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I installed the Ambiance Evolution Theme from a custom PPA, which overwrote the original Ambiance. Same for Midori, Flash and other apps. Is it advisable to downgrade these packages to the Ubuntu-provided versions before an upgrade?

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up vote 3 down vote accepted

Yes it safer to remove PPAs and their packages. Ubuntu upgrades are tested for default installations, not installation in which everything is changed by PPAs. By removing extra repositories (not just PPAs, but also third party repositories) and their associated packages, you return the system to their original state.

After the upgrade, you're free to install your preferred PPAs of course.

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Thanks for your prompt answer! Do you know if there is an application or a script that removes third party repositories and PPAs just to re-enable them as the upgrade completes? – Tigull Jun 27 '11 at 17:32
@Tigull: see How can PPAs be removed?. You need to manually add your programs/ PPAs back afterwards. Your PPAs are listed in files inside the /etc/apt/sources.list.d directory. – Lekensteyn Jun 27 '11 at 17:37

No, it is not safe to simply remove a ppa through the package manager without restoring defaults. This can cause unwanted side effects (e.g. if this were graphics drivers you will have no access to the GUI).

To fully reset your system to defaults and to remove any unwanted ppa we may use the script ppa-purge Install ppa-purge

sudo ppa-purge -purge <nameofppa>

followed by

sudo apt-get update
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