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From: @(#)sysctl.8 8.1 (Berkeley) 6/6/93
$Id$
.Dd September 23, 1994 .Dt SYSCTL 8 .Os .Sh NAME .Nm sysctl .Nd get or set kernel state .Sh SYNOPSIS .Nm sysctl .Op Fl n .Ar name ... .Nm sysctl .Op Fl n .Fl w .Ar name=value ... .Nm sysctl .Op Fl n .Fl aA .Sh DESCRIPTION The .Nm 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 .Fl a flag can be used to list all the currently available string or integer values. The .Fl A flag will list all the known MIB names including tables. Those with string or integer values will be printed as with the .Fl a flag; for the table values, the name of the utility to retrieve them is given.
p The .Fl n flag specifies that the printing of the field name should be suppressed and that only its value should be output. This flag is useful for setting shell variables. For example, to save the pagesize in variable psize, use: d -literal -offset indent -compact set psize=`sysctl -n hw.pagesize` .Ed
p If just a MIB style name is given, the corresponding value is retrieved. If a value is to be set, the .Fl w flag must be specified and the MIB name followed by an equal sign and the new value to be used.
p The information available from .Nm sysctl consists of integers, strings, and tables. The tabular information can only be retrieved by special purpose programs such as .Nm ps , .Nm systat , and .Nm netstat . The string and integer information is summaried below. For a detailed description of these variable see .Xr sysctl 3 . The changeable column indicates whether a process with appropriate privilege can change the value. l -column net.inet.ip.forwardingxxxxxx integerxxx t Sy Name Type Changeable t kern.ostype string no t kern.osrelease string no t kern.osrevision integer no t kern.version string no t kern.maxvnodes integer yes t kern.maxproc integer yes t kern.maxfiles integer yes t kern.argmax integer no t kern.securelevel integer raise only t kern.hostname string yes t kern.hostid integer yes t kern.clockrate struct no t kern.posix1version integer no t kern.ngroups integer no t kern.job_control integer no t kern.saved_ids integer no t kern.link_max integer no t kern.max_canon integer no t kern.max_input integer no t kern.name_max integer no t kern.path_max integer no t kern.pipe_buf integer no t kern.chown_restricted integer no t kern.no_trunc integer no t kern.vdisable integer no t kern.boottime struct no t kern.domainname string yes t kern.update integer yes t kern.osreldate string no t kern.bootfile string yes t vm.loadavg struct no t machdep.console_device dev_t no t net.inet.ip.forwarding integer yes t net.inet.ip.redirect integer yes t net.inet.ip.ttl integer yes t net.inet.icmp.maskrepl integer yes t net.inet.udp.checksum integer yes t hw.machine string no t hw.model string no t hw.ncpu integer no t hw.byteorder integer no t hw.physmem integer no t hw.usermem integer no t hw.pagesize integer no t hw.floatingpoint integer no t user.cs_path string no t user.bc_base_max integer no t user.bc_dim_max integer no t user.bc_scale_max integer no t user.bc_string_max integer no t user.coll_weights_max integer no t user.expr_nest_max integer no t user.line_max integer no t user.re_dup_max integer no t user.posix2_version integer no t user.posix2_c_bind integer no t user.posix2_c_dev integer no t user.posix2_char_term integer no t user.posix2_fort_dev integer no t user.posix2_fort_run integer no t user.posix2_localedef integer no t user.posix2_sw_dev integer no t user.posix2_upe integer no .El .Sh EXAMPLES
p For example, to retrieve the maximum number of processes allowed in the system, one would use the follow request: d -literal -offset indent -compact sysctl kern.maxproc .Ed
p To set the maximum number of processes allowed in the system to 1000, one would use the follow request: d -literal -offset indent -compact sysctl -w kern.maxproc=1000 .Ed
p Information about the system clock rate may be obtained with: d -literal -offset indent -compact sysctl kern.clockrate .Ed
p Information about the load average history may be obtained with d -literal -offset indent -compact sysctl vm.loadavg .Ed .Sh FILES l -tag -width <netinet/icmpXvar.h> -compact t Pa <sys/sysctl.h> definitions for top level identifiers, second level kernel and hardware identifiers, and user level identifiers t Pa <sys/socket.h> definitions for second level network identifiers t Pa <sys/gmon.h> definitions for third level profiling identifiers t Pa <vm/vm_param.h> definitions for second level virtual memory identifiers t Pa <netinet/in.h> definitions for third level Internet identifiers and fourth level IP identifiers t Pa <netinet/icmp_var.h> definitions for fourth level ICMP identifiers t Pa <netinet/udp_var.h> definitions for fourth level UDP identifiers .El .Sh SEE ALSO .Xr sysctl 3 .Sh HISTORY .Nm sysctl first appeared in 4.4BSD.