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SYSCTL(8)               FreeBSD System Manager's Manual              SYSCTL(8)

     sysctl -- get or set kernel state

     sysctl [-bdeNnox] name[=value] ...
     sysctl [-bdeNnox] -a

     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.

     -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, use the following code:

                   listsysctls () { set -A reply $(sysctl -AN ${1%.*}) }
                   compctl -K listsysctls sysctl

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

                   set psize=`sysctl -n hw.pagesize`

     -o      Show opaque variables (which are normally suppressed).  The for-
             mat and length are printed, as well as a hex dump of the first
             sixteen bytes of the value.

     -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 (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, systat, and netstat.

     Some of the variables which cannot be modified during normal system oper-
     ation 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 privi-
     lege can change the value.  String, integer, and devices values can be
     set using sysctl.  For device values, value can be specified as a charac-
     ter device special file name.  Special values off and none denote ``no

     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
     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
     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

     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

     <sys/sysctl.h>        definitions for top level identifiers, second level
                           kernel and hardware identifiers, and user level
     <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 identi-
     <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

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

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

     The sysctl utility presently exploits an undocumented interface to the
     kernel sysctl facility to traverse the sysctl tree and to retrieve format
     and name information.  This correct interface is being thought about for
     the time being.

     A sysctl utility first appeared in 4.4BSD.

     In FreeBSD 2.2, sysctl was significantly remodeled.

FreeBSD 4.10                    March 10, 2002                    FreeBSD 4.10


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