In order to create a SSL Certificate one needs a CSR request for the server first. Under Linux it is very easy to create such an request:
openssl req -new -newkey rsa:2048 -nodes -keyout domain.key -out domain.csr
will do the job. Afterwards you have a csr file and a private key in the directory where you executed the command.
If your private key is protected by a password you can remove the password by:
> openssl rsa -in old.key -out new.key
During this process it is necessary to give the password once. The new key will not be protected by a password any more.