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 32.2 Overall System Options
 ===========================
 
 POSIX defines certain system-specific options that not all POSIX systems
 support.  Since these options are provided in the kernel, not in the
 library, simply using the GNU C Library does not guarantee any of these
 features is supported; it depends on the system you are using.
 
    You can test for the availability of a given option using the macros
 in this section, together with the function 'sysconf'.  The macros are
 defined only if you include 'unistd.h'.
 
    For the following macros, if the macro is defined in 'unistd.h', then
 the option is supported.  Otherwise, the option may or may not be
 supported; use 'sysconf' to find out.   Sysconf.
 
  -- Macro: int _POSIX_JOB_CONTROL
      If this symbol is defined, it indicates that the system supports
      job control.  Otherwise, the implementation behaves as if all
      processes within a session belong to a single process group.  
      Job Control.
 
  -- Macro: int _POSIX_SAVED_IDS
      If this symbol is defined, it indicates that the system remembers
      the effective user and group IDs of a process before it executes an
      executable file with the set-user-ID or set-group-ID bits set, and
      that explicitly changing the effective user or group IDs back to
      these values is permitted.  If this option is not defined, then if
      a nonprivileged process changes its effective user or group ID to
      the real user or group ID of the process, it can't change it back
      again.   Enable/Disable Setuid.
 
    For the following macros, if the macro is defined in 'unistd.h', then
 its value indicates whether the option is supported.  A value of '-1'
 means no, and any other value means yes.  If the macro is not defined,
 then the option may or may not be supported; use 'sysconf' to find out.
  Sysconf.
 
  -- Macro: int _POSIX2_C_DEV
      If this symbol is defined, it indicates that the system has the
      POSIX.2 C compiler command, 'c89'.  The GNU C Library always
      defines this as '1', on the assumption that you would not have
      installed it if you didn't have a C compiler.
 
  -- Macro: int _POSIX2_FORT_DEV
      If this symbol is defined, it indicates that the system has the
      POSIX.2 Fortran compiler command, 'fort77'.  The GNU C Library
      never defines this, because we don't know what the system has.
 
  -- Macro: int _POSIX2_FORT_RUN
      If this symbol is defined, it indicates that the system has the
      POSIX.2 'asa' command to interpret Fortran carriage control.  The
      GNU C Library never defines this, because we don't know what the
      system has.
 
  -- Macro: int _POSIX2_LOCALEDEF
      If this symbol is defined, it indicates that the system has the
      POSIX.2 'localedef' command.  The GNU C Library never defines this,
      because we don't know what the system has.
 
  -- Macro: int _POSIX2_SW_DEV
      If this symbol is defined, it indicates that the system has the
      POSIX.2 commands 'ar', 'make', and 'strip'.  The GNU C Library
      always defines this as '1', on the assumption that you had to have
      'ar' and 'make' to install the library, and it's unlikely that
      'strip' would be absent when those are present.
 
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