Grub & Initramfs update cannot be verified

[Ofnuts]

I get the "pending updates" icon (which I rarely see, since it's supposed to install security updates without asking). So, I eventually click on it, and see a list of updates around grub, initramfs, libcgmanager, and a cople of others. If I tell it to install the updates, it says:

The following pieces of software cannot be verified. WARNING: Installing unverified software represents a security risk, as the presence of unverifiable software can be a sign of tampering. Do you wish to continue?

So, should I?

[GreyGeek]

Which repository is the unverified software coming from?

[Ofnuts]

A priori, the French shadow of the Ubuntu repos..

apt-cache showpkg grub-pc | more
Package: grub-pc
Versions: 
2.02~beta2-9ubuntu1.12 (/var/lib/apt/lists/fr.archive.ubuntu.com_ubuntu_dists_trusty-updates_main_binary
-amd64_Packages)

[GreyGeek]

Have you checked the ID in your key ring against that of the repository?
And, which pkgs in the repository triggered the warning, and which developer signed it, if it is signed?

[Ofnuts]

How can I tell if it's a problem with the repository or with the package contents?

Checking again, the libcgmanager updates are no longer in the pending list, but that list now contains all of the avahi system... (in addition to grub and initramfs).

[GreyGeek]

If "apt-get update" gives you a msg about missing ID(s) it's a repository problem. If "apt-get dist-upgrade" starts downloading and installing packages but complains about a specific package missing or conflicting with some other package that's a pkg problem.