sysctl man page on 4.4BSD

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

     sysctl — get or set kernel state

     sysctl [-n] name ...
     sysctl [-n] -w name=value ...
     sysctl [-n] -aA

     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 -a flag can be used
     to list all the currently available string or integer values.  The -A
     flag will list all the known MIB names including tables.  Those with
     string or integer values will be printed as with the -a flag; for the ta‐
     ble values, the name of the utility to retrieve them is given.

     The -n flag specifies that the printing of the field name should be sup‐
     pressed and that only its value should be output.	This flag is useful
     for setting shell variables.  For example, to save the pagesize in vari‐
     able psize, use:
	   set psize=`sysctl -n hw.pagesize`

     If just a MIB style name is given, the corresponding value is retrieved.
     If a value is to be set, the -w flag must be specified and the MIB name
     followed by an equal sign and the new value to be used.

     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.	The string and integer infor‐
     mation is summaried 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.

     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		     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.link_max		     integer	   no
     kern.max_canon		     integer	   no
     kern.max_input		     integer	   no
     kern.name_max		     integer	   no
     kern.path_max		     integer	   no
     kern.pipe_buf		     integer	   no
     kern.chown_restricted	     integer	   no
     kern.no_trunc		     integer	   no
     kern.vdisable		     integer	   no
     kern.boottime		     struct	   no
     vm.loadavg			     struct	   no
     machdep.console_device	     dev_t	   no
     net.inet.ip.forwarding	     integer	   yes
     net.inet.ip.redirect	     integer	   yes
     net.inet.ip.ttl		     integer	   yes
     net.inet.icmp.maskrepl	     integer	   yes
     net.inet.udp.checksum	     integer	   yes
     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
     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

     The sysctl program can get or set debugging variables that have been
     identified for its display.  This information can be obtained by using
     the command:

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

     For example, to retrieve the maximum number of processes allowed in the
     system, one would use the follow request:
	   sysctl kern.maxproc

     To set the maximum number of processes allowed in the system to 1000, one
     would use the follow 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

     <sys/sysctl.h>	   definitions for top level identifiers, second level
			   kernel and hardware identifiers, and user level
     <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 identi‐
     <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


     sysctl first appeared in 4.4BSD.

BSD			      September 28, 2021			   BSD

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