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
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