How to remove applications from Gnome start-up^by Kev

This is to do with Gnome session start-up, not boot-up or login screen start-up problems.
This was hard to find out about, I hope to save people a lot of bother with this document.
If a Gnome session hangs just after starting up, it could be a fault with one of the applications you have previously selected to run on start-up.
Although there is a Gnome fail-safe setting that should not load such start-up applications, it cannot prevent everything.
Fortunately, you can manually edit or remove the application shortcuts that run such applications.

My own circumstances that prompted me to write this guide:
I have the “Check Gmail” email notifier, the “GShare Daemon” network sharing daemon, the “Gwibber” Twitter client and the “Alarm Clock” notifier on start-up. If the Alarm Clock is faulty, it can hang the entire system, which left me having to hard-reboot with only command-line access. As I said, Gnome fail-safe is not guaranteed, and did not bypass it.
I needed to find where the Gnome applications start-up file was, so I did a
grep -r 'alarm-clock' /* to find it. After searching through a lot of the hard drive, it showed me several occurrences, the most likely being:
/home/kev/.config/autostart/, which it was !
These applications I use have the following details:
Application title Starting script directory and filenameDesktop shortcut
Alarm Clock /usr/bin/alarm-clock alarm-clock.desktop
GShare Daemon /usr/bin/gshared GShare Daemon
Check Gmail /usr/bin/checkgmail checkgmail.desktop
Gwibber /usr/bin/gwibber gwibber.desktop
When you add a start-up application, the Start-Up Manager puts the relevant desktop shortcut into the autostart/ directory. To edit or remove them, you need to be in a Terminal, so choose Ubuntu Recovery mode from the main (GRUB) menu and choose “Drop to root shell prompt with networking”; or if you are in the X login screen, choose “Options”, then “Select Sessions”, then “Failsafe Terminal”, you should have root access.

From the “bash” shell command-line prompt, change to your home directory by typing
cd /home/kev or similar.
Now change to the hidden .config directory by typing
cd .config.
Now change to the autostart directory by typing
cd autostart.
Or a quick, but harder to type version of the above would be:
cd /home/kev/.config/autostart.

Now list the contents of the directory by typing
ls -a
(NOTE: The “-a” option shows all files, including hidden ones.)
The applications you chose should all be here. My ones included the then-faulty alarm-clock.desktop. Remove the applications you want to prevent from starting in the next session by using the rm command, e.g.
rm alarm-clock.desktop.
That will do it, now you can exit the bash shell and return to the Login menu by typing
exit.
If you are happy with everything else, run Ubuntu normally. You can then surf for answers as to why the application went wrong. Mine was something to do with faulty clock updates.
If you knew what was stopping these applications from working, you can edit their shortcuts. You'll need a text editor that will run in a terminal session, I prefer editor, if you want a real challenge, try using vi instead.

Finally, I would strongly recommend having more than one administrator-level user login available to Gnome. I could have saved some bother by being able to login to Gnome as an administrator other than “kev”. I won't go into details here, but it's done from System, Administration, Users And Groups menu options, then Unlock. You cannot have a user called “admin”, but “administrator” is fine, type the username and password very carefully, set the User Priveleges to everything (you never know if you might need control of an obscure facility), and set the Main group to “users” or whatever your other accounts are set to, so that getting to files is easier.
Of course, I do not recommend adding start-up applications to your administrator account as well, otherwise you could be back to square one.