SWAPON(2) Linux Programmer's Manual SWAPON(2)
NAME
swapon(2,8), swapoff - start/stop swapping to file(1,n)/device
SYNOPSIS
#include <unistd.h>
#include <asm/page.h> /* to find PAGE_SIZE */
#include <sys/swap.h>
int swapon(2,8)(const char *path, int swapflags);
int swapoff(const char *path);
DESCRIPTION
swapon(2,8) sets the swap area to the file(1,n) or block device specified by
path. swapoff stops swapping to the file(1,n) or block device specified by
path.
swapon(2,8) 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 a privileged process (one having
the CAP_SYS_ADMIN capability).
PRIORITY
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(7,n,1 builtins) 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(1,8) 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(8,n), -1 is returned, and errno is
set(7,n,1 builtins) appropriately.
ERRORS
EINVAL The file(1,n) path exists, but refers neither to a regular file(1,n) nor
to a block device.
ENFILE The system limit on the total number of open(2,3,n) files has been
reached.
ENOENT The file(1,n) path does not exist.
ENOMEM The system has insufficient memory to start swapping.
EPERM The caller does not have the CAP_SYS_ADMIN capability, or all
MAX_SWAPFILES (earlier 8; 32 since Linux 2.4.10) are in(1,8) use.
CONFORMING TO
These functions are Linux specific and should not be used in(1,8) programs
intended to be portable. The second `swapflags' argument was intro-
duced in(1,8) Linux 1.3.2.
NOTES
The partition or path must be prepared with mkswap(8).
SEE ALSO
mkswap(8), swapoff(8), swapon(2,8)(8)
Linux 2.6.7 2004-10-10 SWAPON(2)