NAME    [Toc]    [Back]

       swapon, swapoff - start/stop swapping to file/device

SYNOPSIS    [Toc]    [Back]

       #include <unistd.h>
       #include <asm/page.h> /* to find PAGE_SIZE */
       #include <sys/swap.h>

       int swapon(const char *path, int swapflags);
       int swapoff(const char *path);

DESCRIPTION    [Toc]    [Back]

       swapon  sets  the  swap	area  to the file or block device specified by
       path.  swapoff stops swapping to the file or block device specified  by
       path.

       swapon takes a swapflags argument.  If swapflags has the SWAP_FLAG_PRE-
       FER bit turned on, the new swap area will have a higher	priority  than
       default.  The priority is encoded as:

	   (prio << SWAP_FLAG_PRIO_SHIFT) & SWAP_FLAG_PRIO_MASK

       These functions may only be used by the super-user.

PRIORITY    [Toc]    [Back]

       Each  swap area has a priority, either high or low.  The default priority
 is low.  Within the low-priority areas, newer areas are even  lower
       priority than older areas.

       All  priorities	set  with  swapflags  are  high-priority,  higher than
       default.  They may have any non-negative value chosen  by  the  caller.
       Higher numbers mean higher priority.

       Swap pages are allocated from areas in priority order, highest priority
       first.  For areas with different priorities, a higher-priority area  is
       exhausted  before  using  a  lower-priority area.  If two or more areas
       have the same priority, and it is the highest priority available, pages
       are allocated on a round-robin basis between them.

       As  of  Linux  1.3.6, the kernel usually follows these rules, but there
       are exceptions.

RETURN VALUE    [Toc]    [Back]

       On success, zero is returned.  On error, -1 is returned, and  errno  is
       set appropriately.

ERRORS    [Toc]    [Back]

       Many other errors can occur if path is not valid.


       EPERM  The  user  is  not  the  super-user,  or more than MAX_SWAPFILES
	      (defined to be 8 in Linux 1.3.6) are in use.

       EINVAL is returned if path exists, but is neither a regular path nor  a
	      block device.

       ENOENT is returned if path does not exist.

       ENOMEM is returned if there is insufficient memory to start swapping.

CONFORMING TO    [Toc]    [Back]

       These  functions  are Linux specific and should not be used in programs
       intended to be portable.  The second `swapflags'  argument  was	introduced
 in Linux 1.3.2.

NOTES    [Toc]    [Back]

       The partition or path must be prepared with mkswap(8).

SEE ALSO    [Toc]    [Back]

       mkswap(8), swapon(8), swapoff(8)



Linux 1.3.6			  1995-07-22			     SWAPON(2)