redhat man page for swapon

SWAPON(2)						     Linux Programmer's Manual							 SWAPON(2)

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

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

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

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

SEE ALSO
       mkswap(8), swapon(8), swapoff(8)

Linux 1.3.6							    1995-07-22								 SWAPON(2)