Okay so I tried to create a swapfile with the dd command. It f--cked up the filesystem. Swapfile is inaccessible and the whole partition seems to be read-only now. Can't change the permissions via the right-click menu. WTF?
Edit: Luckily I had another Puppy installed on the same partition. Rebooting with another Puppy and running fsck fixed the bullshit. 
How to change permissions of read-only partition (Solved)
Moderator: Forum moderators