sysctl(3)

NAME

sysctl, sysctlbyname, sysctlnametomib - get or set system

information

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <sys/types.h>
#include <sys/sysctl.h>
int
sysctl(int   *name,   u_int   namelen,  void  *oldp,  size_t
*oldlenp, void *newp,
        size_t newlen);
int
sysctlbyname(const char *name, void *oldp, size_t  *oldlenp,
void *newp,
        size_t newlen);
int
sysctlnametomib(const char *name, int *mibp, size_t *sizep);

DESCRIPTION

The sysctl() function retrieves system information and al

lows processes
with appropriate privileges to set system information. The

information
available from sysctl() consists of integers, strings, and

tables.
Information may be retrieved and set from the command inter

face using the
sysctl(8) utility.

Unless explicitly noted below, 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 with

out blocking.
Calls to sysctl() are serialized to avoid deadlock.

The state is described using a ``Management Information

Base'' (MIB)
style name, listed in name, which is a namelen length array

of integers.

The 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 sysctl() function.

The information is copied into the buffer specified by oldp.

The size of
the buffer is given by the location specified by oldlenp be

fore 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 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 ENOMEM. If the old value is not de

sired, oldp and
oldlenp should be set to NULL.

The size of the available data can be determined by calling

sysctl() with
the NULL argument for oldp. The size of the available data

will be
returned in the location pointed to by 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.

To set a new value, newp is set to point to a buffer of

length newlen
from which the requested value is to be taken. If a new

value is not to
be set, newp should be set to NULL and newlen set to 0.

The sysctlnametomib() function accepts an ASCII representa

tion of the
name, looks up the integer name vector, and returns the nu

meric representation in the mib array pointed to by mibp. The number of

elements in
the mib array is given by the location specified by sizep

before the
call, and that location gives the number of entries copied

after a successful call. The resulting mib and size may be used in

subsequent
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 sysctl() function runs

in about a
third the time as the same request made via the

sysctlbyname() function).
The 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:

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);

}

The top level names are defined with a CTL_ prefix in and

are as follows.
The next and subsequent levels down are found in the include

files listed
here, and described in separate sections below.

Name Next level names

Description

CTL_DEBUG sys/sysctl.h Debugging
CTL_VFS sys/mount.h File sys

tem
CTL_HW sys/sysctl.h Generic

CPU, I/O
CTL_KERN sys/sysctl.h High ker

nel limits
CTL_MACHDEP sys/sysctl.h Machine

dependent
CTL_NET sys/socket.h Networking
CTL_USER sys/sysctl.h User-level
CTL_VM vm/vm_param.h Virtual

memory

For example, the following retrieves the maximum number of

processes
allowed in the system:

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);

To retrieve the standard search path for the system utili

ties:

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);

CTL_DEBUG

The debugging variables vary from system to system. A de

bugging variable
may be added or deleted without need to recompile sysctl()

to know about
it. Each time it runs, sysctl() gets the list of debugging

variables
from the kernel and displays their current values. The sys

tem defines
twenty (struct ctldebug) variables named debug0 through

debug19. They
are declared as separate variables so that they can be indi

vidually 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 ex

port the variable dospecialcheck as a debugging variable, the following

declaration
would be used:

int dospecialcheck = 1;
struct ctldebug debug5 = { "dospecialcheck", &dospe

cialcheck };

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 getvfsbyname(3) as an example of its use). The remain

ing second
level identifiers are the file system type number returned

by a statfs(2)
call or from VFS_CONF. The third level identifiers avail

able for each
file system are given in the header file that defines the

mount argument
structure for that file system.

CTL_HW

The string and integer information available for the CTL_HW

level is
detailed below. The changeable column shows whether a pro

cess with
appropriate privilege may change the value.

Second level name Type Changeable HW_MACHINE string no
HW_MODEL string no
HW_NCPU integer no
HW_BYTEORDER integer no
HW_PHYSMEM integer no
HW_USERMEM integer no
HW_PAGESIZE integer no
HW_FLOATINGPOINT integer no
HW_MACHINE_ARCH string no

HW_MACHINE

The machine class.

HW_MODEL

The machine model

HW_NCPU

The number of cpus.

HW_BYTEORDER

The byteorder (4,321, or 1,234).

HW_PHYSMEM

The bytes of physical memory.

HW_USERMEM

The bytes of non-kernel memory.

HW_PAGESIZE

The software page size.

HW_FLOATINGPOINT

Nonzero if the floating point support is in hard

ware.

HW_MACHINE_ARCH

The machine dependent architecture type.

CTL_KERN

The string and integer information available for the

CTL_KERN level is
detailed below. The changeable column shows whether a pro

cess 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 aver

age history,
and clock rate information.

Second level name Type

Changeable

KERN_ARGMAX integer no
KERN_BOOTFILE string yes
KERN_BOOTTIME struct timeval no
KERN_CLOCKRATE struct clockinfo no
KERN_FILE struct file no
KERN_HOSTID integer yes
KERN_HOSTNAME string yes
KERN_JOB_CONTROL integer no
KERN_MAXFILES integer yes
KERN_MAXFILESPERPROC integer yes
KERN_MAXPROC integer no
KERN_MAXPROCPERUID integer yes
KERN_MAXVNODES integer yes
KERN_NGROUPS integer no
KERN_NISDOMAINNAME string yes
KERN_OSRELDATE integer no
KERN_OSRELEASE string no
KERN_OSREV integer no
KERN_OSTYPE string no
KERN_POSIX1 integer no
KERN_PROC struct proc no
KERN_PROF node not

applicable
KERN_QUANTUM integer yes
KERN_SAVED_IDS integer no
KERN_SECURELVL integer

raise only
KERN_UPDATEINTERVAL integer no
KERN_VERSION string no
KERN_VNODE struct vnode no

KERN_ARGMAX

The maximum bytes of argument to execve(2).

KERN_BOOTFILE

The full pathname of the file from which the kernel

was loaded.

KERN_BOOTTIME

A struct timeval structure is returned. This struc

ture contains
the time that the system was booted.

KERN_CLOCKRATE

A 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.

KERN_FILE

Return the entire file table. The returned data

consists of a
single struct filehead followed by an array of

struct file, whose
size depends on the current number of such objects

in the system.

KERN_HOSTID

Get or set the host id.

KERN_HOSTNAME

Get or set the hostname.

KERN_JOB_CONTROL

Return 1 if job control is available on this system,

otherwise 0.

KERN_MAXFILES

The maximum number of files that may be open in the

system.

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.

KERN_MAXPROC

The maximum number of concurrent processes the sys

tem will allow.

KERN_MAXPROCPERUID

The maximum number of concurrent processes the sys

tem 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 af

fected if the
limit is changed.

KERN_MAXVNODES

The maximum number of vnodes available on the sys

tem.

KERN_NGROUPS

The maximum number of supplemental groups.

KERN_NISDOMAINNAME

The name of the current YP/NIS domain.

KERN_OSRELDATE

The kernel release version in the format MmmRxx,

where M is the
major version, mm is the two digit minor version, R

is 0 if
release branch, otherwise 1, and xx is updated when

the available
APIs change.

The userland release version is available from parse

this file if
you need to get the release version of the currently

installed
userland.

KERN_OSRELEASE

The system release string.

KERN_OSREV

The system revision string.

KERN_OSTYPE

The system type string.

KERN_POSIX1

The version of IEEE Std 1003.1 (``POSIX.1'') with

which the system attempts to comply.

KERN_PROC

Return selected information about specific running

processes.

For the following names, an array of pairs of struct

proc followed by corresponding struct eproc structures is

returned, whose
size depends on the current number of such objects

in the system.

Third level name Fourth level is:
KERN_PROC_ALL None
KERN_PROC_PID A process ID
KERN_PROC_PGRP A process group
KERN_PROC_TTY A tty device
KERN_PROC_UID A user ID
KERN_PROC_RUID A real user ID

If the third level name is KERN_PROC_ARGS then 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. If the third level name is
KERN_PROC_PATHNAME, the path of the process' text

file is stored.
For KERN_PROC_PATHNAME, a process ID of -1 implies

the current
process.

Third level name Fourth level is: KERN_PROC_ARGS A process ID
KERN_PROC_PATHNAME A process ID

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 ENOENT. The third

level names
for the string and integer profiling information is

detailed
below. The changeable column shows whether a pro

cess with appropriate privilege may change the value.

Third level name Type

Changeable

GPROF_STATE integer

yes
GPROF_COUNT u_short[]

yes
GPROF_FROMS u_short[]

yes
GPROF_TOS struct tostruct

yes
GPROF_GMONPARAM struct gmonparam

no

The variables are as follows:

GPROF_STATE

Returns GMON_PROF_ON or GMON_PROF_OFF to

show that profiling is running or stopped.

GPROF_COUNT

Array of statistical program counter counts.

GPROF_FROMS

Array indexed by program counter of call

from points.

GPROF_TOS

Array of struct tostruct describing destina

tion of calls
and their counts.

GPROF_GMONPARAM

Structure giving the sizes of the above ar

rays.

KERN_QUANTUM

The maximum period of time, in microseconds, for

which a process
is allowed to run without being preempted if other

processes are
in the run queue.

KERN_SAVED_IDS

Returns 1 if saved set-group and saved set-user ID

is available.

KERN_SECURELVL

The system security level. This level may be raised

by processes
with appropriate privilege. It may not be lowered.

KERN_VERSION

The system version string.

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 cur

rent number of
such objects in the system. Each element of the ar

ray contains
the kernel address of a vnode struct vnode * fol

lowed by the
vnode itself struct vnode.

CTL_MACHDEP

The set of variables defined is architecture dependent. The

following
variables are defined for the i386 architecture.

Second level name Type Changeable CPU_CONSDEV dev_t no
CPU_ADJKERNTZ int yes
CPU_DISRTCSET int yes
CPU_BOOTINFO struct bootinfo no
CPU_WALLCLOCK int yes

CTL_NET

The string and integer information available for the CTL_NET

level is
detailed below. The changeable column shows whether a pro

cess with
appropriate privilege may change the value.

Second level name Type

Changeable

PF_ROUTE routing messages no
PF_INET IPv4 values yes
PF_INET6 IPv6 values yes

PF_ROUTE

Return the entire routing table or a subset of it.

The data is
returned as a sequence of routing messages (see

route(4) for the
header file, format and meaning). The length of

each message is
contained in the message header.

The third level name is a protocol number, which is

currently
always 0. The fourth level name is an address fami

ly, which may
be set to 0 to select all address families. The

fifth and sixth
level names are as follows:

Fifth level name Sixth level is: NET_RT_FLAGS rtflags
NET_RT_DUMP None
NET_RT_IFLIST 0 or if_index
NET_RT_IFMALIST 0 or if_index

The NET_RT_IFMALIST name returns information about

multicast
group memberships on all interfaces if 0 is speci

fied, or for the
interface specified by if_index.

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 cur

rently defined
protocols and names are:

Protocol Variable Type Changeable icmp bmcastecho integer yes
icmp maskrepl integer yes
ip forwarding integer yes
ip redirect integer yes
ip ttl integer yes
udp checksum integer yes

The variables are as follows:

icmp.bmcastecho

Returns 1 if an ICMP echo request to a

broadcast or multicast address is to be answered.

icmp.maskrepl

Returns 1 if ICMP network mask requests are

to be
answered.

ip.forwarding

Returns 1 when IP forwarding is enabled for

the host,
meaning that the host is acting as a router.

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.

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.

udp.checksum

Returns 1 when UDP checksums are being com

puted and
checked. Disabling UDP checksums is strong

ly discouraged.

For variables net.inet.*.ipsec, please refer

to ipsec(4).

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.

For variables net.inet6.* please refer to inet6(4).

For variables net.inet6.*.ipsec6, please refer to ipsec(4).

CTL_USER

The string and integer information available for the CTL_US

ER level is
detailed below. The changeable column shows whether a pro

cess with
appropriate privilege may change the value.

Second level name Type Changeable USER_BC_BASE_MAX integer no
USER_BC_DIM_MAX integer no
USER_BC_SCALE_MAX integer no
USER_BC_STRING_MAX integer no
USER_COLL_WEIGHTS_MAX integer no
USER_CS_PATH string no
USER_EXPR_NEST_MAX integer no
USER_LINE_MAX integer no
USER_POSIX2_CHAR_TERM integer no
USER_POSIX2_C_BIND integer no
USER_POSIX2_C_DEV integer no
USER_POSIX2_FORT_DEV integer no
USER_POSIX2_FORT_RUN integer no
USER_POSIX2_LOCALEDEF integer no
USER_POSIX2_SW_DEV integer no
USER_POSIX2_UPE integer no
USER_POSIX2_VERSION integer no
USER_RE_DUP_MAX integer no
USER_STREAM_MAX integer no
USER_TZNAME_MAX integer no

USER_BC_BASE_MAX

The maximum ibase/obase values in the bc(1) utility.

USER_BC_DIM_MAX

The maximum array size in the bc(1) utility.

USER_BC_SCALE_MAX

The maximum scale value in the bc(1) utility.

USER_BC_STRING_MAX

The maximum string length in the bc(1) utility.

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 defi

nition file.

USER_CS_PATH

Return a value for the PATH environment variable

that finds all
the standard utilities.

USER_EXPR_NEST_MAX

The maximum number of expressions that can be nested

within
parenthesis by the expr(1) utility.

USER_LINE_MAX

The maximum length in bytes of a text-processing

utility's input
line.

USER_POSIX2_CHAR_TERM

Return 1 if the system supports at least one termi

nal type capable of all operations described in IEEE Std 1003.2

(``POSIX.2''),
otherwise 0.

USER_POSIX2_C_BIND

Return 1 if the system's C-language development fa

cilities support the C-Language Bindings Option, otherwise 0.

USER_POSIX2_C_DEV

Return 1 if the system supports the C-Language De

velopment Utilities Option, otherwise 0.

USER_POSIX2_FORT_DEV

Return 1 if the system supports the FORTRAN Develop

ment Utilities
Option, otherwise 0.

USER_POSIX2_FORT_RUN

Return 1 if the system supports the FORTRAN Runtime

Utilities
Option, otherwise 0.

USER_POSIX2_LOCALEDEF

Return 1 if the system supports the creation of lo

cales, otherwise 0.

USER_POSIX2_SW_DEV

Return 1 if the system supports the Software Devel

opment Utilities Option, otherwise 0.

USER_POSIX2_UPE

Return 1 if the system supports the User Portability

Utilities
Option, otherwise 0.

USER_POSIX2_VERSION

The version of IEEE Std 1003.2 (``POSIX.2'') with

which the system attempts to comply.

USER_RE_DUP_MAX

The maximum number of repeated occurrences of a reg

ular expression permitted when using interval notation.

USER_STREAM_MAX

The minimum maximum number of streams that a process

may have
open at any one time.

USER_TZNAME_MAX

The minimum maximum number of types supported for

the name of a
timezone.

CTL_VM

The string and integer information available for the CTL_VM

level is
detailed below. The changeable column shows whether a pro

cess with
appropriate privilege may change the value.

Second level name Type

Changeable

VM_LOADAVG struct loadavg no
VM_METER struct vmtotal no
VM_PAGEOUT_ALGORITHM integer yes
VM_SWAPPING_ENABLED integer maybe
VM_V_CACHE_MAX integer yes
VM_V_CACHE_MIN integer yes
VM_V_FREE_MIN integer yes
VM_V_FREE_RESERVED integer yes
VM_V_FREE_TARGET integer yes
VM_V_INACTIVE_TARGET integer yes
VM_V_PAGEOUT_FREE_MIN integer yes

VM_LOADAVG

Return the load average history. The returned data

consists of a
struct loadavg.

VM_METER

Return the system wide virtual memory statistics.

The returned
data consists of a struct vmtotal.

VM_PAGEOUT_ALGORITHM

0 if the statistics-based page management algorithm

is in use or
1 if the near-LRU algorithm is in use.

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.

VM_V_CACHE_MAX

Maximum desired size of the cache queue.

VM_V_CACHE_MIN

Minimum desired size of the cache queue. If the

cache queue size
falls very far below this value, the pageout daemon

is awakened.

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.

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.

VM_V_FREE_TARGET

The total amount of free memory (including cache

memory) that the
pageout daemon tries to maintain.

VM_V_INACTIVE_TARGET

The desired number of inactive pages that the page

out daemon
should achieve when it runs. Inactive pages can be

quickly
inserted into process address space when needed.

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.

RETURN VALUES

The function returns the value 0 if successful; otherwise

the value -1 is
returned and the global variable errno is set to indicate

the error.

FILES

definitions for top level identifiers,

second level
kernel and hardware identifiers, and

user level
identifiers
definitions for second level network

identifiers
definitions for third level profiling

identifiers
definitions for second level virtual

memory identifiers
definitions for third level IPv4/IPv6

identifiers
and fourth level IPv4/v6 identifiers
definitions for fourth level ICMP

identifiers
definitions for fourth level ICMPv6

identifiers
definitions for fourth level UDP iden

tifiers

ERRORS

The following errors may be reported:

[EFAULT] The buffer name, oldp, newp, or length

pointer oldlenp

contains an invalid address.

[EINVAL] The name array is less than two or

greater than

CTL_MAXNAME.

[EINVAL] A non-null newp is given and its speci

fied length in

newlen is too large or too small.

[ENOMEM] The length pointed to by oldlenp is too

short to hold

the requested value.

[ENOMEM] The smaller of either the length pointed

to by oldlenp

or the estimated size of the returned da

ta exceeds the
system limit on locked memory.

[ENOMEM] Locking the buffer oldp, or a portion of

the buffer if

the estimated size of the data to be re

turned is
smaller, would cause the process to ex

ceed its perprocess locked memory limit.

[ENOTDIR] The name array specifies an intermediate

rather than

terminal name.

[EISDIR] The name array specifies a terminal name,

but the

actual name is not terminal.

[ENOENT] The name array specifies a value that is

unknown.

[EPERM] An attempt is made to set a read-only

value.

[EPERM] A process without appropriate privilege

attempts to

set a value.

SEE ALSO

sysconf(3), sysctl(8)

HISTORY

The sysctl() function first appeared in 4.4BSD.

BSD January 23, 2001

BSD