SYSCONF(3)

NAME
sysconf - get configurable system variables

LIBRARY
libc

SYNOPSIS
#include <unistd.h>
long
sysconf(int name);

DESCRIPTION
This interface is defined by p1003.1-88. 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 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_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 p1003.1 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 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 expression permitted when using interval notation.

_SC_2_VERSION
    The version of p1003.2 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 Utilities Option, otherwise -1.

_SC_2_CHAR_TERM
    Return 1 if the system supports at least one terminal type capable of all operations described in p1003.2, 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, 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 Option, otherwise -1.

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. Otherwise, the current variable value is returned.

ERRORS
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.

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

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.

STANDARDS
Except for the fact that values returned by sysconf() may change over the lifetime of the calling process, this function conforms to p1003.1-88.

HISTORY
The sysconf() function first appeared in 4.4BSD.