 @@ -1,1150 +1,1161 @@
-.\"	$NetBSD: sysctl.7,v 1.164 2023/05/29 23:30:47 gutteridge Exp $
+.\"	$NetBSD: sysctl.7,v 1.165 2023/06/18 18:16:40 riastradh Exp $
 .\"
 .\" Copyright (c) 1993
 .\"	The Regents of the University of California.  All rights reserved.
 .\"
 .\" Redistribution and use in source and binary forms, with or without
 .\" modification, are permitted provided that the following conditions
 .\" are met:
 .\" 1. Redistributions of source code must retain the above copyright
 .\"    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
 .\"    documentation and/or other materials provided with the distribution.
 .\" 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.
 .\"
 .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 .\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
 .\"	@(#)sysctl.3	8.4 (Berkeley) 5/9/95
 .\"
 .Dd May 29, 2023
 .Dt SYSCTL 7
 .Os
 .Sh NAME
 .Nm sysctl
 .Nd system information variables
 .Sh DESCRIPTION
 The
 .Xr sysctl 3
 library function and the
 .Xr sysctl 8
 utility are used to get and set values of system variables, maintained
 by the kernel.
 The variables are organized in a tree and identified by a sequence of
 numbers, conventionally separated by dots with the topmost identifier
 at the left side.
 The numbers have corresponding text names.
 The
 .Xr sysctlnametomib 3
 function or the
 .Fl M
 argument to the
 .Xr sysctl 8
 utility can be used to convert the text representation to the
 numeric one.
 .Pp
 The individual sysctl variables are described below, both the textual
 and numeric form where applicable.
 The textual names can be used as argument to the
 .Xr sysctl 8
 utility and in the file
 .Pa /etc/sysctl.conf .
 The numeric names are usually defined as preprocessor constants and
 are intended for use by programs.
 Every such constant expands to one integer, which identifies the
 sysctl variable relative to the upper level of the tree.
 See the
 .Xr sysctl 3
 manual page for programming examples.
 .Ss Top level names
 The top level names are defined with a
 .Va CTL_
 prefix in
 .In sys/sysctl.h ,
 and are as follows.
 The next and subsequent levels down are found in the include files
 listed here, and described in separate sections below.
 .Bl -column "security" ".Dv CTL_SECURITY" ".In uvm/uvm_param.h" "High kernel limits"
 .It Sy Name  Ta Sy Constant     Ta Sy Next level names Ta Sy Description
 .It kern     Ta Dv CTL_KERN     Ta In sys/sysctl.h     Ta High kernel limits
 .It vm       Ta Dv CTL_VM       Ta In uvm/uvm_param.h  Ta Virtual memory
 .It vfs      Ta Dv CTL_VFS      Ta In sys/mount.h      Ta Filesystem
 .It net      Ta Dv CTL_NET      Ta In sys/socket.h     Ta Networking
 .It debug    Ta Dv CTL_DEBUG    Ta In sys/sysctl.h     Ta Debugging
 .It hw       Ta Dv CTL_HW       Ta In sys/sysctl.h     Ta Generic CPU, I/O
 .It machdep  Ta Dv CTL_MACHDEP  Ta In sys/sysctl.h     Ta Machine dependent
 .It user     Ta Dv CTL_USER     Ta In sys/sysctl.h     Ta User-level
 .It ddb      Ta Dv CTL_DDB      Ta In sys/sysctl.h     Ta In-kernel debugger
 .It proc     Ta Dv CTL_PROC     Ta In sys/sysctl.h     Ta Per-process
 .It vendor   Ta Dv CTL_VENDOR   Ta ?                   Ta Vendor specific
 .It emul     Ta Dv CTL_EMUL     Ta In sys/sysctl.h     Ta Emulation settings
 .It security Ta Dv CTL_SECURITY Ta In sys/sysctl.h     Ta Security settings
 .El
 .Ss The debug.* subtree
 The debugging variables vary from system to system.
 A debugging variable may be added or deleted without need to recompile
 .Nm
 to know about it.
 Each time it runs,
 .Nm
 gets the list of debugging variables from the kernel and
 displays their current values.
 The system defines twenty
 .Vt ( struct ctldebug )
 variables named
 .Dv debug0
 through
 .Dv debug19 .
 They are declared as separate variables so that they can be
 individually initialized at the location of their associated variable.
 The loader prevents multiple use of the same variable by issuing errors
 if a variable is initialized in more than one place.
 For example, to export the variable
 .Va dospecialcheck
 as a debugging variable, the following declaration would be used:
 .Pp
 .Bd -literal -offset indent -compact
 int dospecialcheck = 1;
 struct ctldebug debug5 = { "dospecialcheck", &dospecialcheck };
 .Ed
 .Pp
 Note that the dynamic implementation of
 .Nm
 currently in use largely makes this particular
 .Nm
 interface obsolete.
 See
 .Xr sysctl 8
 .\" and
 .\" .Xr sysctl 9
 for more information.
 .Ss The vfs.* subtree
 A distinguished second level name,
 .Li vfs.generic ( Dv VFS_GENERIC ) ,
 is used to get general information about all file systems.
 It has the following third level identifiers:
 .Bl -tag -width "123456"
 .It Li vfs.generic.maxtypenum ( Dv VFS_MAXTYPENUM )
 The highest valid file system type number.
 .It Li vfs.generic.conf ( Dv VFS_CONF )
 Returns configuration information about the file system type given as a fourth
 level identifier.
 .It Li vfs.generic.usermount ( Dv VFS_USERMOUNT )
-Determines if non superuser mounts are allowed, defaults to
+Controls whether users other than the super-user can mount file
-.Dv 0 .
+systems.
 Defaults to
 .Li 0 ,
 so only the super-user can mount file systems.
 .Pp
 File systems mounted by unprivileged users must be mounted with the
 .Li nodev
 and
 .Li nosuid
 .Xr mount 8
 options.
 .It Li vfs.generic.magiclinks ( Dv VFS_MAGICLINKS )
-Controls if expansion of variables is going to be performed on pathnames
+Controls whether expansion of variables is going to be performed on
-or not.
+pathnames or not.
-Defaults to no variable expansion,
+Defaults to
-.Dv 0 .
+.Li 0 ,
 no variable expansion.
 Variables are of the form
 .Li @name
 and the variables supported are described in
 .Xr symlink 7
 under
 .Dq "MAGIC SYMLINKS" .
 .El
 .Pp
 A second level name for controlling the
 .Xr wapbl 4
 (Write Ahead Physical Block Logging file system journaling)
 capabilities with the following third level identifiers:
 .Bl -tag -width "123456"
 .It Li vfs.wapbl.flush_disk_cache
 Controls whether to attempt to flush the disk cache on each commit.
 It defaults to 1 and it should always be on to ensure integrity
 of file system metadata in the event of a power loss.
 For slow disks, turning it off can improve performance.
 .It Li vfs.wapbl.verbose_commit
 For each transaction log commit, print the number of bytes written
 and the time it took to commit as seconds.nanoseconds.
 .El
 .Pp
 The remaining second level identifiers are the file system names, identified
 by the type number returned by a
 .Xr statvfs 2
 call or from
 .Li vfs.generic.conf .
 .Pp
 The third level identifiers available for each file system
 are given in the header file that defines the mount
 argument structure for that file system.
 .Ss The hw.* subtree
 The string and integer information available for the
 .Li hw
 level is detailed below.
 The changeable column shows whether a process with appropriate
 privilege may change the value.
 .Bl -column "hw.machine_arch" "integer" "Changeable" -offset indent
 .It Sy Second level name Ta Sy Type Ta Sy Changeable
 .It hw.alignbytes	integer	no
 .It hw.byteorder	integer	no
 .It hw.cnmagic	string	yes
 .It hw.disknames	string	no
 .It hw.diskstats	struct	no
 .It hw.machine	string	no
 .It hw.machine_arch	string	no
 .It hw.model	string	no
 .It hw.ncpu	integer	no
 .It hw.ncpuonline	integer	no
 .It hw.pagesize	integer	no
 .It hw.physmem	integer	no
 .It hw.physmem64	quad	no
 .It hw.usermem	integer	no
 .It hw.usermem64	quad	no
 .El
 .Bl -tag -width "123456"
 .It Li hw.alignbytes ( Dv HW_ALIGNBYTES )
 Alignment constraint for all possible data types.
 This shows the value
 .Dv ALIGNBYTES
 in
 .In machine/param.h ,
 at the kernel compilation time.
 .It Li hw.byteorder ( Dv HW_BYTEORDER )
 The byteorder (4321, or 1234).
 .It Li hw.cnmagic ( Dv HW_CNMAGIC )
 The console magic key sequence.
 .It Li hw.disknames ( Dv HW_DISKNAMES )
 The list of (space separated) disk device names on the system.
 .It Li hw.iostatnames ( Dv HW_IOSTATNAMES )
 A space separated list of devices that will have I/O statistics
 collected on them.
 .It Li hw.iostats ( Dv HW_IOSTATS )
 Return statistical information on the NFS mounts, disk and tape
 devices on the system.
 An array of
 .Vt struct io_sysctl
 structures is returned,
 whose size depends on the current number of such objects in the system.
 The third level name is the size of the
 .Vt struct io_sysctl .
 The type of object can be determined by examining the
 .Va type
 element of
 .Vt struct io_sysctl .
 Which can be
 .Dv IOSTAT_DISK
 (disk drive),
 .Dv IOSTAT_TAPE
 (tape drive), or
 .Dv IOSTAT_NFS
 (NFS mount).
 .It Li hw.machine ( Dv HW_MACHINE )
 The machine class.
 .It Li hw.machine_arch ( Dv HW_MACHINE_ARCH )
 The machine CPU class.
 .It Li hw.model ( Dv HW_MODEL )
 The machine model.
 .It Li hw.ncpu ( Dv HW_NCPU )
 The number of CPUs configured.
 .It Li hw.ncpuonline ( Dv HW_NCPUONLINE )
 The number of CPUs online.
 .It Li hw.pagesize ( Dv HW_PAGESIZE )
 The software page size.
 .It Li hw.physmem ( Dv HW_PHYSMEM )
 The bytes of physical memory as a 32-bit integer.
 .It Li hw.physmem64 ( Dv HW_PHYSMEM64 )
 The bytes of physical memory as a 64-bit integer.
 .It Li hw.usermem ( Dv HW_USERMEM )
 The bytes of non-kernel memory as a 32-bit integer.
 .It Li hw.usermem64 ( Dv HW_USERMEM64 )
 The bytes of non-kernel memory as a 64-bit integer.
 .El
 .Ss The kern.* subtree
 This subtree includes data generally related to the kernel.
 The string and integer information available for the
 .Li kern
 level is detailed below.
 The changeable column shows whether a process with appropriate
 privilege may change the value.
 .Bl -column "kern.posix_reader_writer_locks" \
 "struct kinfo_drivers" "not applicable"
 .It Sy Second level name Ta Sy Type Ta Sy Changeable
 .It kern.aio_listio_max	integer	yes
 .It kern.aio_max	integer	yes
 .It kern.arandom	integer	no
 .It kern.argmax	integer	no
 .It kern.boothowto	integer	no
 .It kern.boottime	struct timespec	no
 .It kern.buildinfo	string	no
 .\".It kern.bufq	node	not applicable
 .It kern.ccpu	integer	no
 .It kern.clockrate	struct clockinfo	no
 .It kern.consdev	integer	no
 .It kern.coredump	node	not applicable
 .It kern.cp_id	struct	no
 .It kern.cp_time	uint64_t[\|]	no
 .It kern.cryptodevallowsoft	integer	yes
 .It kern.defcorename	string	yes
 .It kern.detachall	integer	yes
 .It kern.domainname	string	yes
 .It kern.drivers	struct kinfo_drivers	no
 .It kern.dump_on_panic	integer	yes
 .It kern.expose_address	integer	yes
 .It kern.file	struct file	no
 .It kern.forkfsleep	integer	yes
 .It kern.fscale	integer	no
 .It kern.fsync	integer	no
 .It kern.hardclock_ticks	integer	no
 .It kern.hostid	integer	yes
 .It kern.hostname	string	yes
 .It kern.iov_max	integer	no
 .It kern.ipc	node	not applicable
 .It kern.job_control	integer	no
 .It kern.labeloffset	integer	no
 .It kern.labelsector	integer	no
 .It kern.login_name_max	integer	no
 .It kern.logsigexit	integer	yes
 .It kern.lwp	struct kinfo_lwp	yes
 .It kern.mapped_files	integer	no
 .It kern.maxfiles	integer	yes
 .It kern.maxlwp	integer	yes
 .It kern.maxpartitions	integer	no
 .It kern.maxphys	integer	no
 .It kern.maxproc	integer	yes
 .It kern.maxptys	integer	yes
 .It kern.maxvnodes	integer	yes
 .It kern.messages	integer	yes
 .It kern.mbuf	node	not applicable
 .It kern.memlock	integer	no
 .It kern.memlock_range	integer	no
 .It kern.memory_protection	integer	no
 .It kern.module	node	not applicable
 .It kern.monotonic_clock	integer	no
 .It kern.mqueue	node	not applicable
 .It kern.msgbuf	integer	no
 .It kern.msgbufsize	integer	no
 .It kern.ngroups	integer	no
 .\".It kern.no_sa_support	integer	yes
 .It kern.ntptime	struct ntptimeval	no
 .It kern.osrelease	string	no
 .It kern.osrevision	integer	no
 .It kern.ostype	string	no
 .\".It kern.panic_now	integer	yes
 .It kern.pipe	node	not applicable
 .It kern.pool	struct pool_sysctl	no
 .\" .It kern.posix	node	not applicable
 .It kern.posix1version	integer	no
 .It kern.posix_aio	integer	no
 .It kern.posix_barriers	integer	no
 .It kern.posix_reader_writer_locks	integer	no
 .\".It kern.posix_sched	integer	yes
 .It kern.posix_semaphores	integer	no
 .It kern.posix_spin_locks	integer	no
 .It kern.posix_threads	integer	no
 .It kern.posix_timers	integer	no
 .It kern.proc	struct kinfo_proc	no
 .It kern.proc2	struct kinfo_proc2	no
 .It kern.proc_args	string	no
 .It kern.profiling	node	not applicable
 .\".It kern.pset	node	not applicable
 .It kern.rawpartition	integer	no
 .It kern.root_device	string	no
 .It kern.root_partition	integer	no
 .It kern.rtc_offset	integer	yes
 .It kern.saved_ids	integer	no
 .It kern.sbmax	integer	yes
 .It kern.sched	node	not applicable
 .It kern.securelevel	integer	raise only
 .It kern.sofixedbuf	boolean	yes
 .It kern.somaxkva	integer	yes
 .It kern.sooptions	integer	yes
 .It kern.synchronized_io	integer	no
 .It kern.timecounter	node	not applicable
 .It kern.timex	struct	no
 .It kern.tkstat	node	not applicable
 .It kern.tty	node	not applicable
 .It kern.urandom	integer	no
 .It kern.usercrypto	integer	yes
 .It kern.userasymcrypto	integer	yes
 .It kern.veriexec	node	not applicable
 .It kern.version	string	no
 .It kern.vnode	struct vnode	no
 .El
 .Bl -tag -width "123456"
 .It Li kern.aio_listio_max
 The maximum number of asynchronous I/O operations in a single list
 I/O call.
 Like with all variables related to
 .Xr aio 3 ,
 the variable may be created and removed dynamically
 upon loading or unloading the corresponding kernel module.
 .It Li kern.aio_max
 The maximum number of asynchronous I/O operations.
 .It Li kern.arandom ( Dv KERN_ARND )
 Returns independent uniformly distributed bytes at random each time, as
 many as requested up to 256, derived from the system entropy pool; see
 .Xr rnd 4 .
 .Pp
 Reading
 .Li kern.arandom
 is equivalent to reading up to 256 bytes at a time from
 .Pa /dev/urandom :
 reading
 .Li kern.arandom
 never blocks, and once the system entropy pool has full entropy, output
 subsequently read from
 .Li kern.arandom
 is fit for use as cryptographic key material.
 For example, the
 .Xr arc4random 3
 library routine uses
 .Li kern.arandom
 internally to seed a cryptographic pseudorandom number generator.
 .It Li kern.argmax ( Dv KERN_ARGMAX )
 The maximum bytes of argument to
 .Xr execve 2 .
 .It Li kern.boothowto
 Flags passed from the boot loader; see
 .Xr reboot 2
 for the meanings of the flags.
 .It Li kern.boottime ( Dv KERN_BOOTTIME )
+A
 .Vt struct timespec
 structure is returned.
 This structure contains the time that the system was booted.
 That time is defined (for this purpose) to be the time at
 which the kernel first started accumulating clock ticks.
 .It Li kern.bufq
 This variable contains information on the
 .Xr bufq 9
 subsystem.
 Currently, the only third level name implemented is
 .Dv kern.bufq.strategies
 which provides a list of buffer queue strategies currently available.
 .It Li kern.buildinfo
 When the kernel is built, the build environment may optionally provide
 arbitrary information to be stored in this variable.
 .It Li kern.ccpu ( Dv KERN_CCPU )
 The scheduler exponential decay value.
 .It Li kern.clockrate ( Dv KERN_CLOCKRATE )
+A
 .Vt struct clockinfo
 structure is returned.
 This structure contains the clock, statistics clock and profiling clock
 frequencies, the number of micro-seconds per hz tick, and the clock
 skew rate.
 Refer to
 .Xr hz 9
 for additional details.
 .It Li kern.consdev ( Dv KERN_CONSDEV )
 Console device.
 .It Li kern.coredump
 Settings related to set-id processes coredumps.
 By default, set-id processes do not dump core in situations where
 other processes would.
 The settings in this node allows an administrator to change this
 behavior.
 .Pp
 The third level name is
 .Dv kern.coredump.setid
 and fourth level variables are described below.
 .Bl -column "kern.coredump.setid.group" "integer" "Changeable" -offset indent
 .It Sy Fourth level name Ta Sy Type Ta Sy Changeable
 .It kern.coredump.setid.dump	integer	yes
 .It kern.coredump.setid.group	integer	yes
 .It kern.coredump.setid.mode	integer	yes
 .It kern.coredump.setid.owner	integer	yes
 .It kern.coredump.setid.path	string	yes
 .El
 .Bl -tag -width "123456"
 .It Li kern.coredump.setid.dump
 If non-zero, set-id processes will dump core.
 .It Li kern.coredump.setid.group
 The group-id for the set-id processes' coredump.
 .It Li kern.coredump.setid.mode
 The mode for the set-id processes' coredump.
 See
 .Xr chmod 1 .
 .It Li kern.coredump.setid.owner
 The user-id that will be used as the owner of the set-id processes'
 coredump.
 .It Li kern.coredump.setid.path
 The path to which set-id processes' coredumps will be saved to.
 Same syntax as kern.defcorename.
 .El
 .It Li kern.cp_id ( Dv KERN_CP_ID )
 Mapping of CPU number to CPU id.
 .It Li kern.cp_time ( Dv KERN_CP_TIME )
 Returns an array of
 .Dv CPUSTATES
 .Vt uint64_t Ns s .
 This array contains the
 number of clock ticks spent in different CPU states.
 On multi-processor systems, the sum across all CPUs is returned unless
 appropriate space is given for one data set for each CPU.
 Data for a specific CPU can also be obtained by adding the number of the
 CPU at the end of the MIB, enlarging it by one.
 .It Li kern.cryptodevallowsoft
 This variable controls userland access to hardware versus software transforms
 in the
 .Xr crypto 4
 system.
 The available values are as follows:
 .Bl -tag -width XX0 -offset indent
 .It Dv < 0
 Always force userlevel requests to use software transforms.
 .It Dv = 0
 If present, use hardware and grant userlevel requests for
 non-accelerated transforms (handling the latter in software).
 .It Dv > 0
 Allow user requests only for transforms which are hardware-accelerated.
 .El
 .It Li kern.defcorename ( Dv KERN_DEFCORENAME )
 Default template for the name of core dump files (see also
 .Li proc.pid.corename
 in the per-process variables
 .Li proc.* ,
 and
 .Xr core 5
 for format of this template).
 The default value is
 .Pa %n.core
 and can be changed with the kernel configuration option
 .Cd options DEFCORENAME
 (see
 .Xr options 4
 ).
 .It Li kern.detachall
 Detach all devices at shutdown.
 .It Li kern.domainname ( Dv KERN_DOMAINNAME )
 Get or set the YP domain name.
 .It Li kern.drivers ( Dv KERN_DRIVERS )
 Return an array of
 .Vt struct kinfo_drivers
 that contains the name and major device numbers of all the device drivers
 in the current kernel.
 The
 .Va d_name
 field is always a NUL terminated string.
 The
 .Va d_bmajor
 field will be set to \-1 if the driver doesn't have a block device.
 .It Li kern.expose_address
 Expose kernel addresses in
 .Xr sysctl 3
 calls used by
 .Xr fstat 1
 and
 .Xr sockstat 1 .
 If it is set to
 .Dv 0
 access is not allowed.
 If it is set to
 .Dv 1
 then only processes that have opened
 .Pa /dev/kmem
 can have access.
 If it is set to
 .Dv 2
 every process is allowed.
 Defaults to
 .Dv 0
 for
 .Dv KASLR
 kernels
 and
 .Dv 1
 otherwise.
 Allowing general access renders KASLR ineffective; allowing only kmem
 accessing programs weakens KASLR if those programs can be subverted
 to leak the addresses.
 .It Li kern.dump_on_panic ( Dv KERN_DUMP_ON_PANIC )
 Perform a crash dump on system
 .Xr panic 9 .
 .It Li kern.file ( Dv KERN_FILE )
 Return the entire file table.
 The returned data consists of a single
 .Vt struct filelist
 followed by an array of
 .Vt struct file ,
 whose size depends on the current number of such objects in the system.
 .It Li kern.forkfsleep ( Dv KERN_FORKFSLEEP )
 If
 .Xr fork 2
 system call fails due to limit on number of processes (either
 the global maxproc limit or user's one), wait for this many
 milliseconds before returning
 .Er EAGAIN
 error to process.
 Useful to keep heavily forking runaway processes in bay.
 Default zero (no sleep).
 Maximum is 20 seconds.
 .It Li kern.fscale ( Dv KERN_FSCALE )
 The kernel fixed-point scale factor.
 .It Li kern.fsync ( Dv KERN_FSYNC )
 Return 1 if the
 .St -p1003.1b-93
 File Synchronization Option is available
 on this system,
 otherwise\ 0.
 .It Li kern.hardclock_ticks ( Dv KERN_HARDCLOCK_TICKS )
 Returns the number of
 .Xr hardclock 9
 ticks.
 .It Li kern.hist
 This variable contains kernel history data if the kernel was
 configured for any of the options
 .Dv UVHMIST ,
 .Dv USB_DEBUG ,
 .Dv BIOHIST ,
 or
 .Dv SCDEBUG .
 (See
 .Xr options 4
 for more details.)
 The third-level names correspond to each available history table.
 The values of the history tables are in an internal format, and can be
 decoded by the
 .Xr vmstat 1
 utility's
 .Fl U
 and
 .Fl u
 options;
 the
 .Fl l
 option can be used to see which tables are available.
 .It Li kern.hostid ( Dv KERN_HOSTID )
 Get or set the host identifier.
 This is aimed to replace the legacy
 .Xr gethostid 3
 and
 .Xr sethostid 3
 system calls.
 .It Li kern.hostname ( Dv KERN_HOSTNAME )
 Get or set the
 .Xr hostname 1 .
 .It Li kern.iov_max ( Dv KERN_IOV_MAX )
 Return the maximum number of
 .Vt iovec
 structures that a process has available for use with
 .Xr preadv 2 ,
 .Xr pwritev 2 ,
 .Xr readv 2 ,
 .Xr recvmsg 2 ,
 .Xr sendmsg 2
 and
 .Xr writev 2 .
 .It Li kern.ipc ( Dv KERN_SYSVIPC )
 Return information about the SysV IPC parameters.
 The third level names for the ipc variables are detailed below.
 .Bl -column "kern.ipc.shm_use_phys" "integer" "Changeable" -offset indent
 .It Sy Third level name Ta Sy Type Ta Sy Changeable
 .It kern.ipc.sysvmsg	integer	no
 .It kern.ipc.sysvsem	integer	no
 .It kern.ipc.sysvshm	integer	no
 .It kern.ipc.sysvipc_info	struct	no
 .It kern.ipc.shmmax	integer	yes
 .It kern.ipc.shmmni	integer	yes
 .It kern.ipc.shmseg	integer	yes
 .It kern.ipc.shmmaxpgs	integer	yes
 .It kern.ipc.shm_use_phys	integer	yes
 .It kern.ipc.msgmni	integer	yes
 .It kern.ipc.msgseg	integer	yes
 .It kern.ipc.semmni	integer	yes
 .It kern.ipc.semmns	integer	yes
 .It kern.ipc.semmnu	integer	yes
 .El
 .Bl -tag -width "123456"
 .It Li kern.ipc.sysvmsg ( Dv KERN_SYSVIPC_MSG )
 Returns 1 if System V style message queue functionality is available
 on this system,
 otherwise\ 0.
 .It Li kern.ipc.sysvsem ( Dv KERN_SYSVIPC_SEM )
 Returns 1 if System V style semaphore functionality is available
 on this system,
 otherwise\ 0.
 .It Li kern.ipc.sysvshm ( Dv KERN_SYSVIPC_SHM )
 Returns 1 if System V style share memory functionality is available
 on this system,
 otherwise\ 0.
 .It Li kern.ipc.sysvipc_info ( Dv KERN_SYSVIPC_INFO )
 Return System V style IPC configuration and run-time information.
 The fourth level name selects the System V style IPC facility.
 .Bl -column "KERN_SYSVIPC_MSG_INFO" "struct shm_sysctl_info" -offset indent
 .It Sy Fourth level name Ta Sy Type
 .It KERN_SYSVIPC_MSG_INFO	struct msg_sysctl_info
 .It KERN_SYSVIPC_SEM_INFO	struct sem_sysctl_info
 .It KERN_SYSVIPC_SHM_INFO	struct shm_sysctl_info
 .El
 .Bl -tag -width "123456"
 .It Li KERN_SYSVIPC_MSG_INFO
 Return information on the System V style message facility.
 The
 .Sy msg_sysctl_info
 structure is defined in
 .In sys/msg.h .
 .It Li KERN_SYSVIPC_SEM_INFO
 Return information on the System V style semaphore facility.
 The
 .Sy sem_sysctl_info
 structure is defined in
 .In sys/sem.h .
 .It Li KERN_SYSVIPC_SHM_INFO
 Return information on the System V style shared memory facility.
 The
 .Sy shm_sysctl_info
 structure is defined in
 .In sys/shm.h .
 .El
 .It Li kern.ipc.shmmax ( Dv KERN_SYSVIPC_SHMMAX )
 Max shared memory segment size in bytes.
 .It Li kern.ipc.shmmni ( Dv KERN_SYSVIPC_SHMMNI )
 Max number of shared memory identifiers.
 .It Li kern.ipc.shmseg ( Dv KERN_SYSVIPC_SHMSEG )
 Max shared memory segments per process.
 .It Li kern.ipc.shmmaxpgs ( Dv KERN_SYSVIPC_SHMMAXPGS )
 Max amount of shared memory in pages.
 .It Li kern.ipc.shm_use_phys ( Dv KERN_SYSVIPC_SHMUSEPHYS )
 Locking of shared memory in physical memory.
 If 0, memory can be swapped
 out, otherwise it will be locked in physical memory.
 .It Li kern.ipc.msgmni
 Max number of message queue identifiers.
 .It Li kern.ipc.msgseg
 Max number of number of message segments.
 .It Li kern.ipc.semmni
 Max number of number of semaphore identifiers.
 .It Li kern.ipc.semmns
 Max number of number of semaphores in system.
 .It Li kern.ipc.semmnu
 Max number of undo structures in system.
 .El
 .It Li kern.job_control ( Dv KERN_JOB_CONTROL )
 Return 1 if job control is available on this system, otherwise\ 0.
 .It Li kern.labeloffset ( Dv KERN_LABELOFFSET )
 The offset within the sector specified by
 .Dv KERN_LABELSECTOR
 of the
 .Xr disklabel 5 .
 .It Li kern.labelsector ( Dv KERN_LABELSECTOR )
 The sector number containing the
 .Xr disklabel 5 .
 .It Li kern.login_name_max ( Dv KERN_LOGIN_NAME_MAX )
 The size of the storage required for a login name, in bytes,
 including the terminating NUL.
 .It Li kern.logsigexit ( Dv KERN_LOGSIGEXIT )
 If this flag is non-zero, the kernel will
 .Xr log 9
 all process exits due to signals which create a
 .Xr core 5
 file, and whether the coredump was created.
 .It Li kern.lwp ( Dv KERN_LWP )
 Returns information about the current light-weight process.
 The
 .Sy kinfo_lwp
 structure is defined in
 .In sys/sysctl.h .
 .It Li kern.mapped_files ( Dv KERN_MAPPED_FILES )
 Returns 1 if the
 .St -p1003.1b-93
 Memory Mapped Files Option is available on this system,
 otherwise\ 0.
 .It Li kern.maxfiles ( Dv KERN_MAXFILES )
 The maximum number of open files that may be open in the system.
 This also controls the maximum file locks per unprivileged user
 enforced by
 .Xr fcntl 2
 and
 .Xr flock 2 .
 .It Li kern.maxpartitions ( Dv KERN_MAXPARTITIONS )
 The maximum number of partitions allowed per disk.
 .It Li kern.maxlwp
 The maximum number of Lightweight Processes (threads) the system allows
 per uid.
 .It Li kern.maxphys ( Dv KERN_MAXPHYS )
 Maximum raw I/O transfer size.
 .It Li kern.maxproc ( Dv KERN_MAXPROC )
 The maximum number of simultaneous processes the system will allow.
 .It Li kern.maxptys ( Dv KERN_MAXPTYS )
 The maximum number of pseudo terminals.
 This value can be both raised and lowered, though it cannot
 be set lower than number of currently used ptys.
 See also
 .Xr pty 4 .
 .It Li kern.maxvnodes ( Dv KERN_MAXVNODES )
 The maximum number of vnodes available on the system.
 This cannot be lowered below the number of currently active vnodes.
 .It Li kern.mbuf ( Dv KERN_MBUF )
 Return information about the mbuf control variables.
 Mbufs are data structures which store network packets and other data
 structures in the networking code, see
 .Xr mbuf 9 .
 The third level names for the mbuf variables are detailed below.
 The changeable column shows whether a process with appropriate
 privilege may change the value.
 .Bl -column "kern.mbuf.nmbclusters_limit" "integer" "Changeable" -offset indent
 .It Sy Third level name Ta Sy Type Ta Sy Changeable
 .\" XXX Changeable? really?
 .It kern.mbuf.mblowat	integer	yes
 .It kern.mbuf.mclbytes	integer	yes
 .It kern.mbuf.mcllowat	integer	yes
 .It kern.mbuf.msize	integer	yes
 .It kern.mbuf.nmbclusters	integer	yes
 .It kern.mbuf.nmbclusters_limit	integer	no
 .El
 .Pp
 The variables are as follows:
 .Bl -tag -width "123456"
 .It Li kern.mbuf.mblowat ( Dv MBUF_MBLOWAT )
 The mbuf low water mark.
 .It Li kern.mbuf.mclbytes ( Dv MBUF_MCLBYTES )
 The mbuf cluster size.
 .It Li kern.mbuf.mcllowat ( Dv MBUF_MCLLOWAT )
 The mbuf cluster low water mark.
 .It Li kern.mbuf.msize ( Dv MBUF_MSIZE )
 The mbuf base size.
 .It Li kern.mbuf.nmbclusters ( Dv MBUF_NMBCLUSTERS )
 The limit on the number of mbuf clusters.
 The variable can only be increased, and only increased on machines with
 direct-mapped pool pages.
 .It Li kern.mbuf.nmbclusters_limit ( Dv MBUF_NMBCLUSTERS_LIMIT )
 The limit of nmbclusters.
 .El
 .It Li kern.memlock ( Dv KERN_MEMLOCK )
 Returns 1 if the
 .St -p1003.1b-93
 Process Memory Locking Option is available on this system,
 otherwise\ 0.
 .It Li kern.memlock_range ( Dv KERN_MEMLOCK_RANGE )
 Returns 1 if the
 .St -p1003.1b-93
 Range Memory Locking Option is available on this system,
 otherwise\ 0.
 .It Li kern.memory_protection ( Dv KERN_MEMORY_PROTECTION )
 Returns 1 if the
 .St -p1003.1b-93
 Memory Protection Option is available on this system,
 otherwise\ 0.
 .It Li kern.messages
 Kernel console message verbosity.
 See
 .Aq Pa sys/reboot.h
 .Bl -column "verbosity" "setting" -offset indent
 .It Sy Value Ta Sy Verbosity Ta Sy sys/reboot.h equivalent
 .It 0 Ta Silent Ta Sy AB_SILENT
 .It 1 Ta Quiet Ta Sy AB_QUIET
 .It 2 Ta Normal Ta Sy AB_NORMAL
 .It 3 Ta Verbose Ta Sy AB_VERBOSE
 .It 4 Ta Debug Ta Sy AB_DEBUG
 .El
 .It Li kern.module
 Settings related to kernel modules.
 The third level names for the settings are described below.
 .Bl -column "kern.module.autounload_unsafe" "integer" "Changeable" -offset indent
 .It Sy Third level name Ta Sy Type Ta Sy Changeable
 .It kern.module.autoload	integer	yes
 .It kern.module.autounload_unsafe	integer	yes
 .It kern.module.autotime	integer	yes
 .It kern.module.verbose	boolean	yes
 .El
 .Pp
 The variables are as follows:
 .Bl -tag -width 6n
 .It Li kern.module.autoload
 A boolean that controls whether kernel modules are loaded automatically.
 See
 .Xr module 7
 for details.
 .It Li kern.module.autounload_unsafe
 A boolean that controls whether the kernel will autounload modules that
 were automatically loaded and have not been audited for autounload.
 .Pp
 By default, only modules that have been audited will be autounloaded,
 and only if they were autoloaded to begin with.
 .It Li kern.module.autotime
 An integer that controls the delay before an attempt is made to
 automatically unload a module that was auto-loaded.
 Setting this value to zero disables the auto-unload function.
 .It Li kern.module.verbose
 A boolean that enables or disables verbose
 debug messages related to kernel modules.
 .El
 .It Li kern.monotonic_clock ( Dv KERN_MONOTONIC_CLOCK )
 Returns the standard version the implementation of the
 .St -p1003.1b-93
 Monotonic Clock Option conforms to,
 otherwise\ 0.
 .It Li kern.mqueue
 Settings related to POSIX message queues; see
 .Xr mqueue 3 .
 This node is created dynamically when
 the corresponding kernel module is loaded.
 The third level names for the settings are described below.
 .Bl -column "kern.mqueue.mq_max_msgsize" "integer" "Changeable" -offset indent
 .It Sy Third level name Ta Sy Type Ta Sy Changeable
 .It kern.mqueue.mq_open_max	integer	yes
 .It kern.mqueue.mq_prio_max	integer	yes
 .It kern.mqueue.mq_max_msgsize	integer	yes
 .It kern.mqueue.mq_def_maxmsg	integer	yes
 .It kern.mqueue.mq_max_maxmsg	integer	yes
 .El
 .Pp
 The variables are:
 .Bl -tag -width "123456"
 .It Li kern.mqueue.mq_open_max
 The maximum number of message queue descriptors any single process can open.
 .It Li kern.mqueue.mq_prio_max
 The maximum priority of a message.
 .It Li kern.mqueue.mq_max_msgsize
 The maximum size of a message in a message queue.
 .It Li kern.mqueue.mq_def_maxmsg
 The default maximum message count.
 .It Li kern.mqueue.mq_max_maxmsg
 The maximum number of messages in a message queue.
 .El
 .It Li kern.msgbuf ( Dv KERN_MSGBUF )
 The kernel message buffer, rotated so that the head of the circular kernel
 message buffer is at the start of the returned data.
 The returned data may contain NUL bytes.
 .It Li kern.msgbufsize ( Dv KERN_MSGBUFSIZE )
 The maximum number of characters that the kernel message buffer can hold.
 .It Li kern.ngroups ( Dv KERN_NGROUPS )
 The maximum number of supplemental groups.
 .\" .It Li kern.no_sa_support
 .\" XXX: Undocumented.
 .It Li kern.ntptime ( Dv KERN_NTPTIME )
+A
 .Vt struct ntptimeval
 structure is returned.
 This structure contains data used by the
 .Xr ntpd 8
 program.
 .It Li kern.osrelease ( Dv KERN_OSRELEASE )
 The system release string.
 .It Li kern.osrevision ( Dv KERN_OSREV )
 The system revision, expressed as an integer.
 .It Li kern.ostype ( Dv KERN_OSTYPE )
 The system type string.
 .\".It Li kern.panic_now
 .\" XXX: Undocumented.
 .It Li kern.pipe ( Dv KERN_PIPE )
 Pipe settings.
 The third level names for the  integer pipe settings is detailed below.
 The changeable column shows whether a process with appropriate
 privilege may change the value.
 .Bl -column "kern.pipe.maxbigpipes" "integer" "Changeable" -offset indent
 .It Sy Third level name Ta Sy Type Ta Sy Changeable
 .It kern.pipe.kvasiz	integer	yes
 .It kern.pipe.maxbigpipes	integer	yes
 .It kern.pipe.maxkvasz	integer	yes
 .It kern.pipe.limitkva	integer	yes
 .It kern.pipe.nbigpipes	integer	yes
 .El
 .Pp
 The variables are as follows:
 .Bl -tag -width "123456"
 .It Li kern.pipe.kvasiz ( Dv KERN_PIPE_KVASIZ )
 Amount of kernel memory consumed by pipe buffers.
 .It Li kern.pipe.maxbigpipes ( Dv KERN_PIPE_MAXBIGPIPES )
 Maximum number of
 .Dq big
 pipes.
 .It Li kern.pipe.maxkvasz ( Dv KERN_PIPE_MAXKVASZ )
 Maximum amount of kernel memory to be used for pipes.
 .It Li kern.pipe.limitkva ( Dv KERN_PIPE_LIMITKVA )
 Limit for direct transfers via page loan.
 .It Li kern.pipe.nbigpipes ( Dv KERN_PIPE_NBIGPIPES )
 Number of
 .Dq big
 pipes.
 .El
 .It Li kern.pool
 Provides statistics about the
 .Xr pool 9
 and
 .Xr pool_cache 9
 subsystems.
 .\" XXX: Undocumented .It Li kern.posix ( ? )
 .\"	 This is a node in which the only variable is semmax.
 .It Li kern.posix1version ( Dv KERN_POSIX1 )
 The version of ISO/IEC 9945
 .Pq St -p1003.1
 with which the system attempts to comply.
 .It Li kern.posix_aio
 The version of
 .St -p1003.1
 and its Asynchronous I/O option to which the system attempts to conform.
 .It Li kern.posix_barriers ( Dv KERN_POSIX_BARRIERS )
 The version of
 .St -p1003.1
 and its
 Barriers
 option to which the system attempts to conform,
 otherwise\ 0.
 .It Li kern.posix_reader_writer_locks ( Dv KERN_POSIX_READER_WRITER_LOCKS )
 The version of
 .St -p1003.1
 and its
 Read-Write Locks
 option to which the system attempts to conform,
 otherwise\ 0.
 .\".It Li kern.posix_sched
 .\" XXX: Undocumented.
 .It Li kern.posix_semaphores ( Dv KERN_POSIX_SEMAPHORES )
 The version of
 .St -p1003.1
 and its
 Semaphores
 option to which the system attempts to conform,
 otherwise\ 0.
 .It Li kern.posix_spin_locks ( Dv KERN_POSIX_SPIN_LOCKS )
 The version of
 .St -p1003.1
 and its
 Spin Locks
 option to which the system attempts to conform,
 otherwise\ 0.
 .It Li kern.posix_threads ( Dv KERN_POSIX_THREADS )
 The version of
 .St -p1003.1
 and its
 Threads
 option to which the system attempts to conform,
 otherwise\ 0.
 .It Li kern.posix_timers ( Dv KERN_POSIX_TIMERS )
 The version of
 .St -p1003.1
 and its
 Timers
 option to which the system attempts to conform,
 otherwise\ 0.
 .It Li kern.proc ( Dv KERN_PROC )
 Return the entire process table, or a subset of it.
 An array of
 .Vt struct kinfo_proc
 structures is returned,
 whose size depends on the current number of such objects in the system.
 The third and fourth level numeric names are as follows:
 .Bl -column "KERN_PROC_SESSION" "Fourth level is:" -offset indent
 .It Sy Third level name Ta Sy Fourth level is :
 .It KERN_PROC_ALL	None
 .It KERN_PROC_GID	A group ID
 .It KERN_PROC_PID	A process ID
 .It KERN_PROC_PGRP	A process group
 .It KERN_PROC_RGID	A real group ID
 .It KERN_PROC_RUID	A real user ID
 .It KERN_PROC_SESSION	A session ID
 .It KERN_PROC_TTY	A tty device
 .It KERN_PROC_UID	A user ID
 .El
 .It Li kern.proc2 ( Dv KERN_PROC2 )
 As for
 .Dv KERN_PROC ,
 but an array of
 .Vt struct kinfo_proc2
 structures are returned.
 The fifth level name is the size of the
 .Vt struct kinfo_proc2
 and the sixth level name is the number of structures to return.
 .It Li kern.proc_args ( Dv KERN_PROC_ARGS )
 Return the argv or environment strings (or the number thereof)
 of a process.
 Multiple strings are returned separated by NUL characters.
 The third level name is the process ID.
 The fourth level name is as follows:
 .Bl -column "KERN_PROG_PATHNAME" "The full pathname of the executable" -offset indent
 .It Dv KERN_PROC_ARGV	The argv strings
 .It Dv KERN_PROC_ENV	The environ strings
 .It Dv KERN_PROC_NARGV	The number of argv strings
 .It Dv KERN_PROC_NENV	The number of environ strings
 .It Dv KERN_PROC_PATHNAME	The full pathname of the executable
 .It Dv KERN_PROC_CWD	The current working directory
 .El
 .It Li kern.profiling ( Dv KERN_PROF )
 Return profiling information about the kernel.
 If the kernel is not compiled for profiling,
 attempts to retrieve any of the
 .Dv KERN_PROF
 values will fail with
 .Er EOPNOTSUPP .
 The third level names for the string and integer profiling information
 is detailed below.
 The changeable column shows whether a process with appropriate
 privilege may change the value.
 .Bl -column "kern.profiling.gmonparam" "struct gmonparam" "Changeable" -offset indent
 .It Sy Third level name Ta Sy Type Ta Sy Changeable
 .It kern.profiling.count	u_short[\|]	yes
 .It kern.profiling.froms	u_short[\|]	yes
 .It kern.profiling.gmonparam	struct gmonparam	no
 .It kern.profiling.state	integer	yes
 .It kern.profiling.tos	struct tostruct	yes
 .El
 .Pp
 The variables are as follows:
 .Bl -tag -width "123456"
 .It Li kern.profiling.count ( Dv GPROF_COUNT )
 Array of statistical program counter counts.
 .It Li kern.profiling.froms ( Dv GPROF_FROMS )
 Array indexed by program counter of call-from points.
 .It Li kern.profiling.gmonparams ( Dv GPROF_GMONPARAM )
 Structure giving the sizes of the above arrays.
 .It Li kern.profiling.state ( Dv GPROF_STATE )
 Profiling state.
 If set to
 .Dv GMON_PROF_ON ,
 starts profiling.
 If set to
 .Dv GMON_PROF_OFF ,
 stops profiling.
 .It Li kern.profiling.tos ( Dv GPROF_TOS )
 Array of
 .Vt struct tostruct
 describing destination of calls and their counts.
 .El
 .\" .It Li kern.pset
 .\" XXX: Undocumented.
 .It Li kern.rawpartition ( Dv KERN_RAWPARTITION )
 The raw partition of a disk (a == 0).
 .It Li kern.root_device ( Dv KERN_ROOT_DEVICE )
 The name of the root device (e.g.,
 .Dq wd0 ) .
 .It Li kern.root_partition ( Dv KERN_ROOT_PARTITION )
 The root partition on the root device (a == 0).
 .It Li kern.rtc_offset ( Dv KERN_RTC_OFFSET )
 Return the offset of real time clock from UTC in minutes.
 .It Li kern.saved_ids ( Dv KERN_SAVED_IDS )
 Returns 1 if saved set-group and saved set-user ID is available.
 .It Li kern.sbmax ( Dv KERN_SBMAX )
 Maximum socket buffer size in bytes.
 .It Li kern.securelevel ( Dv KERN_SECURELVL )
 See
 .Xr secmodel_securelevel 9 .
 .It Li kern.sched ( dynamic )
 Influence the scheduling of LWPs, their priorisation and how they are
 distributed on and moved between CPUs.
 .Bl -column "kern.sched.balance_period" "integer" "Changeable" -offset indent
 .It Sy Third level name	   Sy Type	 Sy Changeable
 .It kern.sched.cacheht_time	   integer	 yes
 .It kern.sched.balance_period	   integer	 yes
 .It kern.sched.average_weight	   integer	 yes
 .It kern.sched.min_catch	   integer	 yes
 .It kern.sched.timesoftints	   integer	 yes
 .It kern.sched.kpreempt_pri	   integer	 yes
 .It kern.sched.upreempt_pri	   integer	 yes
 .It kern.sched.maxts	   integer	 yes
 .It kern.sched.mints	   integer	 yes
 .It kern.sched.name	   string	 no
 .It kern.sched.rtts	   integer	 no
 .It kern.sched.pri_min	   integer	 no
 .It kern.sched.pri_max	   integer	 no
 .El
 .Pp
 The variables are as follows:
 .Bl -tag -width "123456"
 .It Li kern.sched.cacheht_time ( dynamic )
 Cache hotness time in which a LWP is kept on one particular CPU