.\"	$OpenBSD: sysctl.8,v 1.109 2003/10/17 21:04:57 mcbride Exp $
.\"	$NetBSD: sysctl.8,v 1.4 1995/09/30 07:12:49 thorpej Exp $
.\"
.\" Copyright (c) 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
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.\" modification, are permitted provided that the following conditions
.\" are met:
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.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
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.\" 3. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\"	@(#)sysctl.8	8.2 (Berkeley) 5/9/95
.\"
.Dd December 18, 2002
.Dt SYSCTL 8
.Os
.Sh NAME
.Nm sysctl
.Nd get or set kernel state
.Sh SYNOPSIS
.Nm sysctl
.Op Fl n
.Ar variable ...
.Nm sysctl
.Op Fl nq
.Fl w
.Ar variable Ns = Ns Ar value ...
.Nm sysctl
.Op Fl n
.Fl Aa
.Sh DESCRIPTION
The
.Nm
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
.Dq Management Information Base
.Pq MIB
style name, described as a dotted set of components.
.Pp
The options are as follows:
.Bl -tag -width xxx
.It Fl A
List all the known MIB names including tables.
Those with string or integer values will be printed as with the
.Fl a
flag; for the table values, the name of the utility to retrieve them is given.
.It Fl a
List all the currently available string or integer values.
.It Fl n
Suppress printing of the field name, only output the field value.
Useful for setting shell variables.
For example, to set the psize shell variable to the pagesize of the hardware:
.Pp
.Dl # set psize=`sysctl -n hw.pagesize`
.Pp
.It Fl q
Suppress all output when setting a variable.
This option overrides the behaviour of
.Fl n .
.It Fl w
Required to set a variable.
The MIB name should be followed by an equal sign and the new value.
.El
.Pp
The information available from
.Nm
consists of integers, strings, and tables.
The tabular information can only be retrieved by special
purpose programs such as
.Nm ps ,
.Nm systat ,
and
.Nm netstat .
The string and integer information is summarized below.
For a detailed description of these variable see
.Xr sysctl 3 .
The changeable column indicates whether a process with appropriate
privilege can change the value.
.Bl -column net.inet.ip.ipsec-expire-acquirexxxx integerxxx
.It Sy Name	Type	Changeable
.It kern.ostype	string	no
.It kern.osrelease	string	no
.It kern.osrevision	integer	no
.It kern.version	string	no
.It kern.maxvnodes	integer	yes
.It kern.maxproc	integer	yes
.It kern.maxfiles	integer	yes
.It kern.argmax	integer	no
.It kern.securelevel	integer	raise only
.It kern.hostname	string	yes
.It kern.hostid	u_int	yes
.It kern.clockrate	struct	no
.It kern.posix1version	integer	no
.It kern.ngroups	integer	no
.It kern.job_control	integer	no
.It kern.saved_ids	integer	no
.It kern.boottime	struct	no
.It kern.domainname	string	yes
.It kern.maxpartitions	integer	no
.It kern.rawpartition	integer	no
.It kern.osversion	string	no
.It kern.somaxconn	integer	yes
.It kern.sominconn	integer	yes
.It kern.usermount	integer	yes
.It kern.random	struct	no
.It kern.nosuidcoredump	integer	yes
.It kern.fsync	integer	no
.It kern.sysvmsg	integer	no
.It kern.sysvsem	integer	no
.It kern.sysvshm	integer	no
.It kern.arandom	u_int	no
.It kern.msgbufsize	integer	no
.It kern.malloc.buckets	string	no
.It kern.malloc.bucket.<sz>	string	no
.It kern.malloc.kmemnames	string	no
.It kern.malloc.kmemstat.<name>	string	no
.It kern.cp_time	struct	no
.It kern.nchstats	struct	no
.It kern.forkstat	struct	no
.It kern.nselcoll	integer	no
.It kern.tty.tk_nin	int64_t	no
.It kern.tty.tk_nout	int64_t	no
.It kern.tty.tk_rawcc	int64_t	no
.It kern.tty.tk_cancc	int64_t	no
.It kern.ccpu	u_int	no
.It kern.fscale	integer	no
.It kern.nprocs	integer	no
.It kern.stackgap_random	integer	yes
.It kern.usercrypto	integer	yes
.It kern.cryptodevallowsoft	integer	yes
.It kern.splassert	integer	yes
.It kern.nfiles	integer	no
.It kern.ttycount	integer	no
.It kern.numvnodes	integer	no
.It kern.userasymcrypto	integer	yes
.It kern.seminfo.semmni	integer	yes
.It kern.seminfo.semmns	integer	yes
.It kern.seminfo.semmnu	integer	yes
.It kern.seminfo.semmsl	integer	yes
.It kern.seminfo.semopm	integer	yes
.It kern.seminfo.semume	integer	no
.It kern.seminfo.semusz	integer	no
.It kern.seminfo.semvmx	integer	no
.It kern.seminfo.semaem	integer	no
.It kern.shminfo.shmmax	integer	yes
.It kern.shminfo.shmmin	integer	yes
.It kern.shminfo.shmmni	integer	yes
.It kern.shminfo.shmseg	integer	yes
.It kern.shminfo.shmall	integer	yes
.It kern.watchdog.period	integer	yes
.It kern.watchdog.auto	integer	yes
.It kern.emul.nemuls	integer	no
.It kern.emul.other	integer	yes
.It vm.vmmeter	struct	no
.It vm.loadavg	struct	no
.It vm.psstrings	struct	no
.It vm.uvmexp	struct	no
.It vm.swapencrypt.enable	integer	yes
.It vm.swapencrypt.keyscreated	integer	no
.It vm.swapencrypt.keysdeleted	integer	no
.It vm.nkmempages	integer	no
.It vm.anonmin	integer	yes
.It vm.vtextmin	integer	yes
.It vm.vnodemin	integer	yes
.It vm.maxslp	integer	no
.It vm.uspace	integer	no
.It fs.posix.setuid	integer	yes
.It net.inet.ip.forwarding	integer	yes
.It net.inet.ip.redirect	integer	yes
.It net.inet.ip.ttl	integer	yes
.\" .It net.inet.ip.mtu	integer	yes
.It net.inet.ip.sourceroute	integer	yes
.It net.inet.ip.directed-broadcast	integer	yes
.It net.inet.ip.portfirst	integer	yes
.It net.inet.ip.portlast	integer	yes
.It net.inet.ip.porthifirst	integer	yes
.It net.inet.ip.porthilast	integer	yes
.It net.inet.ip.maxqueue	integer	yes
.It net.inet.ip.encdebug	integer	yes
.It net.inet.ip.ipsec-expire-acquire	integer	yes
.It net.inet.ip.ipsec-invalid-life	integer	yes
.It net.inet.ip.ipsec-pfs	integer	yes
.It net.inet.ip.ipsec-soft-allocs	integer	yes
.It net.inet.ip.ipsec-allocs	integer	yes
.It net.inet.ip.ipsec-soft-bytes	integer	yes
.It net.inet.ip.ipsec-bytes	integer	yes
.It net.inet.ip.ipsec-timeout	integer	yes
.It net.inet.ip.ipsec-soft-timeout	integer	yes
.It net.inet.ip.ipsec-soft-firstuse	integer	yes
.It net.inet.ip.ipsec-firstuse	integer	yes
.It net.inet.ip.ipsec-enc-alg	string	yes
.It net.inet.ip.ipsec-auth-alg	string	yes
.It net.inet.ip.mtudisc	integer	yes
.It net.inet.ip.mtudisctimeout	integer	yes
.It net.inet.ip.ipsec-comp-alg	string	yes
.It net.inet.icmp.maskrepl	integer	yes
.It net.inet.icmp.bmcastecho	integer	yes
.It net.inet.icmp.errppslimit	integer	yes
.It net.inet.icmp.rediraccept	integer	yes
.It net.inet.icmp.redirtimeout	integer	yes
.It net.inet.icmp.tstamprepl	integer	yes
.It net.inet.ipip.allow	integer	yes
.It net.inet.tcp.rfc1323	integer	yes
.It net.inet.tcp.keepinittime	integer	yes
.It net.inet.tcp.keepidle	integer	yes
.It net.inet.tcp.keepintvl	integer	yes
.It net.inet.tcp.slowhz	integer	no
.It net.inet.tcp.baddynamic	array	yes
.It net.inet.tcp.recvspace	integer	yes
.It net.inet.tcp.sendspace	integer	yes
.It net.inet.tcp.sack	integer	yes
.It net.inet.tcp.mssdflt	integer	yes
.It net.inet.tcp.rstppslimit	integer	yes
.It net.inet.tcp.ackonpush	integer	yes
.It net.inet.tcp.ecn	integer	yes
.It net.inet.udp.checksum	integer	yes
.It net.inet.udp.baddynamic	array	yes
.It net.inet.udp.recvspace	integer	yes
.It net.inet.udp.sendspace	integer	yes
.It net.inet.gre.allow	integer	yes
.It net.inet.gre.wccp	integer	yes
.It net.inet.esp.enable	integer	yes
.It net.inet.ah.enable	integer	yes
.It net.inet.mobileip.allow	integer	yes
.It net.inet.etherip.allow	integer	yes
.It net.inet.ipcomp.enable	integer	yes
.It net.inet.carp.allow	integer	yes
.It net.inet.carp.preempt	integer	yes
.It net.inet.carp.log	integer	yes
.It net.inet.carp.arpbalance	integer	yes
.It net.inet6.ip6.forwarding	integer	yes
.It net.inet6.ip6.redirect	integer	yes
.It net.inet6.ip6.hlim	integer	yes
.It net.inet6.ip6.maxfragpackets	integer	yes
.It net.inet6.ip6.accept_rtadv	integer	yes
.It net.inet6.ip6.keepfaith	integer	yes
.It net.inet6.ip6.log_interval	integer	yes
.It net.inet6.ip6.hdrnestlimit	integer	yes
.It net.inet6.ip6.dad_count	integer	yes
.It net.inet6.ip6.auto_flowlabel	integer	yes
.It net.inet6.ip6.defmcasthlim	integer	yes
.It net.inet6.ip6.kame_version	string	no
.It net.inet6.ip6.use_deprecated	integer	yes
.It net.inet6.ip6.rr_prune	integer	yes
.It net.inet6.ip6.v6only	integer	no
.It net.inet6.ip6.maxfrags	integer	yes
.It net.inet6.icmp6.rediraccept	integer	yes
.It net.inet6.icmp6.redirtimeout	integer	yes
.It net.inet6.icmp6.nd6_prune	integer	yes
.It net.inet6.icmp6.nd6_delay	integer	yes
.It net.inet6.icmp6.nd6_umaxtries	integer	yes
.It net.inet6.icmp6.nd6_mmaxtries	integer	yes
.It net.inet6.icmp6.nd6_useloopback	integer	yes
.It net.inet6.icmp6.nodeinfo	integer	yes
.It net.inet6.icmp6.errppslimit	integer	yes
.It net.inet6.icmp6.nd6_maxnudhint	integer	yes
.It net.inet6.icmp6.mtudisc_hiwat	integer	yes
.It net.inet6.icmp6.mtudisc_lowat	integer	yes
.It net.inet6.icmp6.nd6_debug	integer	yes
.It net.ipx.ipx.checksum	integer	yes
.It net.ipx.ipx.forwarding	integer	yes
.It net.ipx.ipx.netbios	integer	yes
.It net.ipx.ipx.recvspace	integer	yes
.It net.ipx.ipx.sendspace	integer	yes
.It debug.syncprt	integer	yes
.It debug.busyprt	integer	yes
.It debug.doclusterread	integer	yes
.It debug.doclusterwrite	integer	yes
.It debug.doreallocblks	integer	yes
.It debug.doasyncfree	integer	yes
.It debug.prtrealloc	integer	yes
.It hw.machine	string	no
.It hw.model	string	no
.It hw.ncpu	integer	no
.It hw.byteorder	integer	no
.It hw.physmem	integer	no
.It hw.usermem	integer	no
.It hw.pagesize	integer	no
.It hw.diskstats	struct	no
.It hw.disknames	string	no
.It hw.diskcount	integer	no
.It hw.sensors	struct	no
.It machdep.console_device	dev_t	no
.It machdep.unaligned_print	integer	yes (alpha only)
.It machdep.unaligned_fix	integer	yes (alpha only)
.It machdep.unaligned_sigbus	integer	yes (alpha only)
.It machdep.apmwarn	integer	yes (i386 only)
.It machdep.apmhalt	integer	yes (i386 only)
.It machdep.kbdreset	integer	yes (i386 only)
.It machdep.userldt	integer	yes (i386 only)
.It machdep.allowaperture	integer	yes (XFree86)
.It machdep.led_blink	integer	yes (sparc/sparc64)
.It machdep.ceccerrs	integer	no (sparc64)
.It machdep.cecclast	quad	no (sparc64)
.It user.cs_path	string	no
.It user.bc_base_max	integer	no
.It user.bc_dim_max	integer	no
.It user.bc_scale_max	integer	no
.It user.bc_string_max	integer	no
.It user.coll_weights_max	integer	no
.It user.expr_nest_max	integer	no
.It user.line_max	integer	no
.It user.re_dup_max	integer	no
.It user.posix2_version	integer	no
.It user.posix2_c_bind	integer	no
.It user.posix2_c_dev	integer	no
.It user.posix2_char_term	integer	no
.It user.posix2_fort_dev	integer	no
.It user.posix2_fort_run	integer	no
.It user.posix2_localedef	integer	no
.It user.posix2_sw_dev	integer	no
.It user.posix2_upe	integer	no
.It user.stream_max	integer	no
.It user.tzname_max	integer	no
.It ddb.radix	integer	yes
.It ddb.max_width	integer	yes
.It ddb.max_line	integer	yes
.It ddb.tab_stop_width	integer	yes
.It ddb.panic	integer	yes
.It ddb.console	integer	yes
.It ddb.log	integer	yes
.It vfs.mounts.*	struct	no
.It vfs.ffs.doclusterread	integer	yes
.It vfs.ffs.doclusterwrite	integer	yes
.It vfs.ffs.doreallocblks	integer	yes
.It vfs.ffs.doasyncfree	integer	yes
.It vfs.ffs.max_softdeps	integer	yes
.It vfs.ffs.sd_tickdelay	integer	yes
.It vfs.ffs.sd_worklist_push	integer	no
.It vfs.ffs.sd_blk_limit_push	integer	no
.It vfs.ffs.sd_ino_limit_push	integer	no
.It vfs.ffs.sd_blk_limit_hit	integer	no
.It vfs.ffs.sd_ino_limit_hit	integer	no
.It vfs.ffs.sd_sync_limit_hit	integer	no
.It vfs.ffs.sd_indir_blk_ptrs	integer	no
.It vfs.ffs.sd_inode_bitmap	integer	no
.It vfs.ffs.sd_direct_blk_ptrs	integer	no
.It vfs.ffs.sd_dir_entry	integer	no
.It vfs.nfs.iothreads	integer	yes
.El
.Pp
The
.Nm
program can get or set debugging variables
that have been identified for its display.
This information can be obtained by using the command:
.Pp
.Dl $ sysctl debug
.Pp
In addition,
.Nm
can extract information about the filesystems that have been compiled
into the running system.
This information can be obtained by using the command:
.Pp
.Dl $ sysctl vfs.mounts
.Pp
By default, only filesystems that are actively being used are listed.
Use of the
.Fl A
flag lists all the filesystems compiled into the running kernel.
.Sh FILES
.Bl -tag -width <uvm/uvm_swap_encrypt.h> -compact
.It Aq Pa sys/sysctl.h
definitions for top level identifiers, second level kernel and hardware
identifiers, and user level identifiers
.It Aq Pa dev/rndvar.h
definitions for
.Xr random 4
device's statistics structure
.It Aq Pa sys/socket.h
definitions for second level network identifiers
.It Aq Pa sys/gmon.h
definitions for third level profiling identifiers
.It Aq Pa uvm/uvm_param.h
definitions for second level virtual memory identifiers
.It Aq Pa uvm/uvm_swap_encrypt.h
definitions for third level virtual memory identifiers
.It Aq Pa netinet/in.h
definitions for third level IPv4/v6 identifiers and
fourth level IPv4/v6 identifiers
.It Aq Pa netinet/icmp_var.h
definitions for fourth level ICMP identifiers
.It Aq Pa netinet6/icmp6.h
definitions for fourth level ICMPv6 identifiers
.It Aq Pa netinet/tcp_var.h
definitions for fourth level TCP identifiers
.It Aq Pa netinet/udp_var.h
definitions for fourth level UDP identifiers
.It Aq Pa netipx/ipx_var.h
definitions for third level IPX identifiers and
fourth level IPX identifiers
.It Aq Pa ddb/db_var.h
definitions for second level ddb identifiers
.It Aq Pa sys/mount.h
definitions for second level vfs identifiers
.It Aq Pa nfs/nfs.h
definitions for third level NFS identifiers
.It Aq Pa ufs/ffs/ffs_extern.h
definitions for third level FFS identifiers
.El
.Sh EXAMPLES
To retrieve the maximum number of processes allowed
in the system:
.Pp
.Dl $ sysctl kern.maxproc
.Pp
To set the maximum number of processes allowed
in the system to 1000:
.Pp
.Dl # sysctl -w kern.maxproc=1000
.Pp
To retrieve information about the system clock rate:
.Pp
.Dl $ sysctl kern.clockrate
.Pp
To retrieve information about the load average history:
.Pp
.Dl $ sysctl vm.loadavg
.Pp
To make the
.Xr chown 2
system call use traditional BSD semantics (don't clear setuid/setgid bits):
.Pp
.Dl # sysctl -w fs.posix.setuid=0
.Pp
To set the list of reserved TCP ports that should not be allocated
by the kernel dynamically:
.Pp
.Dl # sysctl -w net.inet.tcp.baddynamic=749,750,751,760,761,871
.Pp
This can be used to keep daemons
from stealing a specific port that another program needs to function.
List elements may be separated by commas and/or whitespace.
.Pp
It is also possible to add or remove ports from the current list:
.Bd -literal -offset indent
# sysctl -w net.inet.tcp.baddynamic=+748
# sysctl -w net.inet.tcp.baddynamic=-871
.Ed
.Pp
To adjust the number of kernel
.Nm nfsio
threads used to service asynchronous
I/O requests on an NFS client machine:
.Pp
.Dl # sysctl -w vfs.nfs.iothreads=4
.Pp
The number of 4 is the default, 20 is the maximum.
See
.Xr nfssvc 2
and
.Xr nfsd 8
for further discussion.
.Pp
To set the amount of shared memory available in the system and
the maximum number of shared memory segments:
.Bd -literal -offset indent
# sysctl -w kern.shminfo.shmmax=33554432
# sysctl -w kern.shminfo.shmseg=32
.Ed
.Sh SEE ALSO
.Xr sysctl 3 ,
.Xr sysctl.conf 5
.Sh HISTORY
.Nm sysctl
first appeared in
.Bx 4.4 .