How To Use A Swap File Instead Of A Swap Partition On Linux
This article explains how to transition from having a swap partition to a swap file. If you don't need to disable any existing swap partition and all you need is to create a swap file and activate it, simply skip steps 1 and 2.
On my Ubuntu 18.04 desktop I had a fairly large swap partition which I wanted to use for other purposes, and move the swap to a file. Ubuntu 18.04 already uses a swap file by default instead of a swap partition, however, I upgraded to the latest Ubuntu version instead of making a clean install, so my system continued to use a swap partition. Therefore I had to move the swap to a file myself.
As a result, the instructions below were tested on my Ubuntu 18.04 desktop. They should work on any Linux distribution though.
It's important to mention that you can't use a swap file with a BTRFS filesystem (thanks to Isaac for mentioning this in the comments).
Also, hibernating (to disk) will no longer work out of the box when using a swap file. This can be done but I can't test it because resuming from hibernation didn't work on my system previously to switching to a swapfile so I just gave up on using hibernation. What's more, most Linux distributions use suspend (to RAM) instead of hibernate (to disk) by default anyway. If you need to enable hibernation with a swapfile, there's some info here. Suspend (to ram) is not affected by this.
1. Turn off your current swap partition.
To see the active swap partition, run:
The command output looks like this in my case:
Now you can turn off the current swap device using this command:
Where
2. Remove your old swap entry from the /etc/fstab file.
To remove the old swap entry, open the
You can open the file with Nano editor from the command line, like this:
And remove the entry containing your swap partition information (you can also just comment out the line by adding a
As you can see, the swap entry should contain
Then press
3. Create a swap file.
To create a swap file of 1GB use this command:
Where:
If you use a different swap file name and path, make sure to use that instead of
4. Set the swap file permission to 600.
Use this so other users won't be able to read your swap file, which may contain sensitive information.
To set the swap file permission to 600, use this command:
5. Format the newly created file as swap:
6. Enable the newly created swap file:
To verify if the new swap file is in use, run:
It should output something like this:
7. Add the newly created swap file to
To use the new swap file each time you boot, you'll need to add it to the
And in this file add the following line:
To save the file (if you've used Nano command line editor) press Ctrl + O, then Enter. To exit Nano editor after you've saved the file press Ctrl + X. Again, remember to not modify anything else in the
8. This step is required for Ubuntu and Debian-based Linux distributions (I'm not sure if others need this too). The file mentioned below exists only if you've hibernated your system at least once, so you can skip this step if you don't have it.
You need to edit the
On my Ubuntu 18.04 desktop I had a fairly large swap partition which I wanted to use for other purposes, and move the swap to a file. Ubuntu 18.04 already uses a swap file by default instead of a swap partition, however, I upgraded to the latest Ubuntu version instead of making a clean install, so my system continued to use a swap partition. Therefore I had to move the swap to a file myself.
As a result, the instructions below were tested on my Ubuntu 18.04 desktop. They should work on any Linux distribution though.
It's important to mention that you can't use a swap file with a BTRFS filesystem (thanks to Isaac for mentioning this in the comments).
Also, hibernating (to disk) will no longer work out of the box when using a swap file. This can be done but I can't test it because resuming from hibernation didn't work on my system previously to switching to a swapfile so I just gave up on using hibernation. What's more, most Linux distributions use suspend (to RAM) instead of hibernate (to disk) by default anyway. If you need to enable hibernation with a swapfile, there's some info here. Suspend (to ram) is not affected by this.
How to Move Swap To A File On Your Linux Filesystem
1. Turn off your current swap partition.
To see the active swap partition, run:
swapon -sThe command output looks like this in my case:
Filename Type Size Used Priority
/dev/sda5 partition 15624188 0 -2Now you can turn off the current swap device using this command:
sudo swapoff /dev/sdXXWhere
/dev/sdXX is the device listed by the swapon -s command (under the Filename section - /dev/sda5 in my case from the example above), so make sure to replace it with your swap partition.2. Remove your old swap entry from the /etc/fstab file.
To remove the old swap entry, open the
/etc/fstab file as root with a text editor, and remove the swap line. Do not modify anything else in the /etc/fstab file! Changing anything else in this file may prevent your system from booting!You can open the file with Nano editor from the command line, like this:
sudo nano /etc/fstabAnd remove the entry containing your swap partition information (you can also just comment out the line by adding a
# in front of it). As an example, in my case the swap entry looks like this:UUID=d1b17f9c-9c5e-4471-854a-3ccaf358c30b none swap sw 0 0As you can see, the swap entry should contain
swap and sw - that's how you know which line to remove (or comment out).Then press
Ctrl + O, then Enter to save the file. To exit Nano editor after you've saved the file press Ctrl + X.3. Create a swap file.
To create a swap file of 1GB use this command:
sudo dd if=/dev/zero of=/swapfile bs=1024 count=1048576Where:
/swapfileis the path and name of the swap file. You can change this to something else.- the number after
count(1048576) equals 1GB. Increase it if you want to use a larger swap file. For example, multiply this number by 5 if you want to use a 5GB swap file (so use 5242880 as thecount=value for a 5GB swap file).
If you use a different swap file name and path, make sure to use that instead of
/swapfile in all the instructions that follow below.4. Set the swap file permission to 600.
Use this so other users won't be able to read your swap file, which may contain sensitive information.
To set the swap file permission to 600, use this command:
sudo chmod 600 /swapfile5. Format the newly created file as swap:
sudo mkswap /swapfile6. Enable the newly created swap file:
sudo swapon /swapfileTo verify if the new swap file is in use, run:
swapon -sIt should output something like this:
Filename Type Size Used Priority
/swapfile file 5242876 0 -27. Add the newly created swap file to
/etc/fstab.To use the new swap file each time you boot, you'll need to add it to the
/etc/fstab file. Open /etc/fstab with a text editor (as root) like Nano:sudo nano /etc/fstabAnd in this file add the following line:
/swapfile none swap sw 0 0To save the file (if you've used Nano command line editor) press Ctrl + O, then Enter. To exit Nano editor after you've saved the file press Ctrl + X. Again, remember to not modify anything else in the
/etc/fstab file! Changing anything else in this file may prevent your system from booting!8. This step is required for Ubuntu and Debian-based Linux distributions (I'm not sure if others need this too). The file mentioned below exists only if you've hibernated your system at least once, so you can skip this step if you don't have it.
You need to edit the
/etc/initramfs-tools/conf.d/resume file and comment out (add a # at the beginning of the line) the RESUME=UUID=... line if you don't plan on hibernating your computer (do not confuse it with sleep / suspend). You can find exact instructions for doing this a bit further down below.If you want to hibernate your computer, you need to edit this line and add the UUID of the partition on which the swap file is located and the resume offset. You can find instructions for doing this by visiting this article (you'll need to follow steps 1, 2, 5 and 6 for this, or just follow the complete article to enable hibernation).
In my case, not doing this resulted in about 15-20 seconds of extra boot time. The
Luckily I noticed a "Gave up waiting for suspend/resume device" message being displayed for a very brief moment while booting, which can be caused by not having the correct swap UUID in
This file is used when resuming from hibernation, and it caused boot delays because we no longer have a swap partition.
To comment out this line in
You'll also need to update initramfs and after that you're done:
systemd-analyze blame command didn't give any info as to why that's happening, so I had to dig quite a bit to find out this is what's causing the boot delay.Luckily I noticed a "Gave up waiting for suspend/resume device" message being displayed for a very brief moment while booting, which can be caused by not having the correct swap UUID in
/etc/initramfs-tools/conf.d/resume.This file is used when resuming from hibernation, and it caused boot delays because we no longer have a swap partition.
To comment out this line in
/etc/initramfs-tools/conf.d/resume, all you have to do is run the command below:sudo sed -i 's/^RESUME=UUID/#RESUME=UUID/g' /etc/initramfs-tools/conf.d/resumeYou'll also need to update initramfs and after that you're done:
sudo update-initramfs -u
