how to add / remove swap file on debian 9


Creating a Swap File

The user you are logged in as must have sudo privileges to be able to activate swap. In this guide, we will add 1G of swap, if you want to create a bigger swap, replace 1G with the size of the swap space you need.

The steps below show how to add swap space on Debian 9.

Start by creating a file which will be used for swap:

$ sudo fallocate -l 1G /swapfile

If fallocate is not installed or you get an error message saying fallocate failed: Operation not supported then use the following command to create the swap file:

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

Only the root user should be able to read and write to the swap file. Issue the command below to set the correct permissions :

sudo chmod 600 /swapfile

Use the mkswap tool to set up a Linux swap area on the file:

sudo mkswap /swapfile

Activate the swap file by typing:

sudo swapon /swapfile

Make the change permanent by opening the /etc/fstab file:

sudo nano /etc/fstab

and pasting the following line:

/swapfile swap swap defaults 0 0

o verify the swap is active use either the swapon or free command as shown below:

sudo swapon --show

Output like:

/swapfile file 1024M 507.4M   -1
sudo free -h
              total        used        free      shared  buff/cache   available
Mem:           488M        158M         83M        2.3M        246M        217M
Swap:          1.0G        506M        517M

Adjusting the Swappiness Value 

Swappiness is a Linux kernel property that defines how often the system will use the swap space. Swappiness can have a value between 0 and 100. A low value will make the kernel to try to avoid swapping whenever possible while a higher value will make the kernel to use the swap space more aggressively.

The default swappiness value is 60. You can check the current swappiness value by typing the following command:

cat /proc/sys/vm/swappiness



While the swappiness value of 60 is OK for most Linux systems, for production servers you may need to set a lower value.

sudo sysctl vm.swappiness=10

The optimal swappiness value depends on your system workload and how the memory is being used. You should adjust this parameter in small increments to find an optimal value

Removing a Swap File

First deactivate the swap space by typing:

sudo swapoff -v /swapfile

Next, remove the swap file entry /swapfile swap swap defaults 0 0 from the /etc/fstab file.

Finally, delete the actual swapfile file:

sudo rm /swapfile

You have learned how to create a swap file and activate and configure swap space on your Debian 9 machine.

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