This post helps you to add swap space on a Ubuntu/Centos server
1 : Login to server and switch as root user
$ su –
or
$ sudo su –
2 : Check your server for any swap files have been enabled
# swapon -s
Output
Filename Type Size Used Priority
The above empty list means, there are no swap files enabled on your server.
3 : Create swap file using dd command
# dd if=/dev/zero of=/swap.dat bs=1024 count=512k
The above command will create a swap file with the name “swap.dat” (you can use different file name) with size of 512 MB. If you need more space for swap, change the count value. For example, if you need 1GB as swap, then count value should be 1024k.
4: Create Linux swap area
# mkswap /swap.dat
5 : Enable created swap file
# swapon /swap.dat
6: Update /etc/fstab
Add the below line on /etc/fstab to enable the swap after server reboot
/swap.dat none swap sw 0 0
7: Set correct permission for swap file
# chown root:root /swap.dat
# chmod 0600 /swap.dat
8: Verify created swap using free command
# free -m
total used free shared buffers cached
Mem: 490 461 28 0 47 103
-/+ buffers/cache: 311 178
Swap: 511 21 490
OR
# swapon -s
Filename Type Size Used Priority
/swap.dat file 524284 21516 -1
Done !!!