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


           POSIX allows an application to test at compile or run time whether cer-
           tain options are supported, or what the value  is  of  certain  config-
           urable constants or limits.
           At  compile time this is done by including <unistd.h> and/or <limits.h>
           and testing the value of certain macros.
           At run time, one can ask for numerical values using the  present  func-
           tion  sysconf().   One  can ask for numerical values that may depend on
           the filesystem a file is in using  the  calls  fpathconf(3)  and  path-
           conf(3).  One can ask for string values using confstr(3).
           The  values obtained from these functions are system configuration con-
           stants.  They do not change during the lifetime of a process.
           For options, typically, there is a  constant  _POSIX_FOO  that  may  be
           defined in <unistd.h>.  If it is undefined, one should ask at run time.
           If it is defined to -1, then the option is not  supported.   If  it  is
           defined to 0, then relevant functions and headers exist, but one has to
           ask at run time what degree of support is available.  If it is  defined
           to  a  value other than -1 or 0, then the option is supported.  Usually
           the value (such as 200112L) indicates the year and month of  the  POSIX
           revision  describing  the  option.   Glibc uses the value 1 to indicate
           support as long as the POSIX revision has not been published yet.   The
           sysconf()  argument  will  be  _SC_FOO.   For  a  list  of options, see
           For variables or limits, typically, there is  a  constant  _FOO,  maybe
           defined in <limits.h>, or _POSIX_FOO, maybe defined in <unistd.h>.  The
           constant will not be defined if the limit is unspecified.  If the  con-
           stant  is  defined,  it  gives  a guaranteed value, and a greater value
           might actually be supported.  If an application wants to take advantage
           of  values which may change between systems, a call to sysconf() can be
           made.  The sysconf() argument will be _SC_FOO.
       POSIX.1 variables
           We give the name of the variable, the name of  the  sysconf()  argument
           used to inquire about its value, and a short description.
           First, the POSIX.1 compatible values.
           ARG_MAX - _SC_ARG_MAX
                  The  maximum  length  of  the arguments to the exec(3) family of
                  functions.  Must not be less than _POSIX_ARG_MAX (4096).
           CHILD_MAX - _SC_CHILD_MAX
                  able  is obsolete.  It was of course called CLK_TCK.  (Note: the
                  macro CLOCKS_PER_SEC does not give information:  it  must  equal
           OPEN_MAX - _SC_OPEN_MAX
                  The  maximum number of files that a process can have open at any
                  time.  Must not be less than _POSIX_OPEN_MAX (20).
                  Size of a page in bytes.  Must not be less than 1.   (Some  sys-
                  tems use PAGE_SIZE instead.)
           RE_DUP_MAX - _SC_RE_DUP_MAX
                  The  number  of  repeated  occurrences  of  a  BRE  permitted by
                  regexec(3)   and   regcomp(3).    Must   not   be   less    than
                  _POSIX2_RE_DUP_MAX (255).
                  The  maximum  number  of streams that a process can have open at
                  any time.  If defined, it has the same value as the  standard  C
                  macro FOPEN_MAX.  Must not be less than _POSIX_STREAM_MAX (8).
                  The  maximum  number of symbolic links seen in a pathname before
                  resolution returns ELOOP.  Must not  be  less  than  _POSIX_SYM-
                  LOOP_MAX (8).
                  The maximum length of terminal device name, including the termi-
                  nating null byte.  Must not  be  less  than  _POSIX_TTY_NAME_MAX
                  The  maximum  number  of  bytes in a timezone name.  Must not be
                  less than _POSIX_TZNAME_MAX (6).
                  indicates the year and month the POSIX.1 standard  was  approved
                  in  the  format  YYYYMML;  the value 199009L indicates the Sept.
                  1990 revision.
       POSIX.2 variables
           Next, the POSIX.2 values, giving limits for utilities.
           BC_BASE_MAX - _SC_BC_BASE_MAX
                  indicates the maximum obase value accepted by the bc(1) utility.
           BC_DIM_MAX - _SC_BC_DIM_MAX
                  indicates the maximum value of elements permitted in an array by
           LINE_MAX - _SC_LINE_MAX
                  The  maximum length of a utility's input line, either from stan-
                  dard input or from a file.  This includes space for  a  trailing
           RE_DUP_MAX - _SC_RE_DUP_MAX
                  The  maximum number of repeated occurrences of a regular expres-
                  sion when the interval notation \{m,n\} is used.
                  indicates the version of the POSIX.2 standard in the  format  of
           POSIX2_C_DEV - _SC_2_C_DEV
                  indicates  whether the POSIX.2 C language development facilities
                  are supported.
           POSIX2_FORT_DEV - _SC_2_FORT_DEV
                  indicates whether the POSIX.2 FORTRAN development utilities  are
           POSIX2_FORT_RUN - _SC_2_FORT_RUN
                  indicates  whether  the  POSIX.2  FORTRAN run-time utilities are
                  indicates  whether  the  POSIX.2   creation   of   locates   via
                  localedef(1) is supported.
           POSIX2_SW_DEV - _SC_2_SW_DEV
                  indicates  whether  the  POSIX.2  software development utilities
                  option is supported.
           These values also exist, but may not be standard.
            - _SC_PHYS_PAGES
                  The number of pages of physical memory.  Note that it is  possi-
                  ble  for the product of this value and the value of _SC_PAGESIZE
                  to overflow.
            - _SC_AVPHYS_PAGES
                  The number of currently available pages of physical memory.
            - _SC_NPROCESSORS_CONF
                  The number of processors configured.
            - _SC_NPROCESSORS_ONLN
                  The number of processors currently online (available).


           If name is invalid, -1 is returned, and errno is set to EINVAL.  Other-
           wise,  the value returned is the value of the system resource and errno


           bc(1),  expr(1), getconf(1), locale(1), confstr(3), fpathconf(3), path-
           conf(3), posixoptions(7)

    GNU 2014-03-20 SYSCONF(3)


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