sysctl man page on OpenBSD

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SYSCTL(8)		OpenBSD System Manager's Manual		     SYSCTL(8)

     sysctl - get or set kernel state

     sysctl [-Aan]
     sysctl [-n] name ...
     sysctl [-nq] name=value ...

     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.

     When retrieving a variable, a subset of the MIB name may be specified to
     retrieve a list of variables in that subset.  For example, to list all
     the machdep variables:

	   $ sysctl machdep

     When setting a variable, the MIB name should be followed by an equal sign
     and the new value.

     The options are as follows:

     -A	  List all the known MIB names including tables.  Those with string or
	  integer values will be printed as with the -a flag; for the table
	  values, the name of the utility to retrieve them is given.

     -a	  List all the currently available string or integer values.  This is
	  the default, if no parameters are given to sysctl.

     -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:

		# set psize=`sysctl -n hw.pagesize`

     -q	  Suppress all output when setting a variable.	This option overrides
	  the behaviour of -n.

	  Attempt to set the specified variable name to value.

     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(1), systat(1), and netstat(1).	 The string and
     integer information is summarized below.  For a detailed description of
     these variables, see sysctl(3).  The changeable column indicates whether
     a process with appropriate privilege can change the value.

     Note: not all of the variables are relevant to all architectures, and a
     few require a kernel compiled with non-standard options(4).

     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	   yes
     kern.maxfiles			     integer	   yes
     kern.argmax			     integer	   no
     kern.securelevel			     integer	   raise only
     kern.hostname			     string	   yes
     kern.hostid			     u_int	   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.maxpartitions			     integer	   no
     kern.rawpartition			     integer	   no
     kern.osversion			     string	   no
     kern.somaxconn			     integer	   yes
     kern.sominconn			     integer	   yes
     kern.usermount			     integer	   yes
     kern.random			     struct	   no
     kern.nosuidcoredump		     integer	   yes
     kern.fsync				     integer	   no
     kern.sysvmsg			     integer	   no
     kern.sysvsem			     integer	   no
     kern.sysvshm			     integer	   no
     kern.arandom			     u_int	   no
     kern.msgbufsize			     integer	   no
     kern.malloc.buckets		     string	   no
     kern.malloc.bucket.<sz>		     string	   no
     kern.malloc.kmemnames		     string	   no
     kern.malloc.kmemstat.<name>	     string	   no
     kern.cp_time			     struct	   no
     kern.nchstats			     struct	   no
     kern.forkstat			     struct	   no
     kern.nselcoll			     integer	   no
     kern.tty.tk_nin			     int64_t	   no
     kern.tty.tk_nout			     int64_t	   no
     kern.tty.tk_rawcc			     int64_t	   no
     kern.tty.tk_cancc			     int64_t	   no
     kern.tty.ttyinfo			     struct	   no
     kern.tty.maxptys			     integer	   yes
     kern.tty.nptys			     integer	   no
     kern.ccpu				     u_int	   no
     kern.fscale			     integer	   no
     kern.nprocs			     integer	   no
     kern.stackgap_random		     integer	   yes
     kern.usercrypto			     integer	   yes
     kern.cryptodevallowsoft		     integer	   yes
     kern.splassert			     integer	   yes
     kern.nfiles			     integer	   no
     kern.ttycount			     integer	   no
     kern.numvnodes			     integer	   no
     kern.userasymcrypto		     integer	   yes
     kern.seminfo.semmni		     integer	   yes
     kern.seminfo.semmns		     integer	   yes
     kern.seminfo.semmnu		     integer	   yes
     kern.seminfo.semmsl		     integer	   yes
     kern.seminfo.semopm		     integer	   yes
     kern.seminfo.semume		     integer	   no
     kern.seminfo.semusz		     integer	   no
     kern.seminfo.semvmx		     integer	   no
     kern.seminfo.semaem		     integer	   no
     kern.shminfo.shmmax		     integer	   yes
     kern.shminfo.shmmin		     integer	   yes
     kern.shminfo.shmmni		     integer	   yes
     kern.shminfo.shmseg		     integer	   yes
     kern.shminfo.shmall		     integer	   yes
     kern.watchdog.period		     integer	   yes			     integer	   yes
     kern.emul.nemuls			     integer	   no
     kern.emul.other			     integer	   yes
     kern.maxclusters			     integer	   yes
     kern.timecounter.tick		     integer	   no
     kern.timecounter.timestepwarnings	     integer	   yes
     kern.timecounter.hardware		     string	   yes
     kern.timecounter.choice		     string	   no
     kern.maxlocksperuid		     integer	   yes
     kern.bufcachepercent		     integer	   yes
     kern.rthreads			     integer	   yes
     kern.consdev			     string	   no
     vm.vmmeter				     struct	   no
     vm.loadavg				     struct	   no
     vm.psstrings			     struct	   no
     vm.uvmexp				     struct	   no
     vm.swapencrypt.enable		     integer	   yes
     vm.swapencrypt.keyscreated		     integer	   no
     vm.swapencrypt.keysdeleted		     integer	   no
     vm.nkmempages			     integer	   no
     vm.anonmin				     integer	   yes
     vm.vtextmin			     integer	   yes
     vm.vnodemin			     integer	   yes
     vm.maxslp				     integer	   no
     vm.uspace				     integer	   no
     fs.posix.setuid			     integer	   yes
     net.inet.divert.recvspace		     integer	   yes
     net.inet.divert.sendspace		     integer	   yes
     net.inet.ip.forwarding		     integer	   yes
     net.inet.ip.redirect		     integer	   yes
     net.inet.ip.ttl			     integer	   yes
     net.inet.ip.sourceroute		     integer	   yes
     net.inet.ip.directed-broadcast	     integer	   yes
     net.inet.ip.portfirst		     integer	   yes
     net.inet.ip.portlast		     integer	   yes
     net.inet.ip.porthifirst		     integer	   yes
     net.inet.ip.porthilast		     integer	   yes
     net.inet.ip.maxqueue		     integer	   yes
     net.inet.ip.encdebug		     integer	   yes
     net.inet.ip.ipsec-expire-acquire	     integer	   yes
     net.inet.ip.ipsec-invalid-life	     integer	   yes
     net.inet.ip.ipsec-pfs		     integer	   yes
     net.inet.ip.ipsec-soft-allocs	     integer	   yes
     net.inet.ip.ipsec-allocs		     integer	   yes
     net.inet.ip.ipsec-soft-bytes	     integer	   yes
     net.inet.ip.ipsec-bytes		     integer	   yes
     net.inet.ip.ipsec-timeout		     integer	   yes
     net.inet.ip.ipsec-soft-timeout	     integer	   yes
     net.inet.ip.ipsec-soft-firstuse	     integer	   yes
     net.inet.ip.ipsec-firstuse		     integer	   yes
     net.inet.ip.ipsec-enc-alg		     string	   yes
     net.inet.ip.ipsec-auth-alg		     string	   yes
     net.inet.ip.mtudisc		     integer	   yes
     net.inet.ip.mtudisctimeout		     integer	   yes
     net.inet.ip.ipsec-comp-alg		     string	   yes
     net.inet.ip.mforwarding		     integer	   yes
     net.inet.ip.multipath		     integer	   yes
     net.inet.icmp.maskrepl		     integer	   yes
     net.inet.icmp.bmcastecho		     integer	   yes
     net.inet.icmp.errppslimit		     integer	   yes
     net.inet.icmp.rediraccept		     integer	   yes
     net.inet.icmp.redirtimeout		     integer	   yes
     net.inet.icmp.tstamprepl		     integer	   yes
     net.inet.ipip.allow		     integer	   yes
     net.inet.tcp.rfc1323		     integer	   yes
     net.inet.tcp.keepinittime		     integer	   yes
     net.inet.tcp.keepidle		     integer	   yes
     net.inet.tcp.keepintvl		     integer	   yes
     net.inet.tcp.slowhz		     integer	   no
     net.inet.tcp.baddynamic		     array	   yes
     net.inet.tcp.sack			     integer	   yes
     net.inet.tcp.mssdflt		     integer	   yes
     net.inet.tcp.rstppslimit		     integer	   yes
     net.inet.tcp.ackonpush		     integer	   yes
     net.inet.tcp.ecn			     integer	   yes
     net.inet.tcp.syncachelimit		     integer	   yes
     net.inet.tcp.synbucketlimit	     integer	   yes
     net.inet.tcp.rfc3390		     integer	   yes
     net.inet.tcp.reasslimit		     integer	   yes
     net.inet.udp.checksum		     integer	   yes
     net.inet.udp.baddynamic		     array	   yes
     net.inet.udp.recvspace		     integer	   yes
     net.inet.udp.sendspace		     integer	   yes
     net.inet.gre.allow			     integer	   yes
     net.inet.gre.wccp			     integer	   yes
     net.inet.esp.enable		     integer	   yes
     net.inet.esp.udpencap		     integer	   yes
     net.inet.esp.udpencap_port		     integer	   yes
     net.inet.ah.enable			     integer	   yes
     net.inet.mobileip.allow		     integer	   yes
     net.inet.etherip.allow		     integer	   yes
     net.inet.ipcomp.enable		     integer	   yes
     net.inet.carp.allow		     integer	   yes
     net.inet.carp.preempt		     integer	   yes
     net.inet.carp.log			     integer	   yes
     net.inet6.ip6.forwarding		     integer	   yes
     net.inet6.ip6.redirect		     integer	   yes
     net.inet6.ip6.hlim			     integer	   yes
     net.inet6.ip6.maxfragpackets	     integer	   yes
     net.inet6.ip6.accept_rtadv		     integer	   yes
     net.inet6.ip6.keepfaith		     integer	   yes
     net.inet6.ip6.log_interval		     integer	   yes
     net.inet6.ip6.hdrnestlimit		     integer	   yes
     net.inet6.ip6.dad_count		     integer	   yes
     net.inet6.ip6.auto_flowlabel	     integer	   yes
     net.inet6.ip6.defmcasthlim		     integer	   yes
     net.inet6.ip6.kame_version		     string	   no
     net.inet6.ip6.use_deprecated	     integer	   yes
     net.inet6.ip6.rr_prune		     integer	   yes
     net.inet6.ip6.v6only		     integer	   no
     net.inet6.ip6.maxfrags		     integer	   yes
     net.inet6.ip6.mforwarding		     integer	   yes
     net.inet6.ip6.multipath		     integer	   yes
     net.inet6.ip6.multicast_mtudisc	     integer	   yes
     net.inet6.icmp6.rediraccept	     integer	   yes
     net.inet6.icmp6.redirtimeout	     integer	   yes
     net.inet6.icmp6.nd6_prune		     integer	   yes
     net.inet6.icmp6.nd6_delay		     integer	   yes
     net.inet6.icmp6.nd6_umaxtries	     integer	   yes
     net.inet6.icmp6.nd6_mmaxtries	     integer	   yes
     net.inet6.icmp6.nd6_useloopback	     integer	   yes
     net.inet6.icmp6.nodeinfo		     integer	   yes
     net.inet6.icmp6.errppslimit	     integer	   yes
     net.inet6.icmp6.nd6_maxnudhint	     integer	   yes
     net.inet6.icmp6.mtudisc_hiwat	     integer	   yes
     net.inet6.icmp6.mtudisc_lowat	     integer	   yes
     net.inet6.icmp6.nd6_debug		     integer	   yes
     debug.syncprt			     integer	   yes
     debug.busyprt			     integer	   yes
     debug.doclusterread		     integer	   yes
     debug.doclusterwrite		     integer	   yes
     debug.doreallocblks		     integer	   yes
     debug.doasyncfree			     integer	   yes
     debug.prtrealloc			     integer	   yes
     hw.machine				     string	   no
     hw.model				     string	   no
     hw.ncpu				     integer	   no
     hw.byteorder			     integer	   no
     hw.physmem				     int64_t	   no
     hw.usermem				     int64_t	   no
     hw.pagesize			     integer	   no
     hw.diskstats			     struct	   no
     hw.disknames			     string	   no
     hw.diskcount			     integer	   no
     hw.sensors.<xname>.<type><numt>	     struct	   no
     hw.cpuspeed			     integer	   no
     hw.setperf				     integer	   yes
     hw.vendor				     string	   no
     hw.product				     string	   no
     hw.version				     string	   no
     hw.serialno			     string	   no
     hw.uuid				     string	   no
     hw.ncpufound			     integer	   no
     machdep.console_device		     dev_t	   no
     machdep.unaligned_print		     integer	   yes
     machdep.unaligned_fix		     integer	   yes
     machdep.unaligned_sigbus		     integer	   yes
     machdep.apmwarn			     integer	   yes
     machdep.apmhalt			     integer	   yes
     machdep.kbdreset			     integer	   yes
     machdep.userldt			     integer	   yes
     machdep.osxsfr			     integer	   no
     machdep.sse			     integer	   no
     machdep.sse2			     integer	   no
     machdep.xcrypt			     integer	   no
     machdep.allowaperture		     integer	   yes
     machdep.led_blink			     integer	   yes
     machdep.ceccerrs			     integer	   no
     machdep.cecclast			     quad	   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
     ddb.radix				     integer	   yes
     ddb.max_width			     integer	   yes
     ddb.max_line			     integer	   yes
     ddb.tab_stop_width			     integer	   yes
     ddb.panic				     integer	   yes
     ddb.console			     integer	   yes
     ddb.log				     integer	   yes
     ddb.trigger			     integer	   yes
     vfs.mounts.*			     struct	   no
     vfs.ffs.doclusterread		     integer	   yes
     vfs.ffs.doclusterwrite		     integer	   yes
     vfs.ffs.doreallocblks		     integer	   yes
     vfs.ffs.doasyncfree		     integer	   yes
     vfs.ffs.max_softdeps		     integer	   yes
     vfs.ffs.sd_tickdelay		     integer	   yes
     vfs.ffs.sd_worklist_push		     integer	   no
     vfs.ffs.sd_blk_limit_push		     integer	   no
     vfs.ffs.sd_ino_limit_push		     integer	   no
     vfs.ffs.sd_blk_limit_hit		     integer	   no
     vfs.ffs.sd_ino_limit_hit		     integer	   no
     vfs.ffs.sd_sync_limit_hit		     integer	   no
     vfs.ffs.sd_indir_blk_ptrs		     integer	   no
     vfs.ffs.sd_inode_bitmap		     integer	   no
     vfs.ffs.sd_direct_blk_ptrs		     integer	   no
     vfs.ffs.sd_dir_entry		     integer	   no
     vfs.ffs.dirhash_dirsize		     integer	   yes
     vfs.ffs.dirhash_maxmem		     integer	   yes
     vfs.ffs.dirhash_mem		     integer	   no
     vfs.nfs.iothreads			     integer	   yes

     The sysctl program can extract information about the filesystems that
     have been compiled into the running system.  This information can be
     obtained by using the command:

	   $ sysctl vfs.mounts

     By default, only filesystems that are actively being used are listed.
     Use of the -A flag lists all the filesystems compiled into the running

     <sys/sysctl.h>	       definitions for top level identifiers, second
			       level kernel and hardware identifiers, and user
			       level identifiers
     <dev/rndvar.h>	       definitions for random(4) device's statistics
     <sys/socket.h>	       definitions for second level network
     <sys/gmon.h>	       definitions for third level profiling
     <uvm/uvm_param.h>	       definitions for second level virtual memory
     <uvm/uvm_swap_encrypt.h>  definitions for third level virtual memory
     <netinet/in.h>	       definitions for third level IPv4/v6 identifiers
			       and fourth level IPv4/v6 identifiers
     <netinet/ip_divert.h>     definitions for fourth level divert identifiers
     <netinet/icmp_var.h>      definitions for fourth level ICMP identifiers
     <netinet6/icmp6.h>	       definitions for fourth level ICMPv6 identifiers
     <netinet/tcp_var.h>       definitions for fourth level TCP identifiers
     <netinet/udp_var.h>       definitions for fourth level UDP identifiers
     <ddb/db_var.h>	       definitions for second level ddb identifiers
     <sys/mount.h>	       definitions for second level vfs identifiers
     <nfs/nfs.h>	       definitions for third level NFS identifiers
     <ufs/ffs/ffs_extern.h>    definitions for third level FFS identifiers
     <machine/cpu.h>	       definitions for second level CPU identifiers

     To retrieve the maximum number of processes allowed in the system:

	   $ sysctl kern.maxproc

     To set the maximum number of processes allowed in the system to 1000:

	   # sysctl kern.maxproc=1000

     To retrieve information about the system clock rate:

	   $ sysctl kern.clockrate

     To retrieve information about the load average history:

	   $ sysctl vm.loadavg

     To make the chown(2) system call use traditional BSD semantics (don't
     clear setuid/setgid bits):

	   # sysctl fs.posix.setuid=0

     To set the list of reserved TCP ports that should not be allocated by the
     kernel dynamically:

	   # sysctl net.inet.tcp.baddynamic=749,750,751,760,761,871

     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.

     It is also possible to add or remove ports from the current list:

	   # sysctl net.inet.tcp.baddynamic=+748
	   # sysctl net.inet.tcp.baddynamic=-871

     To adjust the number of kernel nfsio threads used to service asynchronous
     I/O requests on an NFS client machine:

	   # sysctl vfs.nfs.iothreads=4

     The default is 4; 20 is the maximum.  See nfssvc(2) and nfsd(8) for
     further discussion.

     To set the amount of shared memory available in the system and the
     maximum number of shared memory segments:

	   # sysctl kern.shminfo.shmmax=33554432
	   # sysctl kern.shminfo.shmseg=32

     sysctl(3), options(4), sysctl.conf(5)

     sysctl first appeared in 4.4BSD.

OpenBSD 4.9		       October 11, 2010			   OpenBSD 4.9

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