1.\"- 2.\" SPDX-License-Identifier: BSD-3-Clause 3.\" 4.\" Copyright (c) 1993 5.\" The Regents of the University of California. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. Neither the name of the University nor the names of its contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.Dd October 29, 2024 32.Dt SYSCTL 8 33.Os 34.Sh NAME 35.Nm sysctl 36.Nd get or set kernel state 37.Sh SYNOPSIS 38.Nm 39.Op Fl bdeFhilNnoTtqWx 40.Op Fl B Ar bufsize 41.Op Fl f Ar filename 42.Ar name Ns Op = Ns Ar value Ns Op , Ns Ar value 43.Ar ... 44.Nm 45.Op Fl bdeFhlNnoTtqWx 46.Op Fl B Ar bufsize 47.Fl a 48.Sh DESCRIPTION 49The 50.Nm 51utility retrieves kernel state and allows processes with appropriate 52privilege to set kernel state. 53The state to be retrieved or set is described using a 54.Dq Management Information Base 55.Pq Dq MIB 56style name, described as a dotted set of components. 57.Pp 58The following options are available: 59.Bl -tag -width "-f filename" 60.It Fl A 61Equivalent to 62.Fl o a 63(for compatibility). 64.It Fl a 65List all the currently available values except for those which are 66opaque or excluded from listing via the 67.Dv CTLFLAG_SKIP 68flag. 69This option is ignored if one or more variable names are specified on 70the command line. 71.It Fl b 72Force the value of the variable(s) to be output in raw, binary format. 73No names are printed and no terminating newlines are output. 74This is mostly useful with a single variable. 75.It Fl B Ar bufsize 76Set the buffer size to read from the 77.Nm 78to 79.Ar bufsize . 80This is necessary for a 81.Nm 82that has variable length, and the probe value of 0 is a valid length, such as 83.Va kern.arandom . 84.It Fl d 85Print the description of the variable instead of its value. 86.It Fl e 87Separate the name and the value of the variable(s) with 88.Ql = . 89This is useful for producing output which can be fed back to the 90.Nm 91utility. 92This option is ignored if either 93.Fl N 94or 95.Fl n 96is specified, or a variable is being set. 97.It Fl f Ar filename 98Specify a file which contains a pair of name and value in each line. 99.Nm 100reads and processes the specified file first and then processes the name 101and value pairs in the command line argument. 102.It Fl F 103Print the format of the variable. 104This is additional information to describe the type of the variable and 105most useful with struct types such as clockinfo, timeval, and loadavg. 106.It Fl h 107Format output for human, rather than machine, readability. 108.It Fl i 109Ignore unknown OIDs. 110The purpose is to make use of 111.Nm 112for collecting data from a variety of machines (not all of which 113are necessarily running exactly the same software) easier. 114.It Fl J 115Display only jail prision sysctl variables (CTLFLAG_PRISON). 116.It Fl l 117Show the length of variables along with their values. 118This option cannot be combined with the 119.Fl N 120option. 121.It Fl N 122Show only variable names, not their values. 123This is particularly useful with shells that offer programmable 124completion. 125To enable completion of variable names in 126.Xr zsh 1 Pq Pa ports/shells/zsh , 127use the following code: 128.Bd -literal -offset indent 129listsysctls () { set -A reply $(sysctl -AN ${1%.*}) } 130compctl -K listsysctls sysctl 131.Ed 132.Pp 133To enable completion of variable names in 134.Xr tcsh 1 , 135use: 136.Pp 137.Dl "complete sysctl 'n/*/`sysctl -Na`/'" 138.It Fl n 139Do not show variable names. 140This option is useful for setting shell variables. 141For instance, to save the pagesize in variable 142.Va psize , 143use: 144.Pp 145.Dl "set psize=`sysctl -n hw.pagesize`" 146.It Fl o 147Show opaque variables (which are normally suppressed). 148The format and length are printed, as well as a hex dump of the first 149sixteen bytes of the value. 150.It Fl q 151Suppress some warnings generated by 152.Nm 153to standard error. 154.It Fl T 155Display only variables that are settable via loader (CTLFLAG_TUN). 156.It Fl t 157Print the type of the variable. 158.It Fl V 159Display only VNET sysctl variables (CTLFLAG_VNET). 160.It Fl W 161Display only writable variables that are not statistical. 162Useful for determining the set of runtime tunable sysctls. 163.It Fl X 164Equivalent to 165.Fl x a 166(for compatibility). 167.It Fl x 168As 169.Fl o , 170but prints a hex dump of the entire value instead of just the first 171few bytes. 172.El 173.Pp 174The information available from 175.Nm 176consists of integers, strings, and opaque types. 177The 178.Nm 179utility 180only knows about a couple of opaque types, and will resort to hexdumps 181for the rest. 182The opaque information is much more useful if retrieved by special 183purpose programs such as 184.Xr ps 1 , 185.Xr systat 1 , 186and 187.Xr netstat 1 . 188.Pp 189Some of the variables which cannot be modified during normal system 190operation can be initialized via 191.Xr loader 8 192tunables. 193This can for example be done by setting them in 194.Xr loader.conf 5 . 195Please refer to 196.Xr loader.conf 5 197for more information on which tunables are available and how to set them. 198.Pp 199The string and integer information is summarized below. 200For a detailed description of these variables see 201.Xr sysctl 3 202and 203.Xr security 7 . 204.Pp 205The changeable column indicates whether a process with appropriate 206privilege can change the value. 207String and integer values can be set using 208.Nm . 209.Bl -column security.bsd.unprivileged_read_msgbuf integerxxx 210.It Sy "Name Type Changeable" 211.It Va "kern.ostype string no" 212.It Va "kern.osrelease string no" 213.It Va "kern.osrevision integer no" 214.It Va "kern.version string no" 215.It Va "kern.maxvnodes integer yes" 216.It Va "kern.maxproc integer no" 217.It Va "kern.maxprocperuid integer yes" 218.It Va "kern.maxfiles integer yes" 219.It Va "kern.maxfilesperproc integer yes" 220.It Va "kern.argmax integer no" 221.It Va "kern.securelevel integer raise only" 222.It Va "kern.hostname string yes" 223.It Va "kern.hostid integer yes" 224.It Va "kern.clockrate struct no" 225.It Va "kern.posix1version integer no" 226.It Va "kern.ngroups integer no" 227.It Va "kern.job_control integer no" 228.It Va "kern.saved_ids integer no" 229.It Va "kern.boottime struct no" 230.It Va "kern.domainname string yes" 231.It Va "kern.filedelay integer yes" 232.It Va "kern.dirdelay integer yes" 233.It Va "kern.metadelay integer yes" 234.It Va "kern.osreldate integer no" 235.It Va "kern.bootfile string yes" 236.It Va "kern.corefile string yes" 237.It Va "kern.logsigexit integer yes" 238.It Va "security.bsd.suser_enabled integer yes" 239.It Va "security.bsd.see_other_uids integer yes" 240.It Va "security.bsd.see_other_gids integer yes" 241.It Va "security.bsd.see_jail_proc integer yes" 242.It Va "security.bsd.unprivileged_proc_debug integer yes" 243.It Va "security.bsd.unprivileged_read_msgbuf integer yes" 244.It Va "vm.loadavg struct no" 245.It Va "hw.machine string no" 246.It Va "hw.model string no" 247.It Va "hw.ncpu integer no" 248.It Va "hw.byteorder integer no" 249.It Va "hw.physmem integer no" 250.It Va "hw.usermem integer no" 251.It Va "hw.pagesize integer no" 252.It Va "hw.floatingpoint integer no" 253.It Va "hw.machine_arch string no" 254.It Va "hw.realmem integer no" 255.It Va "machdep.adjkerntz integer yes" 256.It Va "machdep.disable_rtc_set integer yes" 257.It Va "machdep.guessed_bootdev string no" 258.It Va "user.cs_path string no" 259.It Va "user.bc_base_max integer no" 260.It Va "user.bc_dim_max integer no" 261.It Va "user.bc_scale_max integer no" 262.It Va "user.bc_string_max integer no" 263.It Va "user.coll_weights_max integer no" 264.It Va "user.expr_nest_max integer no" 265.It Va "user.line_max integer no" 266.It Va "user.re_dup_max integer no" 267.It Va "user.posix2_version integer no" 268.It Va "user.posix2_c_bind integer no" 269.It Va "user.posix2_c_dev integer no" 270.It Va "user.posix2_char_term integer no" 271.It Va "user.posix2_fort_dev integer no" 272.It Va "user.posix2_fort_run integer no" 273.It Va "user.posix2_localedef integer no" 274.It Va "user.posix2_sw_dev integer no" 275.It Va "user.posix2_upe integer no" 276.It Va "user.stream_max integer no" 277.It Va "user.tzname_max integer no" 278.It Va "user.localbase string no" 279.El 280.Sh FILES 281.Bl -tag -width "<netinet/icmp_var.h>" -compact 282.It In sys/sysctl.h 283definitions for top level identifiers, second level kernel and hardware 284identifiers, and user level identifiers 285.It In sys/socket.h 286definitions for second level network identifiers 287.It In sys/gmon.h 288definitions for third level profiling identifiers 289.It In vm/vm_param.h 290definitions for second level virtual memory identifiers 291.It In netinet/in.h 292definitions for third level Internet identifiers and 293fourth level IP identifiers 294.It In netinet/icmp_var.h 295definitions for fourth level ICMP identifiers 296.It In netinet/udp_var.h 297definitions for fourth level UDP identifiers 298.El 299.Sh EXIT STATUS 300.Ex -std 301.Sh EXAMPLES 302For example, to retrieve the maximum number of processes allowed 303in the system, one would use the following request: 304.Pp 305.Dl Va "sysctl kern.maxproc" 306.Pp 307To set the maximum number of processes allowed 308per uid to 1000, one would use the following request: 309.Pp 310.Dl Va "sysctl kern.maxprocperuid=1000" 311.Pp 312Information about the system clock rate may be obtained with: 313.Pp 314.Dl Va "sysctl kern.clockrate" 315.Pp 316Information about the load average history may be obtained with: 317.Pp 318.Dl Va "sysctl vm.loadavg" 319.Pp 320More variables than these exist, and the best and likely only place 321to search for their deeper meaning is undoubtedly the source where 322they are defined. 323.Sh COMPATIBILITY 324The 325.Fl w 326option has been deprecated and is silently ignored. 327.Sh SEE ALSO 328.Xr sysctl 3 , 329.Xr loader.conf 5 , 330.Xr sysctl.conf 5 , 331.Xr security 7 , 332.Xr loader 8 , 333.Xr jail 8 334.Sh HISTORY 335A 336.Nm 337utility first appeared in 338.Bx 4.4 . 339.Pp 340In 341.Fx 2.2 , 342.Nm 343was significantly remodeled. 344.Sh BUGS 345The 346.Nm 347utility presently exploits an undocumented interface to the kernel 348.Xr sysctl 9 349facility to traverse the sysctl tree and to retrieve format 350and name information. 351This correct interface is being thought about for the time being. 352