sysconf()

Return the value of a configurable system limit

Synopsis:

#include <unistd.h>
#include <limits.h>

long sysconf( int name );

Arguments:

name
The name of the limit that you want to get; see below.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The sysconf() function returns the value of a configurable system limit indicated by name.

Configurable limits are defined in <confname.h>, and include at least the following values:

_SC_AIO_PRIO_DELTA_MAX
The maximum amount by which a process can decrease its asynchronous I/O priority level from its own scheduling priority.
_SC_ARG_MAX
Maximum length of arguments for the exec*() functions, in bytes, including environment data.
_SC_CHILD_MAX
Maximum number of simultaneous processes per real user ID.
_SC_CLK_TCK
The number of intervals per second used to express the value in type clock_t.
_SC_DELAYTIMER_MAX
The maximum number of times a timer can overrun and you can still detect it.
_SC_GETGR_R_SIZE_MAX
If defined (not -1), the maximum size of buffer that you need to supply to getgrgid_r() for any memory that it needs to allocate.
_SC_GETPW_R_SIZE_MAX
If defined (not -1), the maximum size of buffer that you need to supply to getpwent_r() , getpwuid_r() , getspent_r() , or getspnam_r() for any memory that they need to allocate.
_SC_JOB_CONTROL
If this variable is defined, then job control is supported.
_SC_NGROUPS_MAX
The maximum number of simultaneous supplementary group IDs per process.
_SC_OPEN_MAX
Maximum number of files that one process can have open at any given time.
_SC_PAGESIZE
The default size of a thread's guard area.
_SC_RCT_MEM
The minimum amount of memory that the system retains as a resource constraint threshold.
_SC_RCT_SCOID
The minimum number of connection IDs that a server retains as a resource constraint threshold.
_SC_SAVED_IDS
If this variable is defined, then each process has a saved set-user ID and a saved set-group ID.
_SC_SEM_NSEMS_MAX
The maximum number of semaphores that one process can have open at a time. The sysconf() function returns -1 to indicate that this value is indeterminate because that limit applies to both named and unnamed semaphores. The kernel allows an arbitrary number of unnamed semaphores (they're kernel synchronization objects, so the number of them is limited only by the amount of available kernel memory).
_SC_SIGQUEUE_MAX
The maximum number of outstanding realtime signals sent per process.
_SC_THREAD_STACK_MIN
The minimum stack size for a thread.
_SC_TZNAME_MAX
The maximum length of the names for time zones. The value is the same as TZNAME_MAX.
_SC_VERSION
The current POSIX version that is currently supported. A value of 198808L indicates the August (08) 1988 standard, as approved by the IEEE Standards Board.

Returns:

The requested configurable system limit. If name isn't defined for the system, -1 is returned.

Examples:

#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
#include <unistd.h>

int main( void )
   {
    printf( "_SC_ARG_MAX = %ld\n",
         sysconf( _SC_ARG_MAX ) );
    return EXIT_SUCCESS;
  }

Classification:

POSIX 1003.1

Safety:  
Cancellation point No
Interrupt handler No
Signal handler Yes
Thread Yes

Last modified: 2013-12-23

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