~$ sudo mkswap /dev/mapper/ubuntu--vg-swap_1 
mkswap: /dev/mapper/ubuntu--vg-swap_1: warning: don't erase bootbits sectors
        on whole disk. Use -f to force.
Setting up swapspace version 1, size = 6082556 KiB
no label, UUID=d64fbde4-bbe9-4f8f-9a3a-ca5fbbc82ec8