sysconf -- Determine System Configuration Options

SYNOPSIS

 #include <unistd.h>

 long sysconf(int configOpt);

DESCRIPTION

sysconf returns the value of a system configuration option. The configOpt argument can be any of the following symbols, which specify the system configuration option to determine.

_SC_ARG_MAX: returns the value of ARG_MAX, which specifies the maximum number of bytes of argument and environment data that can be passed to an exec function.
_SC_CHILD_MAX: returns the value of CHILD_MAX, which specifies the maximum number of child processes that a user ID (UID) can have running at the same time.
_SC_CLK_TCK: returns the value of the CLK_TCK macro, which is defined in <time.h>. This macro specifies the number of clock ticks in a second.
_SC_JOB_CONTROL: returns the value of the _POSIX_JOB_CONTROL macro, which may be defined in <unistd.h>. This macro specifies that certain job control functions are implemented by the operating system. Certain functions, such as setpgid, will have more functionality if _POSIX_JOB_CONTROL is defined.
_SC_NGROUPS_MAX: returns the value of NGROUPS_MAX, which specifies the maximum number of supplementary group IDs (GIDs) that can be associated with a process.
_SC_OPEN_MAX: returns the value of OPEN_MAX, which specifies the maximum number of files that a single process can have open at one time.
_SC_SAVED_IDS: returns the value of the SAVED_IDS macro, which may be defined in <unistd.h>. This macro specifies that a saved set UID and a saved set GID are implemented. The behavior of certain functions, such as setuid and setgid, is affected by this macro.
_SC_STREAM_MAX: returns the value of the STREAM_MAX macro, which may be defined in <unistd.h>. This macro indicates the maximum number of streams that a process can have open simultaneously.
_SC_TZNAME_MAX: returns the value of the TZNAME_MAX macro, which may be defined in <unistd.h>. This macro indicates the maximum length of the name of a time zone.
_SC_VERSION: returns the value of the VERSION macro, which may be defined in <unistd.h>. This macro indicates the version of the POSIX.1 standard that the system conforms to.

RETURN VALUE

sysconf returns the value associated with the option specified by the configOpt argument. If the symbol corresponding to the specified option exists but is not supported, sysconf returns - 1 but does not change the value of errno. If sysconf fails in any other way, it returns - 1 and sets errno to EINVAL.

EXAMPLE

The following example illustrates the use of sysconf to obtain the value of STREAM_MAX:

  #include <sys/types.h>
  #include <unistd.h>
  #include <stdio.h>
  #include <errno.h>

  main()
  {
     int max_streams;

     errno = 0;

     if ((max_streams = sysconf(_SC_STREAM_MAX)) == -1)
        if (errno == 0)
           printf("STREAM_MAX not supported by this implementation.n");
        else
           perror("sysconf error.");
     else
        printf("STREAM_MAX = %dn", max_streams);
  }

RELATED FUNCTIONS

fpathconf, pathconf