Cannot solve GPG error

I ran sudo apt-get update and at the end I have these errors:

Fetched 14,3 kB in 54s (264 B/s)
Reading package lists... Done
W: GPG error: http://archive.canonical.com saucy 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://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://archive.getdeb.net trusty-getdeb InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY A8A515F046D7E7CF
W: GPG error: https://private-ppa.launchpad.net trusty Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY E131728675254D99
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
W: GPG error: http://archive.ubuntu.com trusty-proposed Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 NO_PUBKEY 3B4FE6ACC0B21F32

It seems my missing keys are:

• 40976EAF437D05B5
• 3B4FE6ACC0B21F32
• 16126D3A3E5C1192
• A040830F7FAC5991
• A8A515F046D7E7CF
• E131728675254D99

I saw most of answers say to run:

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys [MISSING KEY]

I ran that:

$ sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 40976EAF437D05B5
Executing: gpg --ignore-time-conflict --no-options --no-default-keyring --homedir /tmp/tmp.2LrTHdOU28 --no-auto-check-trustdb --trust-model always --keyring /etc/apt/trusted.gpg --primary-keyring /etc/apt/trusted.gpg --keyring /etc/apt/trusted.gpg.d/amandeepgrewal-notifyosdconfig.gpg --keyring /etc/apt/trusted.gpg.d/apandada1-typhoon.gpg --keyring /etc/apt/trusted.gpg.d/brightbox-ppa.gpg --keyring /etc/apt/trusted.gpg.d/chris-lea-node_js-devel.gpg --keyring /etc/apt/trusted.gpg.d/chris-lea-node_js.gpg --keyring /etc/apt/trusted.gpg.d/colingille-freshlight.gpg --keyring /etc/apt/trusted.gpg.d/debian-archive-squeeze-automatic.gpg --keyring /etc/apt/trusted.gpg.d/debian-archive-squeeze-stable.gpg --keyring /etc/apt/trusted.gpg.d/debian-archive-wheezy-automatic.gpg --keyring /etc/apt/trusted.gpg.d/debian-archive-wheezy-stable.gpg --keyring /etc/apt/trusted.gpg.d/diesch-testing.gpg --keyring /etc/apt/trusted.gpg.d/duh-golang.gpg --keyring /etc/apt/trusted.gpg.d/ferramroberto-gsharkdown.gpg --keyring /etc/apt/trusted.gpg.d/finalterm-daily.gpg --keyring /etc/apt/trusted.gpg.d/fkrull-deadsnakes.gpg --keyring /etc/apt/trusted.gpg.d/fossfreedom-byzanz.gpg --keyring /etc/apt/trusted.gpg.d/fossfreedom-packagefixes.gpg --keyring /etc/apt/trusted.gpg.d/gophers-go.gpg --keyring /etc/apt/trusted.gpg.d/leolik-leolik.gpg --keyring /etc/apt/trusted.gpg.d/linrunner-tlp.gpg --keyring /etc/apt/trusted.gpg.d/mactel-support-ppa.gpg --keyring /etc/apt/trusted.gpg.d/me-davidsansome-clementine.gpg --keyring /etc/apt/trusted.gpg.d/michael-gruz-canon-trunk.gpg --keyring /etc/apt/trusted.gpg.d/michael-gruz-canon.gpg --keyring /etc/apt/trusted.gpg.d/moka-stable.gpg --keyring /etc/apt/trusted.gpg.d/numix-ppa.gpg --keyring /etc/apt/trusted.gpg.d/nuvola-player-builders-beta.gpg --keyring /etc/apt/trusted.gpg.d/otto-kesselgulasch-gimp-edge.gpg --keyring /etc/apt/trusted.gpg.d/scopes-packagers-ppa.gpg --keyring /etc/apt/trusted.gpg.d/shutter-ppa.gpg --keyring /etc/apt/trusted.gpg.d/steam.gpg --keyring /etc/apt/trusted.gpg.d/sukso96100-budgie-desktop.gpg --keyring /etc/apt/trusted.gpg.d/ubuntu-sdk-team-ppa.gpg --keyring /etc/apt/trusted.gpg.d/ubuntu-x-swat-x-updates.gpg --keyring /etc/apt/trusted.gpg.d/vajdics-netbeans-installer.gpg --keyring /etc/apt/trusted.gpg.d/webupd8team-atom.gpg --keyring /etc/apt/trusted.gpg.d/webupd8team-brackets.gpg --keyring /etc/apt/trusted.gpg.d/webupd8team-java.gpg --keyring /etc/apt/trusted.gpg.d/webupd8team-sublime-text-3.gpg --keyring /etc/apt/trusted.gpg.d/webupd8team-themes.gpg --keyring /etc/apt/trusted.gpg.d/webupd8team-y-ppa-manager.gpg --keyserver keyserver.ubuntu.com --recv-keys 40976EAF437D05B5
gpg: keyblock resource `/etc/apt/trusted.gpg.d/webupd8team-sublime-text-3.gpg': resource limit
gpg: keyblock resource `/etc/apt/trusted.gpg.d/webupd8team-themes.gpg': resource limit
gpg: keyblock resource `/etc/apt/trusted.gpg.d/webupd8team-y-ppa-manager.gpg': resource limit
gpg: requesting key 437D05B5 from hkp server keyserver.ubuntu.com
gpg: key 437D05B5: "Ubuntu Archive Automatic Signing Key <[email protected]>" not changed
gpg: Total number processed: 1
gpg:              unchanged: 1

I can see unchanged: 1.
I also tried to use y-ppa-manager that also didn't solve the problem.

What caused these errors and how can I solve them?

This looks like the following bug to me.

How to Fix

From a user who fixed it in the bug report:

The solution that worked for me was emptying /etc/apt/trusted.gpg.d, running apt-get update, and then manually adding every key it blocked on to the main /etc/apt/trusted.gpg keyring with apt-key adv as described above.

So, in your case, you should do the following (disclaimer: could not test it ):

sudo mv /etc/apt/trusted.gpg.d/ /etc/apt/trusted.gpg.d.backup
sudo mkdir /etc/apt/trusted.gpg.d
sudo chmod 755 /etc/apt/trusted.gpg.d

Then, for each key you need:

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 40976EAF437D05B5

where you replace the hash with your needed key's hash. As Ionică Bizău noted, multiple keys can be added, separated with a space.

Why it appeared

Apparently, gpg can only handle a limited number of keyrings, and your installation required more. Possibly, this is caused by having many alternative packet sources.

Again, from the bug report:

I asked about the "resource limit" message on the gnupg-users mailing list...
Based on Werner Koch's (the dev) answer...
...the secure apt related programs might be making gpg use more than the maximum number of keyrings that it can handle

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys [MISSING KEY] worked for me.

$ sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys A040830F7FAC5991
Executing: gpg --ignore-time-conflict --no-options --no-default-keyring --homedir /tmp/tmp.cmBVPKdUNm --no-auto-check-trustdb --trust-model always --keyring /etc/apt/trusted.gpg --primary-keyring /etc/apt/trusted.gpg --keyserver keyserver.ubuntu.com --recv-keys A040830F7FAC5991
gpg: requesting key 7FAC5991 from hkp server keyserver.ubuntu.com
gpg: key 7FAC5991: public key "Google, Inc. Linux Package Signing Key <[email protected]>" imported
gpg: Total number processed: 1
gpg:               imported: 1