root@xxx:~# apt-get update
Hit http://ppa.launchpad.net precise Release.gpg
Hit http://ppa.launchpad.net precise Release
Hit http://ppa.launchpad.net precise/main Sources
Get:1 http://us.archive.ubuntu.com precise Release.gpg [198 B]
Hit http://ppa.launchpad.net precise/main i386 Packages
Hit http://ppa.launchpad.net precise/main TranslationIndex
Hit http://ppa.launchpad.net precise/main Translation-en
Get:2 http://us.archive.ubuntu.com precise-updates Release.gpg [198 B]
Get:3 http://us.archive.ubuntu.com precise-security Release.gpg [49.6 kB]
Get:4 http://us.archive.ubuntu.com precise-backports Release.gpg [194 kB]
Get:5 http://us.archive.ubuntu.com precise Release [53.0 kB]
Ign http://us.archive.ubuntu.com precise Release
Get:6 http://us.archive.ubuntu.com precise-updates Release [53.1 kB]
Ign http://us.archive.ubuntu.com precise-updates Release
Get:7 http://us.archive.ubuntu.com precise-security Release [1,274 kB]
Ign http://us.archive.ubuntu.com precise-security Release
W: GPG error: http://us.archive.ubuntu.com precise Release: The following signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key <ftpmaster@ubuntu.com>
W: GPG error: http://us.archive.ubuntu.com precise-updates Release: The following signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key <ftpmaster@ubuntu.com>
E: GPG error: http://us.archive.ubuntu.com precise-security Release: The following signatures were invalid: NODATA 1 NODATA 2
root@xxx:~# vi /etc/apt/sources.list
root@xxx:~# apt-get update
Hit http://ppa.launchpad.net precise Release.gpg
Hit http://ppa.launchpad.net precise Release
Hit http://ppa.launchpad.net precise/main Sources
Get:1 http://en.archive.ubuntu.com precise Release.gpg [198 B]
Hit http://ppa.launchpad.net precise/main i386 Packages
Hit http://ppa.launchpad.net precise/main TranslationIndex
Hit http://ppa.launchpad.net precise/main Translation-en
Get:2 http://en.archive.ubuntu.com precise-updates Release.gpg [198 B]
Get:3 http://en.archive.ubuntu.com precise-security Release.gpg [49.6 kB]
Get:4 http://en.archive.ubuntu.com precise-backports Release.gpg [194 kB]
Get:5 http://en.archive.ubuntu.com precise Release [53.0 kB]
Ign http://en.archive.ubuntu.com precise Release
Get:6 http://en.archive.ubuntu.com precise-updates Release [53.1 kB]
Ign http://en.archive.ubuntu.com precise-updates Release
Get:7 http://en.archive.ubuntu.com precise-security Release [1,274 kB]
Ign http://en.archive.ubuntu.com precise-security Release
W: GPG error: http://en.archive.ubuntu.com precise Release: The following signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key <ftpmaster@ubuntu.com>
W: GPG error: http://en.archive.ubuntu.com precise-updates Release: The following signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key <ftpmaster@ubuntu.com>
E: GPG error: http://en.archive.ubuntu.com precise-security Release: The following signatures were invalid: NODATA 1 NODATA 2