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SYSCONF(3) Library Functions Manual SYSCONF(3) NAME sysconf -- get configurable system variables LIBRARY Standard C Library (libc, -lc) SYNOPSIS #include <unistd.h> long sysconf(int name); DESCRIPTION This interface is defined by IEEE Std 1003.1-1988 ("POSIX.1"). 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 constants for each name value are found in the include file <unistd.h>. Shell pro- grammers who need access to these parameters should use the getconf(1) utility. The available values are as follows: _SC_ARG_MAX The maximum bytes of argument to execve(2). _SC_CHILD_MAX The maximum number of simultaneous processes per user id. _SC_CLK_TCK The frequency of the statistics clock in ticks per second. _SC_IOV_MAX The maximum number of elements in the I/O vector used by readv(2), writev(2), recvmsg(2), and sendmsg(2). _SC_NGROUPS_MAX The maximum number of supplemental groups. _SC_NPROCESSORS_CONF The number of processors configured. _SC_NPROCESSORS_ONLN The number of processors currently online, taking into account cur- rent jail restrictions to report only the number of processors that are usable to the process. _SC_OPEN_MAX One more than the maximum value the system may assign to a new file descriptor. _SC_PAGESIZE The size of a system page in bytes. _SC_PAGE_SIZE Equivalent to _SC_PAGESIZE. _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 Return 1 if job control is available on this system, otherwise -1. _SC_SAVED_IDS Returns 1 if saved set-group and saved set-user ID is available, otherwise -1. _SC_VERSION The version of IEEE Std 1003.1 ("POSIX.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 paren- thesis 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 expression permitted when using interval notation. _SC_2_VERSION The version of IEEE Std 1003.2 ("POSIX.2") with which the system attempts to comply. _SC_2_C_BIND Return 1 if the system's C-language development facilities support 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 capable of all operations described in IEEE Std 1003.2 ("POSIX.2"), other- wise -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, otherwise -1. _SC_2_SW_DEV Return 1 if the system supports the Software Development Utilities Option, otherwise -1. _SC_2_UPE Return 1 if the system supports the User Portability Utilities Op- tion, otherwise -1. _SC_AIO_LISTIO_MAX Maximum number of I/O operations in a single list I/O call sup- ported. _SC_AIO_MAX Maximum number of outstanding asynchronous I/O operations sup- ported. _SC_AIO_PRIO_DELTA_MAX The maximum amount by which a process can decrease its asynchronous I/O priority level from its own scheduling priority. _SC_DELAYTIMER_MAX Maximum number of timer expiration overruns. _SC_MQ_OPEN_MAX The maximum number of open message queue descriptors a process may hold. _SC_RTSIG_MAX Maximum number of realtime signals reserved for application use. _SC_SEM_NSEMS_MAX Maximum number of semaphores that a process may have. _SC_SEM_VALUE_MAX The maximum value a semaphore may have. _SC_SIGQUEUE_MAX Maximum number of queued signals that a process may send and have pending at the receiver(s) at any time. _SC_TIMER_MAX Maximum number of timers per process supported. _SC_GETGR_R_SIZE_MAX Suggested initial value for the size of the group entry buffer. _SC_GETPW_R_SIZE_MAX Suggested initial value for the size of the password entry buffer. _SC_HOST_NAME_MAX Maximum length of a host name (not including the terminating null) as returned from the gethostname() function. _SC_LOGIN_NAME_MAX Maximum length of a login name. _SC_THREAD_STACK_MIN Minimum size in bytes of thread stack storage. _SC_THREAD_THREADS_MAX Maximum number of threads that can be created per process. _SC_TTY_NAME_MAX Maximum length of terminal device name. _SC_SYMLOOP_MAX Maximum number of symbolic links that can be reliably traversed in the resolution of a pathname in the absence of a loop. _SC_ATEXIT_MAX Maximum number of functions that may be registered with atexit(). _SC_XOPEN_VERSION An integer value greater than or equal to 4, indicating the version of the X/Open Portability Guide to which this system conforms. _SC_XOPEN_XCU_VERSION An integer value indicating the version of the XCU Specification to which this system conforms. These values also exist, but may not be standard: _SC_CPUSET_SIZE Size of the kernel cpuset. _SC_PHYS_PAGES The number of pages of physical memory. Note that it is possible that the product of this value and the value of _SC_PAGESIZE will overflow a long in some configurations on a 32bit machine. RETURN VALUES 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. Other- wise, the current variable value is returned. ERRORS The sysconf() function may fail and set errno for any of the errors speci- fied for the library function sysctl(3). In addition, the following error may be reported: [EINVAL] The value of the name argument is invalid. SEE ALSO getconf(1), pathconf(2), confstr(3), sysctl(3) STANDARDS 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"). HISTORY The sysconf() function first appeared in 4.4BSD. BUGS 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. FreeBSD ports 15.quarterly August 30, 2025 SYSCONF(3)
NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | SEE ALSO | STANDARDS | HISTORY | BUGS
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