SWAPONSection: Linux Programmer's Manual (2)
Index Return to Main Contents
NAMEswapon, swapoff - start/stop swapping to file/device
#include <asm/page.h> /* to find PAGE_SIZE */
DESCRIPTIONswapon() 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.
bit turned on, the new swap area will have a higher priority than default.
The priority is encoded within
(prio << SWAP_FLAG_PRIO_SHIFT) & SWAP_FLAG_PRIO_MASK
PriorityEach 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.
RETURN VALUEOn success, zero is returned. On error, -1 is returned, and errno is set appropriately.
- (for swapon()) The specified path is already being used as a swap area.
- The file path exists, but refers neither to a regular file nor to a block device; or, for swapon(), the indicated path does not contain a valid swap signature or resides on an in-memory file system like tmpfs; or, for swapoff(), path is not currently a swap area.
- The system limit on the total number of open files has been reached.
- The file path does not exist.
- The system has insufficient memory to start swapping.
- The caller does not have the CAP_SYS_ADMIN capability. Alternatively, the maximum number of swap files are already in use; see NOTES below.
CONFORMING TOThese 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.
NOTESThe partition or path must be prepared with mkswap(8).
There is an upper limit on the number of swap files that may be used, defined by the kernel constant MAX_SWAPFILES. Before kernel 2.4.10, MAX_SWAPFILES has the value 8; since kernel 2.4.10, it has the value 32. Since kernel 2.6.18, the limit is decreased by 2 if the kernel is built with the CONFIG_MIGRATION option (which reserves two swap table entries for the page migration features of mbind(2) and migrate_pages(2)). Since kernel 2.6.32, the limit is decreased by 1 if the kernel is built with the CONFIG_MEMORY_FAILURE option.
SEE ALSOmkswap(8), swapoff(8), swapon(8)
COLOPHONThis page is part of release 3.22 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.
This document was created by man2html, using the manual pages.
Time: 05:33:05 GMT, December 24, 2015