SYSCTL(3) 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
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 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 sys/resources.h Virtual memory (struct
loadavg)
For example, the following retrieves the maximum number of processes
allowed in the system:
int maxproc;
size_t len = sizeof(maxproc);
sysctlbyname("kern.maxproc", &maxproc, &len, NULL, 0);
To retrieve the standard search path for the system utilities:
char *p;
size_t len;
sysctlbyname("user.cs_path", NULL, &len, NULL, 0);
p = malloc(len);
sysctlbyname("user.cs_path", p, &len, NULL, 0);
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.
Name Type Changeable
hw.activecpu int32_t no
hw.byteorder int32_t no
hw.cacheconfig uint64_t[] no
hw.cachelinesize int64_t no
hw.cachesize uint64_t[] no
hw.cpu64bit_capable int32_t no
hw.cpufamily uint32_t no
hw.cpufrequency int64_t no
hw.cpufrequency_max int64_t no
hw.cpufrequency_min int64_t no
hw.cpusubtype int32_t no
hw.cputhreadtype int32_t no
hw.cputype int32_t no
hw.l1dcachesize int64_t no
hw.l1icachesize int64_t no
hw.l2cachesize int64_t no
hw.l3cachesize int64_t no
hw.logicalcpu int32_t no
hw.logicalcpu_max int32_t no
hw.machine char[] no
hw.memsize int64_t no
hw.model char[] no
hw.ncpu int32_t no
hw.packages int32_t no
hw.pagesize int64_t no
hw.physicalcpu int32_t no
hw.physicalcpu_max int32_t no
hw.tbfrequency int64_t no
hw.byteorder
The byte order (4321 or 1234).
hw.model
The machine model.
hw.ncpu
The number of cpus. This attribute is deprecated and it is
recommended that hw.logicalcpu, hw.logicalcpu_max,
hw.physicalcpu, or hw.physicalcpu_max be used instead.
hw.logicalcpu
The number of logical processors available in the current power
management mode.
hw.logicalcpu_max
The maximum number of logical processors that could be available
this boot.
hw.physicalcpu
The number of physical processors available in the current power
management mode.
hw.physicalcpu_max
The maximum number of physical processors that could be available
this boot.
hw.pagesize
The software page size in 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.
Name Type Changeable
kern.argmax int32_t no
kern.bootargs char[] no
kern.boottime struct timeval no
kern.check_openevt int32_t yes
kern.clockrate struct clockinfo no
kern.coredump int32_t yes
kern.corefile char[] yes
kern.flush_cache_on_write int32_t yes
kern.hostid int32_t yes
kern.hostname char[] yes
kern.job_control int32_t no
kern.maxfiles int32_t yes
kern.maxfilesperproc int32_t yes
kern.maxnbuf int32_t yes
kern.maxproc int32_t yes
kern.maxprocperuid int32_t yes
kern.maxvnodes int32_t yes
kern.msgbuf int32_t yes
kern.nbuf int32_t no
kern.netboot int32_t no
kern.ngroups int32_t no
kern.nisdomainname char[] yes
kern.num_files int32_t no
kern.num_tasks int32_t no
kern.num_taskthreads int32_t no
kern.num_threads int32_t no
kern.num_vnodes int32_t no
kern.nx int32_t yes
kern.osrelease char[] no
kern.osrevision int32_t no
kern.ostype char[] no
kern.osversion char[] yes
kern.posix1version int32_t no
kern.procname char[] yes
kern.safeboot int32_t no
kern.saved_ids int32_t no
kern.secure_kernel int32_t no
kern.securelevel int32_t yes
kern.singleuser int32_t no
kern.sleeptime struct timeval no
kern.slide int32_t no
kern.stack_depth_max int32_t no
kern.stack_size int32_t no
kern.sugid_coredump int32_t yes
kern.sugid_scripts int32_t yes
kern.symfile char[] no
kern.usrstack int32_t no
kern.usrstack64 int64_t no
kern.uuid char[] no
kern.version char[] no
kern.waketime struct timeval no
kern.argmax
The maximum bytes of argument to execve(2).
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.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.osrelease
The system release string.
kern.osrevision
The system revision number.
kern.ostype
The system type string.
kern.posix1version
The version of IEEE Std 1003.1 (“POSIX.1”) with which the system
attempts to comply.
kern.saved_ids
Returns 1 if saved set-group and saved set-user ID is available.
kern.securelevel
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.
CTL_MACHDEP
The set of variables defined is architecture dependent. The following
variables are defined for the i386 architecture.
Name Type Changeable
machdep.cpu.address_bits.physical int32_t no
machdep.cpu.address_bits.virtual int32_t no
machdep.cpu.brand int32_t no
machdep.cpu.brand_string char[] no
machdep.cpu.cache.L2_associativity int32_t no
machdep.cpu.cache.linesize int32_t no
machdep.cpu.cache.size int32_t no
machdep.cpu.core_count int32_t no
machdep.cpu.cores_per_package int32_t no
machdep.cpu.extfamily int32_t no
machdep.cpu.extfeature_bits int64_t no
machdep.cpu.extfeatures char[] no
machdep.cpu.extmodel int32_t no
machdep.cpu.family int32_t no
machdep.cpu.feature_bits int64_t no
machdep.cpu.features char[] no
machdep.cpu.leaf7_feature_bits uint32_t no
machdep.cpu.leaf7_features char[] no
machdep.cpu.logical_per_package int32_t no
machdep.cpu.max_basic uint32_t no
machdep.cpu.max_ext uint32_t no
machdep.cpu.microcode_version int32_t no
machdep.cpu.model int32_t no
machdep.cpu.processor_flag int32_t no
machdep.cpu.signature int32_t no
machdep.cpu.stepping int32_t no
machdep.cpu.thread_count int32_t no
machdep.cpu.tlb.data.large int32_t no
machdep.cpu.tlb.data.large_level1 int32_t no
machdep.cpu.tlb.data.small int32_t no
machdep.cpu.tlb.data.small_level1 int32_t no
machdep.cpu.tlb.inst.large int32_t no
machdep.cpu.tlb.inst.small int32_t no
machdep.cpu.tlb.shared int32_t no
machdep.cpu.ucupdate int32_t yes
machdep.cpu.vendor char[] no
machdep.cpu.xsave.extended_state uint32_t no
machdep.tsc.deep_idle_rebase uint32_t yes
machdep.tsc.frequency int64_t no
machdep.tsc.nanotime.generation uint32_t no
machdep.tsc.nanotime.shift uint32_t no
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
The NET_RT_IFMALIST name returns information about multicast
group memberships on all interfaces if 0 is specified, 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 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.
Name Type Changeable
user.bc_base_max int32_t no
user.bc_dim_max int32_t no
user.bc_scale_max int32_t no
user.bc_string_max int32_t no
user.coll_weights_max int32_t no
user.cs_path char[] no
user.expr_nest_max int32_t no
user.line_max int32_t no
user.posix2_c_bind int32_t no
user.posix2_c_dev int32_t no
user.posix2_char_term int32_t no
user.posix2_fort_dev int32_t no
user.posix2_fort_run int32_t no
user.posix2_localedef int32_t no
user.posix2_sw_dev int32_t no
user.posix2_upe int32_t no
user.posix2_version int32_t no
user.re_dup_max int32_t no
user.stream_max int32_t no
user.tzname_max int32_t 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_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_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_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.
Name Type Changeable
vm.loadavg struct loadavg
no
vm.swapusage struct xsw_usage
no
vm.loadavg
Return the load average history. The returned data consists of a
struct loadavg.
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
<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.
[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.
SEE ALSO
confstr(3), sysconf(3), sysctl(8)
HISTORY
The sysctl() function first appeared in 4.4BSD.
macOS 15.2 May 17, 2013 macOS 15.2