NetBSD/lib/libc/gen/sysctl.3

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.\"	@(#)sysctl.3	8.4 (Berkeley) 5/9/95
.\"
.Dd June 24, 1999
.Dt SYSCTL 3
.Os
.Sh NAME
.Nm sysctl
.Nd get or set system information
.Sh LIBRARY
.Lb libc
.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
.Nm
function retrieves system information and allows processes with
appropriate privileges to set system information.
The information available from
.Nm
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,
.Nm
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
.Nm
are serialized to avoid deadlock.
.Pp
The state is described using a ``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 ENOMEM.
If the old value is not desired,
.Fa oldp
and
.Fa oldlenp
should be set to NULL.
.Pp
The size of the available data can be determined by calling
.Nm
with a 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 NULL and
.Fa newlen
set to 0.
.Pp
The top level names are defined with a CTL_ prefix in
.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 Pa Name	Next level names	Description
.It CTL\_DEBUG	sys/sysctl.h	Debugging
.It CTL\_VFS	sys/mount.h	Filesystem
.It CTL\_HW	sys/sysctl.h	Generic CPU, I/O
.It CTL\_KERN	sys/sysctl.h	High kernel limits
.It CTL\_MACHDEP	sys/sysctl.h	Machine dependent
.It CTL\_NET	sys/socket.h	Networking
.It CTL\_PROC	sys/sysctl.h	Per-process
.It CTL\_USER	sys/sysctl.h	User-level
.It CTL\_VM	vm/vm_param.h	Virtual memory
.El
.Pp
For example, the following retrieves the maximum number of processes allowed
in the system:
.Bd -literal -offset indent -compact
int mib[2], maxproc;
size_t len;
.sp
mib[0] = CTL_KERN;
mib[1] = KERN_MAXPROC;
len = sizeof(maxproc);
sysctl(mib, 2, &maxproc, &len, NULL, 0);
.Ed
.sp
To retrieve the standard search path for the system utilities:
.Bd -literal -offset indent -compact
int mib[2];
size_t len;
char *p;
.sp
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
.Sh CTL_DEBUG
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
.Ns ( Va 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
.Dv dospecialcheck
as a debugging variable, the following declaration would be used:
.Bd -literal -offset indent -compact
int dospecialcheck = 1;
struct ctldebug debug5 = { "dospecialcheck", &dospecialcheck };
.Ed
.Sh CTL_VFS
A distinguished second level name, VFS_GENERIC,
is used to get general information about all filesystems.
One of its third level identifiers is VFS_MAXTYPENUM
that gives the highest valid filesystem type number.
Its other third level identifier is VFS_CONF that
returns configuration information about the filesystem
type given as a fourth level identifier (see
.Xr getvfsbyname 3
as an example of its use).
The remaining second level identifiers are the
filesystem type number returned by a
.Xr statfs 2
call or from VFS_CONF.
The third level identifiers available for each filesystem
are given in the header file that defines the mount
argument structure for that filesystem.
.Sh CTL_HW
The string and integer information available for the CTL_HW level
is detailed below.
The changeable column shows whether a process with appropriate
privilege may change the value.
.Bl -column "Second level nameXXXXXX" integerXXX -offset indent
.It Sy Pa Second level name	Type	Changeable
.It HW\_MACHINE	string	no
.It HW\_MODEL	string	no
.It HW\_NCPU	integer	no
.It HW\_BYTEORDER	integer	no
.It HW\_PHYSMEM	integer	no
.It HW\_USERMEM	integer	no
.It HW\_PAGESIZE	integer	no
.It HW\_MACHINE\_ARCH	string	no
.\".It HW\_DISKNAMES	integer	no
.\".It HW\_DISKSTATS	integer	no
.El
.Pp
.Bl -tag -width "123456"
.It Li HW_MACHINE
The machine class.
.It Li HW_MODEL
The machine model
.It Li HW_NCPU
The number of cpus.
.ne 1i
.It Li HW_BYTEORDER
The byteorder (4,321, or 1,234).
.It Li HW_PHYSMEM
The bytes of physical memory.
.It Li HW_USERMEM
The bytes of non-kernel memory.
.It Li HW_PAGESIZE
The software page size.
.It Li HW_MACHINE_ARCH
The machine cpu class.
.\".It Fa HW_DISKNAMES
.\".It Fa HW_DISKSTATS
.El
.Sh CTL_KERN
The string and integer information available for the CTL_KERN level
is detailed below.
The changeable column shows whether a process with appropriate
privilege 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 Pa Second level name	Type	Changeable
.It KERN\_ARGMAX	integer	no
.It KERN\_AUTONICETIME	integer	yes
.It KERN\_AUTONICEVAL	integer	yes
.It KERN\_BOOTTIME	struct timeval	no
.It KERN\_CHOWN\_RESTRICTED	integer	no
.It KERN\_CLOCKRATE	struct clockinfo	no
.It KERN\_DEFCORENAME	string	yes
.It KERN\_DOMAINNAME	string	yes
.It KERN\_FILE	struct file	no
.It KERN\_FSYNC	integer	no
.It KERN\_HOSTID	integer	yes
.It KERN\_HOSTNAME	string	yes
.It KERN\_IOV\_MAX	integer	no
.It KERN\_JOB\_CONTROL	integer	no
.It KERN\_LINK\_MAX	integer	no
.It KERN\_LOGIN\_NAME\_MAX	integer	no
.It KERN\_MAPPED\_FILES	integer	no
.It KERN\_MAXFILES	integer	yes
.It KERN\_MAXPARTITIONS	integer	no
.It KERN\_MAXPROC	integer	yes
.It KERN\_MAXVNODES	integer	yes
.It KERN\_MAX\_CANON	integer	no
.It KERN\_MAX\_INPUT	integer	no
.It KERN\_MEMLOCK	integer	no
.It KERN\_MEMLOCK\_RANGE	integer	no
.It KERN\_MEMORY\_PROTECTION	integer	no
.It KERN\_MSGBUFSIZE	integer	no
.It KERN\_NAME\_MAX	integer	no
.It KERN\_NGROUPS	integer	no
.It KERN\_NO\_TRUNC	integer	no
.It KERN\_OSRELEASE	string	no
.It KERN\_OSREV	integer	no
.It KERN\_OSTYPE	string	no
.It KERN\_PATH\_MAX	integer	no
.It KERN\_PIPE\_BUF	integer	no
.It KERN\_POSIX1	integer	no
.It KERN\_PROC	struct proc	no
.It KERN\_PROF	node	not applicable
.It KERN\_RAWPARTITION	integer	no
.It KERN\_SAVED\_IDS	integer	no
.It KERN\_SECURELVL	integer	raise only
.It KERN\_SYNCHRONIZED\_IO	integer	no
.It KERN\_SYSVMSG	integer	no
.It KERN\_SYSVSEM	integer	no
.It KERN\_SYSVSHM	integer	no
.It KERN\_VDISABLE	integer	no
.It KERN\_VERSION	string	no
.It KERN\_VNODE	struct vnode	no
.El
.ne 1i
.Pp
.Bl -tag -width "123456"
.It Li KERN_ARGMAX
The maximum bytes of argument to
.Xr execve 2 .
.It Li KERN_AUTONICETIME
The number of seconds of cpu-time a non-root process may accumulate before
having its priority lowered from the default to the value of KERN_AUTONICEVAL.
If set to 0, automatic lowering of priority is not performed, and if set to -1
all non-root processes are immediately lowered.
.It Li KERN_AUTONICEVAL
The priority assigned for automatically niced processes.
.It Li KERN_BOOTTIME
A
.Va struct timeval
structure is returned.
This structure contains the time that the system was booted.
.It Li KERN_CHOWN_RESTRICTED
Return 1 if appropriate privileges are required for the
.Xr chown 2
system call, otherwise 0.
.It Li KERN_CLOCKRATE
A
.Va 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 Li KERN_DEFCORENAME
Default template for the name of core dump files (see also PROC_PID_CORENAME
in the per-process variables CTL_PROC, and
.Xr core 5
for format of this template).  The default value is
.Nm %n.core
and can be changed with the kernel configuration option
.Cd options DEFCORENAME
(see 
.Xr options 4
).
.It Li KERN_DOMAINNAME
Get or set the YP domain name.
.It Li KERN_FILE
Return the entire file table.
The returned data consists of a single
.Va struct filehead
followed by an array of
.Va struct file ,
whose size depends on the current number of such objects in the system.
.It Li KERN_FSYNC
Return 1 if the POSIX 1003.1b File Synchronization Option is available
on this system,
otherwise 0.
.It Li KERN_HOSTID
Get or set the host id.
.It Li KERN_HOSTNAME
Get or set the hostname.
.It Li KERN_IOV_MAX
Return the maximum number of
.Va 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_JOB_CONTROL
Return 1 if job control is available on this system, otherwise 0.
.It Li KERN_LINK_MAX
The maximum file link count.
.It Li KERN_LOGIN_NAME_MAX
The size of the storage required for a login name, in bytes,
including the terminating NUL.
.It Li KERN_MAPPED_FILES
Returns 1 if the POSIX 1003.1b Memory Mapped Files Option is available
on this system,
otherwise 0.
.It Li KERN_MAXFILES
The maximum number of open files that may be open in the system.
.It Li KERN_MAXPARTITIONS
The maximum number of partitions allowed per disk.
.It Li KERN_MAXPROC
The maximum number of simultaneous processes the system will allow.
.It Li KERN_MAXVNODES
The maximum number of vnodes available on the system.
.It Li KERN_MAX_CANON
The maximum number of bytes in terminal canonical input line.
.It Li KERN_MAX_INPUT
The minimum maximum number of bytes for which space is available in
a terminal input queue.
.It Li KERN_MEMLOCK
Returns 1 if the POSIX 1003.1b Process Memory Locking Option is available
on this system,
otherwise 0.
.It Li KERN_MEMLOCK_RANGE
Returns 1 if the POSIX 1003.1b Range Memory Locking Option is available
on this system,
otherwise 0.
.It Li KERN_MEMORY_PROTECTION
Returns 1 if the POSIX 1003.1b Memory Protection Option is available
on this system,
otherwise 0.
.It Li KERN_MSGBUFSIZE
The maximum number of characters that the kernel message buffer can hold.
.It Li KERN_NAME_MAX
The maximum number of bytes in a file name.
.It Li KERN_NGROUPS
The maximum number of supplemental groups.
.It Li KERN_NO_TRUNC
Return 1 if file names longer than KERN_NAME_MAX are truncated.
.It Li KERN_OSRELEASE
The system release string.
.It Li KERN_OSREV
The system revision string.
.It Li KERN_OSTYPE
The system type string.
.It Li KERN_PATH_MAX
The maximum number of bytes in a pathname.
.It Li KERN_PIPE_BUF
The maximum number of bytes which will be written atomically to a pipe.
.It Li KERN_POSIX1
The version of ISO/IEC 9945 (POSIX 1003.1) with which the system
attempts to comply.
.It Li KERN_PROC
Return the entire process table, or a subset of it.
An array of
.Va 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 Pa Third level name	Fourth level is:
.It KERN\_PROC\_ALL	None
.It KERN\_PROC\_PID	A process ID
.It KERN\_PROC\_PGRP	A process group
.It KERN\_PROC\_TTY	A tty device
.It KERN\_PROC\_UID	A user ID
.It KERN\_PROC\_RUID	A real user ID
.El
.It Li KERN_PROF
Return profiling information about the kernel.
If the kernel is not compiled for profiling,
attempts to retrieve any of the KERN_PROF values will
fail with 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 "GPROFXGMONPARAMXXX" "struct gmonparamXXX" -offset indent
.It Sy Pa Third level name	Type	Changeable
.It GPROF\_STATE	integer	yes
.It GPROF\_COUNT	u_short[\|]	yes
.It GPROF\_FROMS	u_short[\|]	yes
.It GPROF\_TOS	struct tostruct	yes
.It GPROF\_GMONPARAM	struct gmonparam	no
.El
.Pp
The variables are as follows:
.Bl -tag -width "123456"
.It Li GPROF_STATE
Returns GMON_PROF_ON or GMON_PROF_OFF to show that profiling
is running or stopped.
.It Li GPROF_COUNT
Array of statistical program counter counts.
.It Li GPROF_FROMS
Array indexed by program counter of call-from points.
.It Li GPROF_TOS
Array of
.Va struct tostruct
describing destination of calls and their counts.
.It Li GPROF_GMONPARAM
Structure giving the sizes of the above arrays.
.El
.It Li KERN_RAWPARTITION
The raw partition of a disk (a == 0).
.It Li KERN_SAVED_IDS
Returns 1 if saved set-group and saved set-user ID is available.
.It Li KERN_SECURELVL
The system security level.
This level may be raised by processes with appropriate privilege.
It may only be lowered by process 1.
.It Li KERN_SYNCHRONIZED_IO
Returns 1 if the POSIX 1003.1b Synchronized I/O Option is available
on this system,
otherwise 0.
.It Li KERN_SYSVMSG
Returns 1 if System V style message queue functionality is available
on this system,
otherwise 0.
.It Li KERN_SYSVSEM
Returns 1 if System V style semaphore functionality is available
on this system,
otherwise 0.
.It Li KERN_SYSVSHM
Returns 1 if System V style share memory functionality is available
on this system,
otherwise 0.
.It Li KERN_VDISABLE
Returns the terminal character disabling value.
.It Li KERN_VERSION
The system version string.
.It Li 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
.Va struct vnode *
followed by the vnode itself
.Va struct vnode .
.El
.Sh 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 Pa Second level name	Type	Changeable
.It Li CPU_CONSDEV	dev_t	no
.El
.Sh CTL_NET
The string and integer information available for the CTL_NET level
is detailed below.
The changeable column shows whether a process with appropriate
privilege may change the value.
.Bl -column "Second level nameXXXXXX" "routing messagesXXX" -offset indent
.It Sy Pa Second level name	Type	Changeable
.It PF\_ROUTE	routing messages	no
.It PF\_INET	IPv4 values	yes
.It PF\_INET6	IPv6 values	yes
.El
.Pp
.Bl -tag -width "123456"
.It Li 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 Pa Fifth level name	Sixth level is:
.It NET\_RT\_FLAGS	rtflags
.It NET\_RT\_DUMP	None
.It NET\_RT\_IFLIST	None
.El
.It Li PF_INET
Get or set various global information about the 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" "Variable nameXX" "integer" "yes" -offset indent
.It Pa Protocol name	Variable name	Type	Changeable
.It ip	forwarding	integer	yes
.It ip	redirect	integer	yes
.It ip	ttl	integer	yes
.It ip	forwsrcrt	integer	yes
.It ip	directed-broadcast	integer	yes
.It ip	allowsrcrt	integer	yes
.It ip	subnetsarelocal	integer	yes
.It ip	mtudisc	integer	yes
.It ip	anonportmin	integer	yes
.It ip	anonportmax	integer	yes
.It ip	mtudisctimeout	integer	yes
.It ip	gifttl	integer	yes
.It icmp	maskrepl	integer	yes
.It tcp	rfc1323	integer	yes
.It tcp	sendspace	integer	yes
.It tcp	recvspace	integer	yes
.It tcp	mssdflt	integer	yes
.It tcp	syn_cache_limit	integer	yes
.It tcp	syn_bucket_limit	integer	yes
.It tcp	syn_cache_interval	integer	yes
.It tcp	init_win	integer	yes
.It tcp	mss_ifmtu	integer	yes
.It tcp	sack	integer	yes
.It tcp	win_scale	integer	yes
.It tcp	timestamps	integer	yes
.It tcp	compat_42	integer	yes
.It tcp	cwm	integer	yes
.It tcp	cwm_burstsize	integer	yes
.It tcp	ack_on_push	integer	yes
.It tcp	keepidle	integer	yes
.It tcp	keepintvl	integer	yes
.It tcp keepcnt	integer	yes
.It tcp	slowhz	integer	no
.It tcp	newreno	integer	yes
.It tcp	log_refused	integer	yes
.It udp	checksum	integer	yes
.It udp	sendspace	integer	yes
.It udp	recvspace	integer	yes
.El
.Pp
The variables are as follows:
.Bl -tag -width "123456"
.It Li ip.forwarding
Returns 1 when IP forwarding is enabled for the host,
meaning that the host is acting as a router.
.It Li ip.redirect
Returns 1 when ICMP redirects may be sent by the host.
This option is ignored unless the host is routing IP packets,
and should normally be enabled on all systems.
.It Li ip.ttl
The maximum time-to-live (hop count) value for an IP packet sourced by
the system.
This value applies to normal transport protocols, not to ICMP.
.It Li ip.forwsrcrt
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.allowsrcrt
Returns 1 if the host accepts source routed packets.
.It Li ip.subnetsarelocal
Returns 1 if subnets are to be considered local addresses.
.It Li ip.mtudisc
Returns 1 if Path MTU Discovery is enabled.
.It Li ip.anonportmin
The lowest port number to use for TCP and UDP ephemeral port allocation.
This cannot be set to less that 1024 or greater than 65535.
.It Li ip.anonportmax
The highest port number to use for TCP and UDP ephemeral port allocation.
This cannot be set to less that 1024 or greater than 65535, and must
be greater than
.Li ip.anonportmin .
.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 ip.gifttl
The maximum time-to-live (hop count) value for an IPv4 packet generated by
.Xr gif 4
tunnel interface.
.It Li icmp.maskrepl
Returns 1 if ICMP network mask requests are to be answered.
.It Li tcp.rfc1323
Returns 1 if RFC1323 extensions to TCP are enabled.
.It Li tcp.sendspace
Returns the default TCP send buffer size.
.It Li tcp.recvspace
Returns the default TCP receive buffer size.
.It Li tcp.mssdflt
Returns the default maximum segment size both advertsized to the peer
and to use when the peer does not advertize a maximum segment size to
us during connection setup.  Do not change this value unless you really
know what you are doing.
.It Li tcp.syn_cache_limit
Returns the maximum number of entries allowed in the TCP compressed state
engine.
.It Li tcp.syn_bucket_limit
Returns the maximum number of entries allowed per hash bucket in the TCP
compressed state engine.
.It Li tcp.syn_cache_interval
Returns the TCP compressed state engine's timer interval.
.It Li tcp.init_win
Returns a value indicating the TCP initial congestion window.  If this
value is 0, an auto-tuning algorithm designed to use an initial window
of approximately 4K bytes is in use.  Otherwise, this value indicates
a fixed number of packets.
.It Li tcp.mss_ifmtu
Returns 1 if TCP calculates the outgoing maximum segment size based on
the MTU of the appropriate interface.  Otherwise, it is calculated based on
the greater of the MTU of the interface, and the largest (non-loopback)
interface MTU on the system.
.It Li tcp.sack
Returns a value which determines the level of Selective Acknowledgement
supported by TCP.  If 2, we will transmit and receive SACK options.
If 1, we will transmit SACK options, but ignore any SACK options received.
If 0, SACK is disabled.
.It Li tcp.win_scale
If rfc1323 is enabled, a value of 1 indicates RFC1323 window scale options,
for increasing the TCP window size, are enabled.
.It Li tcp.timestamps
If rfc1323 is enabled, a value of 1 indicates RFC1323 time stamp options,
used for measuring TCP round trip times, are enabled.
.It Li tcp.compat_42
Returns 1 if work-arounds for bugs in the 4.2BSD TCP implementation are
enabled.  Use of this option is not recommended, although it may be
required in order to communicate with extremely old TCP implementations.
.It Li tcp.cwm
Returns 1 if use of the Hughes/Touch/Heidemann Congestion Window Monitoring
algorithm is enabled.  This algorithm prevents line-rate bursts of packets
that could otherwise occur when data begins flowing on an idle TCP
connection.  These line-rate bursts can contribute to network and router
congestion.  This can be particularly useful on World Wide Web servers
which support HTTP/1.1, which has lingering connections.
.It Li tcp.cwm_burstsize
Returns the Congestion Window Monitoring allowed burst size, in terms
of packet count.
.It Li tcp.ack_on_push
Returns 1 if TCP is to immediately transmit an ACK upon reception of
a packet with PUSH set.  This can avoid losing a round trip time in some
rare situations, but has the caveat of potentially defeating TCP's delayed
ACK algorithm.  Use of this option is generally not recommended, but
the variable exists in case your configuration really needs it.
.It Li tcp.keepidle
Time a connection must be idle before keepalives are sent (if keepalives
are enabled for the connection).  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.keepcnt
Number of keepalive probes sent before declaring a connection dead.  If
set to zero, there is no limit; keepalives will be sent until some kind of
response is received from the peer.
.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.newreno
Returns 1 if the use of J. Hoe's NewReno congestion control algorithm is
enabled.  This algorithm improves the start-up behavior of TCP connections.
.It Li tcp.log_refused
When set to 1, all refused TCP connections to the host are logged.
.It Li udp.checksum
Returns 1 when UDP checksums are being computed and checked.
Disabling UDP checksums is strongly discouraged.
.It Li udp.sendspace
Returns the default UDP send buffer size.
.It Li udp.recvspace
Returns the default UDP receive buffer size.
.El
.Pp
For variables net.*.ipsec, please refer to
.Xr ipsec 4 .
.It Li PF_INET6
Get or set various global information about the 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	gif_hlim	integer	yes
.It ip6	kame_version	string	no
.It ip6	use_deprecated	integer	yes
.It ip6	rr_prune	integer	yes
.It ip6	bindv6only	integer	yes
.It icmp6	rediraccept	integer	yes
.It icmp6	redirtimeout	integer	yes
.It icmp6	errratelimit	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	nd6_proxyall	integer	yes
.It icmp6	nodeinfo	integer	yes
.It tcp6	mssdflt	integer	yes
.It tcp6	do_rfc1323	integer	yes
.It tcp6	keepidle	integer	yes
.It tcp6	keepinterval	integer	yes
.It tcp6	keepcount	integer	yes
.It tcp6	maxpersistidle	integer	yes
.It tcp6	sendspace	integer	yes
.It tcp6	recvspace	integer	yes
.It tcp6	conntimeo	integer	yes
.It tcp6	pmtu	integer	yes
.It tcp6	pmtu_expire	integer	yes
.It tcp6	pmtu_probe	integer	yes
.It tcp6	43maxseg	integer	yes
.It tcp6	syn_cache_limit	integer	yes
.It tcp6	syn_bucket_limit	integer	yes
.It tcp6	syn_cache_interval	integer	yes
.It udp6	sendmax	integer	yes
.It udp6	recvspace	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.
.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.
There are APIs to override the value, as 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.
.It Li ip6.keepfaith
If set to non-zero, it enables
.Dq FAITH
TCP relay IPv6-to-IPv4 translator code in the kernel.
Refer
.Xr faith 4
and
.Xr faithd 8
for detail.
.It Li ip6.log_interval
The variable controls amount of logs generated by IPv6 packet
forwarding engine, by seting interval between log output
.Pq in seconds .
.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 cofigures number of IPv6 DAD
.Pq duplicated address detection
probe packets.
The packets will be generated when IPv6 interface addresses are configured.
.It Li ip6.auto_flowlabel
On connected transport protocol packets,
fill IPv6 flowlabel field to help intermediate routers to 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.
There are APIs to override the value, as documented in
.Xr ip6 4 .
.It Li ip6.gif_hlim
The maximum hop limit value for an IPv6 packet generated by
.Xr gif 4
tunnel interface.
.It Li ip6.kame_version
The string identifies the version of KAME IPv6 stack implemented in the kernel.
.It Li ip6.use_deprecated
The variable controls use of deprecated address, 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 ip6.bindv6only
The variable specifies initial value for
.Dv IPV6_BINDV6ONLY
socket option for
.Dv AF_INET6
socket.
Please refer to
.Xr ip6 4
for detail.
.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,
and the variable is meaningful on IPv6 hosts
.Pq non-router
only.
.It Li icmp6.redirtimeout
The variable specifies lifetime of routing entries generated by incoming
ICMPv6 redirect.
.It Li icmp6.errratelimit
The variable specifies minimum interval between ICMPv6 error messages,
in microseconds.
.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, kernel IPv6 stack will use loopback interface for
local traffic.
.It Li icmp6.nd6_proxyall
The variable enables proxy neighbor advertisements.
.It Li icmp6.nodeinfo
The variable enables, or disables, kernel support for
ICMPv6 node information query/reply.
.El
.Pp
Variables net.*.tcp6 and net.*.udp6 are identical to
net.*.tcp and net.*.udp.
Please refer to
.Li PF_INET
section above.
For variables net.*.ipsec6, please refer to
.Xr ipsec 4 .
.El
.Sh CTL_PROC
The string and integer information available for the CTL_PROC
is detailed below.
The changeable column shows whether a process with appropriate
privilege may change the value.
These values are per-process, and as such may change from one process
to another. When a process is created, the default values are inherited from
its parent. When a set-user-ID or set-group-ID binary is executed, the
value of PROC_PID_CORENAME is reset to the system default value.
The second level name is either the magic value PROC_CURPROC, which
points to the current process, or the PID of the target process.
.Bl -column "USER_COLL_WEIGHTS_MAXXXX" "integerXXX" "yes" -offset indent
.It Sy Pa Third level name	Type	Changeable
.It PROC\_PID\_CORENAME	string	yes
.It PROC\_PID\_LIMIT	node	not applicable
.El
.Bl -tag -width "123456"
.Pp
.It Li PROC_PID_CORENAME
The template used for the core dump file name (see
.Xr core 5
for details). The base name must either be 
.Nm core
or end with the suffix ``.core'' (the super-user may set arbitrary names). By
default it points to KERN_DEFCORENAME.
.It Li PROC_PID_LIMIT
Return resources limits, as defined for the
.Xr getrlimit 2
and 
.Xr setrlimit 2
system calls.
The fourth level name is one of:
.Bl -tag -width PROC_PID_LIMIT_MEMLOCKAA
.It Li PROC_PID_LIMIT_CPU
The maximum amount of cpu time (in seconds) to be used by each process.
.It Li PROC_PID_LIMIT_FSIZE
The largest size (in bytes) file that may be created.
.It Li PROC_PID_LIMIT_DATA
The maximum size (in bytes) of the data segment for a process;
this defines how far a program may extend its break with the
.Xr sbrk 2
system call.
.It Li PROC_PID_LIMIT_STACK
The maximum size (in bytes) of the stack segment for a process;
this defines how far a program's stack segment may be extended.
Stack extension is performed automatically by the system.
.It Li PROC_PID_LIMIT_CORE
The largest size (in bytes)
.Pa core
file that may be created.
.It Li PROC_PID_LIMIT_RSS
The maximum size (in bytes) to which a process's resident set size may
grow.
This imposes a limit on the amount of physical memory to be given to
a process; if memory is tight, the system will prefer to take memory
from processes that are exceeding their declared resident set size.
.It Li PROC_PID_LIMIT_MEMLOCK
The maximum size (in bytes) which a process may lock into memory
using the
.Xr mlock 2
function.
.It Li PROC_PID_LIMIT_NPROC
The maximum number of simultaneous processes for this user id.
.It Li PROC_PID_LIMIT_NOFILE
The maximum number of open files for this process.
.El
.Pp
The fifth level name is one of PROC_PID_LIMIT_TYPE_SOFT or
PROC_PID_LIMIT_TYPE_HARD, to select respectively the soft or hard limit.
Both are of type integer.
.El
.Pp

.Sh CTL_USER
The string and integer information available for the CTL_USER level
is detailed below.
The changeable column shows whether a process with appropriate
privilege may change the value.
.Bl -column "USER_COLL_WEIGHTS_MAXXXX" "integerXXX" -offset indent
.It Sy Pa Second level name	Type	Changeable
.It USER\_BC\_BASE\_MAX	integer	no
.It USER\_BC\_DIM\_MAX	integer	no
.It USER\_BC\_SCALE\_MAX	integer	no
.It USER\_BC\_STRING\_MAX	integer	no
.It USER\_COLL\_WEIGHTS\_MAX	integer	no
.It USER\_CS\_PATH	string	no
.It USER\_EXPR\_NEST\_MAX	integer	no
.It USER\_LINE\_MAX	integer	no
.It USER\_POSIX2\_CHAR\_TERM	integer	no
.It USER\_POSIX2\_C\_BIND	integer	no
.It USER\_POSIX2\_C\_DEV	integer	no
.It USER\_POSIX2\_FORT\_DEV	integer	no
.It USER\_POSIX2\_FORT\_RUN	integer	no
.It USER\_POSIX2\_LOCALEDEF	integer	no
.It USER\_POSIX2\_SW\_DEV	integer	no
.It USER\_POSIX2\_UPE	integer	no
.It USER\_POSIX2\_VERSION	integer	no
.It USER\_RE\_DUP\_MAX	integer	no
.It USER\_STREAM\_MAX	integer	no
.It USER\_TZNAME\_MAX	integer	no
.El
.Bl -tag -width "123456"
.Pp
.It Li USER_BC_BASE_MAX
The maximum ibase/obase values in the
.Xr bc 1
utility.
.It Li USER_BC_DIM_MAX
The maximum array size in the
.Xr bc 1
utility.
.It Li USER_BC_SCALE_MAX
The maximum scale value in the
.Xr bc 1
utility.
.It Li USER_BC_STRING_MAX
The maximum string length in the
.Xr bc 1
utility.
.It Li USER_COLL_WEIGHTS_MAX
The maximum number of weights that can be assigned to any entry of
the LC_COLLATE order keyword in the locale definition file.
.It Li USER_CS_PATH
Return a value for the
.Ev PATH
environment variable that finds all the standard utilities.
.It Li USER_EXPR_NEST_MAX
The maximum number of expressions that can be nested within
parenthesis by the
.Xr expr 1
utility.
.It Li USER_LINE_MAX
The maximum length in bytes of a text-processing utility's input
line.
.It Li 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 Li USER_POSIX2_C_BIND
Return 1 if the system's C-language development facilities support the
C-Language Bindings Option, otherwise 0.
.It Li USER_POSIX2_C_DEV
Return 1 if the system supports the C-Language Development Utilities Option,
otherwise 0.
.It Li USER_POSIX2_FORT_DEV
Return 1 if the system supports the FORTRAN Development Utilities Option,
otherwise 0.
.It Li USER_POSIX2_FORT_RUN
Return 1 if the system supports the FORTRAN Runtime Utilities Option,
otherwise 0.
.It Li USER_POSIX2_LOCALEDEF
Return 1 if the system supports the creation of locales, otherwise 0.
.It Li USER_POSIX2_SW_DEV
Return 1 if the system supports the Software Development Utilities Option,
otherwise 0.
.It Li USER_POSIX2_UPE
Return 1 if the system supports the User Portability Utilities Option,
otherwise 0.
.It Li USER_POSIX2_VERSION
The version of POSIX 1003.2 with which the system attempts to comply.
.It Li USER_RE_DUP_MAX
The maximum number of repeated occurrences of a regular expression
permitted when using interval notation.
.ne 1i
.It Li USER_STREAM_MAX
The minimum maximum number of streams that a process may have open
at any one time.
.It Li USER_TZNAME_MAX
The minimum maximum number of types supported for the name of a
timezone.
.El
.Sh CTL_VM
The string and integer information available for the CTL_VM level
is detailed below.
The changeable column shows whether a process with appropriate
privilege may change the value.
.Bl -column "Second level nameXXXXXX" "struct loadavgXXX" -offset indent
.It Sy Pa Second level name	Type	Changeable
.It VM\_LOADAVG	struct loadavg	no
.It VM\_METER	struct vmtotal	no
.El
.Pp
.Bl -tag -width "123456"
.It Li VM_LOADAVG
Return the load average history.
The returned data consists of a
.Va struct loadavg .
.It Li VM_METER
Return the system wide virtual memory statistics.
The returned data consists of a
.Va struct vmtotal .
.El
.Sh CTL_DDB
The integer information available for the CTL_DDB level is detailed below.
The changeable column shows whether a process with appropriate
privilege may change the value.
.Bl -column "DBCTL_TABSTOPSXXX" "integerXXX" -offset indent
.It Sy Pa Second level name	Type	Changeable
.It DBCTL\_RADIX	integer	yes
.It DBCTL\_MAXOFF	integer	yes
.It DBCTL\_LINES	integer	yes
.It DBCTL\_TABSTOPS	integer	yes
.It DBCTL\_ONPANIC	integer	yes
.It DBCTL\_FROMCONSOLE	integer	yes
.El
.Pp
.Bl -tag -width "123456"
.It Li DBCTL_RADIX
The input and output radix.
.It Li DBCTL_MAXOFF
The maximum symbol offset.
.It Li DBCTL_LINES
Number of display lines.
.It Li DBCTL_TABSTOPS
Tab width.
.It Li DBCTL_ONPANIC
If non-zero, DDB will be entered when the kernel panics.
.It Li DBCTL_FROMCONSOLE
If not zero, DDB may be entered by sending a break on a serial
console or by a special key sequence on a graphics console.
.El
.Pp
These MIB nodes are also available as variables from within the
DDB.  See
.Xr ddb 4
for more details.
.Sh RETURN VALUES
If the call to
.Nm
is successful, the number of bytes copied out is returned.
Otherwise \-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 CTL_MAXNAME.
.It Bq Er EINVAL
A non-null
.Fa newp
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 privilege 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 <netinet/icmpXvar.h> -compact
.It Pa <sys/sysctl.h>
definitions for top level identifiers, second level kernel and hardware
identifiers, and user level identifiers
.It Pa <sys/socket.h>
definitions for second level network identifiers
.It Pa <sys/gmon.h>
definitions for third level profiling identifiers
.It Pa <vm/vm_param.h>
definitions for second level virtual memory identifiers
.It Pa <netinet/in.h>
definitions for third level IPv4/v6 identifiers and
fourth level IPv4/v6 identifiers
.It Pa <netinet/icmp_var.h>
definitions for fourth level ICMP identifiers
.It Pa <netinet/icmp6.h>
definitions for fourth level ICMPv6 identifiers
.It Pa <netinet/tcp_var.h>
definitions for fourth level TCP identifiers
.It Pa <netinet/udp_var.h>
definitions for fourth level UDP identifiers
.El
.Sh SEE ALSO
.Xr sysctl 8 ,
.Xr ipsec 4
.Sh HISTORY
The
.Nm
function first appeared in
.Bx 4.4 .