I would like to open by default all .txt files with emacs, but when I right-click on the file, and go to properties, and then go to the "Open With" tab, emacs doesn't appear.
It is not listed either in "recommended applications" or under "other applications". This may be because I installed emacs from source.
Please how can I always open a file with an application that doesn't appear in that list?
If you have (server-start) in your ~/.emacs init file, you can select gnuclient in Properties->Open With 
Thus, you're not constantly starting and stopping emacs.
(server-start) to ~/.emacs and still it doesn't appear gnuclient. I don't know if it's related with the fact that I installed emacs from source
emacs $x server-start, then bash sudo lsof -cemacs and look for a "socket".
Apr 27, 2016 at 20:46
emacs $x server-start to ~/.emacs?. I don't understand what do you mean by "socket"
I think that if the application does not appear in that list then it is because it is not installed in your pc. So I suggest you instead right click on the file, select "Open with other Application.." > "Find applications online". When it installs then you can now select just as the path you took, and set it as default... Hope that helps you.
When you are in the "properties" section see if GNU Emacs 24 (GUI) is listed in the recommended applications section. If it is, you should be able to on it just once, and then proceed with the option to set it as the default application to .txt files with.
If GNU Emacs 24 (GUI) is not listed in the recommended applications sections, then simply scroll down the "other applications" section until you run into it. From there you should be able to have the option to set it as your default application.
