sysctlbyname(3)

NAME

sysctl, sysctlbyname, sysctlnametomib – get or set system information

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <sys/sysctl.h>

int

sysctl(const int *name, u_int namelen, void *oldp, size_t *oldlenp, const void *newp, size_t newlen);

int

sysctlbyname(const char *name, void *oldp, size_t *oldlenp, const 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	In sys/sysctl.h	Debugging
CTL_VFS	In sys/mount.h	File system
CTL_HW	In sys/sysctl.h	Generic CPU, I/O
CTL_KERN	In sys/sysctl.h	High kernel limits
CTL_MACHDEP	In sys/sysctl.h	Machine dependent
CTL_NET	In sys/socket.h	Networking
CTL_USER	In sys/sysctl.h	User-level
CTL_VM	In 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_FLOATINGPT	integer	no
HW_MACHINE_ARCH	string	no
HW_REALMEM	integer	no
HW_AVAILPAGES	integer	no

HW_MACHINE: The machine class.
HW_MODEL: The machine model
HW_NCPU: The number of cpus.
HW_BYTEORDER: The byteorder (4321 or 1234).
HW_PHYSMEM: Amount of physical memory (in bytes), minus the amount used by the kernel, pre-loaded modules, and (on x86) the dcons buffer.
HW_USERMEM: Amount of memory (in bytes) which is not wired.
HW_PAGESIZE: The software page size.
HW_FLOATINGPT: Nonzero if the floating point support is in hardware.
HW_MACHINE_ARCH: The machine dependent architecture type.
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.
HW_AVAILPAGES: The same value as HW_PHYSMEM, measured in pages rather than bytes.

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_ARND	byte buffer	no
KERN_BOOTFILE	string	yes
KERN_BOOTTIME	struct timeval	no
KERN_CLOCKRATE	struct clockinfo	no
KERN_FILE	struct xfile	no
KERN_HOSTID	integer	yes
KERN_HOSTUUID	string	yes
KERN_HOSTNAME	string	yes
KERN_IOV_MAX	integer	no
KERN_JOB_CONTROL	integer	no
KERN_LOCKF	struct kinfo_lockf	no
KERN_LOGSIGEXIT	integer	yes
KERN_MAXFILES	integer	yes
KERN_MAXFILESPERPROC	integer	yes
KERN_MAXPHYS	integer	no
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	node	not applicable
KERN_PS_STRINGS	integer	no
KERN_SAVED_IDS	integer	no
KERN_SECURELVL	integer	raise only
KERN_UPDATEINTERVAL	integer	no
KERN_USRSTACK	integer	no
KERN_VERSION	string	no

KERN_ARGMAX

The maximum bytes of argument to execve(2).

KERN_ARND

arc4rand(9) Fills the buffer with random bytes from in-kernel random data generator. This is an alternative interface for read(2) of random(4) device, which does not depend on accessibility and correct mounting options of the devfs(4) node.

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 an array of struct xfile, whose size depends on the current number of such objects in the system.

KERN_HOSTID

Get or set the host ID.

KERN_HOSTUUID

Get or set the host's universally unique identifier (UUID).

KERN_HOSTNAME

Get or set the hostname.

KERN_IOV_MAX

The maximum accepted number of elements in an input-output vector (iovec), see readv(2) and writev(2).

KERN_JOB_CONTROL

Return 1 if job control is available on this system, otherwise 0.

KERN_LOCKF

Returns the list of the file advisory locks currently known to kernel.

KERN_LOGSIGEXIT

Controls logging of process exit due to untrapped signals.

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_MAXPHYS

Specifies the maximum block I/O size. Can be changed by the tunable kern.maxphys.

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 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 ⟨osreldate.h⟩; 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 number.

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 struct kinfo_proc structures is returned, whose size depends on the current number of such objects in the system.

Third Level Name	Fourth Level
KERN_PROC_ALL	None
KERN_PROC_PID	A process ID
KERN_PROC_PGRP	A process group
KERN_PROC_SESSION	A session
KERN_PROC_TTY	A tty device
KERN_PROC_UID	effective user ID
KERN_PROC_RUID	A real user ID
KERN_PROC_GID	effective group ID
KERN_PROC_RGID	A real group ID

KERN_PS_STRINGS

Reports the location of the process ps_strings structure after exec, for the ABI of the querying process.

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_USRSTACK

Reports the top of the main thread user stack for the current process.

KERN_VERSION

The system version string.

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, sixth, and seventh level names are as follows:

Fifth level	Sixth Level	Seventh Level
NET_RT_FLAGS	rtflags	None
NET_RT_DUMP	None	None or fib number
NET_RT_IFLIST	0 or if_index	None
NET_RT_IFMALIST	0 or if_index	None
NET_RT_IFLISTL	0 or if_index	None
NET_RT_NHOPS	None	fib number

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

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_LOCALBASE	string	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_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.
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_TOTAL	struct vmtotal	no
VM_SWAPPING_ENABLED	integer	maybe
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_OVERCOMMIT	integer	yes

VM_LOADAVG: Return the load average history. The returned data consists of a struct loadavg.
VM_TOTAL: Return the system wide virtual memory statistics. The returned data consists of a struct vmtotal.
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_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.
VM_OVERCOMMIT: Overcommit behaviour, as described in tuning(7).

RETURN VALUES

The sysctl() 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

In sys/sysctl.h: definitions for top level identifiers, second level kernel and hardware identifiers, and user level identifiers
In sys/socket.h: definitions for second level network identifiers
In sys/gmon.h: definitions for third level profiling identifiers
In vm/vm_param.h: definitions for second level virtual memory identifiers
In netinet/in.h: definitions for third level IPv4/IPv6 identifiers and fourth level IPv4/v6 identifiers
In netinet/icmp_var.h: definitions for fourth level ICMP identifiers
In netinet/icmp6.h: definitions for fourth level ICMPv6 identifiers
In 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.
[ENOMEM]: The smaller of either the length pointed to by oldlenp or the estimated size of the returned data 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 returned is smaller, would cause the process to exceed its per-process 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.
[ECAPMODE]: The process is in capability mode and the variable is not accessible in capability mode.

HISTORY

The sysctl() function first appeared in 4.4BSD.

sysctlbyname(3)

NAME

LIBRARY

SYNOPSIS

DESCRIPTION

CTL_DEBUG

CTL_VFS

CTL_HW

CTL_KERN

CTL_NET

CTL_USER

CTL_VM

RETURN VALUES

FILES

ERRORS

SEE ALSO

HISTORY

History