Ubuntu Linux founder Mark Shuttleworth has apologised for a faulty patch last week that left thousands of users without a graphical user interface - a particularly acute problem for a distribution that specialises in ease of use.

The patch for Ubuntu 6.06 was available to users for about 17 hours, from late on Monday 21 August to the morning of the next day. While the patch didn't delete or corrupt data, and didn't cause any security problems, it left many users to rely on the command line.

The bug affected the X Window system, which is used by most Unix and Linux systems and forms the underpinnings of the Gnome and KDE graphical user interfaces. It appeared to be related to specific hardware, according to developers.

Current patches eliminate the problem, and instructions for those who have been affected by the problematic patch have now been published.

"As a team we made a series of errors, and the result was a desktop that was broken for thousands of users, for several hours. It has been a severe lesson in (quality assurance)," Shuttleworth said in a post on his blog.

"When we learned of the problem, the patch was immediately withdrawn. Mirrors have also been disabled to ensure that the faulty patch isn't available from them," Ubuntu said in a statement. "We have launched an investigation and formal quality process review to understand exactly how this happened and what corrective actions to take."

Ubuntu developers cautioned users to download the latest patches before restarting their systems, to ensure that the faulty patch has not been installed. "Delays to the system of update distribution mean that you should make sure you have fully updated before rebooting your computer," the company stated.

An Ubuntu forum devoted to the problem attracted more than 700 posts. No one debated the seriousness of the problem, but users were divided over what the disaster says about Ubuntu and other free, community-oriented Linux distributions.

For some users it was evidence that Linux is not suitable for non-technical desktop users, exactly the sort Ubuntu is aimed at. "I just don't think Linux is ready for prime-time yet... It's too much work for to little reward," wrote a user called Jay.

Others, though, were more willing to accept that the problem was an exception that Ubuntu should be able to prevent from happening again. One user suggested that such problems were inevitable with "universal" operating systems intended to work on any hardware. "It isn't Ubuntu's fault, except in that it is part of the fashionable cult of universalism doing the rounds at present," he wrote. "It is no different than someone falling off a chair and then blaming gravity for their misfortune."

Developers said the problem was insufficient review of patches before they are made available to the public. Ubuntu is looking at getting patches tested by a "wider, but controlled" body of users before they go public, according to Shuttleworth. "We know now that no amount of internal testing will find certain issues," he wrote.

Ubuntu may also create a rollback mechanism allowing faulty patches to be easily uninstalled.