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  corre­
              sponding 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


       _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  corre­
              sponding 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  corre­
              sponding 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.

              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 develop­
              ment 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 util­
              ities 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

       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)


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