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SYSCONF(3)		   Linux Programmers Manual		   SYSCONF(3)

       sysconf - Get configuration information at runtime


       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  and/or 
       and testing the value of certain macros.

       At run time, one can ask for numerical values using the	present  func
       tion sysconf().	On can ask for numerical values that may depend on the
       file system a file is in using the calls fpathconf(3) and  pathconf(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 .  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
       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 , or _POSIX_FOO, maybe defined in .  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).

	      The max number of simultaneous processes per user ID.  Must  not
	      be less than _POSIX_CHILD_MAX (25).

	      Max  length  of  a  hostname, not including the terminating null
	      byte, as returned by gethostname(2).   Must  not	be  less  than
	      _POSIX_HOST_NAME_MAX (255).

	      Maximum  length  of a login name, including the terminating null
	      byte.  Must not be less than _POSIX_LOGIN_NAME_MAX (9).

       clock ticks - _SC_CLK_TCK
	      The number of clock 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

	      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.)

	      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.

	      indicates the maximum obase value accepted by the bc(1) utility.

	      indicates the maximum value of elements permitted in an array by

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

	      indicates the maximum length of a string accepted by bc(1).

	      indicates the maximum numbers of weights that can be assigned to
	      an   entry  of  the  LC_COLLATE  order  keyword  in  the	locale
	      definition file,

	      is the maximum number of expressions which can be nested	within
	      parentheses by expr(1).

	      The maximum length of a utilitys input line length, either from
	      standard input or from a	file.	This  includes	length	for  a
	      trailing newline.

	      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.

	      indicates whether the POSIX.2 FORTRAN development utilities  are

	      indicates whether the POSIX.2 FORTRAN runtime utilities are sup

	      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.

	      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.

	      The number of currently available pages of physical memory.

	      The number of processors configured.

	      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
       is not changed.	In the case of options, a positive value  is  returned
       if  a queried option is available, and -1 if it is not.	In the case of
       limits, -1 means that there is no definite limit.


       It is difficult to use ARG_MAX because it is not specified how much  of
       the  argument  space  for exec(3) is consumed by the users environment

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

       bc(1),	expr(1),  getconf(1),  locale(1),  fpathconf(3),  pathconf(3),

       This page is part of release 3.05 of the Linux  man-pages  project.   A
       description  of	the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

GNU				  2007-12-12			    SYSCONF(3)

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