How to fix apt-get GPG error NO_PUBKEY Ubuntu 14

This morning when I do apt-get update on my new Ubuntu 14.04 server, I got these error messages:

Reading package lists… Done 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://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://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

After did some small research on Google, I found a way to overcome this GPG NO_PUBKEY error by downloading the missing key using apt-key tools. The command is as follow:

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

Command result:

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Executing: gpg --ignore-time-conflict --no-options --no-default-keyring --homedir /tmp/tmp.nbL6QNuTxI --no-auto-check-trustdb --trust-model always --keyring /etc/apt/trusted.gpg --primary-keyring /etc/apt/trusted.gpg --keyserver keyserver.ubuntu.com --recv-keys 40976EAF437D05B5
gpg: requesting key 437D05B5 from hkp server keyserver.ubuntu.com
gpg: Total number processed: 1
gpg:               imported: 1

Second command:

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apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 3B4FE6ACC0B21F32

Result:

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Executing: gpg --ignore-time-conflict --no-options --no-default-keyring --homedir /tmp/tmp.scMJ2LlY0s --no-auto-check-trustdb --trust-model always --keyring /etc/apt/trusted.gpg --primary-keyring /etc/apt/trusted.gpg --keyserver keyserver.ubuntu.com --recv-keys 3B4FE6ACC0B21F32
gpg: requesting key C0B21F32 from hkp server keyserver.ubuntu.com
gpg: Total number processed: 1
gpg:               imported: 1  (RSA: 1)

Notice that code 40976EAF437D05B5 and 3B4FE6ACC0B21F32 was taken from the error messages above.

Now you can do apt-get update again and you should have no error anymore.

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