SYSCTL(8) | System Manager's Manual | SYSCTL(8) |
sysctl
—
sysctl |
[-AdeMnq ] [-r |
-x ] [name ...] |
sysctl |
[-nq ] [-r |
-x ] -w
name[?]= value
... |
sysctl |
[-en ] [-r |
-x ] -a |
sysctl |
[-nq ] [-r |
-x ] -f
file |
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
‘/’ character may also be used as a separator and a leading
separator character is accepted. If name specifies a
non-leaf node in the MIB, all the nodes underneath name
will be printed.
The following options are available:
-A
-f
file are given. Those
with string or integer values will be printed as with the
-a
flag; for table or structure values that
sysctl
is not able to print, the name of the
utility to retrieve them is given. Errors in retrieving or setting values
will be directed to stdout instead of stderr.-a
-d
-e
=
’. This is useful for producing
output which can be fed back to the sysctl
utility. This option is ignored if -n
is specified
or a variable is being set.-f
#
’) are ignored.
Line continuations with ‘\
’ are
permitted. Remaining lines are processed similarly to command line
arguments of the form name or
name=
value.
The -w
flag is implied by
-f
. Any name arguments are
ignored.-M
sysctl
print the MIB instead of any of the
actual values contained in the MIB. This causes the entire MIB to be
printed unless specific MIB arguments or -f
file are also given.-n
set psize=`sysctl -n hw.pagesize`
-q
-r
sysctl
cannot print directly can be retrieved with
this flag. This option conflicts with the -x
option.-w
=
’ with
no whitespace. To prevent an error if the MIB style name does not exist
(as would be the case with optional kernel components), one can separate
the MIB style name and the value with
‘?=
’. Only integral and string
values can be set via this method.-x
sysctl
print the requested value in a
hexadecimal representation instead of its regular form. If specified more
than once, the output for each value resembles that of
hexdump(1) when given the
-C
flag. This option conflicts with the
-r
option.The ‘proc
’ top-level MIB has
a special semantic: it represent per-process values and as such may differ
from one process to another. The second-level name is the pid of the process
(in decimal form), or the special word
‘curproc
’. For variables below
‘proc.⟨pid⟩.rlimit
’, the
integer value may be replaced with the string
‘unlimited
’ if it matches the magic
value used to disable a limit.
The information available from sysctl
consists of integers, strings, and tables. The tabular information can only
be retrieved by special purpose programs such as ps
,
systat
, and netstat
. See
sysctl(7) for description of
available MIBs.
The syntax for creating new nodes is “//create=new.node.path” followed by one or more of the following attributes separated by commas. The use of a double separator (both ‘/’ and ‘.’ can be used as separators) as the prefix tells sysctl that the first series of tokens is not a MIB name, but a command. It is recommended that the double separator preceding the command not be the same as the separator used in naming the MIB entry so as to avoid possible parse conflicts. The “value” assigned, if one is given, must be last.
sysctl
must be invoked
with -A
or the hidden node must be
specifically requested in order to see itsysctl
default to hexadecimal display of the retrieved valueNew nodes must fit the following set of criteria:
If any of the given parameters describes an invalid configuration,
sysctl
will emit a diagnostic message to the
standard error and exit.
Descriptions can be added by the super-user to any node that does not have one, provided that the node is not marked with the “PERMANENT” flag. The syntax is similar to the syntax for creating new nodes with the exception of the keyword that follows the double separator at the start of the command: “//describe=new.node.path=new node description”. Once a description has been added, it cannot be changed or removed.
When destroying nodes, only the path to the node is necessary,
i.e., “//destroy=old.node.path”. No other parameters are
expected or permitted. Nodes being destroyed must have no children, and
their parent must be writable. Nodes that are marked with the
“PERMANENT
” flag (as assigned by the
kernel) may not be deleted.
In all cases, the initial ‘=’ that follows the command (eg, “create”, “destroy”, or “describe”) may be replaced with another instance of the separator character, provided that the same separator character is used for the length of the name specification.
sysctl
variables set at boot timesysctl kern.maxproc
To set the maximum number of processes allowed in the system to 1000, one would use the following request:
sysctl -w kern.maxproc=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
To view the values of the per-process variables of the current shell, the request:
sysctl proc.$$
To redirect core dumps to the /var/tmp/⟨username⟩ directory,
sysctl -w proc.$$.corename=/var/tmp/%u/%n.core
sysctl -w proc.curproc.corename=/var/tmp/%u/%n.core
To create the root of a new sub-tree called “local” add some children to the new node, and some descriptions:
sysctl -w //create=local sysctl -w //describe=local=my local sysctl tree sysctl -w //create=local.esm_debug,type=int,symbol=esm_debug,flags=w sysctl -w //describe=local.esm_debug=esm driver debug knob sysctl -w //create=local.audiodebug,type=int,symbol=audiodebug,flags=w sysctl -w //describe=local.audiodebug=generic audio debug knob
To destroy that same subtree:
sysctl -w //destroy=local.esm_debug sysctl -w //destroy=local.audiodebug sysctl -w //destroy=local
sysctl
first appeared in 4.4BSD.
August 2, 2011 | NetBSD 9.4 |