SYSCONF(3)               BSD 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 con-
     stants for each name value are found in the include file <unistd.h>.
     Shell programmers 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.

     _SC_OPEN_MAX
             The maximum number of open files per user id.

     _SC_PAGESIZE
             The size of a system page in bytes.

     _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 sys-
             tem 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
             parenthesis 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 IEEE Std 1003.2 (``POSIX.2'') with which the sys-
             tem 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 IEEE Std 1003.2 (``POSIX.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
             Option, 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.

     These values also exist, but may not be standard:

     _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 func-
     tionality that is not supported, -1 is returned and errno is not modi-
     fied.  Otherwise, the current variable value is returned.

ERRORS
     The sysconf() function may fail and set errno for any of the errors spec-
     ified 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.

BSD                            December 14, 2006                           BSD