Official Ubuntu Documentation
This site is where you can find the official documentation developed and maintained by the Ubuntu Documentation Project.
Choose your version of Ubuntu below to access the documentation for that version (find out which version of Ubuntu you are running).
If you don't find what you are looking for, visit the community help wiki for even more material!
Ubuntu 15.04 - the current stable version, released in late April 2015, codenamed Vivid Vervet.
Ubuntu 14.10 - a stable version, released in late October 2014, codenamed Utopic Unicorn.
Ubuntu 14.04 LTS - the current long term support version, released in mid April 2014, codenamed Trusty Tahr.
Ubuntu 12.04 LTS - a long term support version, released in April 2012, codenamed Precise Pangolin.
If your version of Ubuntu is not listed above, it is no longer supported and does not receive security or critical fixes. Documentation for these releases of Ubuntu is no longer supplied, but information on how to upgrade to supported versions of Ubuntu can be found at the Upgrade Notes page.