Checking swap on linux

How To Check Swap Usage Size and Utilization in Linux

H ow do I check swap (paging) usage under Linux operating systems using command bash/ksh line options? How do I check swap usage size on Linux operating system?

Swap space (also known as paging) is nothing but computer memory management involving swapping regions of memory to and from storage. You can see swap usage summary by device using any one of the following commands. You may have to login as root user to use the following commands.

Tutorial details
Difficulty level	Easy
Root privileges	Yes
Requirements	None
Est. reading time	5m

The maximum useful size of a swap area depends on the architecture and the kernel version. For Linux kernels after v2.3.3+ there is no such limitation on swap size.

Check swap usage size and utilization in Linux

The procedure to check swap space usage and size in Linux is as follows:

1. Open a terminal application.
2. To see swap size in Linux, type the command: swapon -s .
3. You can also refer to the /proc/swaps file to see swap areas in use on Linux.
4. Type free -m to see both your ram and your swap space usage in Linux.
5. Finally, one can use the top or htop command to look for swap space Utilization on Linux too.

How to Check Swap Space in Linux using /proc/swaps file

Type the following cat command to see total and used swap size:
# cat /proc/swaps
Sample outputs:

Another option is to type the grep command as follows:
grep Swap /proc/meminfo

Look for swap space in Linux using swapon command

Type the following command to show swap usage summary by device
# swapon -s
Sample outputs:

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Use free command to monitor swap space usage

Use the free command as follows:
# free -g
# free -k
# free -m
Sample outputs:

See swap size in Linux using vmstat command

Type the following vmstat command:
# vmstat
# vmstat 1 5
Sample outputs:

Note down the following output from swap field:

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

top/atop/htop/glances command

Type the following commands:
# atop
# htop
# top
# glances
Sample outputs from top command:

Sample outputs from htop command:

Fig.01: Linux: Swap Memory Usage Command

Linux Find Out What Process Are Using Swap Space

Try smem command:
smem
OR
top

Linux GUI tool to monitor swap space size and usage

Try Gnome or KDE system monitor tool. For example, the GNOME System Monitor shows you what programs are running and how much processor time, memory (including paging/swap space size), and disk space are being used.

Conclusion

This page showed you how to check for swap space size and utilization in Linux. If you see a large percentage of the swap space utilization, then it is time to add more physical RAM to the Linux system. Another option is to increase swap space by adding a swap file on Linux. Please see the following resources for more info:

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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.

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.

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

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.

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.

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.

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 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 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 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:

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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5 ways to check swap on Linux

Published: June 8, 2017 | Modified: June 24, 2020

Learn 5 different ways to check swap space utilization on Linux server using free, swapon, /proc/swaps, top and vmstat/sar commands.

This is a short, handy post explaining how to check swap space on the Linux server with different commands. We already discussed about swap in few of old posts listed below :

In this post we will be seeing 5 ways to check swap space and utilization in the Linux server.

Using free command

Most of the users know this command. Using free you can check memory and swap utilization on the server in a few lines. By default, without any switch it shows numbers in kilobytes.

Using -h (human-readable) switch shows output values in the nearest possible (three-digit) representation.

In the above output you can see the last row shows swap values, total, used, and free! Here swap value you see is a total of all swap devices on the system. You cant get device wise separated swap summery with this command. To view device wise summery you can use the next commands.

Using swapon command

Generally, swapon command is used to turn on swap on partition, logical volume or file. But using -s switch (summery) you can get current swap information.

This command provides you output size in kilobytes. It also shows you device wise swap so that you can see device name (partition, logical volume or file), its type and how much swap it contributing to the system.

Using /proc/swaps file

Another way is to view the content of the process file /proc/swaps for the current swap config. This outputs the same content as we saw in previous command swapon -s . In fact swapon reads this file to print a summary.

Output explanation is already covered above in swapon -s .

Using top command

Another popular well-known monitoring tool top can be used to view swap information. In the top output you can see the header section includes swap details.

Values in a row for the swap are in kilobytes. This information is also available in other advanced iterations or top alike tools like atop , htop or glance .

Using vmstat or sar command

In vmstat you can see the utilization of swap like swap in and swap out but not the devices or total values of swap like we saw in previous commands.

It’s more of swap monitoring. You can generate reports for certain iteration with particular time intervals like sar reporting.

These are 5 ways to get swap information out of your system. If you know any other methods do let us know in comments!

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5 Commands to Check Swap space in Linux

When the physical memory or RAM on our system is full, we end to make use of the swap space on our systems. In this process, the inactive pages of our memory are moved to the swap space, creating more memory resources. This space is especially useful when a system is down on RAM; however, swap space is located on the hard drive and hence slower to access. Therefore, it should not be considered an appropriate alternative to RAM.

In this article, we will describe a few ways to check for available swap space on your Ubuntu system. The commands and procedures described in this article have been run on an Ubuntu 18.04 LTS system.

We are making use of the Ubuntu command line, the Terminal, in order to check swap space on our system. In order to open the Terminal, you can either use the Dash or the Ctrl+alt+T shortcut. Then you can choose the following ways to get swap space information:

The Linux free command

This command is used to check memory and swap utilization on your system in a few lines. Without the use of any switch, the displayed output is printed in kilobytes.

With the -h switch, the free command displays the memory and swap utilization in nearest possible, 3 digit format.

The swapon command

You can use the swapon command to check swap on a particular partition, logical volume or a file. Here, we will use it with the -s (summary) switch in order to get swap details (in kilobytes).

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The top command

The header section of the top command output shows the swap space information, in kilobytes. Other commands that give this information include htop, glances, and itop, etc.

The vmstat command

Through the vmstat command, you can view the swap in and swap out information. However, you can not see the total values of the swap as seen is the previously mentioned commands.

The /proc/swaps file

You can also view the swap size information throough he swap configuration file /proc/swaps. It also displays device-wise swap information so that you can see device name (partition, logical volume or file), its type and how much swap it contributing to the system.

Though the very simple commands described in this article, you can view the swap space on your Ubuntu system and utilize it when your system is running low on RAM resources.

Karim Buzdar

About the Author: Karim Buzdar holds a degree in telecommunication engineering and holds several sysadmin certifications. As an IT engineer and technical author, he writes for various web sites. You can reach Karim on LinkedIn

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