Swap space is a disk space or file that is used to move out inactive pages (processes) when your server’s memory becomes full. It can be configured as a separate partition or a swap file. In this article, we will look at how to create swap file in Linux.
How Does Swap Space work
Typically, processes are loaded into physical memory (RAM) and they run from that location, on a server. As more processes are run on your server, more and more physical RAM is consumed. When your server starts running out of memory, the operating system (Linux) swaps out inactive processes (organized as pages) into a parking space known as swap area. They are loaded back only when they become active once again. This swap area can be a part of your disk, a separate partition altogether, or a separate file known as swap file.
How to Create Swap File in Linux
Here are the steps to create swap file in Linux.
1. Create Swap file
Open terminal and run the following command to create a swap file of 1GB space for your server. If you want to increase it to 2GB just replace 1G with 2G in the command below.
$ sudo fallocate -l 1G /swapfile OR $ sudo dd if=/dev/zero of=/swapfile bs=1024 count=1048576
2. Set Root Permissions
Since it is a sensitive file, only root user should be allowed to read-write to it. So run the following command to enable only root user to use swap file.
$ sudo chmod 600 /swapfile
3. Set up Swap file as Swap area
Next, run the mkswap command to setup the new swap file as swap area.
$ sudo mkswap /swapfile
4. Enable Swap File
Run the following command to enable swap file.
$ sudo swapon /swapfile
However, these changes will be lost on system reboot. To make these changes permanent, open /etc/fstab file in a text editor
$ sudo vi /etc/fstab
and add the following line to it.
/swapfile swap swap defaults 0 0
Save and close the file.
You can verify the swap space with either of the following commands.
$ sudo swapon --show OR $ sudo free -h
5. (Optional) Remove Swap File
If you want to remove the swap file, you need to undo the above steps in reverse order. First, deactivate the swap file with the following swapoff command.
$ sudo swapoff -v /swapfile
Next, open /etc/fstab file and remove the following line from it.
/swapfile swap swap defaults 0 0
Save and close the file.
Finally, delete the actual swap file created in first step at the beginning of this article.
$ sudo rm /swapfile
That’s it. In this article, we have learnt how to create as well as remove swap file in Linux.
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