Create or Remove a swap file in RHEL-based distributions

By default, a swap partition is not present on Cloud Servers, but you can add swap to a server by allocating a swap file. The performance of a swap file is similar to that of a swap partition. However, using a swap file makes it easier to control the swap size without repartitioning a volume. You can control how aggressively the server uses this swap space by modifying the system’s swappiness value.

How to Create and Remove a swap file in Linux CentOS7.

There are two basic types of memory, the Random Access Memory which is used to store data while working on the computer, this type of memory is required to run programs and services and whithout RAM it wouldn't be possible however this data will not be stored once you turn off the computer, precisely its only in charge of a temporary allocation to run such programs.

Whenever we use a hard drive to store data permanently in the computer, mainly allocated in our hard drive which is classified as electro-mechanical data storage device, this allows us to locate this type of data in our system even when we turn off the device, we require data to be transfered to RAM and then CPU will be able to run programs and services as requested.

Then we have Swap File, created in order to use Disk Space whenever we fill up our RAM and used for allocation of data under our kernel memory management.

Usually Swap File is used in Low RAM systems (1GB ~) and it is important to mention that we don't necessarily require swap file to run our Linux enviroment however its recommended to avoid our system presenting a degraded performance whenever we run high demanding programs and processes.

Recommended Swap File Size based on RAM memory.

Procedure

1.- The first step while creating the swap file is to verify the curret swap file size.
We can use free -m and swapon -s to determine the size of the existing swap file (see the image below.)

 free -m

 swapon -s

 swapon -show

A swapon -show will work too and remember that if there's no output or the output is 000, the swap file might not be configured.

2.- To create the swap file we will run the command below:

dd if=/dev/zero of=/swapfile bs=1024 count=1048576`

Here is an explanation of what each part of the command does/

• if= input file (will always be the same)
• of= output file (you can name this file as you want)
• bs= block size (keep value at 1024)
• count= amount of blocks to read and write (will be determined for how much space is required to create swap file for)

• Remember that if we require an specific size we can modify the Count value by mutiplying the bs value for the new size ( in MB) f.e 1024x4096=4194304, the new value for count will be 4194304

  3.- Provide root user read/write permissions to the swap file with the following command:

chmod 600 /swapfile

4.- Setup swap area with the following command:

mkswap /swapfile`

5.- Activate swap memory with swapon /swapfile and using your text editor we need to add /swapfile swap swap defaults 0 0 to the /etc/fstab file.

For more information regarding fstab please visit https://wiki.archlinux.org/index.php/Fstab

6.-Verify that the new swap file is configured with free -m, swapon -s or swapon -show

Removing Swap File

1.- Deactivate swap file with swapoff -v /swapfile then remove the /etc/fstab entry and lastly, remove the swapfile with rm -f /swafile2