Create a Swap file on CentOS 7
Even if you have sufficient memory in your server, it’s still a good idea to have a swap file. In order to reduce disk IO, many cloud providers don’t include one as standard – so you may need to add your own.
If you need a server to try this out on, we recommend our friends at Linode.
Firstly, you can use the following command to check if you have any swap space already:
The following output shows zero swap space
total used free shared buff/cache available Mem: 7822 1390 506 492 5924 5569 Swap: 0 0 0
Now we need to create the swap file – I’m going to create a 4GB file, but you can adjust the values to your needs:
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
We can now test our swap file to make sure all is well. Firstly, running ‘free -m’ again should yield a different result:
total used free shared buff/cache available Mem: 7822 1390 506 492 5924 5569 Swap: 4095 0 4095
And we can check the swap file by using ‘sudo swapon -s’
Filename Type Size Used Priority /swap file 4194300 0 -1
You’re now all setup with your swap file.