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32 .\" From: @(#)sysctl.8 8.1 (Berkeley) 6/6/93
33 .\" $FreeBSD: src/sbin/sysctl/sysctl.8,v 1.23.2.17 2003/05/19 07:49:34 brueffer Exp $
34 .\" $DragonFly: src/sbin/sysctl/sysctl.8,v 1.6 2006/09/21 18:16:07 dillon Exp $
35 .\"
36 .Dd March 10, 2002
37 .Dt SYSCTL 8
38 .Os
39 .Sh NAME
40 .Nm sysctl
41 .Nd get or set kernel state
42 .Sh SYNOPSIS
43 .Nm
44 .Op Fl bdeNnox
45 .Ar name Ns Op = Ns Ar value
46 .Ar ...
47 .Nm
48 .Op Fl bdeNnox
49 .Fl a
50 .Sh DESCRIPTION
51 The
52 .Nm
53 utility retrieves kernel state and allows processes with appropriate
54 privilege to set kernel state.
55 The state to be retrieved or set is described using a
56 .Dq Management Information Base
57 .Pq Dq MIB
58 style name, described as a dotted set of
59 components.
60 .Pp
61 The following options are available:
62 .Bl -tag -width indent
63 .It Fl A
64 Equivalent to
65 .Fl o a
66 (for compatibility).
67 .It Fl a
68 List all the currently available non-opaque values.
69 This option is ignored if one or more variable names are specified on
70 the command line.
71 .It Fl b
72 Force the value of the variable(s) to be output in raw, binary format.
73 No names are printed and no terminating newlines are output.
74 This is mostly useful with a single variable.
75 .It Fl d
76 Print the description of the variable instead of its value.
77 .It Fl e
78 Separate the name and the value of the variable(s) with
79 .Ql = .
80 This is useful for producing output which can be fed back to the
81 .Nm
82 utility.
83 This option is ignored if either
84 .Fl N
85 or
86 .Fl n
87 is specified, or a variable is being set.
88 .It Fl N
89 Show only variable names, not their values.
90 This is particularly useful with shells that offer programmable
91 completion.
92 To enable completion of variable names in
93 .Nm zsh ,
94 use the following code:
95 .Bd -literal -offset indent
96 listsysctls () { set -A reply $(sysctl -AN ${1%.*}) }
97 compctl -K listsysctls sysctl
98 .Ed
99 .It Fl n
100 Show only variable values, not their names.
101 This option is useful for setting shell variables.
102 For instance, to save the pagesize in variable
103 .Va psize ,
104 use:
105 .Pp
106 .Dl "set psize=`sysctl -n hw.pagesize`"
107 .It Fl o
108 Show opaque variables (which are normally suppressed).
109 The format and length are printed, as well as a hex dump of the first
110 sixteen bytes of the value.
111 .It Fl X
112 Equivalent to
113 .Fl x a
114 (for compatibility).
115 .It Fl x
116 As
117 .Fl o ,
118 but prints a hex dump of the entire value instead of just the first
119 few bytes.
120 .El
121 .Pp
122 The information available from
123 .Nm
124 consists of integers, strings, devices
125 .Pq Vt udev_t ,
126 and opaque types.
127 The
128 .Nm
129 utility
130 only knows about a couple of opaque types, and will resort to hexdumps
131 for the rest.
132 The opaque information is much more useful if retrieved by special
133 purpose programs such as
134 .Nm ps ,
135 .Nm systat
136 and
137 .Nm netstat .
138 .Pp
139 Some of the variables which cannot be modified during normal system
140 operation can be initialized via
141 .Xr loader 8
142 tunables.
143 This can for example be done by setting them in
144 .Xr loader.conf 5 .
145 Please refer to
146 .Xr loader.conf 5
147 for more information on which tunables are available and how to set them.
148 .Pp
149 The string and integer information is summarized below.
150 For a detailed description of these variable see
151 .Xr sysctl 3 .
152 .Pp
153 The changeable column indicates whether a process with appropriate
154 privilege can change the value.
155 String, integer, and devices values can be set using
156 .Nm .
157 For device values,
158 .Cm value
159 can be specified as a character device special file name.
160 Special values
161 .Cm off
162 and
163 .Ar none
164 denote
165 .Dq no device .
166 .Bl -column net.inet.ip.forwardingxxxxxx integerxxx
167 .It Sy "Name Type Changeable
168 .It "kern.ostype string no
169 .It "kern.osrelease string no
170 .It "kern.osrevision integer no
171 .It "kern.version string no
172 .It "kern.maxvnodes integer yes
173 .It "kern.maxproc integer no
174 .It "kern.maxprocperuid integer yes
175 .It "kern.maxfiles integer yes
176 .It "kern.maxfilesperproc integer yes
177 .It "kern.argmax integer no
178 .It "kern.securelevel integer raise only
179 .It "kern.hostname string yes
180 .It "kern.hostid integer yes
181 .It "kern.clockrate struct no
182 .It "kern.posix1version integer no
183 .It "kern.ngroups integer no
184 .It "kern.job_control integer no
185 .It "kern.saved_ids integer no
186 .It "kern.boottime struct no
187 .It "kern.domainname string yes
188 .It "kern.filedelay integer yes
189 .It "kern.dirdelay integer yes
190 .It "kern.metadelay integer yes
191 .It "kern.osreldate string no
192 .It "kern.bootfile string yes
193 .It "kern.corefile string yes
194 .It "kern.dumpdev udev_t yes
195 .It "kern.logsigexit integer yes
196 .It "vm.loadavg struct no
197 .It "hw.machine string no
198 .It "hw.model string no
199 .It "hw.ncpu integer no
200 .It "hw.byteorder integer no
201 .It "hw.physmem integer no
202 .It "hw.usermem integer no
203 .It "hw.pagesize integer no
204 .It "hw.floatingpoint integer no
205 .It "hw.machine_arch string no
206 .It "machdep.console_device udev_t no
207 .It "machdep.adjkerntz integer yes
208 .It "machdep.disable_rtc_set integer yes
209 .It "user.cs_path string no
210 .It "user.bc_base_max integer no
211 .It "user.bc_dim_max integer no
212 .It "user.bc_scale_max integer no
213 .It "user.bc_string_max integer no
214 .It "user.coll_weights_max integer no
215 .It "user.expr_nest_max integer no
216 .It "user.line_max integer no
217 .It "user.re_dup_max integer no
218 .It "user.posix2_version integer no
219 .It "user.posix2_c_bind integer no
220 .It "user.posix2_c_dev integer no
221 .It "user.posix2_char_term integer no
222 .It "user.posix2_fort_dev integer no
223 .It "user.posix2_fort_run integer no
224 .It "user.posix2_localedef integer no
225 .It "user.posix2_sw_dev integer no
226 .It "user.posix2_upe integer no
227 .It "user.stream_max integer no
228 .It "user.tzname_max integer no
229 .El
230 .Sh FILES
231 .Bl -tag -width ".In netinet/icmp_var.h" -compact
232 .It In sys/sysctl.h
233 definitions for top level identifiers, second level kernel and hardware
234 identifiers, and user level identifiers
235 .It In sys/socket.h
236 definitions for second level network identifiers
237 .It In sys/gmon.h
238 definitions for third level profiling identifiers
239 .It In vm/vm_param.h
240 definitions for second level virtual memory identifiers
241 .It In netinet/in.h
242 definitions for third level Internet identifiers and
243 fourth level IP identifiers
244 .It In netinet/icmp_var.h
245 definitions for fourth level ICMP identifiers
246 .It In netinet/udp_var.h
247 definitions for fourth level UDP identifiers
248 .El
249 .Sh EXAMPLES
250 For example, to retrieve the maximum number of processes allowed
251 in the system, one would use the following request:
252 .Pp
253 .Dl "sysctl kern.maxproc"
254 .Pp
255 To set the maximum number of processes allowed
256 per uid to 1000, one would use the following request:
257 .Pp
258 .Dl "sysctl kern.maxprocperuid=1000"
259 .Pp
260 The device used for crash dumps can be specified using:
261 .Pp
262 .Dl "sysctl kern.dumpdev=/dev/somedev"
263 .Pp
264 which is equivalent to
265 .Pp
266 .Dl "dumpon /dev/somedev"
267 .Pp
268 Information about the system clock rate may be obtained with:
269 .Pp
270 .Dl "sysctl kern.clockrate"
271 .Pp
272 Information about the load average history may be obtained with:
273 .Pp
274 .Dl "sysctl vm.loadavg"
275 .Pp
276 More variables than these exist, and the best and likely only place
277 to search for their deeper meaning is undoubtedly the source where
278 they are defined.
279 .Sh COMPATIBILITY
280 The
281 .Fl w
282 option has been deprecated and is silently ignored.
283 .Sh SEE ALSO
284 .Xr sysctl 3 ,
285 .Xr loader.conf 5 ,
286 .Xr sysctl.conf 5 ,
287 .Xr loader 8
288 .Sh HISTORY
289 A
290 .Nm
291 utility first appeared in
292 .Bx 4.4 .
293 .Pp
294 In
295 .Fx 2.2 ,
296 .Nm
297 was significantly remodeled.
298 .Sh BUGS
299 The
300 .Nm
301 utility presently exploits an undocumented interface to the kernel
302 sysctl facility to traverse the sysctl tree and to retrieve format
303 and name information.
304 This correct interface is being thought about for the time being.