SWAPON (2)
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
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