How to setup swap file on Linux Server

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When memory is full on a Linux server, some services like MariaDB/MySQL may shut down automatically. To prevent this, you can add extra virtual memory using a swap file. This guide shows how to create a swap file on a Linux server with low RAM.

What is a Swap File?

During Linux installation, the system may ask how much space to allocate for swap. Swap is a form of virtual memory. When physical RAM is full, Linux moves inactive pages to swap space. Total virtual memory = RAM + swap.

Swap can be a swap partition, a swap file, or both. On Windows, swap is usually just a file on disk. Most Linux distros create a swap partition automatically.

Check Current Swap Usage

Use the following command to check your system's current swap:

swapon --show

This will show:

• Number of swap files/partitions
• Size of each
• Current usage
• Priority of each swap device

Higher priority means the system will use that swap first.

How to Create a Swap File

On a VPS with a single root partition, you can't create a new partition for swap, but you can create a swap file instead.

Step 1: Create the Swap File

To create a 512MB swap file:

sudo fallocate -l 512M /swapfile

Or for 1GB:

sudo fallocate -l 1G /swapfile

Step 2: Set Permissions

sudo chmod 600 /swapfile

Step 3: Format the File

sudo mkswap /swapfile

Example output:

Setting up swapspace version 1, size = 524284 KiB
no label, UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx

Step 4: Enable the Swap File

sudo swapon /swapfile

Step 5: Verify It’s Working

sudo swapon --show

Example output:

NAME       TYPE  SIZE  USED  PRIO
/swapfile  file  512M  132K  -1

Step 6: Enable on Boot

Add this line to your /etc/fstab file:

/swapfile none swap defaults 0 0

Note: Use the Tab key (not spaces) to separate each column in /etc/fstab.

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