To quickly add some extra swap do the following (as root):

dd if=/dev/zero of=/extraswap bs=1M count=12288

This will create a 12Gb swapfile in /

chmod 600 /extraswap

This will set the correct permissions on the file.

mkswap /extraswap

This will format the space for use as swap.

swapon -s

This will show what is currently mounted as swap.

If you want this to be a temporary setting just run:

swapon /extraswap

If you want this to be persistent, add this to your /etc/fstab:

/extraswap        none        swap        sw        0 0