sysctl(8) on macos

NAME

sysctl – get or set kernel state

SYNOPSIS

sysctl [-bdeFhilNnotqWx] [-B bufsize] [-f filename] name[=value[,value]] ...

sysctl [-bdeFhlNnotqWx] [-B bufsize] -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 values except for those which are opaque or excluded from listing via the CTLFLAG_SKIP flag. 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.

-B bufsize

Set the buffer size to read from the sysctl to bufsize. This is necessary for a sysctl that has variable length, and the probe value of 0 is a valid length.

-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.

-f filename

Specify a file which contains a pair of name and value in each line. sysctl reads and processes the specified file first and then processes the name and value pairs in the command line argument.

-F

Print the format of the variable. This is additional information to describe the type of the variable and most useful with struct types such as clockinfo, timeval, and loadavg.

-h

Format output for human, rather than machine, readability.

-i

Ignore unknown OIDs. The purpose is to make use of sysctl for collecting data from a variety of machines (not all of which are necessarily running exactly the same software) easier.

-l

Show the length of variables along with their values. This option cannot be combined with the -N option.

-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

Do not show variable 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.

-t

Print the type of the variable.

-W

Display only writable variables. Useful for determining the set of runtime tunable sysctls.

-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, 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).

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

The changeable column indicates whether a process with appropriate privilege can change the value. String and integer values can be set using sysctl.

Name	Type	Changeable
hw.activecpu	integer	no
hw.busfrequency	integer	no
hw.busfrequency_max	integer	no
hw.busfrequency_min	integer	no
hw.byteorder	integer	no
hw.cacheconfig	struct	no
hw.cachelinesize	integer	no
hw.cachesize	struct	no
hw.cpu64bit_capable	integer	no
hw.cpufamily	integer	no
hw.cpufrequency	integer	no
hw.cpufrequency_max	integer	no
hw.cpufrequency_min	integer	no
hw.cpusubtype	integer	no
hw.cputhreadtype	integer	no
hw.cputype	integer	no
hw.l1dcachesize	integer	no
hw.l1icachesize	integer	no
hw.l2cachesize	integer	no
hw.l3cachesize	integer	no
hw.logicalcpu	integer	no
hw.logicalcpu_max	integer	no
hw.memsize	integer	no
hw.ncpu	integer	no
hw.packages	integer	no
hw.pagesize	integer	no
hw.physicalcpu	integer	no
hw.physicalcpu_max	integer	no
hw.tbfrequency	integer	no
kern.argmax	integer	no
kern.bootargs	string	no
kern.boottime	struct	no
kern.clockrate	struct	no
kern.coredump	integer	yes
kern.corefile	string	yes
kern.flush_cache_on_write	integer	yes
kern.hostid	integer	yes
kern.hostname	string	yes
kern.job_control	integer	no
kern.maxfiles	integer	yes
kern.maxfilesperproc	integer	yes
kern.maxnbuf	integer	yes
kern.maxproc	integer	yes
kern.maxprocperuid	integer	yes
kern.maxvnodes	integer	yes
kern.msgbuf	integer	yes
kern.nbuf	integer	no
kern.netboot	integer	no
kern.ngroups	integer	no
kern.nisdomainname	string	yes
kern.num_files	integer	no
kern.num_tasks	integer	no
kern.num_taskthreads	integer	no
kern.num_threads	integer	no
kern.num_vnodes	integer	no
kern.nx	integer	yes
kern.osrelease	string	no
kern.osrevision	integer	no
kern.ostype	string	no
kern.osversion	string	yes
kern.posix1version	integer	no
kern.procname	string	yes
kern.safeboot	integer	no
kern.saved_ids	integer	no
kern.secure_kernel	integer	no
kern.securelevel	integer	yes
kern.singleuser	integer	no
kern.sleeptime	struct	no
kern.slide	integer	no
kern.stack_depth_max	integer	no
kern.stack_size	integer	no
kern.sugid_coredump	integer	yes
kern.sugid_scripts	integer	yes
kern.symfile	string	no
kern.usrstack	integer	no
kern.usrstack64	integer	no
kern.uuid	string	no
kern.version	string	no
kern.waketime	struct	no
machdep.cpu.address_bits.physical	integer	no
machdep.cpu.address_bits.virtual	integer	no
machdep.cpu.brand	integer	no
machdep.cpu.brand_string	string	no
machdep.cpu.cache.L2_associativity	integer	no
machdep.cpu.cache.linesize	integer	no
machdep.cpu.cache.size	integer	no
machdep.cpu.core_count	integer	no
machdep.cpu.cores_per_package	integer	no
machdep.cpu.extfamily	integer	no
machdep.cpu.extfeature_bits	integer	no
machdep.cpu.extfeatures	string	no
machdep.cpu.extmodel	integer	no
machdep.cpu.family	integer	no
machdep.cpu.feature_bits	integer	no
machdep.cpu.features	string	no
machdep.cpu.leaf7_feature_bits	integer	no
machdep.cpu.leaf7_features	string	no
machdep.cpu.logical_per_package	integer	no
machdep.cpu.max_basic	integer	no
machdep.cpu.max_ext	integer	no
machdep.cpu.microcode_version	integer	no
machdep.cpu.model	integer	no
machdep.cpu.processor_flag	integer	no
machdep.cpu.signature	integer	no
machdep.cpu.stepping	integer	no
machdep.cpu.thread_count	integer	no
machdep.cpu.tlb.data.large	integer	no
machdep.cpu.tlb.data.large_level1	integer	no
machdep.cpu.tlb.data.small	integer	no
machdep.cpu.tlb.data.small_level1	integer	no
machdep.cpu.tlb.inst.large	integer	no
machdep.cpu.tlb.inst.small	integer	no
machdep.cpu.tlb.shared	integer	no
machdep.cpu.ucupdate	integer	yes
machdep.cpu.vendor	string	no
machdep.cpu.xsave.extended_state	integer	no
machdep.tsc.deep_idle_rebase	integer	yes
machdep.tsc.frequency	integer	no
machdep.tsc.nanotime.generation	integer	no
machdep.tsc.nanotime.shift	integer	no
net.inet.ip.forwarding	integer	yes
net.inet.ip.portrange.first	integer	yes
net.inet.ip.portrange.hifirst	integer	yes
net.inet.ip.portrange.hilast	integer	yes
net.inet.ip.portrange.last	integer	yes
net.inet.ip.portrange.lowfirst	integer	yes
net.inet.ip.portrange.lowlast	integer	yes
net.inet.ip.redirect	integer	yes
net.inet.ip.ttl	integer	yes
net.inet.udp.checksum	integer	yes
net.inet.udp.maxdgram	integer	yes
vm.loadavg	struct	no
vm.swapusage	struct	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.cs_path	string	no
user.expr_nest_max	integer	no
user.line_max	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.posix2_version	integer	no
user.re_dup_max	integer	no
user.stream_max	integer	no
user.tzname_max	integer	no

Note that the hw.ncpu attribute is deprecated, and one of the more specific MIBs, hw.logicalcpu, hw.logicalcpu_max, hw.physicalcpu, or hw.physicalcpu_max, should be used instead.

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

EXIT STATUS

The sysctl utility exits 0 on success, and >0 if an error occurs.

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

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.

HISTORY

A sysctl utility first appeared in 4.4BSD.

In FreeBSD 2.2, sysctl was significantly remodeled.

sysctl(8)