_pid

(see below)

is nonzero, then .PID will be appended to the core filename.

Paths are interpreted according to the settings that are active for the

crashing process.

That means the crashing process's mount namespace (see

.BR getcwd (2)),

and its root directory (see

.BR chroot (2)).

Since version 2.4, Linux has also provided

a more primitive method of controlling

the name of the core dump file.

If this file contains a nonzero value, then the core dump file includes

the process ID in a name of the form

.IR core.PID .

Since Linux 3.6,

.\" 9520628e8ceb69fa9a4aee6b57f22675d9e1b709

if

This in turn creates the

possibility that a misbehaving collecting program can block

the reaping of a crashed process by simply never exiting.

Since Linux 2.6.32,

.\" commit a293980c2e261bd5b0d2a77340dd04f684caff58

the

processes may be piped to user-space programs in parallel.

If this value is exceeded, then those crashing processes above this value

are noted in the kernel log and their core dumps are skipped.

A value of 0 in this file is special.

It indicates that unlimited processes may be captured in parallel,

but that no waiting will take place (i.e., the collecting

file can be used to control which memory segments are written to the

core dump file in the event that a core dump is performed for the

process with the corresponding process ID.

The value in the file is a bit mask of memory mapping types (see

.BR mmap (2)).

If a bit is set in the mask, then memory mappings of the

This default can be modified at boot time using the

.I coredump_filter

boot option.

The value of this file is displayed in hexadecimal.

(The default value is thus displayed as 33.)

Memory-mapped I/O pages such as frame buffer are never dumped, and

virtual DSO pages are always dumped, regardless of the

.I coredump_filter

value.

A child process created via

.BR fork (2)

inherits its parent's

.I coredump_filter

value is preserved across an

.BR execve (2).

It can be useful to set

.I coredump_filter

in the parent shell before running a program, for example:

.in +4n

.nf

.RB "$" " echo 0x7 > /proc/self/coredump_filter"

.BR gdb (1)

.I gcore

command can be used to obtain a core dump of a running process.

In Linux versions up to and including 2.6.27,

.\" Changed with commit 6409324b385f3f63a03645b4422e3be67348d922

if a multithreaded process (or, more precisely, a process that

.B LS_COLORS

to determine the colors in which the filenames are to be displayed.

This environment variable is usually set by a command like

.RS

eval \`dircolors some_path/dir_colors\`

.RE

found in a system default shell initialization file, like

.I /etc/profile

or

.TP

.B NORMAL \fIcolor-sequence\fR

Specifies the color used for normal (nonfilename) text.

Synonym:

.BR NORM .

.TP

.TP

.B LINK \fIcolor-sequence\fR

Specifies the color used for a symbolic link.

Synonyms:

.BR LNK ,

.BR SYMLINK .

.TP

.B FIFO \fIcolor-sequence\fR

Specifies the color used for a FIFO (named pipe).

Synonym:

.BR PIPE .

.TP

.TP

.B BLK \fIcolor-sequence\fR

Specifies the color used for a block device special file.

Synonym:

.BR BLOCK .

.TP

.B CHR \fIcolor-sequence\fR

Specifies the color used for a character device special file.

Synonym:

.BR CHAR .

.TP

.TP

.B SUID \fIcolor-sequence\fR

Specifies the color used for a file with the set-user-ID attribute set.

Synonym:

.BR SETUID .

.TP

.B SGID \fIcolor-sequence\fR

Specifies the color used for a file with the set-group-ID attribute set.

Synonym:

.BR SETGID .

.TP

.TP

.B STICKY_OTHER_WRITABLE \fIcolor-sequence\fR

Specifies the color used for an other-writable directory with the executable attribute set.

Synonym:

.BR OWT .

.TP

.B OTHER_WRITABLE \fIcolor-sequence\fR

Specifies the color used for an other-writable directory without the executable attribute set.

Synonym:

.BR OWR .

.TP

Specifies the

.I "left code"

for non-ISO\ 6429 terminals (see below).

Synonym:

.BR LEFT .

.TP

Specifies the

.I "right code"

for non-ISO\ 6429 terminals (see below).

Synonym:

.BR RIGHT .

.TP

Specifies the

.I "end code"

for non-ISO\ 6429 terminals (see below).

Synonym:

.BR END .

.TP

codes and harmlessly eliminate them from the output or emulate them.

.B ls

uses ISO 6429 codes by default, assuming colorization is enabled.

ISO 6429 color sequences are composed of sequences of numbers

separated by semicolons.

The most common codes are:

for more details.

If you need a currently unsupported filesystem, insert the corresponding

module or recompile the kernel.

In order to use a filesystem, you have to

.I mount

it; see

.BR mount (8).

Below a short description of the available or historically available

filesystems in the Linux kernel.

See kernel documentation for a comprehensive

.SH EXAMPLE

The default table according to RFC\ 3484 would be specified with the

following configuration file:

.nf

label ::1/128 0

label ::/0 1

or

.I ~/.rhosts

files.

Allow any user to log in from any host:

+

Allow any user from

.I host

with a matching local account to log in:

host

Note: the use of

.I +host

is never a valid syntax,

including attempting to specify that any user from the host is allowed.

Allow any user from

.I host

to log in:

host +

Note: this is distinct from the previous example

since it does not require a matching local account.

Allow

.I user

from

.I host

to log in as any non-root user:

host user

Allow all users with matching local accounts from

.I host

to log in except for

.IR baduser :

host \-baduser

host

Deny all users from

.IR host :

\-host

Note: the use of

.I "\-host\ \-user"

is never a valid syntax,

including attempting to specify that a particular user from the host

is not trusted.

Allow all users with matching local accounts on all hosts in a

.IR netgroup :

+@netgroup

Disallow all users on all hosts in a

.IR netgroup :

\-@netgroup

Allow all users in a

.I netgroup

to log in from

.IR host

as any non-root user:

host +@netgroup

Allow all users with matching local accounts on all hosts in a

.I netgroup

except

.IR baduser :

+@netgroup \-baduser

+@netgroup

Note: the deny statements must always precede the allow statements because

the file is processed sequentially until the first matching rule is found.

.SH SEE ALSO

definition file contains all the information that the

.BR localedef (1)

command needs to convert it into the binary locale database.

The definition files consist of sections which each describe a

locale category in detail.

See

See

.BR locale (7)

for a more detailed description of each category.

.SS LC_ADDRESS

The definition starts with the string

.I LC_ADDRESS

in the first column.

The following keywords are allowed:

.TP

.I postal_fmt

The definition starts with the string

.I LC_CTYPE

in the first column.

The following keywords are allowed:

.TP

.I upper

copied or included from other files.

In case of duplicate rule definitions in the locale file,

only the first rule is used.

A transliteration rule consist of a character to be transliterated

followed by a list of transliteration targets separated by semicolons.

The first target which can be presented in the target character set

.SS LC_COLLATE

Note that glibc does not support all POSIX-defined options,

only the options described below are supported (as of glibc 2.23).

The definition starts with the string

.I LC_COLLATE

in the first column.

The following keywords are allowed:

.TP

.I coll_weight_max

The definition starts with the string

.I LC_IDENTIFICATION

in the first column.

The following keywords are allowed:

.TP

.I title

The definition starts with the string

.I LC_MESSAGES

in the first column.

The following keywords are allowed:

.TP

.I yesexpr

The definition starts with the string

.I LC_MEASUREMENT

in the first column.

The following keywords are allowed:

.TP

.I measurement

The definition starts with the string

.I LC_MONETARY

in the first column.

The following keywords are allowed:

.TP

.I int_curr_symbol

The definition starts with the string

.I LC_NAME

in the first column.

Various keywords are allowed, but only

.IR name_fmt

is mandatory.

The definition starts with the string

.I LC_NUMERIC

in the first column.

The following keywords are allowed:

.TP

.I decimal_point

The definition starts with the string

.I LC_PAPER

in the first column.

The following keywords are allowed:

.TP

.I height

The definition starts with the string

.I LC_TELEPHONE

in the first column.

The following keywords are allowed:

.TP

.I tel_int_fmt

The definition starts with the string

.I LC_TIME

in the first column.

The following keywords are allowed:

.TP

.I abday

are displayed by

.BR login (1)

after a successful login but just before it executes the login shell.

The abbreviation "motd" stands for "message of the day", and this file

has been traditionally used for exactly that (it requires much less disk

space than mail to all users).

is a plain ASCII file that describes known DARPA networks and symbolic

names for these networks.

Each line represents a network and has the following structure:

.RS

.I name number aliases ...

.RE

where the fields are delimited by spaces or tabs.

Empty lines are ignored.

The hash character (\fB#\fP) indicates the start of a comment:

this character, and the remaining characters up to

the end of the current line,

are ignored by library functions that process the file.

The field descriptions are:

.TP

.I name

.I aliases

Optional aliases for the network.

.LP

This file is read by the

.BR route (8)

and

A \(aq#\(aq (number sign) indicates the beginning of a

comment; following characters, up to the end of the line,

are not interpreted by nscd.

Valid services are \fIpasswd\fP, \fIgroup\fP, \fIhosts\fP, \fIservices\fP,

or \fInetgroup\fP.

.B logfile

.I debug-file-name

.RS

Specifies name of the file to which debug info should be written.

.RE

.B debug-level

.I value

.RS

Sets the desired debug level.

The default is 0.

.RE

.B threads

.I number

.RS

requests.

At least five threads will always be created.

.RE

.B max-threads

.I number

.RS

Specifies the maximum number of threads.

The default is 32.

.RE

.B server-user

.I user

.RS

If a separate cache for every user is used (\-S parameter), this

option is ignored.

.RE

.B stat-user

.I user

.RS

Specifies the user who is allowed to request statistics.

.RE

.B reload-count

unlimited |

.I number

before it gets removed.

The default is 5.

.RE

.B paranoia

.I <yes|no>

.RS

Enabling paranoia mode causes nscd to restart itself periodically.

The default is no.

.RE

.B restart-interval

.I time

.RS

mode.

The default is 3600.

.RE

.B enable-cache

.I service

.I <yes|no>

cache.

The default is no.

.RE

.B positive-time-to-live

.I service

.I value

Larger values increase cache hit rates and reduce mean

response times, but increase problems with cache coherence.

.RE

.B negative-time-to-live

.I service

.I value

example untarring the Linux kernel sources as root); should be kept small

to reduce cache coherency problems.

.RE

.B suggested-size

.I service

.I value

should remain a prime number for optimum efficiency.

The default is 211.

.RE

.B check-files

.I service

.I <yes|no>

.IR /etc/netgroup .

The default is yes.

.RE

.B persistent

.I service

.I <yes|no>

mode is set.

The default is no.

.RE

.B shared

.I service

.I <yes|no>

daemon over the socket each time a lookup is performed.

The default is no.

.RE

.B max-db-size

.I service

.I bytes

.IR service .

The default is 33554432.

.RE

.B auto-propagate

.I service

.I <yes|no>

\fI/etc/default/nss\fR

.SH EXAMPLE

The default configuration corresponds to the following configuration file:

.nf

NETID_AUTHORITATIVE=FALSE

SERVICES_AUTHORITATIVE=FALSE

.I /proc/[pid]

There is a numerical subdirectory for each running process; the

subdirectory is named by the process ID.

Each

.I /proc/[pid]

subdirectory contains the

other security modules.

For the purpose of explanation,

examples of how SELinux uses these files are provided below.

This directory is present only if the kernel was configured with

.BR CONFIG_SECURITY .

.TP

.IR /proc/[pid]/attr/current " (since Linux 2.6.0)"

The contents of this file represent the current

security attributes of the process.

In SELinux, this file is used to get the security context of a process.

Prior to Linux 2.6.11, this file could not be used to set the security

context (a write was always denied), since SELinux limited process security

This file represents the attributes to assign to the

process upon a subsequent

.BR execve (2).

In SELinux,

this is needed to support role/domain transitions, and

.BR execve (2)

.BR symlink (2),

and

.BR mknod (2)

SELinux employs this file to support creation of a file

(using the aforementioned system calls)

in a secure state,

The last entry contains two zeros.

See also

.BR getauxval (3).

Permission to access this file is governed by a ptrace access mode

.B PTRACE_MODE_READ_FSCREDS

check; see

.\"

.\" "Clears page referenced bits shown in smaps output"

.\" write-only, writable only by the owner of the process

This is a write-only file, writable only by owner of the process.

The following values may be written to the file:

.RS

.TP

process during the measured interval.

If one is interested only in inspecting the selected mapping types,

then the value 2 or 3 can be used instead of 1.

Further values can be written to affect different properties:

.RS

.TP

Writing any value to

.IR /proc/[pid]/clear_refs

other than those listed above has no effect.

The

.IR /proc/[pid]/clear_refs

file is present only if the

Strings longer than

.B TASK_COMM_LEN

(16) characters are silently truncated.

This file provides a superset of the

.BR prctl (2)

.B PR_SET_NAME

This is a symbolic link to the current working directory of the process.

To find out the current working directory of process 20,

for instance, you can do this:

.in +4n

.nf

.RB "$" " cd /proc/20/cwd; /bin/pwd"

.fi

.in

Note that the

.I pwd

command is often a shell built-in, and might

.BR bash (1),

you may use

.IR "pwd\ \-P" .

.\" The following was still true as at kernel 2.6.13

In a multithreaded process, the contents of this symbolic link

are not available if the main thread has already terminated

(typically by calling

.BR pthread_exit (3)).

Permission to dereference or read

.RB ( readlink (2))

this symbolic link is governed by a ptrace access mode

.RB "$" " strings /proc/1/environ"

.fi

.in

If, after an

.BR execve (2),

the process modifies its environment

this file will

.I not

reflect those changes.

Furthermore, a process may change the memory location that this file refers via

.BR prctl (2)

operations such as

.BR PR_SET_MM_ENV_START .

Permission to access this file is governed by a ptrace access mode

.B PTRACE_MODE_READ_FSCREDS

check; see

are not available if the main thread has already terminated

(typically by calling

.BR pthread_exit (3)).

Permission to dereference or read

.RB ( readlink (2))

this symbolic link is governed by a ptrace access mode

.B PTRACE_MODE_READ_FSCREDS

check; see

.BR ptrace (2).

Under Linux 2.0 and earlier,

.I /proc/[pid]/exe

is a pointer to the binary which was executed,

A

.BR readlink (2)

call on this file under Linux 2.0 returns a string in the format:

[device]:inode

For example, [0301]:1502 would be inode 1502 on device major 03 (IDE,

MFM, etc. drives) minor 01 (first partition on the first drive).

.BR find (1)

with the

.I \-inum

process has open, named by its file descriptor, and which is a

symbolic link to the actual file.

Thus, 0 is standard input, 1 standard output, 2 standard error, and so on.

For file descriptors for pipes and sockets,

the entries will be symbolic links whose content is the

file type with the inode.

A

.BR readlink (2)

call on this file returns a string in the format:

type:[inode]

For example,

.I socket:[2248868]

will be a socket and its inode is 2248868.

For sockets, that inode can be used to find more information

in one of the files under

.IR /proc/net/ .

For file descriptors that have no corresponding inode

(e.g., file descriptors produced by

.BR bpf (2),

and

.BR userfaultfd (2)),

the entry will be a symbolic link with contents of the form

anon_inode:<file-type>

In many cases (but not all), the

.I file-type

is surrounded by square brackets.

For example, an epoll file descriptor will have a symbolic link

whose content is the string

.IR "anon_inode:[eventpoll]" .

.\"The following was still true as at kernel 2.6.13

In a multithreaded process, the contents of this directory

are not available if the main thread has already terminated

(typically by calling

.BR pthread_exit (3)).

Programs that take a filename as a command-line argument,

but don't take input from standard input if no argument is supplied,

and programs that write to a file named as a command-line argument,

.RB "$" " foobar \-i /proc/self/fd/0 \-o /proc/self/fd/1 ..."

.fi

.in

and you have a working filter.

.\" The following is not true in my tests (MTK):

.\" Note that this will not work for

.\" programs that seek on their files, as the files in the fd directory

.\" are not seekable.

.I /proc/self/fd/N

is approximately the same as

.I /dev/fd/N

to

.IR /proc/self/fd ,

in fact.

Most systems provide symbolic links

.IR /dev/stdin ,

.IR /dev/stdout ,

about the corresponding file descriptor.

The content depends on the type of file referred to by the

corresponding file descriptor.

For regular files and directories, we see something like:

.in +4n

.nf

mnt_id: 21

.fi

.in

The fields are as follows:

.RS

.TP

.I flags

will also include the value

.BR O_CLOEXEC .

Before Linux 3.1,

.\" commit 1117f72ea0217ba0cc19f05adbbd8b9a397f5ab7

this field incorrectly displayed the setting of

we see (since Linux 3.8)

.\" commit cbac5542d48127b546a23d816380a7926eee1c25

the following fields:

.in +4n

.nf

pos: 0

eventfd-count: 40

.fi

.in

.I eventfd-count

is the current value of the eventfd counter, in hexadecimal.

For epoll file descriptors (see

.BR epoll (7)),

we see (since Linux 3.8)

.\" commit 138d22b58696c506799f8de759804083ff9effae

the following fields:

.in +4n

.nf

pos: 0

tfd: 7 events: 19 data: 74253d2500000007

.fi

.in

Each of the lines beginning

.I tfd

describes one of the file descriptors being monitored via

The

.I data

field is the data value associated with this file descriptor.

For signalfd file descriptors (see

.BR signalfd (2)),

we see (since Linux 3.8)

.\" commit 138d22b58696c506799f8de759804083ff9effae

the following fields:

.in +4n

.nf

pos: 0

sigmask: 0000000000000006

.fi

.in

.I sigmask

is the hexadecimal mask of signals that are accepted via this

signalfd file descriptor.

.BR SIGQUIT ;

see

.BR signal (7).)

For inotify file descriptors (see

.BR inotify (7)),

we see (since Linux 3.8)

the following fields:

.in +4n

.nf

pos: 0

inotify wd:1 ino:192627 sdev:800001 mask:800afff ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:27261900802dfd73

.fi

.in

Each of the lines beginning with "inotify" displays information about

one file or directory that is being monitored.

The fields in this line are as follows:

.IR fhandle-type ,

and

.IR f_handle .

For fanotify file descriptors (see

.BR fanotify (7)),

we see (since Linux 3.8)

the following fields:

.in +4n

.nf

pos: 0

fanotify ino:19264f sdev:800001 mflags:0 mask:1 ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:4f261900a82dfd73

.fi

.in

The fourth line displays information defined when the fanotify group

was created via

.BR fanotify_init (2):

cancelled_write_bytes: 0

.fi

.in

The fields are as follows:

.RS

.TP

.I /proc/[pid]/io

while process B is updating one of these 64-bit counters,

process A could see an intermediate result.

Permission to access this file is governed by a ptrace access mode

.B PTRACE_MODE_READ_FSCREDS

check; see

\&...

.fi

.in

Although these entries are present for memory regions that were

mapped with the

.BR MAP_FILE

7fc075d2f000\-7fc075e6f000 \-> /dev/zero (deleted)

.fi

.in

This directory appears only if the

.B CONFIG_CHECKPOINT_RESTORE

kernel configuration option is enabled.

See

.BR mmap (2)

for some further information about memory mappings.

Permission to access this file is governed by a ptrace access mode

.B PTRACE_MODE_READ_FSCREDS

check; see

.BR ptrace (2).

The format of the file is:

.IP

.in 4n

The

.I perms

field is a set of permissions:

.nf

.in +5

r = read

p = private (copy on write)

.fi

.in

The

.I offset

field is the offset into the file/whatever;

is the inode on that device.

0 indicates that no inode is associated with the memory region,

as would be the case with BSS (uninitialized data).

The

.I pathname

field will usually be the file that is backing the mapping.

field by looking at the

Offset field in the ELF program headers

.RI ( "readelf\ \-l" ).

There are additional helpful pseudo-paths:

.RS 12

.TP

.BR gdb (1),

.BR strace (1),

or similar.

Under Linux 2.0, there is no field giving pathname.

.TP

.I /proc/[pid]/mem

.BR read (2),

and

.BR lseek (2).

Permission to access this file is governed by a ptrace access mode

.B PTRACE_MODE_ATTACH_FSCREDS

check; see

file, and fixes various other problems with that file

(e.g., nonextensibility,

failure to distinguish per-mount versus per-superblock options).

The file contains lines of the form:

.IP

.in 0n

.BR mount_namespaces (7)).

The format of this file is documented in

.BR fstab (5).

Since kernel version 2.6.15, this file is pollable:

after opening the file for reading, a change in this file

(i.e., a filesystem mount or unmount) causes

.\" Text taken from 3.7 Documentation/filesystems/proc.txt

This file can be used to adjust the badness heuristic used to select which

process gets killed in out-of-memory conditions.

The badness heuristic assigns a value to each candidate task ranging from 0

(never kill) to 1000 (always kill) to determine which process is targeted.

The units are roughly a proportion along that range of

For example, if a task is using all allowed memory,

its badness score will be 1000.

If it is using half of its allowed memory, its score will be 500.

There is an additional factor included in the badness score: root

processes are given 3% extra memory over other tasks.

The amount of "allowed" memory depends on the context

in which the OOM-killer was called.

If it is due to the memory assigned to the allocating task's cpuset

the allowed memory is that configured limit.

Finally, if it is due to the entire system being out of memory, the

allowed memory represents all allocatable resources.

The value of

.I oom_score_adj

is added to the badness score before it

The lowest possible value, \-1000, is

equivalent to disabling OOM-killing entirely for that task,

since it will always report a badness score of 0.

Consequently, it is very simple for user space to define

the amount of memory to consider for each task.

Setting an

A value of \-500, on the other hand, would be roughly

equivalent to discounting 50% of the task's

allowed memory from being considered as scoring against the task.

For backward compatibility with previous kernels,

.I /proc/[pid]/oom_adj

can still be used to tune the badness score.

Its value is

scaled linearly with

.IR oom_score_adj .

Writing to

.IR /proc/[pid]/oom_score_adj

or

file is present only if the

.B CONFIG_PROC_PAGE_MONITOR

kernel configuration option is enabled.

Permission to access this file is governed by a ptrace access mode

.B PTRACE_MODE_READ_FSCREDS

check; see

This read-only file exposes the process's execution domain, as set by

.BR personality (2).

The value is displayed in hexadecimal notation.

Permission to access this file is governed by a ptrace access mode

.B PTRACE_MODE_ATTACH_FSCREDS

check; see

.IR exe ,

and

.IR fd/* .

Note however that this file is not merely a symbolic link.

It provides the same view of the filesystem (including namespaces and the

set of per-process mounts) as the process itself.

An example illustrates this point.

In one terminal, we start a shell in new user and mount namespaces,

and in that shell we create some new mount points:

.nf

.in +4n

$ \fBPS1='sh1# ' unshare \-Urnm\fP

27123

.in

.fi

In a second terminal window, in the initial mount namespace,

we look at the contents of the corresponding mounts in

the initial and new namespaces:

.nf

.in +4n

$ \fBPS1='sh2# ' sudo sh\fP

11

.in

.fi

.\" The following was still true as at kernel 2.6.13

In a multithreaded process, the contents of the

.I /proc/[pid]/root

symbolic link are not available if the main thread has already terminated

(typically by calling

.BR pthread_exit (3)).

Permission to dereference or read

.RB ( readlink (2))

this symbolic link is governed by a ptrace access mode

(Further attempts to write to the file fail with the

.B EPERM

error.)

In Linux 2.6.23,

this file went away, to be replaced by the

.BR prctl (2)

that does not belong to any file.

"Swap" shows how much

would-be-anonymous memory is also used, but out on swap.

The "KernelPageSize" line (available since Linux 2.6.29)

is the page size used by the kernel to back the virtual memory area.

This matches the size used by the MMU in the majority of cases.

To distinguish the two attributes, the "MMUPageSize" line

(also available since Linux 2.6.29)

reports the page size used by the MMU.

The "Locked" indicates whether the mapping is locked in memory

or not.

The "ProtectionKey" line (available since Linux 4.9, on x86 only)

contains the memory protection key (see

.BR pkeys (7))

This entry is present only if the kernel was built with the

.B CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS

configuration option.

The "VmFlags" line (available since Linux 3.8)

represents the kernel flags associated with the virtual memory area,

encoded using the following two-letter codes:

rd - readable

wr - writable

ex - executable

hg - huge page advise flag

nh - no-huge page advise flag

mg - mergeable advise flag

"ProtectionKey" field contains the memory protection key (see

.BR pkeys (5))

associated with the virtual memory area.

Present only if the kernel was built with the

.B CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS

configuration option. (since Linux 4.6)

The

.IR /proc/[pid]/smaps

file is present only if the

This file is provided only if the kernel was built with the

.B CONFIG_STACKTRACE

configuration option.

Permission to access this file is governed by a ptrace access mode

.B PTRACE_MODE_ATTACH_FSCREDS

check; see

.BR ps (1).

It is defined in the kernel source file

.IR fs/proc/array.c "."

The fields, in order, with their proper

.BR scanf (3)

format specifiers, are listed below.

.BR ptrace (2)).

If the check denies access, then the field value is displayed as 0.

The affected fields are indicated with the marking [PT].

.RS

.TP 10

(1) \fIpid\fP \ %d

see the PF_* defines in the Linux kernel source file

.IR include/linux/sched.h .

Details depend on the kernel version.

The format for this field was %lu before Linux 2.6.

.TP

(10) \fIminflt\fP \ %lu

The kernel stores nice values as numbers

in the range 0 (high) to 39 (low),

corresponding to the user-visible nice range of \-20 to 19.

Before Linux 2.6, this was a scaled value based on

the scheduler weighting given to this process.

.\" And back in kernel 1.2 days things were different again.

In kernels before Linux 2.6, this value was expressed in jiffies.

Since Linux 2.6, the value is expressed in clock ticks (divide by

.IR sysconf(_SC_CLK_TCK) ).

The format for this field was %lu before Linux 2.6.

.TP

(23) \fIvsize\fP \ %lu

.BR sched_setscheduler (2)).

Decode using the SCHED_* constants in

.IR linux/sched.h .

The format for this field was %lu before Linux 2.6.22.

.TP

(42) \fIdelayacct_blkio_ticks\fP \ %llu \ (since Linux 2.6.18)

followed by the values of the stack pointer and program counter registers.

The values of all six argument registers are exposed,

although most system calls use fewer registers.

If the process is blocked, but not in a system call,

then the file displays \-1 in place of the system call number,

followed by just the values of the stack pointer and program counter.

If process is not blocked, then the file contains just the string "running".

This file is present only if the kernel was configured with

.BR CONFIG_HAVE_ARCH_TRACEHOOK .

Permission to access this file is governed by a ptrace access mode

.B PTRACE_MODE_ATTACH_FSCREDS

check; see

directory are not available if the main thread has already terminated

(typically by calling

.BR pthread_exit (3)).

.TP

.IR /proc/[pid]/task/[tid]/children " (since Linux 3.5)"

.\" commit 818411616baf46ceba0cff6f05af3a9b294734f7

A space-separated list of child tasks of this task.

Each child task is represented by its TID.

.\" see comments in get_children_pid() in fs/proc/array.c

This option is intended for use by the checkpoint-restore (CRIU) system,

and reliably provides a list of children only if all of the child processes

This makes this interface even more unreliable than classic PID-based

approaches if the inspected task and its children aren't frozen,

and most code should probably not use this interface.

Until Linux 4.2, the presence of this file was governed by the

.B CONFIG_CHECKPOINT_RESTORE

kernel configuration option.

A list of the POSIX timers for this process.

Each timer is listed with a line that starts with the string "ID:".

For example:

.in +4n

.nf

ID: 1

ClockID: 1

.fi

.in

The lines shown for each timer have the following meanings:

.RS

.TP

.BR PR_SET_TIMERSLACK

in

.BR prctl (2).

Permission to access this file is governed by a ptrace access mode

.B PTRACE_MODE_ATTACH_FSCREDS

check; see

.IR /proc/[pid]/wchan " (since Linux 2.6.0)"

The symbolic name corresponding to the location

in the kernel where the process is sleeping.

Permission to access this file is governed by a ptrace access mode

.B PTRACE_MODE_READ_FSCREDS

check; see

followed by the count of available chunks of a certain order in

which these zones are split.

The size in bytes of a certain order is given by the formula:

(2^order)\ *\ PAGE_SIZE

The binary buddy allocator algorithm inside the kernel will split

one chunk into two chunks of a smaller order (thus with half the

size) or combine two contiguous chunks into one larger chunk of

a higher order (thus with double the size) to satisfy allocation

requests and to counter memory fragmentation.

The order matches the column number, when starting to count at zero.

For example on a x86_64 system:

.in -12n

.nf

Node 0, zone DMA 1 1 1 0 2 1 1 0 1 1 3

Node 0, zone Normal 216 55 189 101 84 38 37 27 5 3 587

.fi

.in

In this example, there is one node containing three zones and there

are 11 different chunk sizes.

If the page size is 4 kilobytes, then the first zone called

.I DMA

(on x86 the first 16 megabyte of memory) has 1 chunk of 4 kilobytes

(order 0) available and has 3 chunks of 4 megabytes (order 10) available.

If the memory is heavily fragmented, the counters for higher

order chunks will be zero and allocation of large contiguous areas

will fail.

Further information about the zones can be found in

.IR /proc/zoneinfo .

.TP

If a filesystem is marked with "nodev",

this means that it does not require a block device to be mounted

(e.g., virtual filesystem, network filesystem).

Incidentally, this file may be used by

.BR mount (8)

when no filesystem is specified and it didn't manage to determine the

exists on systems with the IDE bus.

There are directories for each IDE channel and attached device.

Files include:

.in +4n

.nf

cache buffer size in KB

smart_values in hexadecimal

.fi

.in

The

.BR hdparm (8)

utility provides access to this information in a friendly format.

.RI ( /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.

.TP

which uses the

.BR syslog (2)

system call facility to log kernel messages.

Information in this file is retrieved with the

.BR dmesg (1)

program.

it is indexed by page frame number (see the discussion of

.IR /proc/[pid]/pagemap ).

The bits are as follows:

0 - KPF_LOCKED

1 - KPF_ERROR

2 - KPF_REFERENCED

20 - KPF_NOPAGE (since Linux 2.6.31)

21 - KPF_KSM (since Linux 2.6.32)

22 - KPF_THP (since Linux 3.4)

For further details on the meanings of these bits,

see the kernel source file

.IR Documentation/vm/pagemap.txt .

or similar), but touches only 300MB of that memory will show up

as using only 300MB of memory even if it has the address space

allocated for the entire 1GB.

This 1GB is memory which has been "committed" to by the VM

and can be used at any time by the allocating application.

With strict overcommit enabled on the system (mode 2 in

However, the standard

.BR netstat (8)

suite provides much cleaner access to these files.

With the advent of network namespaces,

various information relating to the network stack is virtualized (see

.BR namespaces (7)).

.I /proc/pci

This is a listing of all PCI devices found during kernel initialization

and their configuration.

This file has been deprecated in favor of a new

.I /proc

interface for PCI

which give the status of some part of the SCSI IO subsystem.

These files contain ASCII structures and are, therefore, readable with

.BR cat (1).

You can also write to some of the files to reconfigure the subsystem or

switch certain features on or off.

.TP

The listing is similar to the one seen during bootup.

scsi currently supports only the \fIadd-single-device\fP command which

allows root to add a hotplugged device to the list of known devices.

The command

.in +4n

.nf

Every directory contains one file per registered host.

Every host-file is named after the number the host was assigned during

initialization.

Reading these files will usually show driver and host configuration,

statistics, and so on.

Writing to these files allows different things on different hosts.

For example, with the \fIlatency\fP and \fInolatency\fP commands,

root can switch on and off command latency measurement code in the

the \fI/proc\fP filesystem, and the (deprecated)

.BR sysctl (2)

system call.

String values may be terminated by either \(aq\\0\(aq or \(aq\\n\(aq.

Integer and long values may be written either in decimal or in

hexadecimal notation (e.g. 0x3FFF).

When writing multiple integer or long values, these may be separated

since \fIstdin\fP, \fIstdout\fP

and network sockets also need an inode to handle them.

When you regularly run out of inodes, you need to increase this value.

Starting with Linux 2.4,

there is no longer a static limit on the number of inodes,

and this file is removed.

.IR nr_free_inodes ,

.IR preshrink ,

and four dummy values (always zero).

.I nr_inodes

is the number of inodes the system has allocated.

.\" This can be slightly more than

.\" because Linux allocates them one page full at a time.

.I nr_free_inodes

represents the number of free inodes.

.I preshrink

is nonzero when the

.I nr_inodes

The "dumpable" setting also affects the ownership of files in a process's

.IR /proc/[pid]

directory, as described above.

Three different integer values can be specified:

.RS

.TP

The default value in

.I auto_msgmni

was 1.

Since Linux 3.19, the content of this file has no effect (because

.IR msgmni

.\" FIXME Must document the 3.19 'msgmni' changes.

and

.BR hostname (1),

that is:

.in +4n

.nf

.RB "#" " echo \(aqdarkstar\(aq > /proc/sys/kernel/hostname"

.RB "#" " echo \(aqmydomain\(aq > /proc/sys/kernel/domainname"

.fi

.in

has the same effect as

.in +4n

.nf

.RB "#" " hostname \(aqdarkstar\(aq"

.RB "#" " domainname \(aqmydomain\(aq"

.fi

.in

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

.TP

.I /proc/sys/kernel/version

This file contains a string such as:

#5 Wed Feb 25 21:49:24 MET 1998

The "#5" means that

this is the fifth kernel built from this source base and the

date following it indicates the time the kernel was built.

.\" The following is based on Documentation/sysctl/kernel.txt

This file specifies the system-wide limit on the number of

threads (tasks) that can be created on the system.

Since Linux 4.1,

.\" commit 230633d109e35b0a24277498e773edeb79b4a331

the value that can be written to

the error

.B EINVAL

occurs.

The value written is checked against the available RAM pages.

If the thread structures would occupy too much (more than 1/8th)

of the available RAM pages,

This file defines the amount of free memory (in KiB) on the system that

that should be reserved for users with the capability

.BR CAP_SYS_ADMIN .

The default value in this file is the minimum of [3% of free pages, 8MiB]

expressed as KiB.

The default is intended to provide enough for the superuser

to log in and kill a process, if necessary,

under the default overcommit 'guess' mode (i.e., 0 in

.IR /proc/sys/vm/overcommit_memory ).

Systems running in "overcommit never" mode (i.e., 2 in

.IR /proc/sys/vm/overcommit_memory )

should increase the value in this file to account

.BR top (1))

Otherwise, the superuser may not be able to log in to recover the system.

For example, on x86_64 a suitable value is 131072 (128MiB reserved).

Changing the value in this file takes effect whenever

an application requests memory.

.TP

performing reproducible filesystem benchmarks.

Because writing to this file causes the benefits of caching to be lost,

it can degrade overall system performance.

To free pagecache, use:

echo 1 > /proc/sys/vm/drop_caches

To free dentries and inodes, use:

echo 2 > /proc/sys/vm/drop_caches

To free pagecache, dentries and inodes, use:

echo 3 > /proc/sys/vm/drop_caches

Because writing to this file is a nondestructive operation and dirty objects

are not freeable, the

user should run

transparently without affecting any applications.

But if there is no other up-to-date copy of the data,

it will kill processes to prevent any data corruptions from propagating.

The file has one of the following values:

.RS

.IP 1: 4

Processes can handle this if they want to; see

.BR sigaction (2)

for more details.

This feature is active only on architectures/platforms with advanced machine

check handling and depends on the hardware capabilities.

Applications can override the

.I memory_failure_early_kill

setting individually with the

and command name.

This is helpful to determine why the OOM-killer was invoked

and to identify the rogue task that caused it.

If this contains the value zero, this information is suppressed.

On very large systems with thousands of tasks,

it may not be feasible to dump the memory state information for each one.

Such systems should not be forced to incur a performance penalty in

OOM situations when the information may not be desired.

If this is set to nonzero, this information is shown whenever the

OOM-killer actually kills a memory-hogging task.

The default value is 0.

.TP

.IR /proc/sys/vm/oom_kill_allocating_task " (since Linux 2.6.24)"

.\" The following is from Documentation/sysctl/vm.txt

This enables or disables killing the OOM-triggering task in

out-of-memory situations.

If this is set to zero, the OOM-killer will scan through the entire

tasklist and select a task based on heuristics to kill.

This normally selects a rogue memory-hogging task that

frees up a large amount of memory when killed.

If this is set to nonzero, the OOM-killer simply kills the task that

triggered the out-of-memory condition.

This avoids a possibly expensive tasklist scan.

If

.I /proc/sys/vm/panic_on_oom

is nonzero, it takes precedence over whatever value is used in

.IR /proc/sys/vm/oom_kill_allocating_task .

The default value is 0.

.TP

.IR /proc/sys/vm/overcommit_kbytes " (since Linux 3.14)"

This allows for finer-grained control of

.IR CommitLimit

on systems with extremely large memory sizes.

Only one of

.IR overcommit_kbytes

or

.B MAP_NORESERVE

are not checked, and the default check is very weak,

leading to the risk of getting a process "OOM-killed".

In mode 1, the kernel pretends there is always enough memory,

until memory actually runs out.

One use case for this mode is scientific computing applications

that employ large sparse arrays.

In Linux kernel versions before 2.6.0, any nonzero value implies mode 1.

In mode 2 (available since Linux 2.6), the total virtual address space

that can be allocated

.RI ( CommitLimit

in

.IR /proc/meminfo )

is calculated as

CommitLimit = (total_RAM - total_huge_TLB) *

overcommit_ratio / 100 + total_swap

where:

.RS 12

.IP * 3

of 50, this formula yields a

.I CommitLimit

of 24GB.

Since Linux 3.14, if the value in

.I /proc/sys/vm/overcommit_kbytes

is nonzero, then

.I CommitLimit

is instead calculated as:

CommitLimit = overcommit_kbytes + total_swap

See also the description of

.IR /proc/sys/vm/admiin_reserve_kbytes

and

.\" The following is adapted from Documentation/sysctl/vm.txt

This enables or disables a kernel panic in

an out-of-memory situation.

If this file is set to the value 0,

the kernel's OOM-killer will kill some rogue process.

Usually, the OOM-killer is able to kill a rogue process and the

system will survive.

If this file is set to the value 1,

then the kernel normally panics when out-of-memory happens.

However, if a process limits allocations to certain nodes

because other nodes' memory may be free,

this means the system as a whole may not have reached

an out-of-memory situation yet.

If this file is set to the value 2,

the kernel always panics when an out-of-memory condition occurs.

The default value is 0.

1 and 2 are for failover of clustering.

Select either according to your policy of failover.

In this case, the system reserves an amount of memory that is the minimum

of [3% of current process size,

.IR user_reserve_kbytes ].

The default value in this file is the minimum of [3% of free pages, 128MiB]

expressed as KiB.

If the value in this file is set to zero,

then a user will be allowed to allocate all free memory with a single process

(minus the amount reserved by

.IR /proc/sys/vm/admin_reserve_kbytes ).

Any subsequent attempts to execute a command will result in

"fork: Cannot allocate memory".

Changing the value in this file takes effect whenever

an application requests memory.

.TP

their code does not make undue use of timers.

The goal is to avoid unnecessary wakeups,

thereby optimizing power consumption.

If enabled in the kernel

.RB ( CONFIG_TIMER_STATS ),

but not used,

data-structure overhead.

Even if collection is enabled at runtime, overhead is low:

all the locking is per-CPU and lookup is hashed.

The

.I /proc/timer_stats

file is used both to control sampling facility and to read out the

sampled information.

The

.I timer_stats

functionality is inactive on bootup.

Once sampling is disabled, the sampled information

is kept until a new sample period is started.

This allows multiple readouts.

Sample output from

.IR /proc/timer_stats :

.IP

may find that things are more readable if you use \fIod \-c\fP or \fItr

"\\000" "\\n"\fP to read them.

Alternatively, \fIecho \`cat <file>\`\fP works well.

This manual page is incomplete, possibly inaccurate, and is the kind

of thing that needs to be updated very often.

.\" .SH ACKNOWLEDGEMENTS

.BR procinfo (8),

.BR route (8),

.BR sysctl (8)

The Linux kernel source files:

.IR Documentation/filesystems/proc.txt

.IR Documentation/sysctl/fs.txt ,

even worse, just guessing them.

These numbers will occur in the

protocol field of any IP header.

Keep this file untouched since changes would result in incorrect IP

packages.

Protocol numbers and names are specified by the IANA

(Internet Assigned Numbers Authority).

.\" .. by the DDN Network Information Center.

Each line is of the following format:

.RS

.I protocol number aliases ...

.RE

where the fields are delimited by spaces or tabs.

Empty lines are ignored.

If a line contains a hash mark (#), the hash mark and the part

of the line following it are ignored.

The field descriptions are:

.TP

.I protocol

The protocols definition file.

.SH SEE ALSO

.BR getprotoent (3)

.UR http://www.iana.org\:/assignments\:/protocol\-numbers

.UE

The mapping section starts with the keyword

.I CHARIDS

in the first column.

The mapping lines have the following form:

.TP

.I <symbolic-name> <code-point> comment

and

.BR endservent (3)

support querying this file from programs.

Port numbers are assigned by the IANA (Internet Assigned Numbers

Authority), and their current policy is to assign both TCP and UDP

protocols when assigning a port number.

Therefore, most entries will

have two entries, even for TCP-only services.

Port numbers below 1024 (so-called "low numbered" ports) can be

bound to only by root (see

.BR bind (2),

and not a rogue service run by a user of the machine.

Well-known port numbers specified by the IANA are normally

located in this root-only space.

The presence of an entry for a service in the

.B services

file does not necessarily mean that the service is currently running

.BR inetd.conf (5).

In particular, news (NNTP) and mail (SMTP) servers are often

initialized from the system boot scripts.

The location of the

.B services

file is defined by

.IR <netdb.h> "."

This is usually set to

.IR /etc/services "."

Each line describes one service, and is of the form:

.IP

\f2service-name\ \ \ port\f3/\f2protocol\ \ \ \f1[\f2aliases ...\f1]

sensitive.

.PP

Either spaces or tabs may be used to separate the fields.

Comments are started by the hash sign (#) and continue until the end

of the line.

Blank lines are skipped.

The

.I service-name

should begin in the first column of the file, since leading spaces are

compatibility problems.

For example, a\-z, 0\-9, and hyphen (\-) would seem a

sensible choice.

Lines not matching this format should not be present in the

file.

(Currently, they are silently skipped by

and

.BR getservbyport (3).

However, this behavior should not be relied on.)

.\" The following is not true as at glibc 2.8 (a line with a comma is

.\" ignored by getservent()); it's not clear if/when it was ever true.

.\" As a backward compatibility feature, the slash (/) between the

.\"

This file might be distributed over a network using a network-wide

naming service like Yellow Pages/NIS or BIND/Hesiod.

A sample

.B services

file might look like this:

.BR inetd.conf (5),

.BR protocols (5),

.BR inetd (8)

Assigned Numbers RFC, most recently RFC\ 1700, (AKA STD0002).

in virtual memory.

Since the files on such filesystems typically reside in RAM,

file access is extremely fast.

The filesystem is automatically created when mounting

a filesystem with the type

.BR tmpfs

.B tmpfs

filesystem, see

.BR mount (8).

In order for user-space tools and applications to create

.B tmpfs

filesystems, the kernel must be configured with the

.B CONFIG_TMPFS

option.

The

.BR tmpfs

filesystem supports extended attributes (see

but

.I user

extended attributes are not permitted.

An internal shared memory filesystem is used for

System V shared memory

.RB ( shmget (2))

the kernel was configured with the

.B CONFIG_TMPFS

option.

A

.B tmpfs

filesystem mounted at

.RB ( shm_overview (7))

and POSIX semaphores

.RB ( sem_overview (7)).

The amount of memory consumed by all

.B tmpfs

filesystems is shown in the

.I shared

field displayed by

.BR free (1).

The

.B tmpfs

facility was formerly called

Each line consists of a terminal type, followed by

whitespace, followed by a tty name (a device name without the

.IR /dev/ ") prefix."

This association is used by the program

.BR tset (1)

to set the environment variable

.B TERM

to the default terminal name for

the user's current tty.

This facility was designed for a traditional time-sharing environment

featuring character-cell terminals hardwired to a UNIX minicomputer.

It is little used on modern workstation and personal UNIX systems.

which either can be or are used only by the superuser,

like system-administration commands, daemons,

and hardware-related commands.

As with the commands described in Section 1, the commands described

in this section terminate with an exit status that indicates

whether the command succeeded or failed.

determines the behavior of the cache daemon.

See

.BR nscd.conf (5).

.B nscd

provides caching for accesses of the

.BR passwd (5),

.BR getgrgid (3),

.BR gethostbyname (3),

and others.

There are two caches for each database:

a positive one for items found, and a negative one

for items not found.