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I recently upgraded all local development and CI systems from Ubuntu 12.04 to Ubuntu 12.10.

This killed the local installations of the W3C HTML validator. If the same happened to you, here's how to fix it.

The Problem

The package responsible for providing /usr/share/xml/xhtml was removed. This causes the W3C HTML validator to fail as it requires the above directory to be present in order to find various document type definitions.

It gets a bit worse: the above directory isremoved when installing the w3c-markup-validator package.

The Solution

We need to get /usr/share/xml/xhtml back, copy the files we need somewhere safe, reinstall the W3C HTML validator package and then copy the files we need back to where they should be.

  1. Get /usr/share/xml/xhtml back:

    sudo apt-get install w3c-dtd-xhtml

  2. Copy the files we need somewhere safe:

    cp -R /usr/share/xml/xhtml /usr/share/xml/xhtml.bak

  3. Reinstall the W3C HTML validator:

    sudo apt-get remove w3c-markup-validator

    sudo apt-get install w3c-markup-validator

    This will cause /usr/share/xml/xhtml to be removed!

  4. Copy the files we need back to where they should be:

    cp -R /usr/share/xml/xhtml.bak /usr/share/xml/xhtml

You should find your local installation of the W3C HTML validator now works under Ubuntu 12.10.