Linux man pages : swapon (2)
SWAPON(2) Linux Programmer's Manual SWAPON(2)
swapon, swapoff - start/stop swapping to file/device
#include <asm/page.h> /* to find PAGE_SIZE */
int swapon(const char *path, int swapflags);
int swapoff(const char *path);
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
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.
Each swap area has a priority, either high or low. The default prior-
ity 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
On success, zero is returned. On error, -1 is returned, and errno is
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
ENOENT is returned if path does not exist.
ENOMEM is returned if there is insufficient memory to start swapping.
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.
The partition or path must be prepared with mkswap(8).
mkswap(8), swapon(8), swapoff(8)
Linux 1.3.6 1995-07-22 SWAPON(2)