Here I describe a way to create a swap file and swap extension.

I don’t prefer to create a swap partition from an entire disk partition and I’m not sure there is a reason for that.

Creating a file for swap

First of all you need to create a file for a swap partition:

  • sudo fallocate -l 1G /swap_file

Where:

  • 1G - is size of the file.
  • /swap_file - filename and location.

Then set rights on the file:

  • sudo chmod 600 /swap_file

To check the created file and its rights you can use ls:

  • ls -lh /swap_file

Making the created file a swap

To make a file swap you need to use mkswap and swapon:

  1. sudo mkswap /swap_file
  2. sudo swapon /swap_file

To check current swap extensions you may use swapon and free:

  • swapon --show
  • free -h

Making swap persistent

Previously created swap won’t be persistent and will vanish after system reboot. To prevent that behavior you need to modify fstab file.

First of all, it’s a good practice to create a backup version of existent fstab file:

  • sudo cp /etc/fstab /etc/fstab.bak

Then you need to add created swap file to file systems table (fstab). It’s usually done by modifying /etc/fstab and adding the line that describes swap file location and it’s properties.

Use sudo nano /etc/fstab to modify fstab file. Add the next line at the end of file:

  • /swap_file none swap sw 0 0

Where:

  • /swap_file - location to the swap file.

Modifying swappiness

Kernel parameter vm.swappiness describes the amount of ram will be moved to swap extension if needed. Usually it’s 60% but sometimes my servers stuck when I try to compile something. I prefer it to be 10%.

First thing I do is to use sysctl command to change swappiness right away:

  • sudo sysctl vm.swappiness=10

But changing swappiness that way won’t be persistent so you also need to change sysctl.conf file:

  • sudo nano /etc/sysctl.conf
    • vm.swappiness=10

In order to check current swappiness you can write cat /proc/sys/vm/swappiness in your terminal.

Summing up

  1. sudo fallocate -l 1G /swap_file
  2. sudo chmod 600 /swap_file
  3. sudo mkswap /swap_file
  4. sudo swapon /swap_file
  5. sudo cp /etc/fstab /etc/fstab.bak
  6. sudo nano /etc/fstab
    • /swap_file none swap sw 0 0
  7. sudo sysctl vm.swappiness=10
  8. sudo nano /etc/sysctl.conf
    • vm.swappiness=10
Author: Savelii Pototskii
Date:
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Copyright: CC-BY
Categories: linux