SYSCTL(3)

NAME
sysctl, sysctlbyname, sysctlnametomib - get or set system information

LIBRARY
libc

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 | int32_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 p1003.1 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 p1003.2, 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 p1003.2 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

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.