Reinstall Network-Manager in Ubuntu

 Assumptions: Network-Manager is somehow lost (or currepted) while updating/deleting some software and Internet access is lost. Internet access was there using data-cable usb port using mobile-internet connection.

Get Logical Name of the port: Type in terminal 
<sudo lshw -C network>

you will get list of ports with there logical name

Connect to internet using command:
<sudo dhclient <your_port_name>> e.g. in my case it was <sudo dhclient usb0>

Then reinstall Network-Manager using command:
<sudo apt-get install network-manager>

Done!

Ubuntu Notes: Using 7z in terminal

 I> Compress file using 7z

7z a <compressed_file_name.7z> file1 file2 

II> Decompress file using 7z

7z e <compressed_file_name>.7z

Ubuntu Notes: Commands to Shutdown, Restart

 1> to shutdown computer

sudo poweroff;

sudo shutdown -h now;

2> to restart computer

sudo reboot;

Ubuntu Notes: Set Password for a user in ubuntu

 Type:
sudo passwd <username>

Then type new password and repeat type new password as prompted

DONE!