Error occurring during the signature verification of apt-get update
I could fix this issue following https://chrisjean.com/fix-apt-get-update-the-following-signatures-couldnt-be-verified-because-the-public-key-is-not-available/
briefly :Looking at the error above, apt is telling us that the following keys is missing: 3B4FE6ACC0B21F32. Notice that these are listed multiple times. Each unique key will only need to be added once.
To add these keys, I ran the following commands:
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 40976EAF437D05B5
i fixed this issue after following this https://thecodecloud.in/solved-apt-get-update-the-following-signatures-couldnt-be-verified-because-the-public-key-is-not-available/
i checked the exact error while updating ubuntu repo. Then i used the below command that worked successfully meanwhile we have to copy key from the error and paste in below command.
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys ????????????????