How can I create a swap file?

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 32 GB RAM server with 32 GB 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.

In this example, we create a swap file:

• 32 GiB 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, -l is the same as --length on most systems, and -v is --verbose, more importantly the G means GiB, do not write GB, as it would mean 1000*1000 multiples:

   fallocate -v -l 32G /swapfile 

   Note: DON'T use dd as I found out for Hibernation a contiguous file is needed. (Unclear if also needed for swapping. May need adding some link to docs.)

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

   If your dd does not support status=progress, just leave it out.

   Note, that the size specified here in G is in GiB (multiples of 1024).
   !!! This answer could change my point of view, I'll read it later: https://askubuntu.com/a/1017312/436624

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