`swapon: /mnt/swapfile: skipping - it appears to have holes.`

@lizzy it basically means it's not fully allocated. What's the filesystem you're trying to do this on and how did you create the file?

it's good to note that if you're using something like btrfs you have to use its builtin swapfile functions otherwise you're going to create a major pain in the ass for yourself even if you get it working because of Copy on Write related issues