No swap space. encrypted swap in crypttab not created

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http://askubuntu.com – Today I discovered that my Ubuntu 12.04LTS doesn't have any swap-space. I installed this system from scratch only some weeks ago. I encrypted all the partitions to me needs. I didn't install any swap space in the first place, cause the installation dialog misbehaved when I tried to set up the encrypted swap. I added the encrypted swap-space after finishing the installation by editing /etc/crypttab and /etc/fstab. I might issued some more commands to propagate the changes (I don't remember). The swap-space used to just work fine after that. Today I discovered for coincidence that I don't have (HowTos)