add swap space

login as root

1. create the file
dd if=/dev/zero of=/swapfile1 bs=1024 count=524288

2. make swap
mkswap /swapfile1

3. bring up swap
swapon /swapfile1

4.add it to /etc/fstab
vi /etc/fstab
append
/swapfil1 swap swap defaults 0 0

5.change mod
chmod 0600 /swapfile1

6. check
free -m

reference:
http://www.cyberciti.biz/faq/linux-add-a-swap-file-howto/