Comment 7 for bug 1263540

Ubuntu 14.04 fully up-to-date here:

Hi everyone, thanks to the help of user @TJ- on #ubuntu+1 we were able to discover that the issue I was getting is related to this bug:

[...]
Ign http://archive.ubuntu.com trusty-security/universe Translation-en_US
Fetched 4.737 B in 33s (141 B/s)
Reading package lists... Done
W: GPG error: http://archive.canonical.com trusty Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 NO_PUBKEY 3B4FE6ACC0B21F32
W: GPG error: http://extras.ubuntu.com trusty Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 16126D3A3E5C1192
W: GPG error: http://archive.ubuntu.com trusty Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 NO_PUBKEY 3B4FE6ACC0B21F32
W: GPG error: http://archive.ubuntu.com trusty-updates Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 NO_PUBKEY 3B4FE6ACC0B21F32
W: GPG error: http://archive.ubuntu.com trusty-backports Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 NO_PUBKEY 3B4FE6ACC0B21F32
W: GPG error: http://archive.ubuntu.com trusty-security Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 NO_PUBKEY 3B4FE6ACC0B21F32

What I did:
1. sudo apt-get clean
2. sudo mv /var/lib/apt/lists /var/apt/lists.old
3. mkdir -p /var/lib/apt/lists/partial
4. sudo apt-get update

And got the same error so, next thing was trying to reinstall 'ubuntu-keyring': http://pastebin.com/Zr9TppeL

Other relevant info:
"07:32:49 TJ- | msx: The debian bug explains the issue ... too many keyrings being passed to gpg"
"07:35:23 TJ- | msx: Summary is, remove empty keyrings from "/etc/apt/trusted.gpg.d/"

Issue solved here.