apt-get update 할때 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 EAA903E3A2F4C055위와 같이 에러가 뜬다면 # apt-key adv --keyserver keyserver.ubuntu.com --recv-keys EAA903E3A2F4C055 Executing: gpg --ignore-time-conflict --no-options --no-default-keyring --secret-keyring /tmp/tmp.iQj4LjUa8u --trustdb-na..