8 Useful Commands to Monitor Swap Space Usage in Linux

Memory management is an essential aspect of every System Administrator to improve the performance of a Linux system. It is always a good practice to monitor swap space usage in Linux to ensure that your system operates relative to its memory demands.

Check Linux Swap Space Usage

8 Commands to Check Linux Swap Space Usage

Therefore in this article we are going to look at ways to monitor swap space usage in a Linux systems.

What is Swap space?

Swap space is a restricted amount of physical memory that is allocated for use by the operating system when available memory has been fully utilized. It is memory management that involves swapping sections of memory to and from physical storage.

On most distributions of Linux, it is recommended that you set swap space when installing the operating system. The amount of swap space you can set for your Linux system may depend on the architecture and kernel version.

How do I check Swap space usage in Linux?

We shall look at different commands and tools that can help you to monitor your swap space usage in your Linux systems as follows:

1. Using the swapon Command

This command helps you to specify the devices on which paging and swapping will be done and we shall look at few important options.

To view all devices marked as swap in the /etc/fstab file you can use the --all option. Though devices that are already working as swap space are skipped.

# swapon --all

If you want to view a summary of swap space usage by device, use the --summary option as follows.

# swapon --summary

Filename				Type		Size	Used	Priority
/dev/sda10                              partition	8282108	0	-1

Use --help option to view help information or open the manpage for more usage options.

2. Using /proc/swaps which is equivalent to swapon

The /proc filesystem is a very special virtual filesystem in Linux. It is also referred to as a process information pseudo-file system.

It actually does not contain ‘real’ files but runtime system information, for example system memory, devices mounted, hardware configuration and many more. Therefore you can also refer to it as a control and information base for the kernel.

To understand more about this filesystem read our article: Understanding /proc File System in Linux.

To check swap usage information, you can view the /proc/swaps file using the cat utility.

# cat /proc/swaps

Filename				Type		Size	Used	Priority
/dev/sda10                              partition	8282108	0	-1

3. Using ‘free’ Command

The free command is used to display the amount of free and used system memory. Using the free command with -h option, which displays output in a human readable format.

# free -h

             total       used       free     shared    buffers     cached
Mem:          7.7G       4.7G       3.0G       408M       182M       1.8G
-/+ buffers/cache:       2.7G       5.0G
Swap:         7.9G         0B       7.9G

From the output above, you can see that the last line provides information about the system swap space. For more usage and examples of free command can be found at: 10 free Command to Check Memory Usage in Linux.

4. Using top Command

The top command displays processor activity of your Linux system, tasks managed by kernel in real-time. To understand how the top command works, read this article: 12 top Commands to Check Linux Process Activity

To check swap space usage with the help of ‘top’ command run the following command.

# top
Check Swap Space Using Top Command

Check Swap Space Using Top Command

5. Using atop Command

The atop command is a system monitor that reports about activities of various processes. But importantly it also shows information about free and used memory space.

# atop
Atop Check Swap Usage

Atop Check Swap Usage

To know more about how to install and use atop command in Linux, read this article: Monitor Logging Activity of Linux System Processes

6. Using htop Command

The htop command is used to view processes in an interactive mode and also displays information about memory usage.

# htop
Htop Check Swap Usage

Htop Check Swap Usage

For more information regarding installation and usage about htop command, read this article: Htop – Interactive Linux Process Monitoring

7. Using the Glances Command

This is a cross-platform system monitoring tool that displays information about running processes, cpu load, storage space usage, memory usage, swap space usage and many more.

# glances
Glances Check Swap Usage

Glances Check Swap Usage

For more information regarding installation and usage about glances command, read this article: Glances – An Advanced Real Time Linux System Monitoring Tool

8. Using the vmstat Command

This command is used to display information about virtual memory statistics. To install vmstat on your Linux system, you can read the article below and see more usage examples:

Linux Performance Monitoring with Vmstat

# vmstat
VmStat Check Swap Usage

VmStat Check Swap Usage

You need to take note of the following in the swap field from the output of this command.

  1. si: Amount of memory swapped in from disk (s).
  2. so: Amount of memory swapped to disk (s).

Summary

These are easy methods one can use and follow to monitor swap space usage and hope this article was helpful. In case you need help or want to add any information relating to memory management in Linux systems, please post a comment. Stay connected to Tecmint.

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Aaron Kili

Aaron Kili is a Linux and F.O.S.S enthusiast, an upcoming Linux SysAdmin, web developer, and currently a content creator for TecMint who loves working with computers and strongly believes in sharing knowledge.

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9 Responses

  1. Balamukunda Sahu says:

    Nice artical and nicely explained but i have one query that why to use swap space even if we have lot of free memory?

    • Aaron Kili says:

      @Balamukunda

      Swap space is used to temporarily hold data moved from the system RAM, which is not actively being used by the system or user especially when RAM is filling up. It is therefore a “backup RAM” of sorts. Even if you have enough RAM, it is still recommended to create a swap space for Linux.

      Another reason is that it helps during hibernation of a computer, where the an image of the RAM captured and saved in the swap area. On restarting the computer, that image is reloaded into RAM, thereby enabling you to work from where you had stopped(point of hibernation).

      I hope you find this helpful.

  2. Tomas says:

    Good stuff, but you forgot to mention likely the best tool to monitor swap usage on Linux: smem.

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