I was having a similar issue with this. Specifically the concept of locating, or otherwise creating, the .pam_environment file.
This is the route I followed, courtesy of Deepu Mohan Puthrote's blog post (Link below):
Step One: In your GUI (Graphical User Interface) Locate the file in your 'home' directory called '.pam_environment.' NOTE: Pam_environment is a hidden file, to make it and other files/directories visible press 'Ctrl+H.' If pam_environment does not exist, continue to step two. If pam_environment does exists, skip to step three.
Step Two: This is how you create your pam_environment file. Open your CLI (bash, terminal, or whatever you want to call it) and make sure you are in your home directory (I.e /home/yourname), you can do this with the 'pwd' (print working directory) command. If you are not in your home directory, input 'cd' to revert to your home directory.
Now create the file in question with the following command:
Step Three: In your GUI, open '.pam_environment' in your home directory (remember to make hidden files visible if necessary). When opened, you can input the the commands into the text editor which will create your session wide environment.
For 'PATH' (which I was learning to set) I used something like:
PATH=$PATH:~/usr/sbin:/usr/bin/<----add your directory here ---->
Step Four: Now restart your computer and, if your computer is as old as mine, go make a cup of tea.
Now check that your change has worked. Open your CLI and run the command 'printenv PATH.' Unless I have failed you, you have just successfully created a session wide PATH variable; you should see the PATH variable, or a variant of, displayed on screen with the new value you have defined in your .pam_environment file.
For reference: http://tech.deepumohan.com/2012/12/how-to-set-environment-variable-in.html