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sysconf(3) - sysconf, sysconf - Get configuration information at runtime - man 3 sysconf

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SYSCONF(3)                 Linux Programmer's Manual                SYSCONF(3)



NAME
       sysconf - Get configuration information at runtime

SYNOPSIS
       #include <unistd.h>

       long sysconf(int name);

DESCRIPTION
       POSIX  allows  an  application  to test at compile- or run-time whether
       certain options are supported, or what the value is of certain  config-
       urable constants or limits.

       At  compile time(1,2,n) this is done by including <unistd.h> and/or <limits.h>
       and testing the value of certain macros.

       At run time(1,2,n), one can ask for numerical values using the  present  func-
       tion sysconf().  On can ask for numerical values that may depend on the
       filesystem a file(1,n) is in(1,8) using the calls fpathconf(3)  and  pathconf(3).
       One can ask for string(3,n) 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(1,8) <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 runtime 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 sup-
       port as long as the POSIX revision has not  been  published  yet.   The
       sysconf()  argument  will  be  _SC_FOO.   For  a  list  of options, see
       posixoptions(7).

       For variables or limits, typically, there is  a  constant  _FOO,  maybe
       defined in(1,8) <limits.h>, or _POSIX_FOO, maybe defined in(1,8) <unistd.h>.  The
       constant will not be defined if(3,n) the limit is unspecified.  If the  con-
       stant  is defined, it gives a guaranteed value, and more 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()  parameter
       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,n,1 builtins)() family of
              functions.  Must not be less(1,3) than _POSIX_ARG_MAX (4096).

       CHILD_MAX - _SC_CHILD_MAX
              The max number of simultaneous processes per user id.  Must  not
              be less(1,3) than _POSIX_CHILD_MAX (25).

       HOST_NAME_MAX - _SC_HOST_NAME_MAX
              Max  length  of  a  hostname,  not  including  the final NUL, as
              returned   by   gethostname(2).    Must   not   be   less(1,3)   than
              _POSIX_HOST_NAME_MAX (255).

       LOGIN_NAME_MAX - _SC_LOGIN_NAME_MAX
              Maximum  length  of a login(1,3,5) name, including the final NUL.  Must
              not be less(1,3) than _POSIX_LOGIN_NAME_MAX (9).

       clock(3,n) ticks - _SC_CLK_TCK
              The number of clock(3,n) ticks per second.  The  corresponding  vari-
              able  is  obsolete. It was of course called CLK_TCK.  (Note: the
              macro CLOCKS_PER_SEC does not give information:  it  must  equal
              1000000.)

       OPEN_MAX - _SC_OPEN_MAX
              The  maximum number of files that a process can have open(2,3,n) at any
              time.  Must not be less(1,3) than _POSIX_OPEN_MAX (20).

       PAGESIZE - _SC_PAGESIZE
              Size of a page in(1,8) bytes. Must not be less(1,3) than 1.  (Some systems
              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(1,3)    than
              _POSIX2_RE_DUP_MAX (255).

       STREAM_MAX - _SC_STREAM_MAX
              The  maximum  number  of streams that a process can have open(2,3,n) at
              any time. If defined, it has the same value as  the  standard  C
              macro FOPEN_MAX.  Must not be less(1,3) than _POSIX_STREAM_MAX (8).

       SYMLOOP_MAX
              The  maximum  number of symbolic links seen in(1,8) a pathname before
              resolution returns ELOOP. Must  not  be  less(1,3)  than  _POSIX_SYM-
              LOOP_MAX (8).

       TTY_NAME_MAX - _SC_TTY_NAME_MAX
              The maximum length of terminal device name, including final NUL.
              Must not be less(1,3) than _POSIX_TTY_NAME_MAX (9).

       TZNAME_MAX - _SC_TZNAME_MAX
              The maximum number of bytes in(1,8) a timezone  name.   Must  not  be
              less(1,3) than _POSIX_TZNAME_MAX (6).

       _POSIX_VERSION - _SC_VERSION
              indicates  the  year and month the POSIX.1 standard was approved
              in(1,8) 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(1,8) an array by
              bc(1).

       BC_SCALE_MAX - _SC_BC_SCALE_MAX
              indicates the maximum scale value allowed by bc(1).

       BC_STRING_MAX - _SC_BC_STRING_MAX
              indicates the maximum length of a string(3,n) accepted by bc(1).

       COLL_WEIGHTS_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(1,8) the  locale(3,5,7)  defini-
              tion file(1,n),

       EXPR_NEST_MAX - _SC_EXPR_NEST_MAX
              is  the maximum number of expressions which can be nested within
              parentheses by expr(1,3,n)(1).

       LINE_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 trail-
              ing newline.

       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.

       POSIX2_VERSION - _SC_2_VERSION
              indicates  the  version(1,3,5) of the POSIX.2 standard in(1,8) the format of
              YYYYMML.

       POSIX2_C_DEV - _SC_2_DEV
              indicates whether the POSIX.2 C language development  facilities
              are supported.

       POSIX2_FORT_RUN - _SC_2_FORT_DEV
              indicates  whether the POSIX.2 FORTRAN development utilities are
              supported.

       POSIX2_FORT_RUN - _SC_2_FORT_RUN
              indicates whether the POSIX.2 FORTRAN runtime utilities are sup-
              ported.

       _POSIX2_LOCALEDEF - _SC_2_LOCALEDEF
              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_PAGE_SIZE
              to overflow.

        - _SC_AVPHYS_PAGES
              The number of currently available pages of physical memory.

RETURN VALUE
       If name is invalid, -1 is returned, and errno is set(7,n,1 builtins) to EINVAL.  Other-
       wise, the value returned is the value of the system resource and  errno
       is  not  changed.  In the case of options, a positive value is returned
       if(3,n) a queried option is available, and -1 if(3,n) it is not.  In the case  of
       limits, -1 means that there is no definite limit.

CONFORMING TO
       POSIX.1.

BUGS
       It  is difficult to use ARG_MAX because it is not specified how much of
       the argument space for exec(3,n,1 builtins)() is consumed  by  the  user's  environment
       variables.

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

SEE ALSO
       bc(1), expr(1,3,n)(1), locale(3,5,7)(1), fpathconf(3), pathconf(3), posixoptions(7)



GNU                               1993-04-18                        SYSCONF(3)

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