How to Add Swap Space on CentOS 7

Creating a Swap File 4GB

sudo dd if=/dev/zero of=/swap count=4096 bs=1MiB

Now set the permissions:

sudo chmod 600 /swap

and format the swap file:

sudo mkswap /swap

To enable the swap file just use:

sudo swapon /swap

To make the swap be automatically mounted after reboot, the following command will add it to your fstab config:

sudo echo "/swap swap swap sw 0 0" >> /etc/fstab

source : https://www.netweaver.uk/create-swap-file-centos-7/