[SOLVED] - W: GPG error: .. The following signatures were invalid: BADSIG ... Ubuntu Extras Archive Automatic Signing Key

While trying to UPDATE/UPGRADE your Ubuntu system from the terminal, you might be bumping, time and again into what is called the BAD SIGNATURE error. Something like this:

W: GPG error: http://01.archive.ubuntu.com trusty Release: The following signatures were invalid: BADSIG 16126D3A3E5C1192 Ubuntu Extras Archive Automatic Signing Key <ftpmaster@ubuntu.com>

To solve the bad signature error in your Ubuntu Installation try the following solution:

 sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys your_key_number  
 Example: sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 16126D3A3E5C1192  

Rebuild your software cache:

 sudo apt-get clean   
 cd /var/lib/apt   
 sudo mv lists oldlist   
 sudo mkdir -p lists/partial   
 sudo apt-get clean   
 sudo apt-get update  

If the above solution doesn't work, you may try the solution below:

 $ sudo -i  
 # apt-get clean  
 # cd /var/lib/apt  
 # mv lists lists.old  
 # mkdir -p lists/partial  
 # apt-get clean  
 # apt-get update