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SYSCTL (8) | System administration commands and daemons | Unix Manual Pages | :man

NAME

sysctl - get or set kernel state

CONTENTS

Synopsis
Description
Files
Examples
Compatibility
See Also
History
Bugs

SYNOPSIS

sysctl [-bdehNnox] name [= value] ... sysctl [-bdehNnoqx] -a

DESCRIPTION

The sysctl utility retrieves kernel state and allows processes with appropriate privilege to set kernel state. The state to be retrieved or set is described using a "Management Information Base" ("MIB") style name, described as a dotted set of components.

The following options are available:

-A Equivalent to -o -a (for compatibility).
-a List all the currently available non-opaque values. This option is ignored if one or more variable names are specified on the command line.
-b Force the value of the variable(s) to be output in raw, binary format. No names are printed and no terminating newlines are output. This is mostly useful with a single variable.
-d Print the description of the variable instead of its value.
-e Separate the name and the value of the variable(s) with ‘=’. This is useful for producing output which can be fed back to the sysctl utility. This option is ignored if either -N or -n is specified, or a variable is being set.
-h Format output for human, rather than machine, readability.
-N Show only variable names, not their values. This is particularly useful with shells that offer programmable completion. To enable completion of variable names in zsh 1(ports/shells/zsh), use the following code:
listsysctls () { set -A reply $(sysctl -AN ${1%.*}) }
compctl -K listsysctls sysctl

To enable completion of variable names in tcsh(1), use:

"complete sysctl ’n/*/‘sysctl -Na‘/’"

-n Show only variable values, not their names. This option is useful for setting shell variables. For instance, to save the pagesize in variable psize, use:

"set psize=‘sysctl -n hw.pagesize‘"

-o Show opaque variables (which are normally suppressed). The format and length are printed, as well as a hex dump of the first sixteen bytes of the value.
-q Suppress some warnings generated by sysctl to standard error.
-X Equivalent to -x -a (for compatibility).
-x As -o , but prints a hex dump of the entire value instead of just the first few bytes.

The information available from sysctl consists of integers, strings, devices (Vt dev_t), and opaque types. The sysctl utility only knows about a couple of opaque types, and will resort to hexdumps for the rest. The opaque information is much more useful if retrieved by special purpose programs such as ps(1), systat(1), and netstat(1).

Some of the variables which cannot be modified during normal system operation can be initialized via loader(8) tunables. This can for example be done by setting them in loader.conf(5). Please refer to loader.conf(5) for more information on which tunables are available and how to set them.

The string and integer information is summarized below. For a detailed description of these variable see sysctl(3).

The changeable column indicates whether a process with appropriate privilege can change the value. String, integer, and devices values can be set using sysctl. For device values, value can be specified as a character device special file name. Special values off and none denote "no device".

"Name Type Changeable
"kern.ostype string no
"kern.osrelease string no
"kern.osrevision integer no
"kern.version string no
"kern.maxvnodes integer yes
"kern.maxproc integer no
"kern.maxprocperuid integer yes
"kern.maxfiles integer yes
"kern.maxfilesperproc integer yes
"kern.argmax integer no
"kern.securelevel integer raise only
"kern.hostname string yes
"kern.hostid integer yes
"kern.clockrate struct no
"kern.posix1version integer no
"kern.ngroups integer no
"kern.job_control integer no
"kern.saved_ids integer no
"kern.boottime struct no
"kern.domainname string yes
"kern.filedelay integer yes
"kern.dirdelay integer yes
"kern.metadelay integer yes
"kern.osreldate string no
"kern.bootfile string yes
"kern.corefile string yes
"kern.dumpdev dev_t yes
"kern.logsigexit integer yes
"security.bsd.suser_enabled integer yes
"security.bsd.see_other_uids integer yes
"security.bsd.unprivileged_proc_debug integer yes
"security.bsd.unprivileged_read_msgbuf integer yes
"vm.loadavg struct no
"hw.machine string no
"hw.model string no
"hw.ncpu integer no
"hw.byteorder integer no
"hw.physmem integer no
"hw.usermem integer no
"hw.pagesize integer no
"hw.floatingpoint integer no
"hw.machine_arch string no
"machdep.console_device dev_t no
"machdep.adjkerntz integer yes
"machdep.disable_rtc_set integer yes
"machdep.guessed_bootdev string no
"user.cs_path string no
"user.bc_base_max integer no
"user.bc_dim_max integer no
"user.bc_scale_max integer no
"user.bc_string_max integer no
"user.coll_weights_max integer no
"user.expr_nest_max integer no
"user.line_max integer no
"user.re_dup_max integer no
"user.posix2_version integer no
"user.posix2_c_bind integer no
"user.posix2_c_dev integer no
"user.posix2_char_term integer no
"user.posix2_fort_dev integer no
"user.posix2_fort_run integer no
"user.posix2_localedef integer no
"user.posix2_sw_dev integer no
"user.posix2_upe integer no
"user.stream_max integer no
"user.tzname_max integer no

FILES

In sys/sysctl.h definitions for top level identifiers, second level kernel and hardware identifiers, and user level identifiers
In sys/socket.h definitions for second level network identifiers
In sys/gmon.h definitions for third level profiling identifiers
In vm/vm_param.h definitions for second level virtual memory identifiers
In netinet/in.h definitions for third level Internet identifiers and fourth level IP identifiers
In netinet/icmp_var.h definitions for fourth level ICMP identifiers
In netinet/udp_var.h definitions for fourth level UDP identifiers

EXAMPLES

For example, to retrieve the maximum number of processes allowed in the system, one would use the following request:

"sysctl kern.maxproc"

To set the maximum number of processes allowed per uid to 1000, one would use the following request:

"sysctl kern.maxprocperuid=1000"

The device used for crash dumps can be specified using:

"sysctl kern.dumpdev=/dev/somedev"

which is equivalent to

"dumpon /dev/somedev"

Information about the system clock rate may be obtained with:

"sysctl kern.clockrate"

Information about the load average history may be obtained with:

"sysctl vm.loadavg"

More variables than these exist, and the best and likely only place to search for their deeper meaning is undoubtedly the source where they are defined.

COMPATIBILITY

The -w option has been deprecated and is silently ignored.

SEE ALSO

sysctl(3), loader.conf(5), sysctl.conf(5), loader(8)

HISTORY

BUGS


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