https://help.ubuntu.com/community/Lubuntu/Documentation/RemoveOldKernels

[Jarno Suni]

Xenial has a new way of automatic maintenance: unattended-upgrades 0.90 has new configuration variable 
Unattended-Upgrade::Remove-New-Unused-Dependencies which defaults to true although it is not mentioned in the configuration file. If that works, it is not necessary to enable Unattended-Upgrade::Remove-Unused-Dependencies in /etc/apt/apt.conf.d/50unattended-upgrades in Xenial to get automatic maintenance, if you want it to remove some old kernel packages and related packages only.
 
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Jarno Suni - http://iki.fi/8/ 


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