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SYSCONF(3) Library Functions Manual SYSCONF(3)

sysconf — get configurable system variables

library “libc”

#include <unistd.h>

long
sysconf(int name);

This interface is defined by IEEE Std 1003.1-1988 (“POSIX.1”). A far more complete interface is available using sysctl(3).

The () function provides a method for applications to determine the current value of a configurable system limit or option variable. The name argument specifies the system variable to be queried. Symbolic constants for each name value are found in the include file <unistd.h>.

The available values are as follows:

The maximum bytes of argument to execve(2).
The maximum ibase/obase values in the bc(1) utility.
The maximum array size in the bc(1) utility.
The maximum scale value in the bc(1) utility.
The maximum string length in the bc(1) utility.
The maximum number of simultaneous processes per user id.
The frequency of the statistics clock in ticks per second.
The maximum number of weights that can be assigned to any entry of the LC_COLLATE order keyword in the locale definition file.
The maximum number of expressions that can be nested within parenthesis by the expr(1) utility.
The maximum number of elements in the I/O vector used by readv(2), writev(2), recvmsg(2), and sendmsg(2).
Return 1 if job control is available on this system, otherwise -1.
Returns the L1 cache line size.
The maximum length in bytes of a text-processing utility's input line.
Whether Message Passing option is supported.
The maximum number of open message queue descriptors per process.
The maximum number of message priorities supported by the implementation.
The maximum number of supplemental groups.
The number of processors configured.
The number of processors online.
The maximum number of open files per user id.
The size of a system page in bytes.
Equivalent to _SC_PAGESIZE.
The maximum number of repeated occurrences of a regular expression permitted when using interval notation.
Return 1 if the system supports regular expression handling.
Return 1 if saved set-group and saved set-user ID is available, otherwise -1.
Return 1 if the system supports the POSIX shell.
The minimum maximum number of streams that a process may have open at any one time.
The minimum maximum number of types supported for the name of a timezone.
The version of IEEE Std 1003.1 (“POSIX.1”) with which the system attempts to comply.
Return 1 if the system supports the X/Open Portability Guide Issue 4, Version 2 (“XPG4.2”) Shared Memory Feature for both compilation and execution, or 0 if only compilation support is guaranteed.
Return 1 if the system's C-language development facilities support the C-Language Bindings Option, otherwise -1.
Return 1 if the system supports the C-Language Development Utilities Option, otherwise -1.
Return 1 if the system supports at least one terminal type capable of all operations described in IEEE Std 1003.2 (“POSIX.2”), otherwise -1.
Return 1 if the system supports the FORTRAN Development Utilities Option, otherwise -1.
Return 1 if the system supports the FORTRAN Runtime Utilities Option, otherwise -1.
Return 1 if the system supports the creation of locales, otherwise -1.
Return 1 if the system supports the Software Development Utilities Option, otherwise -1.
Return 1 if the system supports the User Portability Utilities Option, otherwise -1.
The version of IEEE Std 1003.2 (“POSIX.2”) with which the system attempts to comply.

These values also exist, but may not be standard:

The number of pages of physical memory.

If the call to sysconf() is not successful, -1 is returned and errno is set appropriately. Otherwise, if the variable is associated with functionality that is not supported, -1 is returned and errno is not modified. Otherwise, the current variable value is returned.

The sysconf() function may fail and set errno for any of the errors specified for the library function sysctl(3). In addition, the following error may be reported:

[]
The value of the name argument is invalid.

getconf(1), pathconf(2), confstr(3), sysctl(3)

Except for the fact that values returned by sysconf() may change over the lifetime of the calling process, this function conforms to IEEE Std 1003.1-1988 (“POSIX.1”).

_SC_NPROCESSORS_CONF and _SC_NPROCESSORS_ONLN are nonstandard, but implemented in many systems.

The sysconf() function first appeared in 4.4BSD.

The value for _SC_STREAM_MAX is a minimum maximum, and required to be the same as ANSI C's FOPEN_MAX, so the returned value is a ridiculously small and misleading number.

May 12, 2019 DragonFly-5.6.1