gpg is required

[jabla]

If gpg is not installed, the script aborts with the following "unclear" error message:

Abort, signature of checksum file is NOT OK

Therefore the gpg dependency should be listed in the installation instructions.

[gothicVI]

What Ubuntu (based) system comes without gpg?

[jabla]

We have installed ubuntu 18.04 with a netboot mini.iso via pxe.

[pimlie]

I'd assume that setting check_signature=0 would've worked, but have added an automated check if gpg is executable.