Swapon is used to specify devices on which paging and swapping are to take place. Calls to swapon normally occur in the system multi-user initialization file /etc/rc making all swap devices available, so that the paging and swapping activity is interleaved across several devices and files.
Normally, the first form is used:
Display swap usage summary by device. This option is only available if /proc/swaps exists (probably not before kernel 2.1.25).
All devices marked as ``sw swap devices in /etc/fstab'' are made available.
Specify priority for swapon. This option is only available if swapon was compiled under and is used under a 1.3.2 or later kernel. priority is a value between 0 and 32767. See swapon(2) for a full description of swap priorities. Add pri=value to the option field of /etc/fstab for use with swapon -a.