Ubuntu: Where is the default tmux config file?

  This is a tricky one to find, mainly because by default it doesn’t exist. You create your custom configuration file in your home directory in a hidden file like so:  
~/.tmux.conf
  …and add your desired configuration changes to that file. So, if you were the user bob, your config file would be located at:  
/home/bob/.tmux.conf
  Since it is a hidden file (prefixed with a period) you won’t see it on ls – you need to use:  
ls -al
  (or ls -a if you don’t like lists) to see it in the directory.

Ubuntu: Killing a tmux pane

  Opened one too many panes in tmux? You can kill one by selecting it and doing the following:  
[prefix] x
  By default the prefix is ctrl+b – so in this case you would enter ctrl+b then x.   Pane killed!

Ubuntu: How to change tmux’s ctrl+b binding to ctrl+a

  If you’re used to screen you’ll be in the habit of using ctrl+a, for example detaching a session with ctrl+a then d – if you make the move to tmux it’s ctrl+b then d, which can take some getting used to. Often it’s easier to make tmux get used to you! To change tmux from ctrl+b to ctrl+a, make sure tmux isn’t running and create the following file:  
vi ~/.tmux.conf
  Here we have used the text editor vi to create the file. Now add the following:  
unbind C-b set -g prefix C-a
  Save the file. Now the next time you start tmux it should have changed to what you’re used to!