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How to Manage a Swap Partition in Linux

Hitesh Jethva
by Atlantic.Net (273 posts) under Tutorials, VPS Hosting
0 Comments

Swap is a physical space on the disk that is used when the system RAM is full. When the memory usage in a system exceeds the available RAM, the kernel will move the idle page to the swap memory. Swap space can be created on a separate partition or a swap file. If your server is running on a VPS and a swap partition is not present, then you will need to create a swap file.

In this post, we will show how to create and manage a swap space on Linux.

Prerequisites

  • A fresh Ubuntu/CentOS server on the Atlantic.Net Cloud Platform
  • A root password configured on your server

Step 1 – Create Atlantic.Net Cloud Server

First, log in to your Atlantic.Net Cloud Server. Create a new server, choosing Ubuntu/CentOS as the operating system with at least 2GB RAM. Connect to your Cloud Server via SSH and log in using the credentials highlighted at the top of the page.

Once you are logged in to your Ubuntu/CentOS server, run the following command to update your base system with the latest available packages.

apt-get update -y

Or

yum update -y

Step 2 – Verify Swap Partition

Before starting, you will need to check whether Swap is enabled or not in your system.

You can check it with the following command:

swapon --show

If the output is empty that means there is not any swap space active in your system.

Step 3 – Create a Swap File

As you can see, there is not any swap space active in your system. So you will need to create a new swap file to your system.

First, create a swap file with size 4GB using the following command:

dd if=/dev/zero of=/swapfile bs=4096 count=1048576

You should see the following output:

1048576+0 records in
1048576+0 records out
4294967296 bytes (4.3 GB, 4.0 GiB) copied, 9.47796 s, 453 MB/s

Next, set the correct permission on swapfile with the following command:

chmod 600 /swapfile

Next, create a swap area on the swapfile with the following command:

mkswap /swapfile

Output:

Setting up swapspace version 1, size = 4 GiB (4294963200 bytes)
no label, UUID=035ada64-2c1a-407d-9f1a-c0dd02b8dcd4

Next, activate the swap space using the following command:

swapon /swapfile

The above command will activate the swap space temporarily.

To set up it permanently, edit the /etc/fstab file:

nano /etc/fstab

Add the following line:

/swapfile swap swap defaults 0 0
Save and close the file then verify the swap partition with the following command:
swapon --show

You should see the following output:

NAME      TYPE SIZE USED PRIO
/swapfile file   4G   0B   -2

Step 4 – Check Swap Usage

To check the Swap usage information, run the following command:

free -m

You should see the following output:

              total        used        free      shared  buff/cache   available
Mem:           1987          74          69           0        1843        1745
Swap:          4095           0        4095

You can also check it with the following command:

cat /proc/swaps

You should see the following output:

Filename                                Type            Size    Used    Priority
/swapfile                               file            4194300 0       -2

You can also use the top command to check the swap usage in real-time:

top

You should see the following output:

Tasks:  84 total,   1 running,  83 sleeping,   0 stopped,   0 zombie
%Cpu(s):  5.9 us,  5.9 sy,  0.0 ni, 88.2 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
MiB Mem :   1987.7 total,     68.0 free,     74.8 used,   1844.9 buff/cache
MiB Swap:   4096.0 total,   4096.0 free,      0.0 used.   1745.5 avail Mem 

You can also use the vmstat command to check the swap usage:

vmstat 2 6

You should see the following output:

procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu-----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st
 3  0      0  69356  12096 1877228    0    0    35   652   31   59  0  0 99  0  0
 0  0      0  69420  12096 1877228    0    0     0     0   24   42  0  0 100  0  0
 0  0      0  69388  12096 1877228    0    0     0     0   22   40  0  0 100  0  0

Step 5 – Remove a Swap Space

In order to remove the swap space, you will need to deactivate the swap space first. You can do it with the following command:

swapoff -v /swapfile

Next, edit the /etc/fstab file and remove the following line:

nano /etc/fstab

Remove the following line:

/swapfile swap swap defaults 0 0

Next, remove the swap file using the following command:

rm -rf /swapfile

Next, verify whether the swap space is removed or not with the following command:

swapon --show

Conclusion

In the above guide, you learned how to check and create a swap space on Linux. You also learned how to monitor the swap space with different commands. Get started today with your VPS from Atlantic.Net.

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