There are times when running apt-get update in Ubuntu will result in error messages such as the following:
[chris@server ~]$ sudo apt-get update Ign http://security.ubuntu.com trusty-security InRelease Get:1 http://security.ubuntu.com trusty-security Release.gpg [933 B] ... Fetched 21.9 MB in 14s (1,537 kB/s) 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 [chris@server ~]$
If these errors aren’t fixed, apt will have problems when installing or upgrading packages. For example:
[chris@server ~]$ sudo apt-get upgrade Reading package lists... Done Building dependency tree... Done Calculating upgrade... Done ... E: Some packages could not be authenticated [chris@server ~]$
The apt packaging system has a set of trusted keys that determine whether a package can be authenticated and therefore trusted to be installed on the system. Sometimes the system does not have all the keys it needs and runs into this issue. Fortunately, there is a quick fix. Each key that is listed as missing needs to be added to the apt key manager so that it can authenticate the packages.
Looking at the error above, apt is telling us that the following keys are missing: 40976EAF437D05B5 and 3B4FE6ACC0B21F32. Notice that these are listed multiple times. Each unique key will only need to be added once.