The bulk of the environment variable for GF are in the $GF/config directory in asenv.conf and asadminenv.conf.
However, there are also hard code paths in assorted other config and XML file.
But I can't see why a ubuntu update would change any of these value, or move your GF installation.
Worst I could see it is messing with the Java install, but that's not what seems to be happening here.
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