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SWAPON(2)                  Linux Programmer's Manual                 SWAPON(2)

       swapon(2,8), swapoff - start/stop swapping to file(1,n)/device

       #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);

       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

       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:


       These  functions  may  only be used by a privileged process (one having
       the CAP_SYS_ADMIN capability).

       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.

       On  success,  zero is returned.  On error(8,n), -1 is returned, and errno is
       set(7,n,1 builtins) appropriately.

       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

       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.

       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.

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

       mkswap(8), swapoff(8), swapon(2,8)(8)

Linux 2.6.7                       2004-10-10                         SWAPON(2)

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