Case:”W: GPG error: http://ftp.debian.org jessie-backports”(Openning)

Case:

Reading package lists… Done
W: GPG error: http://ftp.debian.org jessie-backports InRelease: Could not execute ‘gpgv’ to verify signature (is gpgv installed?)
W: GPG error: http://mirrordirector.raspbian.org jessie InRelease: Could not execute ‘gpgv’ to verify signature (is gpgv installed?)

Condition:

Linux raspberrypi 4.9.35-v7+ #1014 SMP Fri Jun 30 14:47:43 BST 2017 armv7l GNU/Linux

Solution:

a.Backport(Temporary use backport to update sources).

apt-get install -t jessie-backports roundcube

b.Update official authenticate key or related media key.

# apt-get install debian-archive-keyring // Official Key
# apt-get install debian-multimedia-keyring // Related media key.

or use ‘apt-cache search keyring’ to seek a viable key.

Example:

pi@raspberrypi:~ $ apt-cache policy roundcube
roundcube:
Installed: (none)
Candidate: 0.9.5+dfsg1-4.1
Version table:
1.1.5+dfsg.1-1~bpo8+5 0
100 http://ftp.debian.org/debian/ jessie-backports/main armhf Packages
0.9.5+dfsg1-4.1 0
500 http://mirrordirector.raspbian.org/raspbian/ jessie/main armhf Packages