Google Chrome PPA upgrade invalid signature

Open a terminal and enter the following:

wget -q -O - https://dl-ssl.google.com/linux/linux_signing_key.pub | sudo apt-key add -

That will import Google's updated GPG Key.

You should be able to update the system without any errors.

Source: Google Linux Repositories

This site has the only solution that worked for me on 64-bit Ubuntu 14.04 LTS:

http://www.omgubuntu.co.uk/2016/03/fix-failed-to-fetch-google-chrome-apt-error-ubuntu

(Here's a summary. Please see the site for more detail)

1. Edit google-chrome.list (assuming you’re on the Stable Channel, if not, see the featured comment on the site):

   sudo gedit /etc/apt/sources.list.d/google-chrome.list
   

2. In the text file that opens edit the file so that the line reads:

   deb [arch=amd64] http://dl.google.com/linux/chrome/deb/ stable main
   

3. Try update again

   sudo apt-get update
   

This will work better than these solutions:

apt-key list google

You will see this on this list, take not [E] means expired and look at the last 7FAC 5991

pub   dsa1024 2007-03-08 [SC]
      4CCA 1EAF 950C EE4A B839  76DC A040 830F 7FAC 5991
uid           [ unknown] Google, Inc. Linux Package Signing Key <[email protected]>
sub   elg2048 2007-03-08 [E]

pub   rsa4096 2016-04-12 [SC]
      EB4C 1BFD 4F04 2F6D DDCC  EC91 7721 F63B D38B 4796
uid           [ unknown] Google Inc. (Linux Packages Signing Authority) <[email protected]>
sub   rsa4096 2016-04-12 [S] [expires: 2019-04-12]

You will do now:

sudo apt-key del 7FAC5991

Then you will do these commands:

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

And after that's done you will do this to install keyring from another keyserver:

wget -q -O - https://dl.google.com/linux/linux_signing_key.pub | sudo apt-key add -

And then you do:

sudo apt-get update
sudo apt-get dist-upgrade

Now you are all set. :)