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

     sysctl - get or set kernel state

     sysctl [-bdn] name ...
     sysctl [-bn] -w name=value ...
     sysctl [-bdn] -aAX

     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 the currently available string or integer values.

     -A      List all the known MIB names including opaques.  Those with
             string or integer values will be printed as with the -a flag; for
             the opaque values, information about the format and the length is
             printed in addition the first few bytes is dumped in hex.

     -X      Same as -A except the entire value of opaque variables is

     -n      Specify 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:
                   set psize=`sysctl -n hw.pagesize`

     -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      Display the description rather than the value of the requested

     -w name=value ...
             Set the MIB name to the new value.  If just a MIB style name is
             given, the corresponding value is retrieved.

     The information available from sysctl consists of integers, strings, and
     opaques.  Sysctl 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

     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       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.update                     integer       yes
     kern.osreldate                  string        no
     kern.bootfile                   string        yes
     kern.corefile                   string        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 follow request:
           sysctl kern.maxproc

     To set the maximum number of processes allowed per uid to 1000, one would
     use the follow request:
           sysctl -w 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

     _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
     _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


     Sysctl 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

     Sysctl first appeared in 4.4BSD.

     In FreeBSD 2.2, sysctl was significantly remodeled.

FreeBSD 11.0-PRERELEASE       September 23, 1994       FreeBSD 11.0-PRERELEASE


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