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 introduced in Linux 1.3.2.

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

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