How Linux Works

Swap and Virtual Memory

If you run out of real memory, Linux has a virtual memory system that automatically moves memory pages (chunks) to and from a hard disk. This is called swapping, because the pages of idle programs are swapped to the disk in exchange for active pages residing on the disk. The disk area used to store memory pages is called swap space.

The free command's output includes the current swap usage in kilobytes as follows:

             total       used       free
...           ...        ...        ...
Swap:       514072     189804     324268

Using a Disk Partition as Swap Space

To use an entire disk partition as swap, follow these steps:

1. Make certain that the partition is empty.

2. Run mkswap dev, where dev is the partition's device. This command puts a swap signature on the partition.

3. Execute swapon ...