Getting an error when trying to start the database (end-of-file on communication channel)
If your database is in archive log mode and you don't need it, disable it. This prevents that archive logs are written. Check with archive log list. 

If Automatic archival ist enabled, and you don't need online backups, disable it with alter database noarchivelog; – the database needs to be in nomount state to do it.

With rman you can delete the not needed archivelogs (or backups).


rman target /
delete archivelog all 
exit


This should clean up your FRA. Of course do this only for testing purposes, don't do this in a production environment! But as you are using Ubuntu as base for your installation I don't think it is a production DB.