sudo apt-get update on the latest emonPi image to update the raspbian packages I got error:
Fetched 9,960 kB in 30s (324 kB/s) Reading package lists... Done W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://repo.mosquitto.org jessie InRelease: The following signatures were invalid: KEYEXPIRED 1515017477 KEYEXPIRED 1515017477 KEYEXPIRED 1515017477 W: Failed to fetch http://repo.mosquitto.org/debian/dists/jessie/InRelease W: Some index files failed to download. They have been ignored, or old ones used instead.
This can be fixed by updating the key from Mosquitto like this:
wget http://repo.mosquitto.org/debian/mosquitto-repo.gpg.key sudo apt-key add mosquitto-repo.gpg.key