libc/gen/sysctl.3

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.Dd April 15, 2026
.Dt SYSCTL 3
.Os
.Sh NAME
.Nm sysctl ,
.Nm sysctlbyname ,
.Nm sysctlnametomib
.Nd get or set system information
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/sysctl.h
.Ft int
.Fn sysctl "const int *name" "u_int namelen" "void *oldp" "size_t *oldlenp" "const void *newp" "size_t newlen"
.Ft int
.Fn sysctlbyname "const char *name" "void *oldp" "size_t *oldlenp" "const void *newp" "size_t newlen"
.Ft int
.Fn sysctlnametomib "const char *name" "int *mibp" "size_t *sizep"
.Sh DESCRIPTION
The
.Fn sysctl
function retrieves system information and allows processes with
appropriate privileges to set system information.
The information available from
.Fn sysctl
consists of integers, strings, and tables.
Information may be retrieved and set from the command interface
using the
.Xr sysctl 8
utility.
.Pp
Unless explicitly noted below,
.Fn sysctl
returns a consistent snapshot of the data requested.
Consistency is obtained by locking the destination
buffer into memory so that the data may be copied out without blocking.
Calls to
.Fn sysctl
are serialized to avoid deadlock.
.Pp
The state is described using a ``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 an ASCII representation of the name and internally
looks up the integer name vector.
Apart from that, it behaves the same
as the standard
.Fn sysctl
function.
.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
and after a call that returns with the error code
.Er ENOMEM .
If the amount of data available is greater
than the size of the buffer supplied,
the call supplies as much data as fits in the buffer provided
and returns with the error code
.Er ENOMEM .
If the old value is not desired,
.Fa oldp
and
.Fa oldlenp
should be set to NULL.
.Pp
The size of the available data can be determined by calling
.Fn sysctl
with the
.Dv NULL
argument 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
.Fn sysctlnametomib
function accepts an ASCII representation of the name,
looks up the integer name vector,
and returns the numeric representation in the mib array pointed to by
.Fa mibp .
The number of elements in the mib array is given by the location specified by
.Fa sizep
before the call,
and that location gives the number of entries copied after a successful call.
The resulting
.Fa mib
and
.Fa size
may be used in subsequent
.Fn sysctl
calls to get the data associated with the requested ASCII name.
This interface is intended for use by applications that want to
repeatedly request the same variable (the
.Fn sysctl
function runs in about a third the time as the same request made via the
.Fn sysctlbyname
function).
The
.Fn sysctlnametomib
function is also useful for fetching mib prefixes and then adding
a final component.
For example, to fetch process information
for processes with pid's less than 100:
.Pp
.Bd -literal -offset indent -compact
int i, mib[4];
size_t len;
struct kinfo_proc kp;

/* Fill out the first three components of the mib */
len = 4;
sysctlnametomib("kern.proc.pid", mib, &len);

/* Fetch and print entries for pid's < 100 */
for (i = 0; i < 100; i++) {
	mib[3] = i;
	len = sizeof(kp);
	if (sysctl(mib, 4, &kp, &len, NULL, 0) == -1)
		perror("sysctl");
	else if (len > 0)
		printkproc(&kp);
}
.Ed
.Pp
The top level names are defined with a CTL_ prefix in
.In sys/sysctl.h ,
and are as follows.
The next and subsequent levels down are found in the include files
listed here, and described in separate sections below.
.Bl -column CTLXMACHDEPXXX "Next Level NamesXXXXXX" -offset indent
.It Sy Name Ta Sy Next Level Names Ta Sy Description
.It Dv CTL_DEBUG Ta In sys/sysctl.h Ta Debugging
.It Dv CTL_VFS Ta In sys/mount.h Ta File system
.It Dv CTL_HW Ta In sys/sysctl.h Ta Generic CPU, I/O
.It Dv CTL_KERN Ta In sys/sysctl.h Ta High kernel limits
.It Dv CTL_MACHDEP Ta In sys/sysctl.h Ta Machine dependent
.It Dv CTL_NET Ta In sys/socket.h Ta Networking
.It Dv CTL_USER Ta In sys/sysctl.h Ta User-level
.It Dv CTL_VM Ta In vm/vm_param.h Ta Virtual memory
.El
.Pp
For example, the following retrieves the maximum number of processes allowed
in the system:
.Pp
.Bd -literal -offset indent -compact
int mib[2], maxproc;
size_t len;

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

mib[0] = CTL_USER;
mib[1] = USER_CS_PATH;
sysctl(mib, 2, NULL, &len, NULL, 0);
p = malloc(len);
sysctl(mib, 2, p, &len, NULL, 0);
.Ed
.Ss CTL_DEBUG
The debugging variables vary from system to system.
A debugging variable may be added or deleted without need to recompile
.Fn sysctl
to know about it.
Each time it runs,
.Fn sysctl
gets the list of debugging variables from the kernel and
displays their current values.
The system defines twenty
.Pq Vt "struct ctldebug"
variables named
.Va debug0
through
.Va debug19 .
They are declared as separate variables so that they can be
individually initialized at the location of their associated variable.
The loader prevents multiple use of the same variable by issuing errors
if a variable is initialized in more than one place.
For example, to export the variable
.Va dospecialcheck
as a debugging variable, the following declaration would be used:
.Pp
.Bd -literal -offset indent -compact
int dospecialcheck = 1;
struct ctldebug debug5 = { "dospecialcheck", &dospecialcheck };
.Ed
.Ss CTL_VFS
A distinguished second level name, VFS_GENERIC,
is used to get general information about all file systems.
One of its third level identifiers is VFS_MAXTYPENUM
that gives the highest valid file system type number.
Its other third level identifier is VFS_CONF that
returns configuration information about the file system
type given as a fourth level identifier (see
.Xr getvfsbyname 3
as an example of its use).
The remaining second level identifiers are the
file system type number returned by a
.Xr statfs 2
call or from VFS_CONF.
The third level identifiers available for each file system
are given in the header file that defines the mount
argument structure for that file system.
.Ss 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 Name" integerXXX Changeable -offset indent
.It Sy Second Level Name Ta Sy Type Ta Sy Changeable
.It Dv HW_MACHINE Ta string Ta no
.It Dv HW_MODEL Ta string Ta no
.It Dv HW_NCPU Ta integer Ta no
.It Dv HW_BYTEORDER Ta integer Ta no
.It Dv HW_PHYSMEM Ta integer Ta no
.It Dv HW_USERMEM Ta integer Ta no
.It Dv HW_PAGESIZE Ta integer Ta no
.\".It Dv HW_DISKNAMES Ta integer Ta no
.\".It Dv HW_DISKSTATS Ta integer Ta no
.It Dv HW_FLOATINGPT Ta integer Ta no
.It Dv HW_MACHINE_ARCH Ta string Ta no
.It Dv HW_REALMEM Ta integer Ta no
.It Dv HW_AVAILPAGES Ta integer Ta no
.El
.Bl -tag -width 6n
.It Li HW_MACHINE
The machine class.
.It Li HW_MODEL
The machine model
.It Li HW_NCPU
The number of cpus.
.It Li HW_BYTEORDER
The byteorder (4321 or 1234).
.It Li HW_PHYSMEM
Amount of physical memory (in bytes), minus the amount used by the kernel,
pre-loaded modules, and (on x86) the dcons buffer.
.It Li HW_USERMEM
Amount of memory (in bytes) which is not wired.
.It Li HW_PAGESIZE
The software page size.
.\".It Fa HW_DISKNAMES
.\".It Fa HW_DISKSTATS
.It Li HW_FLOATINGPT
Nonzero if the floating point support is in hardware.
.It Li HW_MACHINE_ARCH
The machine dependent architecture type.
.It Li HW_REALMEM
Amount of memory (in bytes) reported by the firmware.
That value is sometimes not sane; in that case, the kernel reports the max
memory address instead.
.It Li HW_AVAILPAGES
The same value as
.Li HW_PHYSMEM ,
measured in pages rather than bytes.
.El
.Ss 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 "KERNXMAXFILESPERPROCXXX" "struct clockrateXXX" -offset indent
.It Sy Second Level Name Ta Sy Type Ta Sy Changeable
.It Dv KERN_ARGMAX Ta integer Ta no
.It Dv KERN_ARND Ta byte buffer Ta no
.It Dv KERN_BOOTFILE Ta string Ta yes
.It Dv KERN_BOOTTIME Ta struct timeval Ta no
.It Dv KERN_CLOCKRATE Ta struct clockinfo Ta no
.It Dv KERN_FILE Ta struct xfile Ta no
.It Dv KERN_HOSTID Ta integer Ta yes
.It Dv KERN_HOSTUUID Ta string Ta yes
.It Dv KERN_HOSTNAME Ta string Ta yes
.It Dv KERN_IOV_MAX Ta integer Ta no
.It Dv KERN_JOB_CONTROL Ta integer Ta no
.It Dv KERN_LOCKF Ta struct kinfo_lockf Ta no
.It Dv KERN_LOGSIGEXIT Ta integer Ta yes
.It Dv KERN_MAXFILES Ta integer Ta yes
.It Dv KERN_MAXFILESPERPROC Ta integer Ta yes
.It Dv KERN_MAXPHYS Ta integer Ta no
.It Dv KERN_MAXPROC Ta integer Ta no
.It Dv KERN_MAXPROCPERUID Ta integer Ta yes
.It Dv KERN_MAXVNODES Ta integer Ta yes
.It Dv KERN_NGROUPS Ta integer Ta no
.It Dv KERN_NISDOMAINNAME Ta string Ta yes
.It Dv KERN_OSRELDATE Ta integer Ta no
.It Dv KERN_OSRELEASE Ta string Ta no
.It Dv KERN_OSREV Ta integer Ta no
.It Dv KERN_OSTYPE Ta string Ta no
.It Dv KERN_POSIX1 Ta integer Ta no
.It Dv KERN_PROC Ta node Ta not applicable
.It Dv KERN_PS_STRINGS Ta integer Ta no
.It Dv KERN_SAVED_IDS Ta integer Ta no
.It Dv KERN_SECURELVL Ta integer Ta raise only
.It Dv KERN_UPDATEINTERVAL Ta integer Ta no
.It Dv KERN_USRSTACK Ta integer Ta no
.It Dv KERN_VERSION Ta string Ta no
.El
.Bl -tag -width 6n
.It Li KERN_ARGMAX
The maximum bytes of argument to
.Xr execve 2 .
.It Li KERN_ARND
.Xr arc4rand 9
Fills the buffer with random bytes from in-kernel random data generator.
This is an alternative interface for
.Xr read 2
of
.Xr random 4
device, which does not depend on accessibility and correct mounting options
of the
.Xr devfs 4
node.
.It Li KERN_BOOTFILE
The full pathname of the file from which the kernel was loaded.
.It Li KERN_BOOTTIME
A
.Va struct timeval
structure is returned.
This structure contains the time that the system was booted.
.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 skew rate.
.It Li KERN_FILE
Return the entire file table.
The returned data consists of an array of
.Va struct xfile ,
whose size depends on the current number of such objects in the system.
.It Li KERN_HOSTID
Get or set the host ID.
.It Li KERN_HOSTUUID
Get or set the host's universally unique identifier (UUID).
.It Li KERN_HOSTNAME
Get or set the hostname.
.It Li KERN_IOV_MAX
The maximum accepted number of elements in an input-output vector (iovec),
see
.Xr readv 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_LOCKF
Returns the list of the file advisory locks currently known to kernel.
.It Li KERN_LOGSIGEXIT
Controls logging of process exit due to untrapped signals.
.It Li KERN_MAXFILES
The maximum number of files that may be open in the system.
.It Li KERN_MAXFILESPERPROC
The maximum number of files that may be open for a single process.
This limit only applies to processes with an effective uid of nonzero
at the time of the open request.
Files that have already been opened are not affected if the limit
or the effective uid is changed.
.It Li KERN_MAXPHYS
Specifies the maximum block I/O size.
Can be changed by the tunable
.Ev kern.maxphys .
.It Li KERN_MAXPROC
The maximum number of concurrent processes the system will allow.
.It Li KERN_MAXPROCPERUID
The maximum number of concurrent processes the system will allow
for a single effective uid.
This limit only applies to processes with an effective uid of nonzero
at the time of a fork request.
Processes that have already been started are not affected if the limit
is changed.
.It Li KERN_MAXVNODES
The maximum number of vnodes available on the system.
.It Li KERN_NGROUPS
The maximum number of supplemental groups.
.It Li KERN_NISDOMAINNAME
The name of the current YP/NIS domain.
.It Li KERN_OSRELDATE
The kernel release version in the format
.Ar M Ns Ar mm Ns Ar R Ns Ar xx ,
where
.Ar M
is the major version,
.Ar mm
is the two digit minor version,
.Ar R
is 0 if release branch, otherwise 1,
and
.Ar xx
is updated when the available APIs change.
.Pp
The userland release version is available from
.In osreldate.h ;
parse this file if you need to get the release version of
the currently installed userland.
.It Li KERN_OSRELEASE
The system release string.
.It Li KERN_OSREV
The system revision number.
.It Li KERN_OSTYPE
The system type string.
.It Li KERN_POSIX1
The version of
.St -p1003.1
with which the system
attempts to comply.
.It Li KERN_PROC
Return selected information about specific running processes.
.Pp
For the following names, an array of
.Va struct kinfo_proc
structures is returned,
whose size depends on the current number of such objects in the system.
.Bl -column "Third Level NameXXXXXX" "Fourth LevelXXXXXX" -offset indent
.It Sy Third Level Name Ta Sy Fourth Level
.It Dv KERN_PROC_ALL Ta None
.It Dv KERN_PROC_PID Ta A process ID
.It Dv KERN_PROC_PGRP Ta A process group
.It Dv KERN_PROC_SESSION Ta A session
.It Dv KERN_PROC_TTY Ta A tty device
.It Dv KERN_PROC_UID Ta An effective user ID
.It Dv KERN_PROC_RUID Ta A real user ID
.It Dv KERN_PROC_GID Ta An effective group ID
.It Dv KERN_PROC_RGID Ta A real group ID
.El
.Pp
For the following names, the miscellaneous information about the target
process, which is specified by the fourth level of the oid name,
is returned.
A process ID of
.Li \-1
specifies the current process.
.Bl -column "Third Level NameXXXXXX" "TypeXXXXXX" -offset indent
.It Sy Third Level Name Ta Sy Fourth Level
.It Dv KERN_PROC_ARGS Ta "Set of strings"
.It Dv KERN_PROC_PATHNAME Ta "String"
.It Dv KERN_PROC_KSTACK Ta "struct kinfo_stack []"
.It Dv KERN_PROC_VMMAP Ta "struct kinfo_vmentry []"
.It Dv KERN_PROC_FILEDESC Ta "struct kinfo_file []"
.It Dv KERN_PROC_GROUPS Ta "gid_t []"
.It Dv KERN_PROC_ENV Ta "Set of strings"
.It Dv KERN_PROC_AUXV Ta "Elf_Auxinfo []"
.It Dv KERN_PROC_RLIMIT Ta "struct rlimit"
.It Dv KERN_PROC_PS_STRINGS Ta "Pointer to struct ps_strings"
.It Dv KERN_PROC_UMASK Ta "Integer/short"
.It Dv KERN_PROC_OSREL Ta "Integer"
.It Dv KERN_PROC_SIGTRAMP Ta "struct kinfo_sigtramp"
.It Dv KERN_PROC_CWD Ta "struct kinfo_file"
.It Dv KERN_PROC_NFDS Ta "Integer"
.It Dv KERN_PROC_SIGFASTBLK Ta "Address"
.It Dv KERN_PROC_VM_LAYOUT Ta "struct kinfo_vm_layout"
.It Dv KERN_PROC_RLIMIT_USAGE Ta "rlim_t []"
.It Dv KERN_PROC_KQUEUE Ta "struct kinfo_knote []"
.El
.Pp
.Bl -tag -compact
.It Dv KERN_PROC_ARGS
The command line argument
array is returned in a flattened form, i.e., zero-terminated arguments
follow each other.
The total size of array is returned.
It is also possible for a process to set its own process title this way.
.It Dv KERN_PROC_PATHNAME
The path of the process' text file is returned.
.It Dv KERN_PROC_KSTACK
The in-kernel call stacks for the threads of the specified process.
.It Dv KERN_PROC_VMMAP
The description of the map entries for the process.
Also refer to
.Xr kinfo_getvmmap 3 .
.It Dv KERN_PROC_FILEDESC
The file descriptors for files opened in the specified process.
Also refer to
.Xr kinfo_getfile 3 .
.It Dv KERN_PROC_GROUPS
Groups associated with the process.
.It Dv KERN_PROC_ENV
The set of strings representing the environment of the specified process.
.Pp
Note that from the kernel point of view, environment exists only at the
time of
.Xr execve 2
system call.
This node method tries to reconstruct the environment from the known
breadcrumbs left in the process address space, but it is not guaranteed
to succeed or to represent the current value as maintained by the program.
.It Dv KERN_PROC_AUXV
The set of ELF auxv entries.
See the note above about environment, which is also applicable to auxv.
.It Dv KERN_PROC_RLIMIT
Additinal OID name element must be supplied, specifiing the resource name
as in
.Xr getrlimit 2 .
The call returns the given resource limit for the process.
.It Dv KERN_PROC_PS_STRINGS
Returns the location of the
.Vt ps_strings
structure at the time of the last call to
.Xr execve 2
in the specified process.
.It Dv KERN_PROC_UMASK
The current umask value, see
.Xr umask 2 .
.It Dv KERN_PROC_OSREL
The value of osrel for the process, that is the osrel the currently executed
image was compiled for.
Read from the note of the elf executable at
.Xr execve 2
time.
Might be modified by the process.
.It Dv KERN_PROC_SIGTRAMP
Structure describing the address range of the signal trampoline in the
process address space,
where, simplifying, the kernel passes control for signal delivery.
.It Dv KERN_PROC_CWD
Returns the current working directory for the process.
.It Dv KERN_PROC_NFDS
Returns the total number of opened file descriptors for the process.
.It Dv KERN_PROC_SIGFASTBLK
Returns the address of the
.Xr sigfastblock 2
location, if active.
.It Dv KERN_PROC_VM_LAYOUT
Fills a structure describing process virtual address space layout.
.It Dv KERN_PROC_RLIMIT_USAGE
Like
.Dv KERN_PROC_RLIMIT ,
but instead of the limit, returns the accounted resource usage.
If the MIB is of the form
.Li kern.proc.rlimit_usage\&. Ns Va pid ,
usage values for all resources are returned.
If the MIB is of the form
.Li kern.proc.rlimit_usage\&. Ns Va pid Ns \&. Ns Va resource ,
the usage value for the specified resource is returned.
For resources which do not have a meaningful current value,
.Li \-1
is returned.
.It Dv KERN_PROC_KQUEUE
Fills an array of structures describing events registered with
the specified kqueue.
The next two node's values are the
.Va pid
and
.Va kqfd ,
the process ID of the process, and the file descriptor of the kqueue
in that process, to query.
.El
.It Li KERN_PS_STRINGS
Reports the location of the process
.Vt ps_strings
structure after exec, for the ABI of the querying process.
.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 not be lowered.
.It Li KERN_USRSTACK
Reports the top of the main thread user stack for the current process.
.It Li KERN_VERSION
The system version string.
.El
.Ss 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 Second Level Name Ta Sy Type Ta Sy Changeable
.It Dv PF_ROUTE Ta routing messages Ta no
.It Dv PF_INET Ta IPv4 values Ta yes
.It Dv PF_INET6 Ta IPv6 values Ta yes
.El
.Bl -tag -width 6n
.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, sixth, and seventh level names are as follows:
.Bl -column -offset indent "Fifth Level" "Sixth Level" "Seventh Level"
.It Sy Fifth level Ta Sy Sixth Level Ta Sy Seventh Level
.It Dv NET_RT_FLAGS Ta rtflags Ta None
.It Dv NET_RT_DUMP Ta None Ta None or fib number
.It Dv NET_RT_IFLIST Ta 0 or if_index Ta None
.It Dv NET_RT_IFMALIST Ta 0 or if_index Ta None
.It Dv NET_RT_IFLISTL Ta 0 or if_index Ta None
.It Dv NET_RT_NHOPS Ta None Ta fib number
.El
.Pp
The
.Dv NET_RT_IFMALIST
name returns information about multicast group memberships on all interfaces
if 0 is specified, or for the interface specified by
.Va if_index .
.Pp
The
.Dv NET_RT_IFLISTL
is like
.Dv NET_RT_IFLIST ,
just returning message header structs with additional fields allowing the
interface to be extended without breaking binary compatibility.
The
.Dv NET_RT_IFLISTL
uses 'l' versions of the message header structures:
.Va struct if_msghdrl
and
.Va struct ifa_msghdrl .
.Pp
.Dv NET_RT_NHOPS
returns all nexthops for specified address family in given fib.
.It Li PF_INET
Get or set various global information about the IPv4
(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 ProtocolXX VariableXX TypeXX ChangeableXX
.It Sy Protocol Ta Sy Variable Ta Sy Type Ta Sy Changeable
.It icmp Ta bmcastecho Ta integer Ta yes
.It icmp Ta maskrepl Ta integer Ta yes
.It ip Ta forwarding Ta integer Ta yes
.It ip Ta redirect Ta integer Ta yes
.It ip Ta ttl Ta integer Ta yes
.It udp Ta checksum Ta integer Ta yes
.El
.Pp
The variables are as follows:
.Bl -tag -width 6n
.It Li icmp.bmcastecho
Returns 1 if an ICMP echo request to a broadcast or multicast address is
to be answered.
.It Li icmp.maskrepl
Returns 1 if ICMP network mask requests are to be answered.
.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 udp.checksum
Returns 1 when UDP checksums are being computed and checked.
Disabling UDP checksums is strongly discouraged.
.Pp
For variables net.inet.*.ipsec, please refer to
.Xr ipsec 4 .
.El
.It Li PF_INET6
Get or set various global information about the IPv6
(Internet Protocol version 6).
The third level name is the protocol.
The fourth level name is the variable name.
.Pp
For variables net.inet6.* please refer to
.Xr inet6 4 .
For variables net.inet6.*.ipsec6, please refer to
.Xr ipsec 4 .
.El
.Ss 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 Ta Sy Type Ta Sy Changeable
.It Dv USER_BC_BASE_MAX Ta integer Ta no
.It Dv USER_BC_DIM_MAX Ta integer Ta no
.It Dv USER_BC_SCALE_MAX Ta integer Ta no
.It Dv USER_BC_STRING_MAX Ta integer Ta no
.It Dv USER_COLL_WEIGHTS_MAX Ta integer Ta no
.It Dv USER_CS_PATH Ta string Ta no
.It Dv USER_EXPR_NEST_MAX Ta integer Ta no
.It Dv USER_LINE_MAX Ta integer Ta no
.It Dv USER_LOCALBASE Ta string Ta no
.It Dv USER_POSIX2_CHAR_TERM Ta integer Ta no
.It Dv USER_POSIX2_C_BIND Ta integer Ta no
.It Dv USER_POSIX2_C_DEV Ta integer Ta no
.It Dv USER_POSIX2_FORT_DEV Ta integer Ta no
.It Dv USER_POSIX2_FORT_RUN Ta integer Ta no
.It Dv USER_POSIX2_LOCALEDEF Ta integer Ta no
.It Dv USER_POSIX2_SW_DEV Ta integer Ta no
.It Dv USER_POSIX2_UPE Ta integer Ta no
.It Dv USER_POSIX2_VERSION Ta integer Ta no
.It Dv USER_RE_DUP_MAX Ta integer Ta no
.It Dv USER_STREAM_MAX Ta integer Ta no
.It Dv USER_TZNAME_MAX Ta integer Ta no
.El
.Bl -tag -width 6n
.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_LOCALBASE
Return the value of localbase that has been compiled into system utilities
that need to have access to resources provided by a port or package.
.It Li USER_POSIX2_CHAR_TERM
Return 1 if the system supports at least one terminal type capable of
all operations described in
.St -p1003.2 ,
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
.St -p1003.2
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.
.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
.Ss 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 Ta Sy Type Ta Sy Changeable
.It Dv VM_LOADAVG Ta struct loadavg Ta no
.It Dv VM_TOTAL Ta struct vmtotal Ta no
.It Dv VM_SWAPPING_ENABLED Ta integer Ta maybe
.It Dv VM_V_FREE_MIN Ta integer Ta yes
.It Dv VM_V_FREE_RESERVED Ta integer Ta yes
.It Dv VM_V_FREE_TARGET Ta integer Ta yes
.It Dv VM_V_INACTIVE_TARGET Ta integer Ta yes
.It Dv VM_V_PAGEOUT_FREE_MIN Ta integer Ta yes
.It Dv VM_OVERCOMMIT Ta integer Ta yes
.El
.Bl -tag -width 6n
.It Li VM_LOADAVG
Return the load average history.
The returned data consists of a
.Va struct loadavg .
.It Li VM_TOTAL
Return the system wide virtual memory statistics.
The returned data consists of a
.Va struct vmtotal .
.It Li VM_SWAPPING_ENABLED
1 if process swapping is enabled or 0 if disabled.
This variable is
permanently set to 0 if the kernel was built with swapping disabled.
.It Li VM_V_FREE_MIN
Minimum amount of memory (cache memory plus free memory)
required to be available before a process waiting on memory will be
awakened.
.It Li VM_V_FREE_RESERVED
Processes will awaken the pageout daemon and wait for memory if the
number of free and cached pages drops below this value.
.It Li VM_V_FREE_TARGET
The total amount of free memory (including cache memory) that the
pageout daemon tries to maintain.
.It Li VM_V_INACTIVE_TARGET
The desired number of inactive pages that the pageout daemon should
achieve when it runs.
Inactive pages can be quickly inserted into
process address space when needed.
.It Li VM_V_PAGEOUT_FREE_MIN
If the amount of free and cache memory falls below this value, the
pageout daemon will enter "memory conserving mode" to avoid deadlock.
.It Li VM_OVERCOMMIT
Overcommit behaviour, as described in
.Xr tuning 7 .
.El
.Sh RETURN VALUES
.Rv -std
.Sh FILES
.Bl -tag -width <netinet/icmpXvar.h> -compact
.It In sys/sysctl.h
definitions for top level identifiers, second level kernel and hardware
identifiers, and user level identifiers
.It In sys/socket.h
definitions for second level network identifiers
.It In sys/gmon.h
definitions for third level profiling identifiers
.It In vm/vm_param.h
definitions for second level virtual memory identifiers
.It In netinet/in.h
definitions for third level IPv4/IPv6 identifiers and
fourth level IPv4/v6 identifiers
.It In netinet/icmp_var.h
definitions for fourth level ICMP identifiers
.It In netinet/icmp6.h
definitions for fourth level ICMPv6 identifiers
.It In netinet/udp_var.h
definitions for fourth level UDP 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.
.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 ENOMEM
The smaller of either the length pointed to by
.Fa oldlenp
or the estimated size of the returned data exceeds the
system limit on locked memory.
.It Bq Er ENOMEM
Locking the buffer
.Fa oldp ,
or a portion of the buffer if the estimated size of the data
to be returned is smaller,
would cause the process to exceed its per-process locked memory limit.
.It Bq Er ENOTDIR
The
.Fa name
array specifies an intermediate rather than terminal name.
.It Bq Er EISDIR
The
.Fa name
array specifies a terminal name, but the actual name is not terminal.
.It Bq Er ENOENT
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.
.El
.Sh SEE ALSO
.Xr confstr 3 ,
.Xr kinfo_getproc 3 ,
.Xr kvm 3 ,
.Xr sysconf 3 ,
.Xr sysctl 8
.Sh HISTORY
The
.Fn sysctl
function first appeared in
.Bx 4.4 .