Linux swap: what it is and how to use it

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If you are a Linux user you have definitely heard about Linux Swap, but you may not know what it is exactly or have only superficial knowledge about it. Time to change that!

I mention Linux swap and swappiness in almost every article on things to do after installing Linux. You know that Linux swap is somehow related to RAM and swappiness can affect your system performance. It is time to explain what it is and how to use it in little more details.

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What is Linux Swap?

The Linux Kernel divides RAM into chunks of memories and the swapping process is when the Linux Kernel uses a hard disk space (swap space) to store information from RAM and thus releases some RAM space. That is why when you install a Linux distribution, the installation wizard usually asks you to assign some space for the system and another for the swap.

Using swap is a very useful way to extend the RAM because it provides the necessary additional memory when the RAM space has been exhausted and a process has to be continued. It is especially recommended when you have less than 1Gb of RAM. Although in the end, everything depends on you.

Do you need Linux Swap?

This is a question many novice users ask themselves when they begin to discover Linux. In fact, this will depend on the use and amount of RAM your computer has. Regarding the use, there are processes and applications that really use a lot of memory, for example, Google Chrome. However, most of the current equipment comes with at least 8Gb of RAM and that makes the swap process less necessary. Nevertheless, having a swap space is desirable even if you have a lot of RAM.

For example, usually, when your RAM gets full and the Linux kernel has no space to write into, your system will crash. On the other hand, if you have a swap space, it will be used by the Linux kernel and your system will keep working, though much slower. So, it is safer to have swap space.

Note: swap space has one disadvantage – it is much slower than RAM. So, adding a swap space will not make your computer faster, it will only help to overcome some limitations posed by RAM size.

Linux Swap Partition

I recommend that you create the swap partition during the installation of your Linux distribution. In general, these are the recommended sizes for the swap partition.

  • If your computer has 1Gb of RAM or less, then the swap partition should be twice the size of the RAM.
  • But, If you have between 2gb and 4gb of RAM, the size of the swap partition should be half the RAM.
  • Finally, If you have more than 4gb of RAM, then it is enough to have 2Gb.

But everything depends on your use case.

You can check the type and size of your swap with this command:

swapon
Swapon output

Swapon output

Above, I have a swap partition of 2Gb.

Linux Swap File

Alternatively, you can create a Linux Swap File after the installation. The modern Linux Kernel allows Swapping to a swap file instead of a swap partition. A swap file has an advantage over a swap partition that you can change the size of your swap any time easily by changing a swap file size.

If you want to create a swap file, run this command first:

sudo fallocate -l 1G /swapfile

Note: this command is to create a 1Gb swap file. Replace 1G with the value you want.

Next, you have to set the correct permissions.

sudo chmod 600 /swapfile

Then, format the file to swap.

sudo mkswap /swapfile

Finally, enable the swap.

sudo swapon /swapfile
Creating a Linux swap file

Creating a Linux swap file

If you want the changes to be permanent, you need to edit the /etc/fstab file and add the following.

/swapfile swap swap defaults 0 0
3.- Add the linux swap file to the fstab

3.- Add the Linux swap file to the fstab

In the end, check the status of the swapfile:

sudo free -h
4.- Check the Linux swap file status

4. Check the Linux swap file status

If you see the size of a swap file in the total column, you have done everything correctly.

How to remove a Linux Swap File

In case you need to remove a Linux swap file for any reason, you need to follow these steps.

First, deactivate the swap.

sudo swapoff -v /swapfile

If you created the entry in the /etc/fstab file, remove it. To remind you, it is the line: /swapfile swap swap defaults 0 0 entry.

Finally, delete the actual Linux Swap File.

sudo rm /swapfile
5.- Removing a Linux swwap file

5.- Removing a Linux swap file

How to adjust the Swappiness value

Swappiness is a property of the Linux Kernel to define how often the swap space will be used.  As you know RAM is faster than a hard drive. So, every time you need to use swap, you will notice that some processes and applications will run slower. However, you can adjust the system to use much more RAM than swap. This can help improve overall system performance.

Normally, the default swappiness value is 60. The smaller this value, the more of your RAM will be used.

To verify the swappiness value, run this command:

cat /proc/sys/vm/swappiness

You should see the value of 60.

Show the swappiness default value

Show the swappiness default value

If you want to modify the default value, you need to edit the file /etc/sysctl.conf.

sudo nano /etc/sysctl.conf

And add the following (10 is the most commonly recommended value):

vm.swappiness=10
Change the swappiness value

Change the swappiness value

Save the file and close it with Ctrl+O and Ctrl+X shortcuts. In order to apply the changes, you need to reboot the system.

This way your Linux kernel will use more RAM and less swap, but it still will swap when your RAM memory gets critically full. Usually, this setting is recommended when you have more than 4Gb of RAM.

Conclusion

In conclusion, it is safer to have some swap space on your computer. You can use either a swap partition or a swap file. The latter becomes more and more common.

Linux swap is a technical concept but knowing how it works can improve the performance of the system. Just play with the swappiness value.

There are also many other things you can do to improve your Linux experience.

Do you have anything to add about Linux swap? Have you changed the default value of swappiness? Let me know in the comments.

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