SYSCTL(8) BSD System Manager's Manual SYSCTL(8)
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 com-
mand 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`
-w name=value
Used to set values. The MIB name ( name ) followed by an equal sign and the new value ( value ) to be used.
-X Same as -A, but prints a hex dump of the entire value instead of just the first few bytes.
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
vm.swapusage 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.memsize 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 request:
sysctl kern.maxproc
To set the maximum number of processes allowed in the system to 1000, one would use the 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
Information about the system's swap space usage may be obtained with:
sysctl vm.swapusage
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.
BSD
June 2, 2019 BSD