How can I create a swap file?

Question

I know how to create and use a swap partition but can I also use a file instead?

How can I create a swap file on a Linux system?

Answer 1

Let's start with the basic information, you should inspect what vm.swappiness is set, and if set wisely to a more acceptable value than 60, which is the default, you should have no problem. This command can be run as normal user:

sysctl vm.swappiness

For instance, I have 32GB RAM server with 32GB swap file with vm.swappiness = 1. Quoting the Wikipedia:

vm.swappiness = 1: Kernel version 3.5 and over, as well as Red Hat kernel version 2.6.32-303 and over: Minimum amount of swapping without disabling it entirely.

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In this example, we create a swap file:

• 8GB in size,

• Located in / (the root directory).

Change these two things accordingly to your needs.

1. Open terminal and become root (su); if you have sudo enabled, you may also do for example sudo -i; see man sudo for all options):

   sudo -i
   

2. Allocate space for the swap file:

   dd if=/dev/zero of=/swapfile bs=1G count=8
   

Optionally, if your system supports it, you may add status=progress to that command line.

Note, that the size specified here in G is in GiB (multiples of 1024).

3. Change permissions of the swap file, so that only root can access it:

   chmod 600 /swapfile
   

4. Make this file a swap file:

   mkswap /swapfile
   

5. Enable the swap file:

   swapon /swapfile
   

6. Verify, whether the swap file is in use:

   cat /proc/swaps
   

7. Open a text editor you are skilled in with this file, e.g. nano if unsure:

   nano /etc/fstab
   

8. To make this swap file available after reboot, add the following line:

   /swapfile        none        swap        sw        0        0
   

Answer 2

$ sudo fallocate -l 1G /swapfile
$ sudo dd if=/dev/zero of=/swapfile bs=1024 count=1048576
$ sudo chmod 600 /swapfile
$ sudo mkswap /swapfile
$ sudo swapon /swapfile

Editor's note: Step 1 and Step 2 are interchangeable.

Answer 3

Please check the script for creating a SWAP Memory of 16GB:

#!/bin/bash
#find Free
free -h
#Checking availability space
df -h
#swap Off
sudo swapoff /swapfile
#Allocate swap
sudo fallocate -l 16G /swapfile
#correct amount of space was reserved
ls -lh /swapfile
#file only accessible to root
sudo chmod 600 /swapfile
#amount of space was reserved for the root
ls -lh /swapfile
#now mark the file as swap space
sudo mkswap /swapfile
#Swap On
sudo swapon /swapfile
#swap Show
sudo swapon --show
#statment 
echo -e "\n\n Swap 16Gb done"
exit 0