How To Add Swap Space on Ubuntu 22.04

Step 1 – Checking the System for Swap Information

Before we begin, we can check if the system already has some swap space available. It is possible to have multiple swap files or swap partitions, but generally one should be enough.

We can see if the system has any configured swap by typing:

sudo swapon --show

If you don’t get back any output, this means your system does not have swap space available currently.

You can verify that there is no active swap using the free utility:

free -h

As you can see in the Swap row of the output, no swap is active on the system.

Step 2 – Checking Available Space on the Hard Drive Partition

Before we create our swap file, we’ll check our current disk usage to make sure we have enough space. Do this by entering:

df -h

Output
Filesystem      Size  Used Avail Use% Mounted on
udev            474M     0  474M   0% /dev
tmpfs            99M  932K   98M   1% /run
/dev/vda1        25G  1.4G   23G   7% /
tmpfs           491M     0  491M   0% /dev/shm
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs           491M     0  491M   0% /sys/fs/cgroup
/dev/vda15      105M  3.9M  101M   4% /boot/efi
/dev/loop0       55M   55M     0 100% /snap/core18/1705
/dev/loop1       69M   69M     0 100% /snap/lxd/14804
/dev/loop2       28M   28M     0 100% /snap/snapd/7264
tmpfs            99M     0   99M   0% /run/user/1000

Step 3 – Creating a Swap File

Now that we know our available hard drive space, we can create a swap file on our filesystem. We will allocate a file of the size that we want called swapfile in our root (/) directory.

The best way of creating a swap file is with the fallocate program. This command instantly creates a file of the specified size.

Since the server in our example has 1G of RAM, we will create a 1G file in this guide. Adjust this to meet the needs of your own server:

sudo fallocate -l 1G /swapfile

-rw-r--r-- 1 root root 1.0G Apr 25 11:14 /swapfile

Our file has been created with the correct amount of space set aside.

Step 4 – Enabling the Swap File

Now that we have a file of the correct size available, we need to actually turn this into swap space.

First, we need to lock down the permissions of the file so that only users with root privileges can read the contents. This prevents normal users from being able to access the file, which would have significant security implications.

Make the file only accessible to root by typing:

sudo chmod 600 /swapfile

verify the permissions change by typing:

ls -lh /swapfile

Output
-rw------- 1 root root 1.0G Apr 25 11:14 /swapfile

As you can see, only the root user has the read and write flags enabled.

We can now mark the file as swap space by typing:

sudo mkswap /swapfile

sudo swapon /swapfile

Verify that the swap is available by typing:

sudo swapon --show

Output
NAME      TYPE SIZE USED PRIO
/swapfile file 1.0G   0B   -2

We can check the output of the free utility again to corroborate our findings:

free -h

Output
              total        used        free      shared  buff/cache   available
              Mem:           985M        220M        511M         13M        253M        647M
              Swap:          1.0G          0B        1.0G

Our swap has been set up successfully and our operating system will begin to use it as necessary.

Step 5 – Making the Swap File Permanent

Our recent changes have enabled the swap file for the current session. However, if we reboot, the server will not retain the swap settings automatically. We can change this by adding the swap file to our /etc/fstab file.

Back up the /etc/fstab file in case anything goes wrong:

sudo cp /etc/fstab /etc/fstab.bak

Add the swap file information to the end of your /etc/fstab file by typing:

echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab

Next we’ll review some settings we can update to tune our swap space.