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

       sysconf - Get configuration information at runtime

       #include <unistd.h>

       long sysconf(int name);

       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:

	      The maximum length of the arguments to the exec() family of functions;  the  corre-
	      sponding macro is ARG_MAX.

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

	      The number of clock ticks per second; the corresponding macro  was  CLK_TCK.   This
	      macro  is  obsolete now. (Note that the macro CLOCKS_PER_SEC does not give informa-
	      tion: it must equal 1000000.)

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

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

	      The  maximum  number  of files that a process can have open at any time, the corre-
	      sponding macro is OPEN_MAX.

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

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

	      indicates the year and month the	POSIX.1  standard  was	approved  in  the  format
	      YYYYMML;the  value  199009L  indicates  the Sept. 1990 revision.	The corresponding
	      macro is _POSIX_VERSION.

       Next, the POSIX.2 values:

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

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

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

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

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

	      The  maximum number of repeated occurrences of a regular expression when the inter-
	      val 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 corre-
	      sponding macro is POSIX2_VERSION.

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

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

	      indicates  whether the POSIX.2 FORTRAN runtime utilities are supported.  The corre-
	      sponding macro is POSIX2_FORT_RUN.

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

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

       SUSv2 also lists

	      The size of a page (in bytes).

       These values also exist, but may not be standard.

	      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.

	      The number of currently available pages of physical memory.

       If  name  is  invalid,  -1  is returned, and errno is set to EINVAL.  Otherwise, 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, and the variable errno is not changed.


       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.

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

GNU					    1993-04-18				       SYSCONF(3)
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