SYSCONF(3) BSD Programmer's Manual SYSCONF(3)
sysconf - get configurable system variables
#include <unistd.h> long sysconf(int name);
This interface is defined by IEEE Std 1003.1-1988 ("POSIX"). A far more complete interface is available using sysctl(3). The sysconf() 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 con- stants for each name value are found in the include file <unistd.h>. The available values are as follows: _SC_ARG_MAX The maximum bytes of arguments to exec(3) (including the environ- ment). _SC_CHILD_MAX The maximum number of simultaneous processes per user ID. _SC_CLK_TCK The number of clock ticks per second. _SC_NGROUPS_MAX The maximum number of supplemental groups. _SC_OPEN_MAX The maximum number of open files per user ID. _SC_STREAM_MAX The minimum maximum number of streams that a process may have open at any one time. _SC_TZNAME_MAX The minimum maximum number of types supported for the name of a timezone. _SC_JOB_CONTROL Returns 1 if job control is available on this system, otherwise -1. _SC_SAVED_IDS Returns 1 if saved set-group-ID and saved set-user-ID is avail- able, otherwise -1. _SC_VERSION The version of ISO/IEC 9945 (POSIX 1003.1) with which the system attempts to comply. _SC_BC_BASE_MAX The maximum ibase/obase values in the bc(1) utility. _SC_BC_DIM_MAX The maximum array size in the bc(1) utility. _SC_BC_SCALE_MAX The maximum scale value in the bc(1) utility. _SC_BC_STRING_MAX The maximum string length in the bc(1) utility. _SC_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. _SC_EXPR_NEST_MAX The maximum number of expressions that can be nested within parentheses by the expr(1) utility. _SC_LINE_MAX The maximum length in bytes of a text-processing utility's input line. _SC_RE_DUP_MAX The maximum number of repeated occurrences of a regular expres- sion permitted when using interval notation. _SC_2_VERSION The version of POSIX 1003.2 with which the system attempts to comply. _SC_2_C_BIND Return 1 if the system's C-language development facilities sup- port the C-Language Bindings Option, otherwise -1. _SC_2_C_DEV Return 1 if the system supports the C-Language Development Utili- ties Option, otherwise -1. _SC_2_CHAR_TERM Return 1 if the system supports at least one terminal type capa- ble of all operations described in POSIX 1003.2, otherwise -1. _SC_2_FORT_DEV Return 1 if the system supports the FORTRAN Development Utilities Option, otherwise -1. _SC_2_FORT_RUN Return 1 if the system supports the FORTRAN Runtime Utilities Op- tion, otherwise -1. _SC_2_LOCALEDEF Return 1 if the system supports the creation of locales, other- wise -1. _SC_2_SW_DEV Return 1 if the system supports the Software Development Utili- ties Option, otherwise -1. _SC_2_UPE Return 1 if the system supports the User Portability Utilities Option, otherwise -1. _SC_PAGESIZE The size of a system page in bytes. _SC_FSYNC Return 1 if the system supports the File Synchronisation Option, otherwise -1. _SC_XOPEN_SHM Return 1 if the system supports the Shared Memory Option, other- wise -1. _SC_SEM_NSEMS_MAX The maximum number of semaphores in the system or -1 if the sys- tem does not support the Semaphores Option. _SC_SEM_VALUE_MAX The maximum value a semaphore may have or -1 if the system does not support the Semaphores Option. _SC_GETGR_R_SIZE_MAX The maximum length of a group entry buffer. Returns -1 as there is no safe maximum. _SC_GETPW_R_SIZE_MAX The maximum length of a password entry buffer. Returns -1 as there is no safe maximum.
If the call to sysconf() is not successful, -1 is returned and errno is set appropriately. Otherwise, if the variable is associated with func- tionality that is not supported, -1 is returned and errno is not modi- fied. 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: [EINVAL] The value of the name argument is invalid.
The sysconf() function conforms to IEEE Std 1003.1-1988 ("POSIX").
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. MirOS BSD #10-current April 19, 1994 2
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