I'm using Ubuntu 15.04. I don't know what has happened; when I start and enter the passphrase, this message appears:
Please enter passphrase for disk ubuntu--vg-swap_1 (cryptswap1) on none!
What should I do?
If your root partition is not encrypted, or if you're not sure, try this: Boot off a Ubuntu install DVD or USB stick and select Try Ubuntu.
If you are able to see your files, edit /etc/fstab and remove the line that looks like this:
/dev/mapper/ubuntu--vg-swap_1 none swap sw 0 0
Reboot and it shouldn't ask you for a passphrase.
If you can't see any files then your root partition is encrypted. I personally haven't experienced this issue, so I can't speak with certainty, but the system shouldn't need to access the swap partition to boot... try pushing enter a few times and see if it gives up and continues booting.