GPG error, signatures public key not available TRIED A LOT

apt-get update returns :

W: GPG error: http://pl.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://pl.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://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://deb.torproject.org trusty InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY EE8CBC9E886DDD89
W: GPG error: http://security.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
W: GPG error: http://dl.google.com stable Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY A040830F7FAC5991
W: GPG error: http://dl.google.com stable Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY A040830F7FAC5991

I've tried many recommended solutions from old questions but nothing seems to help.

• sudo apt-get clean

• sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 40976EAF437D05B5 (with all the missing keys)

• I installed lauchpad-getkeys which is supposed to restore keys automatically

Any ideas?

The apt present in Ubuntu is suffering from a gpg resource limit bug in apt

You can easily fix this going to /etc/apt/trusted.gpg.d and removing unused keys (usually from PPAs you don't use anymore) until get below 40 keys.

Then ran sudo apt-get update

You are probably affected by bug 1263540. I suggest you try:

1. sudo apt-get clean
2. sudo mv /var/lib/apt/lists /var/lib/apt/lists.old
3. mkdir -p /var/lib/apt/lists/partial
4. Remove any 0 lenght files in /etc/apt/trusted.gpg.d/
5. sudo apt-get update

If it doesn't work restore /var/lib/apt/lists backed up in step 2.

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