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http://www.ubuntu.com/: central official resource that links to all
- http://manpages.ubuntu.com: lots of generated LTS manpages. Renders see cross links as HTML anchors.
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Stack Exchange for Ubuntu. Sometimes you get fast answers, sometimes not.
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https://bugs.launchpad.net/ubuntu/: official bug tracker.
Includes bugs on the officially supported packages, e.g.: restricted: https://bugs.launchpad.net/ubuntu/+source/nvidia-graphics-drivers-304