Add also to

vi /etc/cron.d/munin-plugin-apt
03  * * * *    root    apt update > /dev/null 2>&1
18  * * * *    root    apt-get  update > /dev/null 2>&1
33  * * * *    root    apt upgrade > /dev/null 2>&1
48 * * * *    root    apt-get upgrade > /dev/null 2>&1

#   service cron reload

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Problems:
:/etc/munin/plugins# munin-run apt
pending.value 3
pending.extinfo file libmagic-mgc libmagic1
hold.value 0
---
:/etc/munin/plugins# munin-run apt_all
pending_stable.value 0
hold_stable.value 0
pending_testing.value 0
hold_testing.value 0
pending_unstable.value 0
hold_unstable.value 0