SYSCONF(3)

NAME
sysconf - Get configuration information at runtime

SYNOPSIS
#include <unistd.h>

long sysconf(int name);

DESCRIPTION
sysconf() provides a way for the application to determine values for system limits or options at runtime.

The equivalent macros defined in <unistd.h> can only give conservative values; if an application wants to take advantage of values which may change, a call to sysconf() can be made, which may yield more liberal results.

For getting information about a particular file, see fpathconf() or pathconf().

The following values are supported for name. First, the POSIX.1 compatible values:

_SC_ARG_MAX
    The maximum length of the arguments to the exec() family of functions; the corresponding macro is ARG_MAX.

_SC_CHILD_MAX
    The number of simultaneous processes per user id, the corresponding macro is _POSIX_CHILD_MAX.

_SC_CLK_TCK
    The number of clock ticks per second; the corresponding macro is CLK_TCK.

_SC_STREAM_MAX
    The maximum number of streams that a process can have open at any time. The corresponding POSIX macro is STREAM_MAX, the corresponding standard C macro is FOPEN_MAX.

_SC_TZNAME_MAX
    The maximum number of bytes in a timezone name, the corresponding macro is TZNAME_MAX.

_SC_OPEN_MAX
    The maximum number of files that a process can have open at any time, the corresponding macro is _POSIX_OPEN_MAX.

_SC_JOB_CONTROL
    This indicates whether POSIX - style job control is supported, the corresponding macro is _POSIX_JOB_CONTROL.

_SC_SAVED_IDS
    This indicates whether a process has a saved set-user-ID and a saved set-group-ID; the corresponding macro is _POSIX_SAVED_IDS.

_SC_VERSION
    indicates the year and month the POSIX.1 standard was approved in the format YYYYMML;the value 199009L indicates the most recent revision, 1990.

Next, the POSIX.2 values:

_SC_BC_BASE_MAX
    indicates the maximum obase value accepted by the bc(1) utility; the corresponding macro is BC_BASE_MAX.

_SC_BC_DIM_MAX
    indicates the maximum value of elements permitted in an array by bc(1); the corresponding macro is BC_DIM_MAX.

_SC_BC_SCALE_MAX
    indicates the maximum scale value allowed by bc(1); the corresponding macro is BC_SCALE_MAX.

_SC_BC_STRING_MAX
    indicates the maximum length of a string accepted by bc(1); the corresponding macro is BC_STRING_MAX.

_SC_COLL_WEIGHTS_MAX
    indicates the maximum numbers of weights that can be assigned to an entry of the LC_COLLATE order keyword in the locale definition file; the corresponding macro is COLL_WEIGHTS_MAX.

_SC_EXPR_NEST_MAX
    is the maximum number of expressions which can be nested within parentheses by expr(1). The corresponding macro is EXPR_NEST_MAX.

_SC_LINE_MAX
    The maximum length of a utility's input line length, either from standard input or from a file. This includes length for a trailing newline. The corresponding macro is LINE_MAX.

_SC_RE_DUP_MAX
    The maximum number of repeated occurrences of a regular expression when the interval notation \{m,n\} is used. The value of the corresponding macro is RE_DUP_MAX.

_SC_2_VERSION
    indicates the version of the POSIX.2 standard in the format of YYYYMML. The corresponding macro is POSIX2_VERSION.

_SC_2_DEV
    indicates whether the POSIX.2 C language development facilities are supported. The corresponding macro is POSIX2_C_DEV.

_SC_2_FORT_DEV
    indicates whether the POSIX.2 FORTRAN development utilities are supported. The corresponding macro is POSIX2_FORT_RUN.

_SC_2_FORT_RUN
    indicates whether the POSIX.2 FORTRAN runtime utilities are supported. The corresponding macro is POSIX2_FORT_RUN.

_SC_2_LOCALEDEF
    indicates whether the POSIX.2 creation of locates via localedef(1) is supported. The corresponding macro is _POSIX2_LOCALEDEF.

_SC_2_SW_DEV
    indicates whether the POSIX.2 software development utilities option is supported. The corresponding macro is POSIX2_SW_DEV.

SUSv2 also lists

_SC_PAGESIZE _SC_PAGE_SIZE
    The size of a page (in bytes).

These values also exist, but may not be standard.

_SC_PHYS_PAGES
    The number of pages of physical memory. Note that it is possible for the product of this value and the value of _SC_PAGE_SIZE to overflow.

_SC_AVPHYS_PAGES
    The number of currently available pages of physical memory.

RETURN VALUE
The value returned is the value of the system resource, 1 if a queried option is available, 0 if it is not, or -1 on error. The variable errno is not set.

CONFORMING TO
POSIX.1, proposed POSIX.2

BUGS
It is difficult to use ARG_MAX because it is not specified how much of the argument space for exec() is consumed by the user's environment variables.

Some returned values may be huge; they are not suitable for allocating memory.

POSIX.2 is not yet an approved standard; the information in this manpage is subject to change.

SEE ALSO
bc(1), expr(1), locale(1), fpathconf(3), pathconf(3)