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 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 representation of the name, looks up the integer name vector, and returns the numeric 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 <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 File system

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 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 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 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 remaining second level identifiers are the file system type number returned by a 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.

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_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.

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_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 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 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 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. 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

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.

Third level name

Fourth level is:

KERN_PROC_ARGS

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 process 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 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 necessarily a consistent snapshot of the system. The returned data consists of an array whose size depends on the current number of such objects in the system. Each element of the array contains the kernel address of a vnode 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

0 or 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 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 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 computed and checked. Disabling UDP checksums is strongly 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_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 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 facilities support the C-Language Bindings Option, otherwise 0.

USER_POSIX2_C_DEV

Return 1 if the system supports the C-Language Development Utilities 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, otherwise 0.

USER_POSIX2_SW_DEV

Return 1 if the system supports the Software Development 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 regular 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 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 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 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.

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.

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 identifiers

<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

See Also

sysconf(3) , sysctl(8)

History

The sysctl() function first appeared in 4.4BSD.

Table of Contents

• Name
• Library
• Synopsis
• Description
• Return Values
• Errors
• Files
• See Also
• History