Following on from my last post I've been migrating more services into EC2 from my current hosting provider. Another task I found myself needing to do was creating swap files for my EC2 instances. This was another task for which I had completely forgotten the step.
For my use case, I needed to create a 1GiB swap file. To create the file I first tried to use
$ fallocate -l 1G /mnt/swapfile
I found out later that on XFS fallocate has some issues creating files without holes/gaps, so these files don't work as swap files. Instead, I used
$ dd if=/dev/zero of=/mnt/swapfile bs=1MiB count=1024
This will create a 1024MiB (or 1 GiB) file at
/mnt/swapfile. The next step is to set the correct permissions:
$ chmod 600 /mnt/swapfile
Then, we format the file as a swap file:
$ mkswap /mnt/swapfile
After this we can mount it as swap!
$ swapon /mnt/swapfile
We can verify that the swap has been added successfully using
swapon -s which produces something like:
Filename Type Size Used Priority
/mnt/swapfile file 1048572 0 -1
The final step is to ensure that the swap is added on boot. To do this we need to add an entry to
/mnt/swapfile none swap sw 0 0
With that in place, the swap will be added after each reboot so you won't need to manually run
swapon every time.