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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 1.7 2007/10/02 12:57:00 hasso 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 "hw.sensors.<xname>.<type><numt> struct no"
207 .It "machdep.console_device udev_t no"
208 .It "machdep.adjkerntz integer yes"
209 .It "machdep.disable_rtc_set integer yes"
210 .It "user.cs_path string no"
211 .It "user.bc_base_max integer no"
212 .It "user.bc_dim_max integer no"
213 .It "user.bc_scale_max integer no"
214 .It "user.bc_string_max integer no"
215 .It "user.coll_weights_max integer no"
216 .It "user.expr_nest_max integer no"
217 .It "user.line_max integer no"
218 .It "user.re_dup_max integer no"
219 .It "user.posix2_version integer no"
220 .It "user.posix2_c_bind integer no"
221 .It "user.posix2_c_dev integer no"
222 .It "user.posix2_char_term integer no"
223 .It "user.posix2_fort_dev integer no"
224 .It "user.posix2_fort_run integer no"
225 .It "user.posix2_localedef integer no"
226 .It "user.posix2_sw_dev integer no"
227 .It "user.posix2_upe integer no"
228 .It "user.stream_max integer no"
229 .It "user.tzname_max integer no"
230 .El
231 .Sh FILES
232 .Bl -tag -width ".In netinet/icmp_var.h" -compact
233 .It In sys/sysctl.h
234 definitions for top level identifiers, second level kernel and hardware
235 identifiers, and user level identifiers
236 .It In sys/socket.h
237 definitions for second level network identifiers
238 .It In sys/gmon.h
239 definitions for third level profiling identifiers
240 .It In vm/vm_param.h
241 definitions for second level virtual memory identifiers
242 .It In netinet/in.h
243 definitions for third level Internet identifiers and
244 fourth level IP identifiers
245 .It In netinet/icmp_var.h
246 definitions for fourth level ICMP identifiers
247 .It In netinet/udp_var.h
248 definitions for fourth level UDP identifiers
249 .El
250 .Sh EXAMPLES
251 For example, to retrieve the maximum number of processes allowed
252 in the system, one would use the following request:
253 .Pp
254 .Dl "sysctl kern.maxproc"
255 .Pp
256 To set the maximum number of processes allowed
257 per uid to 1000, one would use the following request:
258 .Pp
259 .Dl "sysctl kern.maxprocperuid=1000"
260 .Pp
261 The device used for crash dumps can be specified using:
262 .Pp
263 .Dl "sysctl kern.dumpdev=/dev/somedev"
264 .Pp
265 which is equivalent to
266 .Pp
267 .Dl "dumpon /dev/somedev"
268 .Pp
269 Information about the system clock rate may be obtained with:
270 .Pp
271 .Dl "sysctl kern.clockrate"
272 .Pp
273 Information about the load average history may be obtained with:
274 .Pp
275 .Dl "sysctl vm.loadavg"
276 .Pp
277 More variables than these exist, and the best and likely only place
278 to search for their deeper meaning is undoubtedly the source where
279 they are defined.
280 .Sh COMPATIBILITY
281 The
282 .Fl w
283 option has been deprecated and is silently ignored.
284 .Sh SEE ALSO
285 .Xr sysctl 3 ,
286 .Xr loader.conf 5 ,
287 .Xr sysctl.conf 5 ,
288 .Xr loader 8
289 .Sh HISTORY
290 A
291 .Nm
292 utility first appeared in
293 .Bx 4.4 .
294 .Pp
295 In
296 .Fx 2.2 ,
297 .Nm
298 was significantly remodeled.
299 .Sh BUGS
300 The
301 .Nm
302 utility presently exploits an undocumented interface to the kernel
303 sysctl facility to traverse the sysctl tree and to retrieve format
304 and name information.
305 This correct interface is being thought about for the time being.