Adding swap after installation

Adding swap after installation

_{by Bryanpwo edited by joekamprad (12.08.2020) + (24.02.2021) + (28.09.2023) + (09.09.2025)}

To add after installation there are two options:

1. creating a swap partition by shrinking space and adding a partition using Gparted on the Live ISO

2. creating a swap file.

Making a swap partition with Gparted

Boot your machine with the Live ISO and open Gparted. Select the last partition on your HDD (this can either be the Root partition or the Home partition, depending on how you partitioned your disk) and shrink the partition by leaving a disk space free equal to the size of your RAM or double the size, that’s up to you. Then select the free space and mark it as a swap partition, let Gparted do its work, and boot back into your installed system and swap should be recognized by systemd. To check enter:

swapon --show

Making a swap file

The above method is the easiest one, but it can damage the partition that you’ve shrunk. So you can also make a swap file.

Commands like cp(1) or truncate(1) create files with holes. These files will be rejected by swapon.

Preallocated files created by fallocate(1) may be interpreted as files with holes too depending of the filesystem.

As documented here: swapon.8#Files_with_holes

So as Archwiki recommends better use dd command with some danger of using a Destroyer of Disks.

!! This following step is only needed if you run on Btrfs filesystem !!

_{Notes if you are using Btrfs}

Note: Swap files on file systems spanning multiple devices are not supported. See btrfs(5) § SWAPFILE SUPPORT for all limitations.

To properly initialize a swap file, first create a non-snapshotted subvolume to host the file, e.g.

sudo btrfs subvolume create /swap

Tip: Consider creating the subvolume directly below the top-level subvolume, e.g. @swap. Then, make sure the subvolume is mounted to /swap (or any other accessible location).

Create the swap file:

sudo btrfs filesystem mkswapfile --size 8g --uuid clear /swap/swapfile

If --size is omitted, the default of 2GiB is used.

Further for all file systems:

Use mkswap to create a swap file the size of your choosing. For example, creating a 8 GiB swap file:

sudo mkswap -U clear --size 8G --file /swapfile

To make the file as swap space and finally to enable the file:

sudo swapon /swapfile

Edit the fstab configuration to add an entry for the swap file:

/etc/fstab

/swapfile none swap defaults 0 0

Note: The swap file must be specified by its location on the file system, not by its UUID or LABEL.

to check:

swapon --show

Remove swap file:

To remove a swap file, it must be turned off first and then can be removed:

sudo swapoff /swapfile
sudo rm -f /swapfile

Finally, remove the relevant entry from /etc/fstab.

For more details about swap usage in general and options:

https://wiki.archlinux.org/title/Swap

Swappiness: https://wiki.archlinux.org/title/Swap#Swappiness

zswap: https://wiki.archlinux.org/title/Zswap

zram: https://wiki.archlinux.org/title/Zram