mkswap

Understanding Swap Space

Before diving into mkswap, let’s understand its purpose. When your system runs low on RAM, the kernel uses a process called swapping (or paging). It moves inactive data from RAM to the swap space on your hard drive, freeing up RAM for active processes. This prevents system crashes due to memory exhaustion. However, accessing data from the hard drive is slower than from RAM, so excessive swapping can lead to performance degradation. Therefore, having an appropriately sized swap partition is important for system stability and performance.

Creating a Swap File with mkswap

The simplest way to create swap space is by using a swap file. This is a regular file on your filesystem that’s formatted for swap usage. Let’s walk through the process:

1. Create the file:

First, we need to create an empty file of the desired size. Let’s create a 2GB swap file:

sudo fallocate -l 2G /swapfile

fallocate is a safer and faster way to create a file of a specific size. If fallocate isn’t available, you can use dd:

sudo dd if=/dev/zero of=/swapfile bs=1M count=2048 status=progress

This command uses dd to create a 2GB file (2048 MB).

2. Format the file as swap space:

Now, we use mkswap to format the file for swap usage:

sudo mkswap /swapfile

This command initializes the file’s structure to be used as swap space.

3. Enable the swap space:

Finally, we need to activate the newly created swap file:

sudo swapon /swapfile

4. Make it permanent:

To ensure the swap file is automatically activated on each boot, add the following line to your /etc/fstab file:

/swapfile none swap sw 0 0

You’ll need root privileges to edit this file (sudo nano /etc/fstab). The fields represent:

• /swapfile: The path to the swap file.
• none: No filesystem.
• swap: Swap filesystem type.
• sw: Swap options (usually sw).
• 0 0: Dump and fsck options (usually 0 0).

Creating a Swap Partition with mkswap (Less Common)

Alternatively, you can create a swap partition during disk partitioning (often during installation). This method involves partitioning your hard drive and assigning a partition to swap space. Once the partition is created (e.g., /dev/sda5), you’ll need to format it with mkswap:

sudo mkswap /dev/sda5

And then enable it:

sudo swapon /dev/sda5

Again, add the relevant line to your /etc/fstab file to make the swap partition persistent across reboots.

Checking Swap Usage

You can check your current swap usage with the following commands:

swapon --show
free -h

swapon --show shows information about your active swap areas, while free -h provides a summary of memory and swap usage, including how much is used and available.

Removing Swap Space

To remove a swap file or partition, you first need to disable it:

sudo swapoff /swapfile  # Or /dev/sda5 for a partition

Then, you can delete the file or partition:

sudo rm /swapfile   # Or use a partitioning tool for a partition

Remember to remove the corresponding line from /etc/fstab after removing the swap space. Failing to do so might lead to errors on boot.