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SYSCONF(3) Library Functions Manual SYSCONF(3)

sysconf — get configurable system variables

#include <unistd.h>

long
sysconf(int name);

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 arguments to execve(2) (including the environment).
The maximum number of simultaneous processes per user ID.
The number of clock ticks per second.
The maximum number of supplemental groups.
The maximum number of open files per user ID.
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 time zone.
Returns 1 if job control is available on this system, otherwise -1.
Returns 1 if saved set-group-ID and saved set-user-ID is available, otherwise -1.
The version of ISO/IEC 9945 (POSIX 1003.1) with which the system attempts to comply.
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 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 parentheses by the expr(1) utility.
The maximum length in bytes of a text-processing utility's input line.
The maximum number of repeated occurrences of a regular expression permitted when using interval notation.
The version of POSIX 1003.2 with which the system attempts to comply.
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 POSIX 1003.2, 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 size of a system page in bytes.
Return 1 if the system supports the File Synchronisation Option, otherwise -1.
Return 1 if the system supports the Shared Memory Option, otherwise -1.
The maximum number of semaphores in the system or -1 if the system does not support the Semaphores Option.
The maximum value a semaphore may have or -1 if the system does not support the Semaphores Option.
The number of pages of physical memory.
The number of pages of physical memory not currently in use by the system.
The maximum size of the data buffer for the () and () functions.
The maximum size of the data buffer for the () and () functions.
The maximum length of a login name.
The level of support for thread-safe (re-entrant) functions.
The number of processors configured.
The number of processors online (capable of running processes).
The maximum size of a hostname, not counting NULL.
Return the POSIX version of the implementation of the Monotonic Clock option that this system conforms to, or -1 if unavailable.

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(2). In addition, the following error may be reported:

[]
The value of the name argument is invalid.

pathconf(2), sysctl(2)

The sysconf() function conforms to IEEE Std 1003.1-1988 (“POSIX.1”). The constants _SC_NPROCESSORS_CONF and _SC_NPROCESSORS_ONLN are not part of the standard, but are provided by 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.

August 11, 2019 OpenBSD-7.6