GNS3 2.0.3 & GNS3 2.1.0 Error on Ubuntu 16.04LTS: uBridge is not available, path doesn't exist.

GNS3 2.0.3 ERROR:
"uBridge is not available, path doesn't exist, or you just installed GNS3 and need to restart your user session to refresh user permissions"

Solution:

I came across the above uBridge error, while running GNS3 2.0.3 stable version (also tried the development version of GNS3 2.1.0, but stuck at the same error), on my Ubuntu 16.04LTS Machine. Applied almost all available solutions on GNS3 forums and other blogs but nothing worked. Finally, I was able to figure out the following solution, which did the charm! 

Step-1: Open a terminal (Ctrl+Alt+t), and login as root/Superuser 
rana@Ubuntu16:~$ su - 
Password: 
root@Ubuntu16:~$

Step-2: Update repository 
root@Ubuntu16:~$apt-get update 

Step-3: Install 'sudo' 
While trying and working around other available solutions, I suspect that something went wrong with 'sudo' too, this step can be exempted/skipped if 'sudo' is working correctly for you - (which can be checked with 'sudo ls' command) 
root@Ubuntu16:~$apt install sudo 

Step-4: Add the user ('rana' in my case) to group sudo 
root@Ubuntu16:~$usermod -aG sudo rana 

Step-5: Reboot the machine
root@Ubuntu16:~$reboot

Step6: After reboot, reconfigure ubridge 
rana@Ubuntu16:~$sudo dpkg-reconfigure ubridge 

Step-7: Run GNS3, test it and enjoy learning!!! 

[The same answer and other suggested workarounds related to this particular error can also be found at GNS3 Community Forums]

HTH, 
Rana Tauqeer.