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Mac OS X / Darwin man pages : sysctl (8)
sysctl (8)

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Name

sysctl - get or set kernel state

Synopsis

sysctl [-bn] name ...
sysctl [-bn] -w name=value ...
sysctl [-bn] -a
sysctl [-bn] -A
sysctl [-bn] -X

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
List all MIB variables including 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.

-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.

-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`

-X
Same as -A but prints a hex dump of the entire value instead of just the first few bytes.

-w name=value
Used to set values. The MIB name ( name ) followed by an equal sign and the new value ( value ) to be used.

If just a MIB style name is given, the corresponding value is retrieved.

The information available from sysctl consists of integers, strings, and tables. The tabular information can only be retrieved by special purpose programs such as ps, systat, and netstat. 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.

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 yes
kern.maxfiles
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.link_max
integer no
kern.max_canon
integer no
kern.max_input
integer no
kern.name_max
integer no
kern.path_max
integer no
kern.pipe_buf
integer no
kern.chown_restricted
integer no
kern.no_trunc
integer no
kern.vdisable
integer no
kern.boottime
struct no
vm.loadavg
struct no machdep.console_device dev_t no
net.inet.ip.forwarding
integer yes
net.inet.ip.redirect
integer yes
net.inet.ip.ttl
integer yes
net.inet.icmp.maskrepl
integer yes
net.inet.udp.checksum
integer yes
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
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

The sysctl program can get or set debugging variables that have been identified for its display. This information can be obtained by using the command:

sysctl debug
In addition, sysctl can extract information about the filesystems that have been compiled into the running system. This information can be obtained by using the command:

sysctl vfs
By default, only filesystems that are actively being used are listed. Use of the -A flag lists all the filesystems compiled into the running kernel.

Examples

For example, to retrieve the maximum number of processes allowed in the system, one would use the follow request: sysctl kern.maxproc

To set the maximum number of processes allowed in the system to 1000, one would use the follow request:
sysctl -w kern.maxproc=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

Files

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

See Also

sysctl(3)

History

sysctl first appeared in 4.4BSD.

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