How to Check Swap Space in Linux

You can check swap the same way you check memory usage in Linux: using the free command.

If you use the free command with human readable output (with option -h), it will show you the RAM and Swap uses.

free -h

For my system, it shows the following output:

              total        used        free      shared  buff/cache   available
Mem:           7.5G        5.8G        365M        726M        1.4G        787M
Swap:           14G        1.1G         13G

As you can see in the above output, my system has 14 GB of total swap space and out of that 1.1 GB is being used. Around 13 GB of swap space is free.

There are more ways to check swap usage in Linux and you may get some additional information about swap as well.

Other ways to check swap usage in Linux

My favorite way to check swap usage in Linux is by using the swapon command. This is a command dedicated for handling swap memory. Apart from giving accurate information about the swap space being used, it also tells you if the swap space is a partition or a swap file.

You can use it like this:

swapon --show

As you can see in the output, the total swap space is 14.9 GB (not 14 GB as free command showed). 1.1 GB is being used and it’s a swap partition, not a swap file.

NAME           TYPE       SIZE USED PRIO
/dev/nvme0n1p4 partition 14.9G 1.1G   -2

Using swap file is a better idea because you easily increase swap size on Linux with it. Changing swap partition is not a good idea.

Another way to get swap memory details is by using the /proc/meminfo file. The proc directory in Linux filesystem hierarchy stores system usage information for running processes.

cat /proc/meminfo | grep -i swap

Here’s the output:

SwapCached:       164116 kB
SwapTotal:      15625212 kB
SwapFree:       13714756 kB

You can also check swap usage in Linux with top or htop or any other system monitoring tool.

On a related note, you can learn about clearing the swap memory in Linux.

Bonus Tip: Find out which process is using swap space in Linux

You can use an open source utility smem to get more accurate memory usage in Linux. smem is not installed by default so you will have to install it using your distribution’s package manager.

In Ubuntu, smem is available in the universe repository. You can install it using this command:

sudo apt install smem

Once installed, you can use smem to check which process is using how much swap on your system.

You can simply use smem command in the terminal but if your focus is to check swap usage, I suggest reverse sorting it on swap in the following manner:

smem -rs swap

It will show all the running process in reverse order of swap utilization:

  PID User     Command                         Swap      USS      PSS      RSS 
 3931 abhishek /opt/google/chrome/chrome     147668   296852   300926   341716 
 7483 abhishek /opt/google/chrome/chrome -   141524   392900   398545   464700 
15774 abhishek /opt/google/chrome/chrome -   127256   454080   456262   525048 
 1400 abhishek Telegram --                   122060    20528    22514    24832 
 3964 abhishek /opt/google/chrome/chrome -   108436   101632   111780   138312 
 2774 abhishek /usr/bin/gnome-shell          101936   204676   210229   225780 
 9170 abhishek /opt/google/chrome/chrome -    71620    68184    70255   121364 
  473 abhishek /opt/google/chrome/chrome -    57768   265880   267665   334252 
 8733 abhishek /opt/google/chrome/chrome -    52236    47280    48685   104332 
 9422 abhishek /opt/google/chrome/chrome -    41520    62708    64566   120084 

The memory utilization is in kb.

Well, I hope you now know how to check swap memory usage in Linux. You may also want to learn about clearing swap on Linux.

If you are using swap file, you can learn to increase swap size in this video on our YouTube channel:

If you have questions or suggestions, please let me know in the comments below.