You need to use dd command to create swapfile. Next you need to use mkswap command to set up a Linux swap area on a device or in a file.
a) Login as the root user
b) Type following command to create 512MB swap file (1024 * 1024MB = 1048576 block size):
# dd if=/dev/zero of=/swapfile1 bs=1024 count=1048576
c) Set up a Linux swap area:
# mkswap /swapfile
d) Activate /swapfile1 swap space immediately:
# swapon /swapfile
e) To activate /swapfile1 after Linux system reboot, add entry to /etc/fstab file. Open this file using text editor such as vi:
# vi /etc/fstab
Append following line:
/swapfile swap swap defaults 0 0
So next time Linux comes up after reboot, it enables the new swap file for you automatically.
g) How do I verify swap is activated or not?
Simply use free command:
$ free -m