How can you log out via the terminal?

11.10 and above

gnome-session-quit

11.04 and previous versions

dbus-send --session --type=method_call --print-reply --dest=org.gnome.SessionManager /org/gnome/SessionManager org.gnome.SessionManager.Logout uint32:1

(via DoR, see his answer to "Reboot without sudoer privileges?" for more dbus goodness!)

or alternatively, you can use

gnome-session-save --force-logout

--force-logout in contrast to just --logout will not ask the user to deal with unsaved documents and so on.

is this the easiest way? no simple one line command like sudo logout?? I will never remember all that.

Yes, there is a command called logout, but it concerns the Terminal. gnome-session-save is the program that actually quits the gnome-session, which you can of course kill, but that wouldn't qualify as logging out. :-)

Notice as well that these commands don't require you to be root.

You can always add an alias to your system if you want to have a shorter command.

Open ~/.bash_aliases with a text editor, or create it if it isn't there, and add something like this to it:

alias logout-gnome="gnome-session-save --force-logout"

(.bashrc is a script that is run every time a new virtual terminal is started up, you should set up all your permanent aliases there, see also: How to create a permanent "alias"?)

I had installed mate desktop and none of the menus worked, even the f-keys didn't work. I managed to get xterm through browsing with file manager.

The only thing that worked was :

sudo pkill -u username

11.10 and above

Here's my personal solution!

In the terminal, run:

gedit ~/.bash_aliases

And add:

alias log-out="gnome-session-quit"

to the file! Now you just have to run log-out!