SDB:Troubleshooting

Troubleshooting is process of systematic search for the source of a problem by elimination of potential causes. It can be applied to software and hardware problems.

Introduction

This is written as a help to users that would like to find source of problems with computer, but have no previous experience. This is, for now, just to give a basic idea how the simplest form of troubleshooting works. Later it will be added more about computer subsystems (parts) and how to handle it. The intention is not to write comprehensive guide or troubleshooting assistants as there is a lot of high quality articles about this topic on the web, like PC Guide.

Basics

The most common source of problems are recent changes:

those that you know about and
those that happened without your knowledge.

and after that are the faulty components.

While you may think that nothing can happen without you knowledge, because you are the only computer user, think again.

Example: Printer installation

Yesterday you installed shiny new printer. It worked flawlessly. Today printer silently ignores your requests.

You start with printer troubleshooting, reinstallation of CUPS, change configuration settings, and after hours, you decide to replace printer with old one. Whoops. It is not connected to computer. How come?

Nobody told you about today's mom's effort to remove dust around the computer, as her contribution to your opensource efforts.

Connect it, but it doesn't work again. OK, during "troubleshooting" you changed configuration, so now you have to revert "recent changes": reinstall drivers, restore old settings and it works!

This tell us that we can't take for granted that we know all possible causes of a problem and the best practice is to start troubleshooting from scratch including all possible reasons for device failure:

recent changes of any kind
faulty components for any reason

Changes

Hardware

moving computer
connecting and disconnecting hardware
changing hardware

Software

new application
new kernel and drivers

Components

software
hardware

Device Troubleshooting

When said:"We have to include all possible reasons" problem is where to start. Experienced troubleshooters start from the most obvious. If computer or attached device doesn't work at all, than:

check signal lights
- is device turned on
- does device have a power
check connections:
- to the wall outlet,
- between devices,
try to use it from different application.

Why? The simplest possible cause doesn't take much time to check and correct, and it helps to self esteem if you find that computer is unplugged right in the beginning, instead after call to the help desk that will suggest the same.

For instance, a printer doesn't print:

check lights on printer control panel
check printer cable, is it connected on both sides, and is it properly seated,
check is printer connected to power outlet,
check do you have power in outlet.

This might look too obvious, but after some time spent in a business all repairers have collection of "stupid errors" that none of them will admit they have done. It was something that should be checked first, but it was skipped, and found later after long testing when nothing else was left to be checked. After that very first checks have a look at SDB:How to Report a Printing Issue for some basic tests how to diagnose the cause of a printing issue.

Software Troubleshooting

This is not possible without some knowledge about structure, functions and dependencies of installed and used software, but if some function doesn't work after software update, than reversing a change is good idea. Linux distributions come with installation source that doesn't change between releases and we can always "update" software package to version that is included on installation medium. Troubleshooting/How to revert changes?

If after that software works than update delivered either bug (software error) or it is incompatible with the rest of the system. The second usually comes if we update parts of system to newer version that maintainers of distribution have no idea that we did. Most often target of such updates are desktops, where user is looking for new features forgetting on (or not knowing of) complex dependencies between software components. Reversing such change is not trivial and many times is easier to install all from scratch than to repair.

Resources

Internet

Search Engines

On Computer

Software Manuals

Printed

Device manuals

External Links

http://www.pcguide.com/ PC Guide, by Charles M. Kozierok. While some information might be outdated, or not applicable in Linux, PC Guide will help you to understand better your computer.

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