Dear administrators of StackExchange/AskUbuntu, restriction "You must have 50 reputation to comment" blocks many useful comments and tips !!! I'm not a geek who spends his leisure time here and has 50 reputations, I'm just a common being who's using Ubuntu and who has found this site by a search engine when trying to resolve an issue (upgrade of 20 to 22 in my case). I've finally resolved the issue and I'd like to share the how-to with the others on AskUbuntu. With this restriction, I simply cannot and therefore hundreds of other "not-geek-beings" will spend their time again struggling with the same issue... Please remove it, it doesn't harmonize with Linux philosophy.