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

     sysctl - get or set kernel state

     sysctl [-bdehiNnoRTtqx] [-B bufsize] [-f filename] name[=value] ...
     sysctl [-bdehNnoRTtqx] [-B bufsize] -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.

     -B bufsize
             Set the buffer size to read from the sysctl to bufsize.  This is
             necessary for a sysctl that has variable length, and the probe
             value of 0 is a valid length, such as kern.arandom.

     -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.

     -f filename
             Specify a file which contains a pair of name and value in each
             line.  sysctl reads and processes the specified file first and
             then processes the name and value pairs in the command line

     -h      Format output for human, rather than machine, readability.

     -i      Ignore unknown OIDs.  The purpose is to make use of sysctl for
             collecting data from a variety of machines (not all of which are
             necessarily running exactly the same software) easier.

     -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(1) (ports/shells/zsh), use
             the following code:

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

             To enable completion of variable names in tcsh(1), use:

                   complete sysctl 'n/*/`sysctl -Na`/'

     -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`

     -o      Show 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.

     -q      Suppress some warnings generated by sysctl to standard error.

     -T      Display only variables that are settable via loader

     -t      Print the type of the variable.

     -W      Display only writable variables that are not statistical.  Useful
             for determining the set of runtime tunable sysctls.

     -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, 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(1), systat(1), and netstat(1).

     Some of the variables which cannot be modified during normal system
     operation 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
     privilege can change the value.  String and integer values can be set
     using sysctl.

     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.logsigexit                          integer       yes
     security.bsd.suser_enabled               integer       yes
     security.bsd.see_other_uids              integer       yes
     security.bsd.unprivileged_proc_debug     integer       yes
     security.bsd.unprivileged_read_msgbuf    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
     hw.realmem                               integer       no
     machdep.adjkerntz                        integer       yes
     machdep.disable_rtc_set                  integer       yes
     machdep.guessed_bootdev                  string        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
     user.stream_max                          integer       no
     user.tzname_max                          integer       no

     <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
     <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

     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

     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

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

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

     A sysctl utility first appeared in 4.4BSD.

     In FreeBSD 2.2, sysctl was significantly remodeled.

     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.

FreeBSD 11.1-RELEASE-p4        December 10, 2015       FreeBSD 11.1-RELEASE-p4
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