xref: /netbsd-src/lib/libc/gen/sysctl.3 (revision ce666bb8ce77792a3948ca697c2fdad578a542a7)

.\"	$NetBSD: sysctl.3,v 1.159 2005/12/01 18:08:10 wiz Exp $
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.\"	@(#)sysctl.3	8.4 (Berkeley) 5/9/95
.\"
.Dd December 1, 2005
.Dt SYSCTL 3
.Os
.Sh NAME
.Nm sysctl ,
.Nm sysctlbyname ,
.Nm sysctlgetmibinfo ,
.Nm sysctlnametomib
.Nd get or set system information
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/param.h
.In sys/sysctl.h
.Ft int
.Fn sysctl "int *name" "u_int namelen" "void *oldp" "size_t *oldlenp" \
"void *newp" "size_t newlen"
.Ft int
.Fn sysctlbyname "const char *sname" "void *oldp" "size_t *oldlenp" \
"void *newp" "size_t newlen"
.Ft int
.Fn sysctlgetmibinfo "const char *sname" "int *name" "u_int *namelenp" \
"char *cname" "size_t *csz" "struct sysctlnode **rnode" "int v"
.Ft int
.Fn sysctlnametomib "const char *sname" "int *name" "size_t *namelenp"
.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
.Fn sysctlbyname
function accepts a string representation of a MIB entry and internally
maps it to the appropriate numeric MIB representation.
Its semantics are otherwise no different from
.Fn sysctl .
.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
.Dv NULL .
.Pp
The size of the available data can be determined by calling
.Nm
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
.Fn sysctlnametomib
function can be used to map the string representation of a MIB entry
to the numeric version.
The
.Fa name
argument should point to an array of integers large enough to hold the
MIB, and
.Fa namelenp
should indicate the number of integer slots available.
Following a successful translation, the size_t indicated by
.Fa namelenp
will be changed to show the number of slots consumed.
.Pp
The
.Fn sysctlgetmibinfo
function performs name translation similar to
.Fn sysctlnametomib ,
but also canonicalizes the name (or returns the first erroneous token
from the string being parsed) into the space indicated by
.Fa cname
and
.Fa csz .
.Fa csz
should indicate the size of the buffer pointed to by
.Fa cname
and on return, will indicate the size of the returned string including
the trailing
.Sq nul
character.
.Pp
The
.Fa rnode
and
.Fa v
arguments to
.Fn sysctlgetmibinfo
are used to provide a tree for it to parse into, and to get back
either a pointer to, or a copy of, the terminal node.
If
.Fa rnode
is
.Dv NULL ,
.Fn sysctlgetmibinfo
uses its own internal tree for parsing, and checks it against the
kernel at each call, to make sure that the name-to-number mapping is
kept up to date.
The
.Fa v
argument is ignored in this case.
If
.Fa rnode
is not
.Dv NULL
but the pointer it references is, on a successful return,
.Fa rnode
will be adjusted to point to a copy of the terminal node.
The
.Fa v
argument indicates which version of the
.Nm
node structure the caller wants.
The application must later
.Fn free
this copy.
If neither
.Fa rnode
nor the pointer it references are
.Dv NULL ,
the pointer is used as the address of a tree over which the parsing is
done.
In this last case, the tree is not checked against the kernel, no
refreshing of the mappings is performed, and the value given by
.Fa v
must agree with the version indicated by the tree.
It is recommended that applications always use
.Dv SYSCTL_VERSION
as the value for
.Fa v ,
as defined in the include file
.Pa sys/sysctl.h .
.Pp
The top level names are defined with a 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 CTL\_KERN	sys/sysctl.h	High kernel limits
.It CTL\_VM	uvm/uvm_param.h	Virtual memory
.It CTL\_VFS	sys/mount.h	Filesystem
.It CTL\_NET	sys/socket.h	Networking
.It CTL\_DEBUG	sys/sysctl.h	Debugging
.It CTL\_HW	sys/sysctl.h	Generic CPU, I/O
.It CTL\_MACHDEP	sys/sysctl.h	Machine dependent
.It CTL\_USER	sys/sysctl.h	User-level
.It CTL\_DDB	sys/sysctl.h	In-kernel debugger
.It CTL\_PROC	sys/sysctl.h	Per-process
.It CTL\_VENDOR	?	Vendor specific
.It CTL\_EMUL	sys/sysctl.h	Emulation settings
.It CTL\_SECURITY	sys/sysctl.h	Security settings
.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, \*[Am]maxproc, \*[Am]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, \*[Am]len, NULL, 0);
p = malloc(len);
sysctl(mib, 2, p, \*[Am]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
.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", \*[Am]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.
.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.
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" "struct disk_sysctlXXX" -offset indent
.It Sy 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\_PHYSMEM64	quad	no
.It HW\_USERMEM	integer	no
.It HW\_USERMEM64	quad	no
.It HW\_PAGESIZE	integer	no
.\".It HW\_DISKNAMES	struct	no
.\".It HW\_DISKSTATS	struct	no
.It HW\_MACHINE\_ARCH	string	no
.It HW\_ALIGNBYTES	integer	no
.It HW\_DISKNAMES	string	no
.It HW\_DISKSTATS	struct disk_sysctl	no
.It HW\_CNMAGIC	string	yes
.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 as a 32-bit integer.
.It Li HW_PHYSMEM64
The bytes of physical memory as a 64-bit integer.
.It Li HW_USERMEM
The bytes of non-kernel memory as a 32-bit integer.
.It Li HW_USERMEM64
The bytes of non-kernel memory as a 64-bit integer.
.It Li HW_PAGESIZE
The software page size.
.It Li HW_MACHINE_ARCH
The machine CPU class.
.It Li HW_ALIGNBYTES
Alignment constraint for all possible data types.
This shows the value
.Dv ALIGNBYTES
in
.Pa /usr/include/machine/param.h ,
at the kernel compilation time.
.It Li HW_DISKNAMES
The list of (space separated) disk device names on the system.
.It Li HW_DISKSTATS
Return statistical information on the disk devices on the system.
An array of
.Va struct disk_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
.Va struct disk_sysctl .
.It Li HW_CNMAGIC
The console magic key sequence.
.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 "KERNXPOSIXXREADERXWRITERXLOCKS" "struct clockrateXXX" -offset indent
.It Sy 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\_CCPU	integer	no
.It KERN\_CLOCKRATE	struct clockinfo	no
.It KERN\_CP\_TIME	uint64_t[\|]	no
.It KERN\_DEFCORENAME	string	yes
.It KERN\_DOMAINNAME	string	yes
.It KERN\_DRIVERS	struct kinfo_drivers	no
.It KERN\_FILE	struct file	no
.It KERN\_FORKFSLEEP	integer	yes
.It KERN\_FSCALE	integer	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\_LABELOFFSET	integer	no
.It KERN\_LABELSECTOR	integer	no
.It KERN\_LOGIN\_NAME\_MAX	integer	no
.It KERN\_LOGSIGEXIT	integer	yes
.It KERN\_MAPPED\_FILES	integer	no
.It KERN\_MAXFILES	integer	yes
.It KERN\_MAXPARTITIONS	integer	no
.It KERN\_MAXPROC	integer	yes
.It KERN\_MAXPTYS	integer	yes
.It KERN\_MAXVNODES	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\_MONOTONIC\_CLOCK	integer	no
.It KERN\_MSGBUF	char[\|]	no
.It KERN\_MSGBUFSIZE	integer	no
.It KERN\_NGROUPS	integer	no
.It KERN\_NTPTIME	struct ntptimeval	no
.It KERN\_OSRELEASE	string	no
.It KERN\_OSREV	integer	no
.It KERN\_OSTYPE	string	no
.It KERN\_POSIX1	integer	no
.It KERN\_POSIX\_BARRIERS	integer	no
.It KERN\_POSIX\_READER\_WRITER\_LOCKS	integer	no
.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\_PROF	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\_SECURELVL	integer	raise only
.It KERN\_SYNCHRONIZED\_IO	integer	no
.It KERN\_SYSVIPC\_INFO	node	not applicable
.It KERN\_SYSVMSG	integer	no
.It KERN\_SYSVSEM	integer	no
.It KERN\_SYSVSHM	integer	no
.It KERN\_TKSTAT	node	not applicable
.It KERN\_VERIEXEC	node	not applicable
.It KERN\_VERSION	string	no
.It KERN\_VNODE	struct vnode	no
.It KERN\_HARDCLOCK\_TICKS	integer		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_CCPU
The scheduler exponential decay value.
.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_CP_TIME
Returns an array of CPUSTATES uint64_ts.
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_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_DRIVERS
Return an array of
.Va 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_FILE
Return the entire file table.
The returned data consists of a single
.Va struct filelist
followed by an array of
.Va struct file ,
whose size depends on the current number of such objects in the system.
.It Li KERN_FSCALE
The kernel fixed-point scale factor.
.It Li 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_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_LABELOFFSET
The offset within the sector specified by KERN_LABELSECTOR of the
.Xr disklabel 5 .
.It Li KERN_LABELSECTOR
The sector number containing the
.Xr disklabel 5 .
.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_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_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_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
The maximum number of vnodes available on the system.
This can only be raised.
.It Li KERN_MBUF
Return information about the mbuf control variables.
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 "MBUFXNMBCLUSTERSXXX" "struct integerXXX" -offset indent
.It Sy Third level name	Type	Changeable
.It MBUF\_MSIZE	integer	yes
.It MBUF\_MCLBYTES	integer	yes
.It MBUF\_NMBCLUSTERS	integer	yes
.It MBUF\_MBLOWAT	integer	yes
.It MBUF\_MCLLOWAT	integer	yes
.El
.Pp
The variables are as follows:
.Bl -tag -width "123456"
.It Li MBUF_MSIZE
The mbuf base size.
.It Li MBUF_MCLBYTES
The mbuf cluster size.
.It Li 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 MBUF_MBLOWAT
The mbuf low water mark.
.It Li MBUF_MCLLOWAT
The mbuf cluster low water mark.
.El
.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_MONOTONIC_CLOCK
Returns the standard version the implementation of the POSIX 1003.1b
Monotonic Clock Option conforms to,
otherwise 0.
.It Li KERN_MSGBUF
The kernel message buffer, rotated so that the head of the circular kernel
message buffer is returned at the start of the buffer specified by
.Fa oldp .
The returned data may contain NUL bytes.
.It Li KERN_MSGBUFSIZE
The maximum number of characters that the kernel message buffer can hold.
.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_NTPTIME
A
.Va struct ntptimeval
structure is returned.
This structure contains data used by the
.Xr ntpd 8
program.
.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_POSIX1
The version of ISO/IEC 9945 (POSIX 1003.1) with which the system
attempts to comply.
.It Li 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
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_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
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
The version of
.St -p1003.1
and its
Threads
option to which the system attempts to conform,
otherwise 0.
.It Li 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
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 Sy 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\_SESSION	A session ID
.It KERN\_PROC\_TTY	A tty device
.It KERN\_PROC\_UID	A user ID
.It KERN\_PROC\_RUID	A real user ID
.It KERN\_PROC\_GID	A group ID
.It KERN\_PROC\_RGID	A real group ID
.El
.It Li KERN_PROC2
As for KERN_PROC, but an array of
.Va struct kinfo_proc2
structures are returned.
The fifth level name is the size of the
.Va struct kinfo_proc2
and the sixth level name is the number of structures to return.
.It Li 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 "Third level nameXXXXXX" -offset indent
.It KERN\_PROC\_ARGV	The argv strings
.It KERN\_PROC\_NARGV	The number of argv strings
.It KERN\_PROC\_ENV	The environ strings
.It KERN\_PROC\_NENV	The number of environ strings
.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 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
Profiling state.
If set to GMON_PROF_ON, starts profiling.
If set to GMON_PROF_OFF, stops profiling.
.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_ROOT_DEVICE
The name of the root device (e.g.,
.Dq wd0 ) .
.It Li KERN_ROOT_PARTITION
The root partition on the root device (a == 0).
.It Li KERN_RTC_OFFSET
Return the offset of real time clock from UTC in minutes.
.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_SYSVIPC_INFO
Return System V style IPC configuration and run-time information.
The third level name selects the System V style IPC facility.
.Bl -column "KERN_SYSVIPC_MSG_INFOXXX" "struct shm_sysctl_infoXXX" -offset indent
.It Sy Third level name	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
.Pp
.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
.Aq Pa 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
.Aq Pa 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
.Aq Pa sys/shm.h .
.El
.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_TKSTAT
Return information about the number of characters sent and received
on ttys.
The third level names for the tty statistic variables are detailed below.
The changeable column shows whether a process
with appropriate privilege may change the value.
.Bl -column "KERNXTKSTATXRAWCCXXX" "struct integerXXX" -offset indent
.It Sy Third level name	Type	Changeable
.It KERN\_TKSTAT\_NIN	quad	no
.It KERN\_TKSTAT\_NOUT	quad	no
.It KERN\_TKSTAT\_CANCC	quad	no
.It KERN\_TKSTAT\_RAWCC	quad	no
.El
.Pp
The variables are as follows:
.Bl -tag -width "123456"
.It Li KERN_TKSTAT_NIN
The total number of input characters.
.It Li KERN_TKSTAT_NOUT
The total number of output characters.
.It Li KERN_TKSTAT_CANCC
The number of canonical input characters.
.It Li KERN_TKSTAT_RAWCC
The number of raw input characters.
.El
.It Li KERN_VERIEXEC
Tunings for Verified Exec.
Third level names for the veriexec variables are detailed below.
The changeable column shows whether a process with appropriate
privilege may change the value or only raise it.
Only the superuser can modify these variables.
.Bl -column "VERIEXECXALGORITHMSXXX" "struct integerXXX" -offset indent
.It Sy Third level name	Type	Changeable
.It VERIEXEC\_VERBOSE	integer	yes
.It VERIEXEC\_STRICT	integer	raise only
.It VERIEXEC\_ALGORITHMS	string	no
.It VERIEXEC\_COUNT	node	not applicable
.El
.Pp
The variables are as follows:
.Bl -tag -width "123456"
.It Li VERIEXEC_VERBOSE
Controls the verbosity level of Verified Exec.
If 0, only the minimal
indication required will be given about what's happening - fingerprint
mismatches, removal of entries from the tables, modification of a
fingerprinted file.
If 1, more messages will be printed (ie., when a file with a valid
fingerprint is accessed).
Verbose level 2 is debug mode.
.It Li VERIEXEC_STRICT
Controls the strict level of Verified Exec.
The strict level defines how
Verified Exec will treat various situations.
In strict level 0, the system is in learning mode and will only warn about
fingerprint mismatches, aswell as allow removal of fingerprinted files.
It is the only level where fingerprints can be loaded.
In strict level 1, the system is in IDS mode.
It will deny access to files with mismatched fingerprints.
In strict level 2, the system is in IPS mode.
It has all effects of
strict level 1, plus it will deny write access to monitored files,
prevent their removal, and enforce access type (direct, indirect, file).
Strict level 3 operates as lockdown mode.
It will have all effects of
strict level 2, but it will also prevent access to non-monitored files.
Furthermore, it will prevent addition of new files to the system, and
allow writing only to files opened before the strict level was raised.
.It Li VERIEXEC_ALGORITHMS
Returns a string with the supported algorithms in Verified Exec.
.It Li VERIEXEC_COUNT
Variables are added to this node as new hash tables are created to
contain Verified Exec data for a new device.
Each variable in the node
will have a name in the form of
.No dev_ Ns Aq id
where
.Aq id
is the device id.
For example, the variable for the root device may be dev_0.
The value of this
variable will be the amount of fingerprinted files on the device.
.El
.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 .
.It Li KERN_HARDCLOCK_TICKS
Returns the number of
.Xr hardclock 9
ticks.
.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 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.
The second and third levels are typically the protocol family and
protocol number, though this is not always the case.
.Bl -column "Second level nameXXXXXX" "routing messagesXXX" -offset indent
.It Sy Second level name	Type	Changeable
.It PF\_ROUTE	routing messages	no
.It PF\_INET	IPv4 values	yes
.It PF\_INET6	IPv6 values	yes
.It PF\_KEY	IPsec key management 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 Sy 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 Sy 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 ip	grettl	integer	yes
.It ip	lowportmin	integer	yes
.It ip	lowportmax	integer	yes
.It ip	maxfragpacket	integer	yes
.It ip	checkinterface	integer	yes
.It icmp	maskrepl	integer	yes
.It icmp	errppslimit	integer	yes
.It icmp	rediraccept	integer	yes
.It icmp	redirtimeout	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	init_win_local	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 tcp	rstppslimit	integer	yes
.It tcp	ident	struct	no
.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
If set to 1, enables IP forwarding for the host,
meaning that the host is acting as a router.
.It Li ip.redirect
If set to 1, 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
If set to 1, enables forwarding of source-routed packets for the host.
This value may only be changed if the kernel security level is less than 1.
.It Li ip.directed-broadcast
If set to 1, enables directed broadcast behavior for the host.
.It Li ip.allowsrcrt
If set to 1, the host accepts source routed packets.
.It Li ip.subnetsarelocal
If set to 1, subnets are to be considered local addresses.
.It Li ip.mtudisc
If set to 1, enables Path MTU Discovery (RFC 1191).
When Path MTU Discovery is enabled, the transmitted TCP segment
size will be determined by the advertised maximum segment size
(MSS) from the remote end, as constrained by the path MTU.
If MTU Discovery is disabled, the transmitted segment size will
never be greater than
.Li tcp.mssdflt
(the local maximum segment size).
.It Li ip.anonportmin
The lowest port number to use for TCP and UDP ephemeral port allocation.
This cannot be set to less than 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 than 1024 or greater than 65535, and must
be greater than
.Li ip.anonportmin .
.It Li ip.mtudisctimeout
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 ip.grettl
The maximum time-to-live (hop count) value for an IPv4 packet generated by
.Xr gre 4
tunnel interface.
.It Li ip.lowportmin
The lowest port number to use for TCP and UDP reserved port allocation.
This cannot be set to less than 0 or greater than 1024, and must
be smaller than
.Li ip.lowportmax .
.It Li ip.lowportmax
The highest port number to use for TCP and UDP reserved port allocation.
This cannot be set to less than 0 or greater than 1024, and must
be greater than
.Li ip.lowportmin .
.It Li ip.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 ip.checkinterface
If set to non-zero, the host will reject packets addressed to it
that arrive on an interface not bound to that address.
Currently, this must be disabled if ipnat is used to translate the
destination address to another local interface, or if addresses
are added to the loopback interface instead of the interface where
the packets for those packets are received.
.It Li icmp.maskrepl
If set to 1, 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 icmp.rediraccept
If set to non-zero, the host will accept ICMP redirect packets.
Note that routers will never accept ICMP redirect packets,
and the variable is meaningful on IP hosts only.
.It Li icmp.redirtimeout
The variable specifies lifetime of routing entries generated by incoming
ICMP redirect.
This defaults to 600 seconds.
.It Li tcp.rfc1323
If set to 1, enables RFC 1323 extensions to TCP.
.It Li tcp.sendspace
The default TCP send buffer size.
.It Li tcp.recvspace
The default TCP receive buffer size.
.It Li tcp.mssdflt
The default maximum segment size both advertised to the peer
and to use when either the peer does not advertise a maximum segment size to
us during connection setup or Path MTU Discovery
.Li ( ip.mtudisc )
is disabled.
Do not change this value unless you really know what you are doing.
.It Li tcp.syn_cache_limit
The maximum number of entries allowed in the TCP compressed state
engine.
.It Li tcp.syn_bucket_limit
The maximum number of entries allowed per hash bucket in the TCP
compressed state engine.
.It Li tcp.syn_cache_interval
The TCP compressed state engine's timer interval.
.It Li tcp.init_win
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.init_win_local
Like
.Li tcp.init_win ,
but used when communicating with hosts on a local network.
.It Li tcp.mss_ifmtu
If set to 1, TCP calculates the outgoing maximum segment size based on
the MTU of the appropriate interface.
If set to 0, 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
If set to 1, enables RFC 2018 Selective ACKnowledgement.
.It Li tcp.win_scale
If rfc1323 is enabled, a value of 1 indicates RFC 1323 window scale options,
for increasing the TCP window size, are enabled.
.It Li tcp.timestamps
If rfc1323 is enabled, a value of 1 indicates RFC 1323 time stamp options,
used for measuring TCP round trip times, are enabled.
.It Li tcp.compat_42
If set to 1, enables work-arounds for bugs in the 4.2BSD TCP implementation.
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
If set to 1, enables use of the Hughes/Touch/Heidemann Congestion Window
Monitoring algorithm.
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
The Congestion Window Monitoring allowed burst size, in terms
of packet count.
.It Li tcp.ack_on_push
If set to 1, 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
If set to 1, enables the use of J.
Hoe's NewReno congestion control algorithm.
This algorithm improves the start-up behavior of TCP connections.
.It Li tcp.log_refused
If set to 1, refused TCP connections to the host will be logged.
.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
If set to 1, UDP checksums are being computed.
Received non-zero UDP checksums are always checked.
Disabling UDP checksums is strongly discouraged.
.It Li udp.sendspace
The default UDP send buffer size.
.It Li udp.recvspace
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 Sy 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	v6only	integer	yes
.It ip6	anonportmin	integer	yes
.It ip6	anonportmax	integer	yes
.It ip6	lowportmin	integer	yes
.It ip6	lowportmax	integer	yes
.It ip6	maxfrags	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
.It udp6	sendspace	integer	yes
.It udp6	recvspace	integer	yes
.El
.Pp
The variables are as follows:
.Bl -tag -width "123456"
.It Li ip6.forwarding
If set to 1, enables IPv6 forwarding for the node,
meaning that the node is acting as a router.
If set to 0, disables IPv6 forwarding for the node,
meaning that the node is acting as a host.
IPv6 specification defines node behavior for
.Dq router
case and
.Dq host
case quite differently, and changing this variable during operation
may cause serious trouble.
It is recommended to configure the variable at bootstrap time,
and bootstrap time only.
.It Li ip6.redirect
If set to 1, 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 setting 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 configures 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 RFC 2462 5.5.4.
.It Li ip6.rr_prune
The variable specifies interval between IPv6 router renumbering prefix
babysitting, in seconds.
.It Li ip6.v6only
The variable specifies initial value for
.Dv IPV6_V6ONLY
socket option for
.Dv AF_INET6
socket.
Please refer to
.Xr ip6 4
for detail.
.It Li ip6.anonportmin
The lowest port number to use for TCP and UDP ephemeral port allocation.
This cannot be set to less than 1024 or greater than 65535.
.It Li ip6.anonportmax
The highest port number to use for TCP and UDP ephemeral port allocation.
This cannot be set to less than 1024 or greater than 65535, and must
be greater than
.Li ip6.anonportmin .
.It Li ip6.lowportmin
The lowest port number to use for TCP and UDP reserved port allocation.
This cannot be set to less than 0 or greater than 1024, and must
be smaller than
.Li ip6.lowportmax .
.It Li ip6.lowportmax
The highest port number to use for TCP and UDP reserved port allocation.
This cannot be set to less than 0 or greater than 1024, and must
be greater than
.Li ip6.lowportmin .
.It Li ip6.maxfrags
The maximum number of fragments the node will accept.
0 means that the node will not accept any fragments.
\-1 means that the node will accept as many fragments as it receives.
The flag is provided basically for avoiding possible DoS attacks.
.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.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 RFC 2461 ,
in seconds.
.It Li icmp6.nd6_umaxtries
The variable specifies
.Dv MAX_UNICAST_SOLICIT
constant in IPv6 neighbor discovery specification
.Pq RFC 2461 .
.It Li icmp6.nd6_mmaxtries
The variable specifies
.Dv MAX_MULTICAST_SOLICIT
constant in IPv6 neighbor discovery specification
.Pq RFC 2461 .
.It Li icmp6.nd6_useloopback
If set to non-zero, kernel IPv6 stack will use 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, responses 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 are subject to rate limitation
and will not go out from the node.
Negative value disables 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 layer
will take 3 consecutive hints in maximum.
After receiving 3 hints, neighbor discovery layer will perform
normal neighbor discovery process.
.It Li icmp6.mtudisc_hiwat
.It Li icmp6.mtudisc_lowat
The variables define the maximum number of routing table entries,
created due to path MTU discovery
.Pq prevents denial-of-service attacks with ICMPv6 too big messages .
When IPv6 path MTU discovery happens, we keep path MTU information into
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, kernel IPv6 neighbor discovery code will generate
debugging messages.
The debug outputs are useful to diagnose IPv6 interoperability issues.
The flag must be set to 0 for normal operation.
.El
.Pp
We reuse net.*.tcp for
.Tn TCP
over
.Tn IPv6 ,
and therefore we do not have variables net.*.tcp6.
Variables net.inet6.udp6 have identical meaning to net.inet.udp.
Please refer to
.Li PF_INET
section above.
For variables net.*.ipsec6, please refer to
.Xr ipsec 4 .
.It Li PF_KEY
Get or set various global information about the IPsec key management.
The third level name is the variable name.
The currently defined variable and names are:
.Bl -column "blockacq_lifetime" "integer" "yes" -offset indent
.It Sy Variable name	Type	Changeable
.It debug	integer	yes
.It spi_try	integer	yes
.It spi_min_value	integer	yes
.It spi_max_value	integer	yes
.It larval_lifetime	integer	yes
.It blockacq_count	integer	yes
.It blockacq_lifetime	integer	yes
.It esp_keymin	integer	yes
.It esp_auth	integer	yes
.It ah_keymin	integer	yes
.El
The variables are as follows:
.Bl -tag -width "123456"
.It Li debug
Turn on debugging message from within the kernel.
The value is a bitmap, as defined in
.Pa /usr/include/netkey/key_debug.h .
.It Li spi_try
The number of times the kernel will try to obtain an unique SPI
when it generates it from random number generator.
.It Li spi_min_value
Minimum SPI value when generating it within the kernel.
.It Li spi_max_value
Maximum SPI value when generating it within the kernel.
.It Li larval_lifetime
Lifetime for LARVAL SAD entries, in seconds.
.It Li blockacq_count
Number of ACQUIRE PF_KEY messages to be blocked after an ACQUIRE message.
It avoids flood of ACQUIRE PF_KEY from being sent from the kernel to the
key management daemon.
.It Li blockacq_lifetime
Lifetime of ACQUIRE PF_KEY message.
.It Li esp_keymin
Minimum ESP key length, in bits.
The value is used when the kernel creates proposal payload
on ACQUIRE PF_KEY message.
.It Li esp_auth
Whether ESP authentication should be used or not.
Non-zero value indicates that ESP authentication should be used.
The value is used when the kernel creates proposal payload
on ACQUIRE PF_KEY message.
.It Li ah_keymin
Minimum AH key length, in bits,
The value is used when the kernel creates proposal payload
on ACQUIRE PF_KEY message.
.El
.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 Third level name	Type	Changeable
.It PROC\_PID\_CORENAME	string	yes
.It PROC\_PID\_LIMIT	node	not applicable
.It PROC\_PID\_STOPFORK	int	yes
.It PROC\_PID\_STOPEXEC	int	yes
.It PROC\_PID\_STOPEXIT	int	yes
.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.
.It Li PROC_PID_STOPFORK
If non zero, the process' children will be stopped after
.Xr fork 2
calls.
The children is created in the SSTOP state and is never scheduled
for running before being stopped.
This feature helps attaching a process with a debugger such as
.Xr gdb 1
before it had the opportunity to actually do anything.
.Pp
This value is inherited by the process's children, and it also
apply to emulation specific system calls that fork a new process, such as
.Fn sproc
or
.Fn clone .
.It Li PROC_PID_STOPEXEC
If non zero, the process will be stopped on next
.Xr exec 3
call.
The process created by
.Xr exec 3
is created in the SSTOP state and is never scheduled for running
before being stopped.
This feature helps attaching a process with a debugger such as
.Xr gdb 1
before it had the opportunity to actually do anything.
.Pp
This value is inherited by the process's children.
.It Li PROC_PID_STOPEXIT
If non zero, the process will be stopped on when it has cause to exit,
either by way of calling
.Xr exit 3 ,
.Xr _exit 2 ,
or by the receipt of a specific signal.
The process is stopped before any of its resources or vm space is
released allowing examination of the termination state of a process
before it disappears.
This feature can be used to examine the final conditions of the
process's vmspace via
.Xr pmap 1
or its resource settings with
.Xr sysctl 8
before it disappears.
.Pp
This value is also inherited by the process's children.
.El
.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 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
.It USER\_ATEXIT\_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.
.It Li USER_ATEXIT_MAX
The maximum number of functions that may be registered with
.Xr atexit 3 .
.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 Second level name	Type	Changeable
.It VM\_ANONMAX	int	yes
.It VM\_ANONMIN	int	yes
.It VM\_BUFCACHE	int	yes
.It VM\_BUFMEM	int	no
.It VM\_BUFMEM_LOWATER	int	yes
.It VM\_BUFMEM_HIWATER	int	yes
.It VM\_EXECMAX	int	yes
.It VM\_EXECMIN	int	yes
.It VM\_FILEMAX	int	yes
.It VM\_FILEMIN	int	yes
.It VM\_LOADAVG	struct loadavg	no
.It VM\_MAXSLP	int	no
.It VM\_METER	struct vmtotal	no
.It VM\_NKMEMPAGES	int	no
.It VM\_USPACE	int	no
.It VM\_UVMEXP	struct uvmexp	no
.It VM\_UVMEXP2	struct uvmexp_sysctl	no
.El
.Pp
.Bl -tag -width "123456"
.It Li VM_ANONMAX
The percentage of physical memory which will be reclaimed
from other types of memory usage to store anonymous application data.
.It Li VM_ANONMIN
The percentage of physical memory which will be always be available for
anonymous application data.
.It Li VM_BUFCACHE
The percentage of kernel memory which will be available
for the buffer cache.
.It Li VM_BUFMEM
The amount of kernel memory that is being used by the buffer cache.
.It Li VM_BUFMEM_LOWATER
The minimum amount of kernel memory to reserve for the
buffer cache.
.It Li VM_BUFMEM_HIWATER
The maximum amount of kernel memory to be used for the
buffer cache.
.It Li VM_EXECMAX
The percentage of physical memory which will be reclaimed
from other types of memory usage to store cached executable data.
.It Li VM_EXECMIN
The percentage of physical memory which will be always be available for
cached executable data.
.It Li VM_FILEMAX
The percentage of physical memory which will be reclaimed
from other types of memory usage to store cached file data.
.It Li VM_FILEMIN
The percentage of physical memory which will be always be available for
cached file data.
.It Li VM_LOADAVG
Return the load average history.
The returned data consists of a
.Va struct loadavg .
.It Li VM_MAXSLP
The value of the maxslp kernel global variable.
.It Li VM_METER
Return system wide virtual memory statistics.
The returned data consists of a
.Va struct vmtotal .
.It Li VM_USPACE
The number of bytes allocated for each kernel stack.
.It Li VM_UVMEXP
Return system wide virtual memory statistics.
The returned data consists of a
.Va struct uvmexp .
.It Li VM_UVMEXP2
Return system wide virtual memory statistics.
The returned data consists of a
.Va struct uvmexp_sysctl .
.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 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 CTL_SECURITY
The security level contains various security-related settings for
the system. Available settings are detailed below.
.Bl -column "SECURITY_CURTAIN" "integerXXX" -offset indent
.It Sy Second level name	Type	Changeable
.It SECURITY_CURTAIN	integer	yes
.El
.Pp
.Bl -tag -width "123456"
.It Li SECURITY_CURTAIN
If non-zero, will filter return objects according to the user-id
requesting information about them, preventing from users any
access to objects they don't own.
.Pp
At the moment, it affects
.Xr ps 1 ,
.Xr netstat 1
(for
.Dv PF_INET ,
.Dv PF_INET6 ,
and
.Dv PF_UNIX
PCBs), and
.Xr w 1 .
.El
.Sh CTL_VENDOR
The "vendor" toplevel name is reserved to be used by vendors who wish to
have their own private MIB tree.
Intended use is to store values under
.Dq vendor.\*[Lt]yourname\*[Gt].* .
.Sh DYNAMIC OPERATIONS
Several meta-identifiers are provided to perform operations on the
.Nm
tree itself, or support alternate means of accessing the data
instrumented by the
.Nm
tree.
.Bl -column CTLXCREATESYMXXX
.It Sy Name	Description
.It CTL\_QUERY	Retrieve a mapping of names to numbers below a given node
.It CTL\_CREATE	Create a new node
.It CTL\_CREATESYM	Create a new node by its kernel symbol
.It CTL\_DESTROY	Destroy a node
.It CTL\_DESCRIBE	Retrieve node descriptions
.El
.Pp
The core interface to all of these meta-functions is the structure
that the kernel uses to describe the tree internally, as defined in
.Aq Pa sys/sysctl.h
as:
.Pp
.Bd -literal
struct sysctlnode {
        uint32_t sysctl_flags;          /* flags and type */
        int32_t sysctl_num;             /* mib number */
        char sysctl_name[SYSCTL_NAMELEN]; /* node name */
        uint32_t sysctl_ver;        /* node's version vs. rest of tree */
        uint32_t __rsvd;
        union {
                struct {
                        uint32_t suc_csize; /* size of child node array */
                        uint32_t suc_clen; /* number of valid children */
                        struct sysctlnode* suc_child; /* array of child nodes */
                } scu_child;
                struct {
                        void *sud_data; /* pointer to external data */
                        size_t sud_offset; /* offset to data */
                } scu_data;
                int32_t scu_alias;      /* node this node refers to */
                int32_t scu_idata;      /* immediate "int" data */
                u_quad_t scu_qdata;     /* immediate "u_quad_t" data */
        } sysctl_un;
        size_t _sysctl_size;            /* size of instrumented data */
        sysctlfn _sysctl_func;          /* access helper function */
        struct sysctlnode *sysctl_parent; /* parent of this node */
        const char *sysctl_desc;        /* description of node */
};

#define sysctl_csize    sysctl_un.scu_child.suc_csize
#define sysctl_clen     sysctl_un.scu_child.suc_clen
#define sysctl_child    sysctl_un.scu_child.suc_child
#define sysctl_data     sysctl_un.scu_data.sud_data
#define sysctl_offset   sysctl_un.scu_data.sud_offset
#define sysctl_alias    sysctl_un.scu_alias
#define sysctl_idata    sysctl_un.scu_idata
#define sysctl_qdata    sysctl_un.scu_qdata
.Ed
.Pp
Querying the tree to discover the name to number mapping permits
dynamic discovery of all the data that the tree currently has
instrumented.
For example, to discover all the nodes below the
CTL_VFS node:
.Pp
.Bd -literal -offset indent -compact
struct sysctlnode query, vfs[128];
int mib[2];
size_t len;
.sp
mib[0] = CTL_VFS;
mib[1] = CTL_QUERY;
memset(\*[Am]query, 0, sizeof(query));
query.sysctl_flags = SYSCTL_VERSION;
len = sizeof(vfs);
sysctl(mib, 2, \*[Am]vfs[0], \*[Am]len, \*[Am]query, sizeof(query));
.Ed
.Pp
Note that a reference to an empty node with
.Fa sysctl_flags
set to
.Dv SYSCTL_VERSION
is passed to sysctl in order to indicate the version that the program
is using.
All dynamic operations passing nodes into sysctl require that the
version be explicitly specified.
.Pp
Creation and destruction of nodes works by constructing part of a new
node description (or a description of the existing node) and invoking
CTL_CREATE (or CTL_CREATESYM) or CTL_DESTROY at the parent of the new
node, with a pointer to the new node passed via the
.Fa new
and
.Fa newlen
arguments.
If valid values for
.Fa old
and
.Fa oldlenp
are passed, a copy of the new node once in the tree will be returned.
If the create operation fails because a node with the same name or MIB
number exists, a copy of the conflicting node will be returned.
.Pp
The minimum requirements for creating a node are setting the
.Fa sysctl_flags
to indicate the new node's type,
.Fa sysctl_num
to either the new node's number (or CTL_CREATE or CTL_CREATESYM if a
dynamically allocated MIB number is acceptable),
.Fa sysctl_size
to the size of the data to be instrumented (which must agree with the
given type), and
.Fa sysctl_name
must be set to the new node's name.
Nodes that are not of type
.Dq node
must also have some description of the data to be instrumented, which
will vary depending on what is to be instrumented.
.Pp
If existing kernel data is to be covered by this new node, its address
should be given in
.Fa sysctl_data
or, if CTL_CREATESYM is used,
.Fa sysctl_data
should be set to a string containing its name from the kernel's symbol
table.
If new data is to be instrumented and an initial value is available,
the new integer or quad type data should be placed into either
.Fa sysctl_idata
or
.Fa sysctl_qdata ,
respectively, along with the SYSCTL_IMMEDIATE flag being set, or
.Fa sysctl_data
should be set to point to a copy of the new data, and the
SYSCTL_OWNDATA flag must be set.
This latter method is the only way that new string and struct type
nodes can be initialized.
Invalid kernel addresses are accepted, but any attempt to access those
nodes will return an error.
.Pp
The
.Fa sysctl_csize ,
.Fa sysctl_clen ,
.Fa sysctl_child ,
.Fa sysctl_parent ,
and
.Fa sysctl_alias
members are used by the kernel to link the tree together and must be
.Dv NULL
or 0.
Nodes created in this manner cannot have helper functions, so
.Fa sysctl_func
must also be
.Dv NULL .
If the
.Fa sysctl_ver
member is non-zero, it must match either the version of the parent or
the version at the root of the MIB or an error is returned.
This can be used to ensure that nodes are only added or removed from a
known state of the tree.
Note: It may not be possible to determine the version at the root
of the tree.
.Pp
This example creates a new subtree and adds a node to it that controls the
.Fa audiodebug
kernel variable, thereby making it tunable at at any time, without
needing to use
.Xr ddb 4
or
.Xr kvm 3
to alter the kernel's memory directly.
.Pp
.Bd -literal -offset indent -compact
struct sysctlnode node;
int mib[2];
size_t len;
.sp
mib[0] = CTL_CREATE;		/* create at top-level */
len = sizeof(node);
memset(\*[Am]node, 0, len);
node.sysctl_flags = SYSCTL_VERSION|CTLFLAG_READWRITE|CTLTYPE_NODE;
snprintf(node.sysctl_name, sizeof(node.sysctl_name), "local");
node.sysctl_num = CTL_CREATE;	/* request dynamic MIB number */
sysctl(\*[Am]mib[0], 1, \*[Am]node, \*[Am]len, \*[Am]node, len);
.sp
mib[0] = node.sysctl_num;	/* use new MIB number */
mib[1] = CTL_CREATESYM;		/* create at second level */
len = sizeof(node);
memset(\*[Am]node, 0, len);
node.sysctl_flags = SYSCTL_VERSION|CTLFLAG_READWRITE|CTLTYPE_INT;
snprintf(node.sysctl_name, sizeof(node.sysctl_name), "audiodebug");
node.sysctl_num = CTL_CREATE;
node.sysctl_data = "audiodebug"; /* kernel symbol to be used */
sysctl(\*[Am]mib[0], 2, NULL, NULL, \*[Am]node, len);
.Ed
.Pp
The process for deleting nodes is similar, but less data needs to
be supplied.
Only the
.Fa sysctl_num
field
needs to be filled in; almost all other fields must be left blank.
The
.Fa sysctl_name
and/or
.Fa sysctl_ver
fields can be filled in with the name and version of the existing node
as additional checks on what will be deleted.
If all the given data fail to match any node, nothing will be deleted.
If valid values for
.Fa old
and
.Fa oldlenp
are supplied and a node is deleted, a copy of what was in the MIB tree
will be returned.
.Pp
This sample code shows the deletion of the two nodes created in the
above example:
.Pp
.Bd -literal -offset indent -compact
int mib[2];
.sp
len = sizeof(node);
memset(\*[Am]node, 0, len);
node.sysctl_flags = SYSCTL_VERSION;
.sp
mib[0] = 3214;			/* assumed number for "local" */
mib[1] = CTL_DESTROY;
node.sysctl_num = 3215;		/* assumed number for "audiodebug" */
sysctl(\*[Am]mib[0], 2, NULL, NULL, \*[Am]node, len);
.sp
mib[0] = CTL_DESTROY;
node.sysctl_num = 3214;		/* now deleting "local" */
sysctl(\*[Am]mib[0], 1, NULL, NULL, \*[Am]node, len);
.Ed
.Pp
Descriptions of each of the nodes can also be retrieved, if they are
available.
Descriptions can be retrieved in bulk at each level or on a per-node
basis.
The layout of the buffer into which the descriptions are returned is a
series of variable length structures, each of which describes its own
size.
The length indicated includes the terminating
.Sq nul
character.
Nodes that have no description or where the description is not
available are indicated by an empty string.
The
.Fa descr_ver
will match the
.Fa sysctl_ver
value for a given node, so that descriptions for nodes whose number
have been recycled can be detected and ignored or discarded.
.Pp
.Bd -literal
struct sysctldesc {
        int32_t         descr_num;      /* mib number of node */
        uint32_t        descr_ver;      /* version of node */
        uint32_t        descr_len;      /* length of description string */
        char            descr_str[1];   /* not really 1...see above */
};
.Ed
.Pp
The
.Fn NEXT_DESCR
macro can be used to skip to the next description in the retrieved
list.
.Pp
.Bd -literal -offset indent -compact
struct sysctlnode desc;
struct sysctldesc *d;
char buf[1024];
int mib[2];
size_t len;
.sp
/* retrieve kern-level descriptions */
mib[0] = CTL_KERN;
mib[1] = CTL_DESCRIBE;
d = (struct sysctldesc *)\*[Am]buf[0];
len = sizeof(buf);
sysctl(mib, 2, d, \*[Am]len, NULL, 0);
while ((caddr_t)d \*[Lt] (caddr_t)\*[Am]buf[len]) {
	printf("node %d: %.*s\\n", d-\*[Gt]descr_num, d-\*[Gt]descr_len,
	    d-\*[Gt]descr_str);
	d = NEXT_DESCR(d);
}
.sp
/* retrieve description for kern.securelevel */
memset(\*[Am]desc, 0, sizeof(desc));
desc.sysctl_flags = SYSCTL_VERSION;
desc.sysctl_num = KERN_SECURELEVEL;
d = (struct sysctldesc *)\*[Am]buf[0];
len = sizeof(buf);
sysctl(mib, 2, d, \*[Am]len, \*[Am]desc, sizeof(desc));
printf("kern.securelevel: %.*s\\n", d-\*[Gt]descr_len, d-\*[Gt]descr_str);
.Ed
.Pp
Descriptions can also be set as follows, subject to the following rules:
.Pp
.Bl -bullet -compact
.It
The kernel securelevel is at zero or lower
.It
The caller has super-user privileges
.It
The node does not currently have a description
.It
The node is not marked as
.Dq permanent
.El
.Pp
.Bd -literal -offset indent -compact
struct sysctlnode desc;
int mib[2];
.sp
/* presuming the given top-level node was just added... */
mib[0] = 3214; /* mib numbers taken from previous examples */
mib[1] = CTL_DESCRIBE;
memset(\*[Am]desc, 0, sizeof(desc));
desc.sysctl_flags = SYSCTL_VERSION;
desc.sysctl_num = 3215;
desc.sysctl_desc = "audio debug control knob";
sysctl(mib, 2, NULL, NULL, \*[Am]desc, sizeof(desc));
.Ed
.Pp
Upon successfully setting a description, the new description will be
returned in the space indicated by the
.Fa oldp
and
.Fa oldlenp
arguments.
.Pp
The
.Fa sysctl_flags
field in the struct sysctlnode contains the sysctl version, node type
information, and a number of flags.
The macros
.Fn SYSCTL_VERS ,
.Fn SYSCTL_TYPE ,
and
.Fn SYSCTL_FLAGS
can be used to access the different fields.
Valid flags are:
.Bl -column CTLFLAGXPERMANENTXXX
.It Sy Name	Description
.It CTLFLAG\_READONLY	Node is read-only
.It CTLFLAG\_READONLY1	Node becomes read-only at securelevel 1
.It CTLFLAG\_READONLY2	Node becomes read-only at securelevel 2
.It CTLFLAG\_READWRITE	Node is writable by the superuser
.It CTLFLAG\_ANYWRITE	Node is writable by anyone
.It CTLFLAG\_PRIVATE	Node is readable only by the superuser
.It CTLFLAG\_PERMANENT	Node cannot be removed (cannot be set by
processes)
.It CTLFLAG\_OWNDATA	Node owns data and does not instrument
existing data
.It CTLFLAG\_IMMEDIATE	Node contains instrumented data and does not
instrument existing data
.It CTLFLAG\_HEX	Node's contents should be displayed in a hexadecimal
form
.It CTLFLAG\_ROOT	Node is the root of a tree (cannot be set at
any time)
.It CTLFLAG\_ANYNUMBER	Node matches any MIB number (cannot be set by
processes)
.It CTLFLAG\_HIDDEN	Node not displayed by default
.It CTLFLAG\_ALIAS	Node refers to a sibling node (cannot be set
by processes)
.It CTLFLAG\_OWNDESC	Node owns its own description string space
.El
.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 FILES
.Bl -tag -width \*[Lt]netinet6/udp6Xvar.h\*[Gt] -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 uvm/uvm_param.h
definitions for second level virtual memory identifiers
.It Aq Pa netinet/in.h
definitions for third level IPv4/v6 identifiers and
fourth level IPv4/v6 identifiers
.It Aq Pa netinet/icmp_var.h
definitions for fourth level ICMP identifiers
.It Aq Pa netinet/icmp6.h
definitions for fourth level ICMPv6 identifiers
.It Aq Pa netinet/tcp_var.h
definitions for fourth level TCP identifiers
.It Aq Pa netinet/udp_var.h
definitions for fourth level UDP identifiers
.It Aq Pa netinet6/udp6_var.h
definitions for fourth level IPv6 UDP identifiers
.It Aq Pa netinet6/ipsec.h
definitions for fourth level IPsec identifiers
.It Aq Pa netkey/key_var.h
definitions for third level PF_KEY identifiers
.It Aq Pa machine/cpu.h
definitions for second level machdep identifiers
.El
.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, or the requested value is temporarily
unavailable.
.It Bq Er EINVAL
The
.Fa name
array is zero 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, or the given value is not acceptable for
the given node.
.It Bq Er ENOMEM
The length pointed to by
.Fa oldlenp
is too short to hold the requested value.
.It Bq Er EISDIR
The
.Fa name
array specifies an intermediate rather than terminal name.
.It Bq Er ENOTDIR
The
.Fa name
array specifies a node below a node that addresses data.
.It Bq Er ENOENT
The
.Fa name
array specifies a node that does not exist in the tree.
.It Bq Er ENOENT
An attempt was made to destroy a node that does not exist, or to
create or destroy a node below a node that does not exist.
.It Bq Er ENOTEMPTY
An attempt was made to destroy a node that still has children.
.It Bq Er EOPNOTSUPP
The
.Fa name
array specifies a value that is unknown or a meta-operation was
attempted that the requested node does not support.
.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 or to
create or destroy a node.
.It Bq Er EPERM
An attempt to change a value protected by the current kernel security
level is made.
.El
.Sh SEE ALSO
.Xr ipsec 4 ,
.Xr tcp 4 ,
.Xr sysctl 8
.\" .Xr sysctl 9
.Sh HISTORY
The
.Nm
function first appeared in
.Bx 4.4 .