sysctl
—
get or set kernel state
sysctl |
[-bdehiNnoTtqWx ] [-B
bufsize] [-f
filename]
name[=value[,value]]
... |
sysctl |
[-bdehNnoTtqWx ] [-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
argument.
-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
- Do not show variable 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 (CTLFLAG_TUN).
-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 |
integer |
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 |
user.localbase |
string |
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 identifiers
<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
The sysctl
utility exits 0 on success,
and >0 if an error occurs.
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 defined.
The -w
option has been deprecated and is silently
ignored.
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.