Configure and manage swap space

In this guide, you will learn how to create and manage swap space on a Linux system. Swap space is a designated area on disk where Linux temporarily moves data from RAM when physical memory is fully utilized. This process helps ensure that active applications have sufficient RAM to operate efficiently.

Consider the following scenario that demonstrates how swap space is used:

• A computer has 4 GB of RAM.
• A video editor uses 2 GB of RAM.
• An audio editor uses another 2 GB of RAM.
• With no free RAM available, a 2-GB swap partition is activated.
• When launching an additional application like Chrome, Linux shifts inactive data (for example, from the video editor) into swap space to free up RAM.

Below are the detailed steps and commands to set up and manage swap space on your Linux system.

Checking Active Swap Space

Before making changes, you can verify your current swap configuration. To display active swap areas, run:

$ swapon --show
NAME         TYPE      SIZE  USED PRIO
/dev/dm-1   partition  2G    0B   -2

You can also review all disk partitions using the lsblk command:

$ lsblk
NAME       MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
vda        8:0    0  20G  0 disk 
├─vda1    8:1    0   1G  0 part /boot
├─vda2    8:2    0  19G  0 part 
├─cs-root 253:0   0  17G  0 lvm  /
└─cs-swap 253:1   0   2G  0 lvm  [SWAP] 
vdb        8:16   0  10G  0 disk 
├─vdb1    8:17   0   4G  0 part 
├─vdb2    8:18   0   4G  0 part 
└─vdb3    8:19   0   2G  0 part

In this output, the swap partition on /dev/dm-1 is active (2 GB), while /dev/vdb3 is present but not yet enabled for swap usage.

Preparing and Enabling a Swap Partition

Before you can activate a partition as swap space, it must be formatted accordingly. Use the mkswap command to initialize the partition:

$ sudo mkswap /dev/vdb3
Setting up swapspace version 1, size = 2 GiB (2146435076 bytes)
no label, UUID=6d6f451e-5fa4-4cd5-b627-b0f39c810002

Then, enable the swap partition with the swapon command in verbose mode to display details:

$ sudo swapon --verbose /dev/vdb3
swapon: /dev/vdb3: found signature [pagesize=4096, signature=swap]
swapon: /dev/vdb3: pagesize=4096, swapsize=2146435072, devsize=2146435072
swapon /dev/vdb3

Reconfirm the swap status:

$ swapon --show
NAME          TYPE      SIZE   USED PRIO
/dev/dm-1    partition  2G     0B   -2

Making the Swap Configuration Persistent

By default, swap space is not activated after a reboot. To ensure that the swap partition is enabled automatically at startup, add an appropriate entry in the /etc/fstab file. This will also help maintain system stability by ensuring that swap is consistently available. For more details on achieving persistent mounts, refer to the file system documentation.

Disabling Swap Space

There might be times when you need to disable a swap partition—such as for system maintenance or configuration changes. To disable swap temporarily, execute:

$ sudo swapoff /dev/vdb3

Creating and Using a Swap File

In addition to swap partitions, Linux supports swap files. Swap files can be a flexible alternative when dedicated partitions are not available.

Step 1: Creating the Swap File

First, allocate space for the swap file using the dd command. For example, to create a 128 MB swap file:

$ sudo dd if=/dev/zero of=/swap bs=1M count=128

To create a larger 2 GB swap file with progress updates, run:

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

Here:

• if=/dev/zero reads zeros.
• of=/swap specifies the output file location.
• bs=1M sets the block size to 1 megabyte.
• count determines how many blocks are allocated.
• status=progress displays the progress.

Step 2: Setting Secure Permissions

Ensure that your swap file is secure by adjusting the permissions so that only the root user can access it:

$ sudo chmod 600 /swap

Step 3: Formatting the File as Swap

Initialize the file as swap space with the mkswap command:

$ sudo mkswap /swap
Setting up swapspace version 1, size = 2 GiB (2147487952 bytes)
no label, UUID=cff8e9dc-54fa-4661-a48e-497610b2f07b

Step 4: Enabling the Swap File

Activate the swap file using the swapon command:

$ sudo swapon --verbose /swap
swapon: /swap: found signature [pagesize=4096, signature=swap]
swapon: /swap: pagesize=4096, swapsize=2147483648, devsize=2147483648
swapon /swap

Verify that your swap space is active by running:

$ swapon --show
NAME          TYPE      SIZE   USED PRIO
/dev/dm-1    partition 2G   268K -2
/swap        file      2G    0B   -3

Conclusion

This article has covered both methods for implementing swap space on Linux: using a dedicated swap partition and creating a swap file. In both cases, the steps involve initializing with mkswap, activating with swapon, and verifying the swap status. For persistent swap configurations across reboots or more advanced setups, consult additional system administration resources.

Now try these steps in your practice environment for enhanced system performance and efficient memory management.