SYSCTL(3) BSD Library Functions Manual 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 allows 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 interface 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 without 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 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 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 desired, oldp and
oldlenp should be set to NULL.
The size of the available data can be determined by calling sysctl() with
a NULL parameter 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 representation of the
name, looks up the integer name vector, and returns the numeric represen‐
tation 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 suc‐
cessful 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 repeat‐
edly 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 infor‐
mation 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 <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.
Name Next level names Description
CTL_DEBUG sys/sysctl.h Debugging
CTL_VFS sys/mount.h Filesystem
CTL_HW sys/sysctl.h Generic CPU, I/O
CTL_KERN sys/sysctl.h High kernel 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 utilities:
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 debugging 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 system defines
twenty (struct ctldebug) variables named debug0 through debug19. They
are declared as separate variables so that they can be individually ini‐
tialized at the location of their associated variable. The loader pre‐
vents multiple use of the same variable by issuing errors if a variable
is initialized in more than one place. For example, to export the vari‐
able dospecialcheck as a debugging variable, the following declaration
would be used:
int dospecialcheck = 1;
struct ctldebug debug5 = { "dospecialcheck", &dospecialcheck };
CTL_VFS
A distinguished second level name, VFS_GENERIC, is used to get general
information about all filesystems. One of its third level identifiers is
VFS_MAXTYPENUM that gives the highest valid filesystem type number. Its
other third level identifier is VFS_CONF that returns configuration
information about the filesystem type given as a fourth level identifier
(see getvfsbyname(3) as an example of its use). The remaining second
level identifiers are the filesystem type number returned by a 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.
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.
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_SENSORS node not applicable
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 hardware.
HW_MACHINE_ARCH
The machine dependent architecture type.
HW_SENSORS
Third level comprises an array of struct sensordev structures
containing information about devices that may attach hardware
monitoring sensors.
Third, fourth and fifth levels together comprise an array of
struct sensor structures containing snapshot readings of hardware
monitoring sensors. In such usage, third level indicates the
numerical representation of the sensor device name to which the
sensor is attached (device's xname and number shall be matched
with the help of struct sensordev structure above), fourth level
indicates sensor type and fifth level is an ordinal sensor number
(unique to the specified sensor type on the specified sensor
device).
The sensordev and sensor structures and sensor_type enumeration
are defined in <sys/sensors.h>.
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.
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_MAXPOSIXLOCKSPERUID 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 structure contains
the time that the system was booted.
KERN_CLOCKRATE
A struct clockinfo structure is returned. This structure con‐
tains the clock, statistics clock and profiling clock frequen‐
cies, 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 effec‐
tive uid is changed.
KERN_MAXPROC
The maximum number of concurrent processes the system will allow.
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.
KERN_MAXVNODES
The maximum number of vnodes available on the system.
KERN_NGROUPS
The maximum number of supplemental groups.
KERN_NISDOMAINNAME
The name of the current YP/NIS domain.
KERN_OSRELDATE
The system release date in YYYYMM format (January 1996 is encoded
as 199601).
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 the entire process table, or a subset of it. An array of
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:
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
Adding the flag KERN_PROC_FLAG_LWP to the third level name sig‐
nals that information about all light weight processes of the
selected processes should be returned.
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 process with appro‐
priate 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 pro‐
filing 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 destination of calls
and their counts.
GPROF_GMONPARAM
Structure giving the sizes of the above arrays.
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 nec‐
essarily 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 struct vnode * followed 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 process 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 family, 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 None
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:
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 mul‐
ticast 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 nor‐
mal transport protocols, not to ICMP.
udp.checksum
Returns 1 when UDP checksums are being computed and
checked. Disabling UDP checksums is strongly discour‐
aged.
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 vari‐
ables net.inet6.*.ipsec6, please refer to ipsec(4).
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.
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 definition 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 terminal type capa‐
ble 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 facilities sup‐
port the C-Language Bindings Option, otherwise 0.
USER_POSIX2_C_DEV
Return 1 if the system supports the C-Language Development Utili‐
ties Option, otherwise 0.
USER_POSIX2_FORT_DEV
Return 1 if the system supports the FORTRAN Development 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 locales, other‐
wise 0.
USER_POSIX2_SW_DEV
Return 1 if the system supports the Software Development Utili‐
ties 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 regular expres‐
sion 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 process 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 awak‐
ened.
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 pageout 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
Upon successful completion, the value 0 is returned; otherwise the
value -1 is returned and the global variable errno is set to indicate the
error.
FILES
<sys/sysctl.h> definitions for top level identifiers, second level
kernel and hardware identifiers, and user level
identifiers
<sys/socket.h> definitions for second level network identifiers
<sys/gmon.h> definitions for third level profiling identifiers
<vm/vm_param.h> definitions for second level virtual memory identi‐
fiers
<netinet/in.h> definitions for third level IPv4/IPv6 identifiers
and fourth level IPv4/v6 identifiers
<netinet/icmp_var.h> definitions for fourth level ICMP identifiers
<netinet/icmp6.h> definitions for fourth level ICMPv6 identifiers
<netinet/udp_var.h> definitions for fourth level UDP identifiers
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 specified length in
newlen is too large or too small.
[ENOMEM] The length pointed to by oldlenp is too short to hold
the requested value.
[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 ALSOsysconf(3), sysctl(8)HISTORY
The sysctl() function first appeared in 4.4BSD.
BSD January 23, 2001 BSD
