when I run
sudo apt-get update command on terminal it tells the following error.
W: GPG error: http://ppa.launchpad.net precise Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY A777609328949509
to fix this, I also run the following command.
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys A777609328949509
but everything went into vein. Plzzz help.