Can't install updates
first install Y-PPA manager: for this you have to download deb package, you cant install through PPA, since you cant update software list.
click on this link to download debthen open it and click on Advanced Option.
- then click on the second option( try to import all missing GPG keys) shown in image below:
- wait for some time. Then click on third option (try to fix all GPG BADSIG errors)
You need to wait for some time untill its shows you notification that its done ! in case you have upgraded your Ubuntu recently, you have to click on "Re-enable working PPAs after Ubuntu upgrade"
then run
sudo apt-get updateAfter this you can go back to thing you were trying to do.