Is it SAFE to add a 18.04 repo in 20.04?
124502
how to resolve unmet dependencies and file collisions due mixing diferent repositories?
22506
Is there a way to find out whether an updated program/package lands in the official Ubuntu release repositories?
39582
Difference between "ppa-purge" and "add-apt-repository -r"?
105335
How do I upgrade my Ubuntu server from one LTS version to another? Is this safe?
155733
What are the specifics of 18.04's ten year support?
35146
Will apt-get dist-upgrade upgrade my system to newer version?
64509
Can't update from official repositories [Error 409]
131474
How to only install updates from a specific repository?
64558
What does `do-release-upgrade` really do?
109902
Will I lose the already installed applications if I upgrade from ubuntu 18.04 to 20.04
119971
Install 17.10 on 32 bit machine
129223
Ubuntu upgrade from 17.04 to 18.04
117112
Why isn't Ubuntu moving its repositories to old-releases anymore?
60659
Install newer package version from trusty-backports
24165
Upgrade to version newer than repositories
139103
Is is possible to skip the confirmation step while adding a repository?
123413
Will apt-get dist-upgrade upgrade my system to a newer version?