The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 31A5F97FED8A569E
W: GPG error: http://www.beerorkid.com edgy Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 31A5F97FED8A569E
W: GPG error: http://ubuntu.compiz.net edgy Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 31A5F97FED8A569E
W: You may want to run apt-get update to correct these problems

apt-get update
E: Could not open lock file /var/lib/apt/lists/lock - open (13 Permission denied)
E: Unable to lock the list directory

any idea how i fix this