path: root/lib/libc/gen/sysctl.3

.\"	$OpenBSD: sysctl.3,v 1.73 2001/08/07 16:51:12 pvalchev 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. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
.\"	California, Berkeley and its contributors.
.\" 4. 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.
.\"
.Dd June 4, 1993
.Dt SYSCTL 3
.Os
.Sh NAME
.Nm sysctl
.Nd get or set system information
.Sh SYNOPSIS
.Fd #include <sys/param.h>
.Fd #include <sys/sysctl.h>
.Ft int
.Fn sysctl "int *name" "u_int namelen" "void *oldp" "size_t *oldlenp" "void *newp" "size_t newlen"
.Sh DESCRIPTION
The
.Fn sysctl
function retrieves system information and allows processes with
appropriate privileges to set system information.
The information available from
.Fn sysctl
consists of integers, strings, and tables.
Information may be retrieved and set from the command interface
using the
.Xr sysctl 8
utility.
.Pp
Unless explicitly noted below,
.Fn sysctl
returns a consistent snapshot of the data requested.
Consistency is obtained by locking the destination
buffer into memory so that the data may be copied out without blocking.
Calls to
.Fn sysctl
are serialized to avoid deadlock.
.Pp
The state is described using a
.Dq Management Information Base (MIB)
style name, listed in
.Fa name ,
which is a
.Fa namelen
length array of integers.
.Pp
The information is copied into the buffer specified by
.Fa oldp .
The size of the buffer is given by the location specified by
.Fa oldlenp
before the call,
and that location gives the amount of data copied after a successful call.
If the amount of data available is greater
than the size of the buffer supplied,
the call supplies as much data as fits in the buffer provided
and returns with the error code
.Er ENOMEM .
If the old value is not desired,
.Fa oldp
and
.Fa oldlenp
should be set to
.Dv NULL .
.Pp
The size of the available data can be determined by calling
.Fn sysctl
with a
.Dv NULL
parameter for
.Fa oldp .
The size of the available data will be returned in the location pointed to by
.Fa oldlenp .
For some operations, the amount of space may change often.
For these operations,
the system attempts to round up so that the returned size is
large enough for a call to return the data shortly thereafter.
.Pp
To set a new value,
.Fa newp
is set to point to a buffer of length
.Fa newlen
from which the requested value is to be taken.
If a new value is not to be set,
.Fa newp
should be set to
.Dv NULL
and
.Fa newlen
set to 0.
.Pp
The top level names are defined with a
.Dv CTL_
prefix in
.Aq Pa 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.
.Pp
.Bl -column CTLXMACHDEPXXX "Next level namesXXXXXX" -offset indent
.It Sy Name	Next level names	Description
.It Dv CTL_DEBUG No "	sys/sysctl.h	Debugging"
.It Dv CTL_FS No "	sys/sysctl.h	File system"
.It Dv CTL_HW No "	sys/sysctl.h	Generic CPU, I/O"
.It Dv CTL_KERN No "	sys/sysctl.h	High kernel limits"
.It Dv CTL_MACHDEP No "	sys/sysctl.h	Machine dependent"
.It Dv CTL_NET No "	sys/socket.h	Networking"
.It Dv CTL_USER No "	sys/sysctl.h	User-level"
.It Dv CTL_VM No "	vm/vm_param.h	Virtual memory"
.El
.Pp
For example, the following retrieves the maximum number of processes allowed
in the system:
.Pp
.Bd -literal -offset indent -compact
int mib[2], maxproc;
size_t len;

mib[0] = CTL_KERN;
mib[1] = KERN_MAXPROC;
len = sizeof(maxproc);
sysctl(mib, 2, &maxproc, &len, NULL, 0);
.Ed
.Pp
To retrieve the standard search path for the system utilities:
.Pp
.Bd -literal -offset indent -compact
int mib[2];
size_t len;
char *p;

mib[0] = CTL_USER;
mib[1] = USER_CS_PATH;
sysctl(mib, 2, NULL, &len, NULL, 0);
p = malloc(len);
sysctl(mib, 2, p, &len, NULL, 0);
.Ed
.Ss CTL_DEBUG
The debugging variables vary from system to system.
A debugging variable may be added or deleted without need to recompile
.Fn sysctl
to know about it.
Each time it runs,
.Fn sysctl
gets the list of debugging variables from the kernel and
displays their current values.
The system defines twenty
.Li struct ctldebug
variables named
.Va debug0
through
.Va 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
.Ss CTL_FS
The string and integer information available for the
.Dv CTL_FS
level is detailed below.
The changeable column shows whether a process with appropriate
privileges may change the value.
.Bl -column "Second level nameXXXXXX" integerXXX -offset indent
.It Sy Second level name	Type	Changeable
.It Dv FS_POSIX_SETUID No "	integer	yes"
.El
.Pp
.Bl -tag -width "123456"
.It Dv FS_POSIX_SETUID
When this variable is set, ownership changes on a file will cause
the
.Va S_ISUID
and
.Va S_ISGID
bits to be cleared.
As detailed in
.Xr securelevel 7 ,
this variable may not be changed if the securelevel is > 0.
.El
.Ss CTL_HW
The string and integer information available for the
.Dv CTL_HW
level is detailed below.
The changeable column shows whether a process with appropriate
privileges may change the value.
.Bl -column "Second level nameXXXXXX" integerXXX -offset indent
.It Sy Second level name	Type	Changeable
.It Dv HW_MACHINE No "	string	no"
.It Dv HW_MODEL No "	string	no"
.It Dv HW_NCPU No "	integer	no"
.It Dv HW_BYTEORDER No "	integer	no"
.It Dv HW_PHYSMEM No "	integer	no"
.It Dv HW_USERMEM No "	integer	no"
.It Dv HW_PAGESIZE No "	integer	no"
.It Dv HW_DISKNAMES No "	string	no"
.It Dv HW_DISKSTATS No "	struct	no"
.It Dv HW_DISKCOUNT No "	integer	no"
.El
.Pp
.Bl -tag -width "123456"
.It Dv HW_MACHINE
The machine class.
.It Dv HW_MODEL
The machine model
.It Dv HW_NCPU
The number of CPUs.
.It Dv HW_BYTEORDER
The byteorder (4321 or 1234).
.It Dv HW_PHYSMEM
The bytes of physical memory.
.It Dv HW_USERMEM
The bytes of non-kernel memory.
.It Dv HW_PAGESIZE
The software page size.
.It Dv HW_DISKNAMES
A comma-separated list of disk names.
.It Dv HW_DISKSTATS
An array of
.Li struct diskstats
structures containing disk statistics.
.It Dv HW_DISKCOUNT
The number of disks currently attached to the system.
.El
.Ss CTL_KERN
The string and integer information available for the
.Dv CTL_KERN
level is detailed below.
The changeable column shows whether a process with appropriate
privileges may change the value.
The types of data currently available are process information,
system vnodes, the open file entries, routing table entries,
virtual memory statistics, load average history, and clock rate
information.
.Bl -column "KERNXCHOWNXRESTRICTEDXXX" "struct clockrateXXX" -offset indent
.It Sy Second level name	Type	Changeable
.It Dv KERN_ARGMAX No "	integer	no"
.It Dv KERN_ARND No "	integer	no"
.It Dv KERN_BOOTTIME No "	struct timeval	no"
.It Dv KERN_CLOCKRATE No "	struct clockinfo	no"
.It Dv KERN_CPTIME No "	long[CPUSTATES]	no"
.It Dv KERN_DOMAINNAME No "	string	yes"
.It Dv KERN_FILE No "	struct file	no"
.It Dv KERN_FSYNC No "	integer	no"
.It Dv KERN_FORKSTAT No "	struct forkstat	no"
.It Dv KERN_HOSTID No "	integer	yes"
.It Dv KERN_HOSTNAME No "	string	yes"
.It Dv KERN_JOB_CONTROL No "	integer	no"
.It Dv KERN_MALLOCSTATS No "	node	no"
.It Dv KERN_MAXFILES No "	integer	yes"
.It Dv KERN_MAXPARTITIONS No "	integer	no"
.It Dv KERN_MAXPROC No "	integer	yes"
.It Dv KERN_MAXVNODES No "	integer	yes"
.It Dv KERN_MSGBUFSIZE No "	integer	no"
.It Dv KERN_NCHSTATS No "	struct nchstats	no"
.It Dv KERN_NGROUPS No "	integer	no"
.It Dv KERN_NPROCS No "	integer	no"
.It Dv KERN_NSELCOLL No "	integer	no"
.It Dv KERN_NTPTIME No "	struct ntptimeval	no"
.It Dv KERN_NOSUIDCOREDUMP No "	integer	yes"
.It Dv KERN_OSRELEASE No "	string	no"
.It Dv KERN_OSREV No "	integer	no"
.It Dv KERN_OSTYPE No "	string	no"
.It Dv KERN_POSIX1 No "	integer	no"
.It Dv KERN_PROC No "	struct proc	no"
.It Dv KERN_PROF No "	node	not applicable"
.It Dv KERN_RAWPARTITION No "	integer	no"
.It Dv KERN_RND No "	struct rndstats	no"
.It Dv KERN_SAVED_IDS No "	integer	no"
.It Dv KERN_SECURELVL No "	integer	raise only"
.It Dv KERN_SOMINCONN No "	integer	yes"
.It Dv KERN_SOMAXCONN No "	integer	yes"
.It Dv KERN_SYSVMSG No "	integer	no"
.It Dv KERN_SYSVSEM No "	integer	no"
.It Dv KERN_SYSVSHM No "	integer	no"
.It Dv KERN_TTY No "	node	not applicable"
.It Dv KERN_USERMOUNT No "	integer	yes"
.It Dv KERN_VERSION No "	string	no"
.It Dv KERN_VNODE No "	struct vnode	no"
.El
.Pp
.Bl -tag -width "123456"
.It Dv KERN_ARGMAX
The maximum bytes of argument to
.Xr exec 2 .
.It Dv KERN_ARND
Returns a random integer from the kernel
.Fn arc4random
function.
This can be useful if
.Pa /dev/arandom
is not available (see
.Xr random 4 ) .
.It Dv KERN_BOOTTIME
A
.Li struct timeval
structure is returned.
This structure contains the time that the system was booted.
.It Dv KERN_CLOCKRATE
A
.Li 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.
.It Dv KERN_CPTIME
An array of longs, of size
.Li CPUSTATES
is returned, containing statistics about the number of ticks spent by
the system in interrupt processing, user processes (niced or normal),
system processing, or idling.
.It Dv KERN_DOMAINNAME
Get or set the YP domain name.
.It Dv KERN_FILE
Return the entire file table.
The returned data consists of a single
.Li struct filehead
followed by an array of
.Li struct file ,
whose size depends on the current number of such objects in the system.
.It Dv KERN_FSYNC
Return 1 if the File Synchronisation Option is available on this system,
otherwise 0.
.It Dv KERN_FORKSTAT
A
.Li struct forkstat
structure is returned.
This structure contains information about the number of
.Xr fork 2 ,
.Xr vfork 2 ,
.Xr rfork 2
system calls as well as kernel thread creations since system startup,
and the number of pages of virtual memory involved in each.
.It Dv KERN_HOSTID
Get or set the host ID.
.It Dv KERN_HOSTNAME
Get or set the hostname.
.It Dv KERN_JOB_CONTROL
Return 1 if job control is available on this system, otherwise 0.
.It Dv KERN_MAXFILES
The maximum number of open files that may be open in the system.
.It Dv KERN_MAXPARTITIONS
The maximum number of partitions allowed per disk.
.It Dv KERN_MAXPROC
The maximum number of simultaneous processes the system will allow.
.It Dv KERN_MAXVNODES
The maximum number of vnodes available on the system.
.It Dv KERN_MSGBUFSIZE
The size of the kernel message buffer.
.It Dv KERN_NCHSTATS
A
.Li struct nchstats
structure is returned.
This structure contains information the
filename to
.Xr inode 5
mapping cache.
.It Dv KERN_NGROUPS
The maximum number of supplemental groups.
.It Dv KERN_NPROCS
The number of entries in the kernel process table.
.It Dv KERN_NOSUIDCOREDUMP
Programs with their set-user-ID bit set will not dump core when this is set.
.It Dv KERN_NSELCOLL
Number of
.Xr select 2
collisions.
.It Dv KERN_NTPTIME
Returns a
.Li strct ntptimeval ,
containing kernel precision timekeeping information.
.It Dv KERN_OSRELEASE
The system release string.
.It Dv KERN_OSREV
The system revision number.
.It Dv KERN_OSTYPE
The system type string.
.It Dv KERN_POSIX1
The version of ISO/IEC 9945 (POSIX 1003.1) with which the system
attempts to comply.
.It Dv KERN_PROC
Return the entire process table, or a subset of it.
An array of
.Li struct kinfo_proc
structures is returned,
whose size depends on the current number of such objects in the system.
The third and fourth level names are as follows:
.Bl -column "Third level nameXXXXXX" "Fourth level is:XXXXXX" -offset indent
.It Sy Third level name	Fourth level is:
.It Dv KERN_PROC_ALL No "	None"
.It Dv KERN_PROC_PID No "	A process ID"
.It Dv KERN_PROC_PGRP No "	A process group"
.It Dv KERN_PROC_TTY No "	A tty device"
.It Dv KERN_PROC_UID No "	A user ID"
.It Dv KERN_PROC_RUID No "	A real user ID"
.El
.It Dv KERN_MALLOCSTATS
Return kernel memory bucket statistics.
The third level names are detailed below.
There are no changeable values in this branch.
.Bl -column "KERN_MALLOC_HIGH_WATERMARK" "string" -offset indent
.It Sy Third level name	Type
.It Dv KERN_MALLOC_BUCKETS	string
.It Dv KERN_MALLOC_BUCKET	node
.It Dv KERN_MALLOC_KMEMNAMES	string
.It Dv KERN_MALLOC_KMEMSTATS	node
.El
.Pp
The variables are as follows:
.Bl -tag -width "123456"
.It Dv KERN_MALLOC_BUCKETS
Return a comma-separated list of the bucket sizes used by the kernel.
.It Dv KERN_MALLOC_BUCKET.<size>
A node containing the statistics for the memory bucket of the
specified size (in decimal notation, the number of bytes per bucket
element, e.g., 16, 32, 128).
Each node returns a
.Li struct kmembuckets .
.Pp
If a value is specified that does not correspond directly to a
bucket size, the statistics for the closest larger bucket size will be
returned instead.
.Pp
Note that bucket sizes are typically powers of 2.
.It Dv KERN_MALLOC_KERNNAMES
Return a comma-separated list of the names of the kernel
.Xr malloc 9
types.
.It Dv KERN_MALLOC_KMEMSTATS
A node containing the statistics for the memory types of the specified
name.
Each node returns a
.Li struct kmemstats .
.El
.Pp
.It 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
privileges may change the value.
.Bl -column "GPROFXGMONPARAMXXX" "struct gmonparamXXX" -offset indent
.It Sy Third level name	Type	Changeable
.It Dv GPROF_STATE No "	integer	yes"
.It Dv GPROF_COUNT No "	u_short[\|]	yes"
.It Dv GPROF_FROMS No "	u_short[\|]	yes"
.It Dv GPROF_TOS No "	struct tostruct	yes"
.It Dv GPROF_GMONPARAM No "	struct gmonparam	no"
.El
.Pp
The variables are as follows:
.Bl -tag -width "123456"
.It Dv GPROF_STATE
Returns
.Dv GMON_PROF_ON
or
.Dv GMON_PROF_OFF
to show that profiling is running or stopped.
.It Dv GPROF_COUNT
Array of statistical program counter counts.
.It Dv GPROF_FROMS
Array indexed by program counter of call-from points.
.It Dv GPROF_TOS
Array of
.Li struct tostruct
describing destination of calls and their counts.
.It Dv GPROF_GMONPARAM
Structure giving the sizes of the above arrays.
.El
.It Dv KERN_RAWPARTITION
The raw partition of a disk (a == 0).
.It Dv KERN_RND
Returns statistics about the
.Pa /dev/random
device in a
.Li struct rndstats
structure.
.It Dv KERN_SAVED_IDS
Returns 1 if saved set-group-ID and saved set-user-ID are available.
.It Dv KERN_SECURELVL
The system security level.
This level may be raised by processes with appropriate privileges.
It may only be lowered by process 1.
.It Dv KERN_SOMAXCONN
Upper bound on the number of half-open connections a process can allow
to be associated with a socket, using
.Xr listen 2 .
The default value is 128.
.It Dv KERN_SOMINCONN
Lower bound on the number of half-open connections a process can allow
to be associated with a socket, using
.Xr listen 2 .
The default value is 80.
.It Dv KERN_SYSVMSG
Returns 1 if System V style message queue functionality is available on this
system, otherwise 0.
.It Dv KERN_SYSVSEM
Returns 1 if System V style semaphore functionality is available on this
system, otherwise 0.
.It Dv KERN_SYSVSHM
Returns 1 if System V style share memory functionality is available on this
system, otherwise 0.
.It Dv KERN_TTY
Return statistics information about tty input/output.
The third level names information is detailed below.
The changeable column shows whether a process with appropriate
privileges may change the value.
.Bl -column "KERN_TTY_TKRAWCCXXX" "int64_tXX" -offset indent
.It Sy Third level name	Type	Changeable
.It Dv KERN_TTY_TKNIN No "	int64_t	no"
.It Dv KERN_TTY_TKNOUT No "	int64_t	no"
.It Dv KERN_TTY_TKRAWCC No "	int64_t	no"
.It Dv KERN_TTY_TKCANCC No "	int64_t	no"
.El
.Pp
The variables are as follows:
.Bl -tag -width "123456"
.It Dv KERN_TTY_TKNIN
Returns the number of input characters from a
.Xr tty 4 .
.It Dv KERN_TTY_TKNOUT
Returns the number of output characters on a
.Xr tty 4 .
.It Dv KERN_TTY_TKRAWCC
Return the number of input characters in raw mode.
.It Dv KERN_TTY_TKCANCC
Return the number of input characters in canonical mode.
.El
.It Dv KERN_USERMOUNT
Return non-zero if regular users can issue
.Xr mount 2
requests.
The default value is 0.
.It Dv KERN_VERSION
The system version string.
.It Dv KERN_VNODE
Return the entire vnode table.
Note, the vnode table is not necessarily a consistent snapshot of
the system.
The returned data consists of an array whose size depends on the
current number of such objects in the system.
Each element of the array contains the kernel address of a vnode
.Li struct vnode *
followed by the vnode itself
.Li struct vnode .
.El
.Ss CTL_MACHDEP
The set of variables defined is architecture dependent.
Most architectures define at least the following variables.
.Bl -column "CONSOLE_DEVICEXXX" "integerXXX" -offset indent
.It Sy Second level name	Type	Changeable
.It Dv CPU_CONSDEV No "	dev_t	no"
.El
.Ss CTL_NET
The string and integer information available for the
.Dv CTL_NET
level is detailed below.
The changeable column shows whether a process with appropriate
privileges may change the value.
.Bl -column "Second level nameXXXXXX" "routing messagesXXX" -offset indent
.It Sy Second level name	Type	Changeable
.It Dv PF_ROUTE No "	routing messages	no"
.It Dv PF_INET No "	IPv4 values	yes"
.It Dv PF_INET6 No "	IPv6 values	yes"
.El
.Pp
.Bl -tag -width "123456"
.It Dv PF_ROUTE
Return the entire routing table or a subset of it.
The data is returned as a sequence of routing messages (see
.Xr route 4
for the header file, format, and meaning).
The length of each message is contained in the message header.
.Pp
The third level name is a protocol number, which is currently always 0.
The fourth level name is an address family, which may be set to 0 to
select all address families.
The fifth and sixth level names are as follows:
.Bl -column "Fifth level nameXXXXXX" "Sixth level is:XXX" -offset indent
.It Sy Fifth level name	Sixth level is:
.It Dv NET_RT_FLAGS No "	rtflags"
.It Dv NET_RT_DUMP No "	None"
.It Dv NET_RT_IFLIST No "	None"
.El
.It Dv PF_INET
Get or set various global information about IPv4
.Pq Internet Protocol version 4 .
The third level name is the protocol.
The fourth level name is the variable name.
The currently defined protocols and names are:
.Bl -column "Protocol name" "ipsec-soft-bytes" "integer" -offset indent
.It Sy Protocol name	Variable name	Type	Changeable
.It ip	forwarding	integer	yes
.It ip	redirect	integer	yes
.It ip	ttl	integer	yes
.It ip	sourceroute	integer	yes
.It ip	directed-broadcast	integer	yes
.It ip	portfirst	integer	yes
.It ip	portlast	integer	yes
.It ip	porthifirst	integer	yes
.It ip	porthilast	integer	yes
.It ip	maxqueue	integer	yes
.It ip	encdebug	integer	yes
.It ip	ipsec-invalid-life	integer	yes
.It ip	ipsec-pfs	integer	yes
.It ip	ipsec-soft-allocs	integer	yes
.It ip	ipsec-allocs	integer	yes
.It ip	ipsec-soft-bytes	integer	yes
.It ip	ipsec-bytes	integer	yes
.It ip	ipsec-timeout	integer	yes
.It ip	ipsec-soft-timeout	integer	yes
.It ip	ipsec-soft-firstuse	integer	yes
.It ip	ipsec-firstuse	integer	yes
.It ip	ipsec-enc-alg	string	yes
.It ip	ipsec-auth-alg	string	yes
.It ip	ipsec-comp-alg	string	yes
.It ip	ipsec-expire-acquire	integer	yes
.It ip	mtudisc	integer	yes
.It ip	mtudisctimeout	integer	yes
.It icmp	maskrepl	integer	yes
.It icmp	bmcastecho	integer	yes
.It icmp	errppslimit	integer	yes
.It ipip	allow	integer	yes
.It tcp	rfc1323	integer	yes
.It tcp	ident	structure	no
.It tcp	keepinittime	integer	yes
.It tcp	keepidle	integer	yes
.It tcp	keepintvl	integer	yes
.It tcp	slowhz	integer	yes
.It tcp	baddynamic	array	yes
.It tcp	recvspace	integer	yes
.It tcp	sendspace	integer	yes
.It tcp	sack	integer	yes
.It tcp	mssdflt	integer	yes
.It tcp	rstppslimit	integer	yes
.It udp	checksum	integer	yes
.It udp	baddynamic	array	yes
.It udp	recvspace	integer	yes
.It udp	sendspace	integer	yes
.It gre	allow	integer	yes
.It esp	enable	integer	yes
.It ah	enable	integer	yes
.It ipcomp	enable	integer	yes
.It mobileip	allow	integer	yes
.It etherip	allow	integer	yes
.El
.Pp
The variables are as follows:
.Bl -tag -width "123456"
.It Li ip.forwarding
Returns 1 when
.Tn IP
forwarding is enabled for the host,
indicating the host is acting as a router.
.It Li ip.redirect
Returns 1 when
.Tn ICMP
redirects may be sent by the host.
This option is ignored unless the host is routing
.Tn IP
packets,
and should normally be enabled on all systems.
.It Li ip.ttl
The maximum time-to-live (hop count) value for an
.Tn IP
packet sourced by
the system.
This value applies to normal transport protocols, not to
.Tn ICMP .
.It Li ip.sourceroute
Returns 1 when forwarding of source-routed packets is enabled for
the host.
This value may only be changed if the kernel security
level is less than 1.
.It Li ip.directed-broadcast
Returns 1 if directed broadcast behavior is enabled for the host.
.It Li ip.encdebug
Returns 1 when error message reporting is enabled for the host.
If the kernel has been compiled with the
.Dv ENCDEBUG
option,
then debugging information will also be reported when this variable is set.
.It Li ip.ipsec-invalid-life
The lifetime of embryonic Security Associations (SAs that key management
daemons have reserved but not fully established yet) in seconds.
If set to less than or equal to zero, embryonic SAs will not expire.
The default value is 60.
.It Li ip.ipsec-pfs
If set to any non-zero value, the kernel will ask the key management
daemons to use Perfect Forward Secrecy when establishing IPsec
Security Associations.
Perfect Forward Secrecy makes IPsec Security Associations
cryptographically distinct from each other, such that breaking the key
for one such SA does not compromise any others.
Requiring PFS for every security association significantly increases the
computational load of
.Xr isakmpd 8
exchanges.
The default value is 1.
.It Li ip.ipsec-soft-allocs
The number of IPsec flows that can use a security association before a
message is sent by the kernel to key management for renegotiation
of the security association.
If set to less than or equal to zero, no message is sent to key
management.
The default value is 0.
.It Li ip.ipsec-allocs
The number of IPsec flows that can use a security association before
it will expire.
If set to less than or equal to zero, the security association will not
expire because of this counter.
The default value is 0.
.It Li ip.ipsec-soft-bytes
The number of bytes that will be processed by a security association
before a message is sent by the kernel to key management for
renegotiation of the security association.
If set to less than or equal to zero, no message is sent to key
management.
The default value is 0.
.It Li ip.ipsec-bytes
The number of bytes that will be processed by a security association
before it will expire.
If set to less than or equal to zero, the security association will not
expire because of this counter.
The default value is 0.
.It Li ip.ipsec-soft-timeout
The number of seconds after a security association is established
before a message is sent by the kernel to key management for
renegotiation of the security association.
If set to less than or equal to zero, no message is sent to key
management.
The default value is 80000 seconds.
.It Li ip.ipsec-timeout
The number of seconds after a security association is established
before it will expire.
If set to less than or equal to zero, the security association will
not expire because of this timer.
The default value is 86400 seconds.
.It Li ip.ipsec-soft-firstuse
The number of seconds after a security association is first used
before a message is sent by the kernel to key management for
renegotiation of the security association.
If set to less than or equal to zero, no message is sent to key
management.
The default value is 3600 seconds.
.It Li ip.ipsec-firstuse
The number of seconds after a security association is first use before
it will expire.
If set to less than or equal to zero, the security association will
not expire because of this timer.
The default value is 7200 seconds.
.It Li ip.ipsec-enc-alg
This is the default encryption algorithm the kernel will instruct key
management daemons to negotiate when establishing security
associations on behalf of the kernel.
Such security associations can occur as a result of a process having
requested some security level through
.Xr setsockopt 3 ,
or as a result of dynamic
.Xr vpn 8
entries.
Supported values are des, 3des, blowfish, cast128, and skipjack.
If set to any other value, it is left to the key management daemons to
select an encryption algorithm for the security association.
The default value is 3des.
.It Li ip.ipsec-auth-alg
This is the default authentication algorithm the kernel will instruct
key management daemons to negotiate when establishing security
associations on behalf of the kernel.
Such security associations can occur as a result of a process having
requested some security level through
.Xr setsockopt 3 ,
or as a result of dynamic
.Xr vpn 8
entries.
Supported values are hmac-md5, hmac-sha1, and hmac-ripemd160.
If set to any other value, it is left to the key management daemons to
select an authentiction algorithm for the security association.
The default value is hmac-sha1.
.It Li ip.ipsec-expire-acquire
How long should the kernel allow key management to dynamically acquire
security associations, before re-sending a request.
The default value is 30 seconds.
.It Li ip.ipsec-keep-invalid
How long half-created security associations should be kept by the kernel
(these are created by key management daemons while negotiating).
The default value is 60 seconds.
.It Li ip.mtudisc
Returns 1 if Path MTU Discovery is enabled.
.It Li ip.mtudisctimeout
Returns the number of seconds in which a route added by the Path MTU
Discovery engine will time out.
When the route times out, the Path MTU Discovery engine will attempt
to probe a larger path MTU.
.It Li ipip.allow
If set to 0, incoming IP-in-IP packets will not be processed.
If set to any other value, processing will occur; furthermore, if set
to 2, no checks for spoofing of loopback addresses will be done.
This is useful only for debugging purposes, and should never be used
in production systems.
.It Li gre.allow
If set to 0, incoming GRE packets will not be processed.
If set to any other value, processing will occur.
.It Li mobileip.allow
If set to 0, incoming MobileIP encapsulated packets (RFC 2004) will not be processed.
If set to any other value, processing will occur.
.It Li etherip.allow
If set to 0, incoming Ethernet-in-IPv4 packets will not be processed.
If set to any other value, processing will occur.
.It Li icmp.maskrepl
Returns 1 if
.Tn ICMP
network mask requests are to be answered.
.It Li icmp.errppslimit
The variable specifies the maximum number of outgoing ICMP error messages
per second.
ICMP error messages that exceeded the value are subject to rate limitation
and will not go out from the node.
Negative value disables rate limitation.
.It Li tcp.rfc1323
Returns 1 if RFC1323 extensions to
.Tn TCP
are enabled.
.It Li tcp.baddynamic
An array of
.Li in_port_t
is returned specifying the bitmask of
.Tn TCP
ports between 512
and 1023 inclusive that should not be allocated dynamically
by the kernel (i.e., they must be bound specifically by port number).
.It Li tcp.ident
A structure
.Li struct tcp_ident_mapping
specifying a local and foreign endpoint of a
.Tn TCP
socket is filled in with the euid and ruid of the process that owns the socket.
If no such socket exists then the euid and ruid values are both
set to -1.
.It Li tcp.keepidle
If the socket option
.Pa SO_KEEPALIVE
has been set, time a connection needs to be idle before keepalives are sent.
See also tcp.slowhz.
.It Li tcp.keepintvl
Time after a keepalive probe is sent until, in the absence of any response,
another probe is sent.
See also tcp.slowhz.
.It Li tcp.slowhz
The units for tcp.keepidle and tcp.keepintvl; those variables are in ticks
of a clock that ticks tcp.slowhz times per second.
(That is, their values must be divided by the tcp.slowhz value to get times
in seconds.)
.It Li tcp.sendspace
Returns the default
.Tn TCP
send buffer size.
.It Li tcp.recvspace
Returns the default
.Tn TCP
receive buffer size.
.It Li tcp.sack
Returns 1 if RFC2018 Selective Acknowledgements are enabled.
.It Li tcp.mssdflt
The maximum segment size that is used as default for non-local connections.
The default value is 512.
.It Li tcp.rstppslimit
The variable specifies the maximum number of outgoing TCP RST packets
per second.
TCP RST packet that exceeded the value are subject to rate limitation
and will not go out from the node.
Negative value disables rate limitation.
.It Li udp.checksum
Returns 1 when
.Tn UDP
checksums are being computed and checked.
Disabling
.Tn UDP
checksums is strongly discouraged.
.It Li udp.baddynamic
Analogous to
.Li tcp.baddynamic
but for
.Tn UDP
sockets.
.It Li udp.sendspace
Returns the default
.Tn UDP
send buffer size.
.It Li udp.recvspace
Returns the default
.Tn UDP
receive buffer size.
.El
.It Dv PF_INET6
Get or set various global information about IPv6
.Pq Internet Protocol version 6 .
The third level name is the protocol.
The fourth level name is the variable name.
The currently defined protocols and names are:
.Bl -column "Protocol name" "Variable nameXX" "integer" "yes" -offset indent
.It Pa Protocol name	Variable name	Type	Changeable
.It ip6	forwarding	integer	yes
.It ip6	redirect	integer	yes
.It ip6	hlim	integer	yes
.It ip6	maxfragpackets	integer	yes
.It ip6	accept_rtadv	integer	yes
.It ip6	keepfaith	integer	yes
.It ip6	log_interval	integer	yes
.It ip6	hdrnestlimit	integer	yes
.It ip6	dad_count	integer	yes
.It ip6	auto_flowlabel	integer	yes
.It ip6	defmcasthlim	integer	yes
.It ip6	kame_version	string	no
.It ip6	use_deprecated	integer	yes
.It ip6	rr_prune	integer	yes
.It icmp6	rediraccept	integer	yes
.It icmp6	redirtimeout	integer	yes
.It icmp6	nd6_prune	integer	yes
.It icmp6	nd6_delay	integer	yes
.It icmp6	nd6_umaxtries	integer	yes
.It icmp6	nd6_mmaxtries	integer	yes
.It icmp6	nd6_useloopback	integer	yes
.It icmp6	nodeinfo	integer	yes
.It icmp6	errppslimit	integer	yes
.It icmp6	nd6_maxnudhint	integer	yes
.It icmp6	mtudisc_hiwat	integer	yes
.It icmp6	mtudisc_lowat	integer	yes
.It icmp6	nd6_debug	integer	yes
.El
.Pp
The variables are as follows:
.Bl -tag -width "123456"
.It Li ip6.forwarding
Returns 1 when IPv6 forwarding is enabled for the node,
meaning that the node is acting as a router.
Returns 0 when IPv6 forwarding is disabled for the node,
meaning that the node is acting as a host.
Note that IPv6 defines node behavior for the
.Dq router
and
.Dq host
cases quite differently, and changing this variable during operation
may cause serious trouble.
Hence, this variable should only be set at bootstrap time.
.It Li ip6.redirect
Returns 1 when ICMPv6 redirects may be sent by the node.
This option is ignored unless the node is routing IP packets,
and should normally be enabled on all systems.
.It Li ip6.hlim
The default hop limit value for an IPv6 unicast packet sourced by the node.
This value applies to all the transport protocols on top of IPv6.
Methods for overriding this value are documented in
.Xr ip6 4 .
.It Li ip6.maxfragpackets
The maximum number of fragmented packets the node will accept.
0 means that the node will not accept any fragmented packets.
-1 means that the node will accept as many fragmented packets as it receives.
The flag is provided basically for avoiding possible DoS attacks.
.It Li ip6.accept_rtadv
If set to non-zero, the node will accept ICMPv6 router advertisement packets
and autoconfigures address prefixes and default routers.
The node must be a host
.Pq not a router
for the option to be meaningful (see
.Li ip6.forwarding Ns ).
.It Li ip6.keepfaith
If set to non-zero, enables the
.Dq FAITH
TCP relay IPv6-to-IPv4 translator code in the kernel.
Refer to
.Xr faith 4
and
.Xr faithd 8
for more details.
.It Li ip6.log_interval
This variable permits adjusting the amount of logs generated by the
IPv6 packet forwarding engine.  The value indicates the number of
seconds of interval which must elapse between log output.
.It Li ip6.hdrnestlimit
The number of IPv6 extension headers permitted on incoming IPv6 packets.
If set to 0, the node will accept as many extension headers as possible.
.It Li ip6.dad_count
The variable configures the number of IPv6 DAD
.Pq duplicated address detection
probe packets.
These packets are generated when IPv6 interfaces are first brought up.
.It Li ip6.auto_flowlabel
On connected transport protocol packets,
fill IPv6 flowlabel field to help intermediate routers identify
packet flows.
.It Li ip6.defmcasthlim
The default hop limit value for an IPv6 multicast packet sourced by the node.
This value applies to all the transport protocols on top of IPv6.
Methods for overriding this value are documented in
.Xr ip6 4 .
.It Li ip6.kame_version
The string identifies the version of the KAME IPv6 stack implemented
in the kernel.
.It Li ip6.use_deprecated
The variable controls use of deprecated addresses, specified in
RFC2462 5.5.4.
.It Li ip6.rr_prune
The variable specifies interval between IPv6 router renumbering prefix
babysitting in seconds.
.It Li icmp6.rediraccept
If set to non-zero, the host will accept ICMPv6 redirect packets.
Note that IPv6 routers will never accept ICMPv6 redirect packets,
so the variable is only meaningful on IPv6 hosts, not on routers.
.It Li icmp6.redirtimeout
The variable specifies the lifetime of routing entries generated by
incoming ICMPv6 redirects.
.It Li icmp6.nd6_prune
The variable specifies interval between IPv6 neighbor cache babysitting
in seconds.
.It Li icmp6.nd6_delay
The variable specifies
.Dv DELAY_FIRST_PROBE_TIME
timing constant in IPv6 neighbor discovery specification
.Pq RFC2461 ,
in seconds.
.It Li icmp6.nd6_umaxtries
The variable specifies
.Dv MAX_UNICAST_SOLICIT
constant in IPv6 neighbor discovery specification
.Pq RFC2461 .
.It Li icmp6.nd6_mmaxtries
The variable specifies
.Dv MAX_MULTICAST_SOLICIT
constant in IPv6 neighbor discovery specification
.Pq RFC2461 .
.It Li icmp6.nd6_useloopback
If set to non-zero, IPv6 will use the loopback interface for local traffic.
.It Li icmp6.nodeinfo
The variable enables responses to ICMPv6 node information queries.
If you set the variable to 0, reponses will not be generated for
ICMPv6 node information queries.
Since node information queries can have a security impact, it is
possible to fine tune which responses should be answered.
Two separate bits can be set.
.Bl -tag -width "12345"
.It 1
Respond to ICMPv6 FQDN queries, e.g.
.Li ping6 -w .
.It 2
Respond to ICMPv6 node addresses queries, e.g.
.Li ping6 -a .
.El
.It Li icmp6.errppslimit
The variable specifies the maximum number of outgoing ICMPv6 error messages
per second.
ICMPv6 error messages that exceeded the value is subject to rate limitation
and will not go out from the node.
A negative value will disable the rate limitation.
.It Li icmp6.nd6_maxnudhint
IPv6 neighbor discovery permits upper layer protocols to supply reachability
hints, to avoid unnecessary neighbor discovery exchanges.
The variable defines the number of consecutive hints the neighbor discovery
layer will take.
For example, by setting the variable to 3, neighbor discovery can take
take a maximum of 3 consecutive hints.
After receiving 3 hints, the neighbor discovery layer will instead perform
the normal neighbor discovery process.
.It Li icmp6.mtudisc_hiwat
.It Li icmp6.mtudisc_lowat
These variables define the maximum number of routing table entries,
created due to path MTU discovery
.Pq preventing denial-of-service attacks with ICMPv6 too big messages .
After IPv6 path MTU discovery happens, path MTU information is kept in
the routing table.
If the number of routing table entries exceed the value,
the kernel will not attempt to keep the path MTU information.
.Li icmp6.mtudisc_hiwat
is used when we have verified ICMPv6 too big messages.
.Li icmp6.mtudisc_lowat
is used when we have unverified ICMPv6 too big messages.
Verification is performed by using address/port pairs kept in connected pcbs.
Negative value disables the upper limit.
.It Li icmp6.nd6_debug
If set to non-zero, IPv6 neighbor discovery will generate debugging
messages.
The debug outputs are useful for diagnosing IPv6 interoperability issues.
The flag must be set to 0 for normal operation.
.El
.Pp
We reuse
.Li net.inet.tcp
and
.Li net.inet.udp
for
.Tn TCP/UDP
over
.Tn IPv6 .
.El
.Ss CTL_USER
The string and integer information available for the
.Dv CTL_USER
level is detailed below.
The changeable column shows whether a process with appropriate
privileges may change the value.
.Bl -column "USER_COLL_WEIGHTS_MAXXXX" "integerXXX" -offset indent
.It Sy Second level name	Type	Changeable
.It Dv USER_BC_BASE_MAX No "	integer	no"
.It Dv USER_BC_DIM_MAX No "	integer	no"
.It Dv USER_BC_SCALE_MAX No "	integer	no"
.It Dv USER_BC_STRING_MAX No "	integer	no"
.It Dv USER_COLL_WEIGHTS_MAX No "	integer	no"
.It Dv USER_CS_PATH No "	string	no"
.It Dv USER_EXPR_NEST_MAX No "	integer	no"
.It Dv USER_LINE_MAX No "	integer	no"
.It Dv USER_POSIX2_CHAR_TERM No "	integer	no"
.It Dv USER_POSIX2_C_BIND No "	integer	no"
.It Dv USER_POSIX2_C_DEV No "	integer	no"
.It Dv USER_POSIX2_FORT_DEV No "	integer	no"
.It Dv USER_POSIX2_FORT_RUN No "	integer	no"
.It Dv USER_POSIX2_LOCALEDEF No "	integer	no"
.It Dv USER_POSIX2_SW_DEV No "	integer	no"
.It Dv USER_POSIX2_UPE No "	integer	no"
.It Dv USER_POSIX2_VERSION No "	integer	no"
.It Dv USER_RE_DUP_MAX No "	integer	no"
.It Dv USER_STREAM_MAX No "	integer	no"
.It Dv USER_TZNAME_MAX No "	integer	no"
.El
.Bl -tag -width "123456"
.Pp
.It Dv USER_BC_BASE_MAX
The maximum ibase/obase values in the
.Xr bc 1
utility.
.It Dv USER_BC_DIM_MAX
The maximum array size in the
.Xr bc 1
utility.
.It Dv USER_BC_SCALE_MAX
The maximum scale value in the
.Xr bc 1
utility.
.It Dv USER_BC_STRING_MAX
The maximum string length in the
.Xr bc 1
utility.
.It Dv USER_COLL_WEIGHTS_MAX
The maximum number of weights that can be assigned to any entry of
the
.Dv LC_COLLATE
order keyword in the locale definition file.
.It Dv USER_CS_PATH
Return a value for the
.Ev PATH
environment variable that finds all the standard utilities.
.It Dv USER_EXPR_NEST_MAX
The maximum number of expressions that can be nested within
parenthesis by the
.Xr expr 1
utility.
.It Dv USER_LINE_MAX
The maximum length in bytes of a text-processing utility's input
line.
.It Dv USER_POSIX2_CHAR_TERM
Return 1 if the system supports at least one terminal type capable of
all operations described in POSIX 1003.2, otherwise 0.
.It Dv USER_POSIX2_C_BIND
Return 1 if the system's C-language development facilities support the
C-Language Bindings Option, otherwise 0.
.It Dv USER_POSIX2_C_DEV
Return 1 if the system supports the C-Language Development Utilities Option,
otherwise 0.
.It Dv USER_POSIX2_FORT_DEV
Return 1 if the system supports the FORTRAN Development Utilities Option,
otherwise 0.
.It Dv USER_POSIX2_FORT_RUN
Return 1 if the system supports the FORTRAN Runtime Utilities Option,
otherwise 0.
.It Dv USER_POSIX2_LOCALEDEF
Return 1 if the system supports the creation of locales, otherwise 0.
.It Dv USER_POSIX2_SW_DEV
Return 1 if the system supports the Software Development Utilities Option,
otherwise 0.
.It Dv USER_POSIX2_UPE
Return 1 if the system supports the User Portability Utilities Option,
otherwise 0.
.It Dv USER_POSIX2_VERSION
The version of POSIX 1003.2 with which the system attempts to comply.
.It Dv USER_RE_DUP_MAX
The maximum number of repeated occurrences of a regular expression
permitted when using interval notation.
.It Dv USER_STREAM_MAX
The maximum number of streams that a process may have open
at any one time.
.It Dv USER_TZNAME_MAX
The minimum maximum number of types supported for the name of a
timezone.
.El
.Ss CTL_DDB
Integer information and settable variables are available for the
.Dv CTL_DDB level, as described below.
More information is also available in
.Xr ddb 4 .
.Bl -column "Second level nameXXXXXX" "struct loadavgXXX" -offset indent
.It Sy Second level name	Type	Changeable
.It Dv DBCTL_RADIX No "	integer	yes"
.It Dv DBCTL_MAXWIDTH No "	integer	yes"
.It Dv DBCTL_TABSTOP No "	integer	yes"
.It Dv DBCTL_PANIC No "	integer	yes"
.It Dv DBCTL_CONSOLE No "	integer	yes"
.El
.Pp
.Bl -tag -width "123456"
.It Dv DBCTL_RADIX
Determines the default radix or base for non-prefixed numbers
entered into
.Xr ddb 4 .
This variable is also available as the ddb $radix variable.
.It Dv DBCTL_MAXWIDTH
Determines the maximum width of a line in
.Xr ddb 4 .
This variable is also available as the ddb $maxwidth variable.
.It Dv DBCTL_TABSTOP
Width of a tab stop in
.Xr ddb 4 .
This variable is also available as the ddb $tabstops variable.
.It Dv DBCTL_PANIC
When this variable is set, system panics may drop into the
kernel debugger.
As described in
.Xr securelevel 7 ,
a security level greater than 1 blocks modification of this variable.
.Xr ddb 4 .
.It Dv DBCTL_CONSOLE
When this variable is set, an architecture dependent magic key sequence
on the console or a debugger button will permit entry into the
kernel debugger.
As described in
.Xr securelevel 7 ,
a security level greater than 1 blocks modification of this variable.
.El
.Ss CTL_VM
The string and integer information available for the
.Dv CTL_VM
level is detailed below.
The changeable column shows whether a process with appropriate
privileges may change the value.
.Bl -column "Second level nameXXXXXX" "struct loadavgXXX" -offset indent
.It Sy Second level name	Type	Changeable
.It Dv VM_LOADAVG No "	struct loadavg	no"
.It Dv VM_METER No "	struct vmtotal	no"
.It Dv VM_SWAPENCRYPT No "	swap encrypt values	yes"
.It Dv VM_UVMEXP No "	struct uvmexp	no"
.It Dv VM_VMMETER No "	struct vmtotal	no"
.El
.Pp
.Bl -tag -width "123456"
.It Dv VM_LOADAVG
Return the load average history.
The returned data consists of a
.Li struct loadavg .
.It Dv VM_METER
Return the system wide virtual memory statistics.
The returned data consists of a
.Li struct vmtotal .
.It Dv VM_SWAPENCRYPT
Contains statistics about swap encryption.
The string and integer information available for the third level is
detailed below.
.Bl -column "Third level nameXXXXXX" "struct loadavgXXX" -offset indent
.It Sy Third level name	Type	Changeable
.It Dv SWPENC_ENABLE No "	integer	yes"
.It Dv SWPENC_CREATED No "	integer	no"
.It Dv SWPENC_DELETED No "	integer	no"
.El
.Bl -tag -width "123456"
.It Dv SWPENC_ENABLE
Set to 1 to enable swap encryption for all processes.
A 0 disables swap encryption.
Pages still on swap receive a grandfather clause.
Turning this option on does not affect legacy swap data already on the disk,
but all newly written data will be encrypted.
When swap encryption is turned on, automatic
.Xr crash 8
dumps are disabled.
.It Dv SWPENC_CREATED
The number of encryption keys that have been randomly created.
The swap partition is divided into sections of normally 512KB.
Each section has its own encryption key.
.It Dv SWPENC_DELETED
The number of encryption keys that have been deleted, thus effectivly
erasing the data that has been encrypted with them.
Encryption keys are deleted when their reference counter reaches zero.
.El
.It Dv VM_UVMEXP
Contains statistics about the UVM memory management system.
.It Dv VM_METER:
Contains statistics about the memory management system, using the old
VM format.
.El
.Ss CTL_VFS
The string and integer information available for the
.Dv CTL_VFS
level is detailed below.
The changeable column shows whether a process with appropriate
privileges may change the value.
.Bl -column "Second level nameXXXXXX" "struct loadavgXXX" -offset indent
.It Sy Second level name	Type	Changeable
.It Dv VFS_GENERIC No "	vm generic info	no"
.It Dv filesystem # No "	filesystem info	no"
.El
.Pp
.Bl -tag -width "123456"
.It Dv VFS_GENERIC
This second level identifier requests generic information about the
vfs layer.
Within it, the following third level identifiers exist:
.Pp
.Bl -column "Third level nameXXXXXX" "struct loadavgXXX" -offset indent
.It Sy Third level name	Type	Changeable
.It Dv VFS_MAXTYPENUM No "	int	no"
.It Dv VFS_CONF No "	struct vfsconf	no"
.El
.It filesystem #
After finding the filesystem dependent vfc_typenum using
.Dv VFS_GENERIC
with
.Dv VFS_CONF ,
it is possible to access filesystem dependent information.
.Pp
Some filesystems may contain settings.
.Bl -tag -width "123"
.It ffs
.Bl -column "Third level nameXXX" "struct loadavgXXX" -offset ind
.It Sy Third level name	Type	Changeable
.It Dv FFS_CLUSTERREAD No "	int	yes"
.It Dv FFS_CLUSTERWRITE No "	int	yes"
.It Dv FFS_REALLOCBLOCKS No "	int	yes"
.It Dv FFS_ASYNCFREE No "	int	yes"
.El
.It nfs
.Bl -column "Third level nameXXX" "struct loadavgXXX" -offset ind
.It Sy Third level name	Type	Changeable
.It Dv NFS_NFSSTATS No "	struct nfsstats	yes"
.It Dv NFS_NIOTHREADS No "	int	yes"
.El
.El
.El
.Sh RETURN VALUES
If the call to
.Fn sysctl
is unsuccessful, \-1 is returned and
.Va errno
is set appropriately.
.Sh ERRORS
The following errors may be reported:
.Bl -tag -width Er
.It Bq Er EFAULT
The buffer
.Fa name ,
.Fa oldp ,
.Fa newp ,
or length pointer
.Fa oldlenp
contains an invalid address.
.It Bq Er EINVAL
The
.Fa name
array is less than two or greater than
.Dv CTL_MAXNAME .
.It Bq Er EINVAL
A non-null
.Fa newp
pointer is given and its specified length in
.Fa newlen
is too large or too small.
.It Bq Er ENOMEM
The length pointed to by
.Fa oldlenp
is too short to hold the requested value.
.It Bq Er ENOTDIR
The
.Fa name
array specifies an intermediate rather than terminal name.
.It Bq Er EOPNOTSUPP
The
.Fa name
array specifies a value that is unknown.
.It Bq Er EPERM
An attempt is made to set a read-only value.
.It Bq Er EPERM
A process without appropriate privileges attempts to set a value.
.It Bq Er EPERM
An attempt to change a value protected by the current kernel security
level is made.
.El
.Sh FILES
.Bl -tag -width <uvm/uvmXswapXencrypt.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 sys/socket.h
definitions for second level network identifiers
.It Aq Pa sys/gmon.h
definitions for third level profiling identifiers
.It Aq Pa vm/vm_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
.Tn IP
and
.Tn IPv6
identifiers
.It Aq Pa netinet/icmp_var.h
definitions for fourth level
.Tn ICMP
identifiers
.It Aq Pa netinet/icmp6.h
definitions for fourth level
.Tn ICMPv6
identifiers
.It Aq Pa netinet/tcp_var.h
definitions for fourth level
.Tn TCP
identifiers
.It Aq Pa netinet/udp_var.h
definitions for fourth level
.Tn UDP
identifiers
.El
.Sh SEE ALSO
.Xr sysctl 8
.Sh HISTORY
The
.Fn sysctl
function first appeared in
.Bx 4.4 .