Debugging

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#title The Ubuntu X Debugger's Handbook
||<tablestyle="float:right; font-size: 0.9em; background:#F1F1ED;margin: 0 0 1em 1em;" style="padding:2.0em;">'''Contents'''[[BR]][[TableOfContents(2)]]||

= X and Ubuntu =

The X Windows System is a critical component in the Ubuntu operating
system. X is not without its bugs, but fortunately debugging X issues
is not rocket science.

The vast majority of Ubuntu X issues fall into one of several distinct
categories, and based on the way they manifest, there are several
different tactics that can be employed in a nearly paint-by-numbers
fashion to isolate them.

Even non-developers can help! The goal of this handbook is to give
folks a toolset for rendering these bugs easily solvable.

Also see:
  * ["X/Troubleshooting"] - Tips for analyzing and troubleshooting bugs


= Bug Reporting =

The lifecycle of a bug report begins, unsurprisingly, with the
preliminary report. How a bug is initially reported can have a huge
effect on how it's handled and how quickly it gets fixed.


== Choosing a Good Title ==

Your title should communicate two things: The symptom you're seeing,
and whatever is unique or unusual about your system. Otherwise, your
bug may not get proper attention.

''' Examples: '''
|| '''BAD''':|| Crazy screen issues on boot ||
|| '''BAD''':|| Multiple problems with CD today ||
|| '''BAD''':|| Not able to login or start X after updating ||
|| '''BAD''':|| Randomly doesn't work ||
|| '''GOOD''':|| [Feisty] Screen briefly corrupts during boot with -nv (NVidia 6100) ||
|| '''GOOD''':|| [Hardy Alpha-3] Alt-CD (only) selected wrong driver (Matrox / BenQ FP91+) ||
|| '''GOOD''':|| [Gutsy] Periodic crashes w/ high CPU on Dell Latitude D505 (-intel 855GM) ||
|| '''GOOD''':|| [Dapper,Edgy] Wrong default refresh rates on 16:10 LCD panels ||
|| '''GOOD''':|| After update to -intel 2.0-0ubuntu3, X fails with 'Invalid mode' error ||

== Do's and Don't's ==

||<tablestyle="width: 80%;" style="background-color: #FF8080;"> DON'T: || Assume "they must already know about this" ||
||<style="background-color: lightgreen;"> DO: || Look for existing bug reports that match your problem ||
||||||
||<style="background-color: #FF8080;"> DON'T: || Assume a "similar" bug is exactly what you're seeing ||
||<style="background-color: lightgreen;"> DO: || File a new bug, but mention the ID's of all bugs that sound similar. Someone can dupe them together later. ||
||||||
||<style="background-color: #FF8080;"> DON'T: || Add "me too" responses. Wastes everyone's time. ||
||<style="background-color: lightgreen;"> DO: || Add missing data (photos, logs) to add to an existing bug's "knowledge base". Or if you just wish to be notified, then Subscribe yourself to the bug. ||
||||||
||<style="background-color: #FF8080;"> DON'T: || Post bugs with only a brief description of the problem ||
||<style="background-color: lightgreen;"> DO: || Post relevant logs, config files, and data (see table below) '''ALWAYS ATTACH YOUR /var/log/Xorg.0.log''' ||
||||||
||<style="background-color: #FF8080;"> DON'T: || Assume "everyone" is seeing this same bug ||
||<style="background-color: lightgreen;"> DO: || Consider what is unique about your system ||
||||||
||<style="background-color: #FF8080;"> DON'T: || Assume others will "just know" how the bug occurs ||
||<style="background-color: lightgreen;"> DO: || Itemize the exact steps that result in the issue. Can you reproduce it at will? ||
||||||
||<style="background-color: #FF8080;"> DON'T: || Fire and forget. Abandoned bugs rarely get fixed. ||
||<style="background-color: lightgreen;"> DO: || Follow up on your bug from time to time, even if it seems ignored. Report if the issue goes away or remains when new Ubuntu's come out. ||


== What to Include in Bug Reports ==

|| '''Problem class:''' || '''Things to Include:''' ||
||<|5(^> '''General X bug''' || Description of problem ||
|| Paste in output of {{{lspci -nn | grep VGA}}} ||
|| Attach /etc/X11/xorg.conf ||
|| Attach /var/log/Xorg.0.log ||
|| Attach output of `lspci -vvnn` ||
||<|7(^> '''Wrong resolutions, refresh rates, or monitor specs''' || Resolution, rate, or other parameter expected ||
|| Resolutions, rates, or other parameters actually obtained ||
|| /etc/X11/xorg.conf ||
|| /var/log/Xorg.0.log ||
|| output of `lspci -vvnn` ||
|| output of `sudo ddcprobe` ||
|| output of `xrandr` ||
||<|5(^> '''Wrong font dpi or size''' || Are you running GNOME, KDE, XFCE, or ...? ||
|| Affected (and unaffected) applications ||
|| /var/log/Xorg.0.log ||
|| output of `sudo ddcprobe` ||
|| Screenshot showing font differences ||
||<|11(^> '''X crash, lockup, freeze, exit, or doesn't start/shutdown''' || Detailed description of problem ||
|| List any versions you tried that did not have this issue ||
|| Detailed list of steps to reproduce ||
|| How complete is the X failure? [[BR]] + Does ctrl+alt+f1 take you to a console? [[BR]] + Does ctrl+alt+backspace restart X? [[BR]] + Does mouse pointer still move? [[BR]] + Does the keyboard LED come on when hitting the CAPSLOCK key? ||
|| /etc/X11/xorg.conf ||
|| /var/log/Xorg.0.log ||
|| /var/log/Xorg.0.log.old ||
|| ~/.xsession-errors ||
|| output of `lspci -vvnn` ||
|| output of `cat /proc/acpi/video/*/DOS` ||
|| output of `sudo cat /proc/acpi/dsdt` ||
||<|4(^> '''Keyboard, touchpad, and mouse issues''' || Description of the problem ||
|| /var/log/Xorg.0.log ||
|| output of `xprop -root` ||
|| output of `gconftool-2 -R /desktop/gnome/peripherals` ||
||<|4(^> '''Screen display corruption''' || Photo of the screen ||
|| Description of the problem ||
|| Does it also occur if DRI is disabled? ||
|| /var/log/Xorg.0.log ||
||<|3(^> '''Bad video playback''' || /etc/X11/xorg.conf ||
|| /var/log/Xorg.0.log ||
|| output of `lspci -vvnn` ||


= Bug Triage =

Ubuntu receives a huge amount of bug reports, many of which are
important and valid issues needing attention. Even so, nearly all X bugs
are initially reported without information necessary for classification
and analysis. This is where the bug triaging role comes in.

Bug triaging for Ubuntu's Xorg components does not require any
particular expertise with X, just regular Linux know-how should be
sufficient. As a bug triager, your role is twofold: First as a coach
to help bug reporters in maximizing their chances of getting the bug
addressed by providing complete information, and second as a filter to
help developers focus their time on important and/or easy-to-fix bugs.


After initially reported, a bug is reviewed and several basic things are
checked by the bug triager:

== INITIAL TRIAGE: ==
Do a query for NEW bugs, and for each bug try to move its state to Incomplete, Invalid, etc.:
1. '''Is it definitely an X bug?''' Sometimes things get misfiled, and sometimes reports are just invalid, or are really just support requests and should be directed to '''Launchpad Answers''' instead. If unsure, leave it as is.

2. '''Is it clearly a dupe of an already known bug?''' Ideally reporters should do a cursory scan of existing bug reports to see if it's obviously already in the system, but not all reporters do. If unsure, don't dupe it - someone can handle this later.

3. '''Is the title descriptive enough?''' Watch out for generic titles like "Randomly crashes", "X won't start", or "Corrupted graphics after suspend/resume" because these are just common symptoms and will tend to accumulate me too reports from people with the same symptom but actually a different bug.

4. '''Is there at least the basic minimum amount of data present?''' If not, mark it '''Incomplete''' and see below for a table of what kinds of files and command output is needed. Once you think the basic required info is present, move it to the Confirmed state.

== FINAL TRIAGE: ==
Do a query for INCOMPLETE-WITH-RESPONSE bugs, and for each bug try to move its state to Completed or etc.:
5. '''Take action if now obvious, or ask for additional information.''' Often by this point, additional information has come to light indicating the bug is resolved, a dupe, or invalid, so you can just set the state accordingly at this point.

6. '''Handle 'me-too' replies.''' Often, additional users will report that they too have the "same" problem, yet don't give evidence to that fact so it's hard to say. As a general rule it is preferred for users to report bugs independently unless they present evidence that it is the same (e.g. identical error messages, steps to reproduce, hardware, etc.) In particular, for third party confirmation of an issue it's best for them to post evidence (log files, screenshots, etc.) that they're seeing the same thing. Often the original information request was not answered by the original reporter, but another user has answered in their place - in this case be extremely careful that the second reporter has exactly the same issue, and is not simply piggybacking on a report that 'sounds roughly similar'; gently encourage them to file a new report on their issue if it's not the same.

7. '''Review log files for error messages or other obvious anomalies.''' Highlight these in the bug report, and search launchpad for other reports of that same error message. Mention these as potential dupes, or dupe them where obvious.

8. '''Tidy up the bug report.''' This may involve improving the bug's title or wordsmithing the description to clarify it. Also, make sure it has an Importance assigned to it (see below).

Also do a query for INCOMPLETE-WITHOUT-RESPONSE. In some cases, the bugs actually do have a response, so the above procedure can be used. In most cases, we're still waiting on a response. If a long period (say, 60 days) has passed since the first unanswered request, the bug can be closed as out of date, usually with a request to please test against the latest development version of Ubuntu, and reopen the bug with the requested info if the problem still exists.

== Marking Bugs Ready to be Upstreamed ==

Often bugs are best solved upstream, so many of our bugs should be filed upstream with them. However, it's important to ensure we send them only quality reports that have a high chance of being solved. It's our job to filter out reports that lack information or otherwise are inappropriate for upstream. This work can be divided into two steps: Marking bugs for upstreaming, and filing the upstream reports.

A bug is ready for upstreaming if it meets all the following criteria:
* The original reporter (or a secondary reporter who has proven to have *exactly* the same issue) is active on the Launchpad bug and can follow up on requests
* The issue has be verified using upstream's git-head of xserver and/or the relevant driver
* The issue is not Ubuntu-specific, and not likely to be a kernel issue
* The bug has complete set of log files, backtraces with debug symbols (if its a crash), config files, screenshots, etc. as appropriate.
* The bug has a solid set of steps to reproduce it on demand (if it occurs randomly or intermittently, upstream won't accept it.)

To mark a bug as ready for upstream, click "Also affects project", then leave the URL empty and click "Add to bug report", and "Confirm". This will leave a blank upstream task to search on later.

== Reporting X issues upstream ==

To get issues addressed effectively, its important to provide complete information and clean, high-quality reports them. Indeed, much of the above bug work is geared with the objective of gathering sufficient information that upstream will be able to deal effectively with the problem.

Do a query on "Bugs that need reported upstream". This searches for bugs with an empty project task. For each bug, do a search to see if the same bug is already reported upstream. Take care though - many times a bug *looks* similar but isn't; if there is *any* doubt, file a new bug and just mention the possible dupe, and let the experts decide.

Here are some guidelines for getting best results from bugs upstreamed to bugzilla.freedesktop.org:

 * Always ask the original reporter to join the discussion at bugzilla, and also subscribe them to the bug report after filing it.
 * Focus each bug report on a single issue. Even if the Launchpad bug has multiple "me too" comments, only focus the upstream bug on one of these.
 * Attach complete logs, config files, screenshots, photos, and all other collected evidence
 * Be prepared to follow through on additional information requests, testing, and so on
 * Include a prominent link back to the launchpad bug (not only for upstream; this gives you a convenient back-link to the original bug).


== Bug Importance ==

Bug "Importance" is not the same thing as Development Priority. Importance is an indication of the severity of the issue, not an indication of when it will be fixed (although a bug's importance is a factor to consider when prioritizing).

'''Low''': These bugs are merely cosmetic or make things inconvenient, or occur only rarely.

'''Medium''': Most bugs are medium importance. They hamper use of the system in some fashion, sometimes requiring an inconvenient workaround or other unusual steps (like disabling hardware or software features or reverting to older versions) to get around it.

'''High''': These are serious bugs that are preventing users from using the system, either with no known workaround or an extremely cumbersome one.

'''Critical''': This importance level is not often used, and is saved for widespread catastrophic failures, like X failing to start for all Ubuntu users.

A bug that affects a lot of users may deserve one bump up from where it would be otherwise. A bug which was not well reported, that can't be reproduced, or that only occurs in obscure situations may have its importance bumped down one step.

The bug triager should make an attempt to set an appropriate importance, but don't worry about getting it perfect; it can be adjusted later.

== Bug Priority ==

The priority for a bug is determined by the developers themselves, based on a variety of factors, and so the bug triager does not need to do anything with regard to priority usually.

One factor that can drive a bug to a high priority is if there is a known, tested fix for it, that simply needs integrated into the development version of Ubuntu.

There are two ways priority is indicated in Launchpad:

1. '''Milestones''': Bugs that are assigned to a milestone will gain priority attention during that development cycle. Do not milestone bugs until after they've been fully triaged and have all necessary information available to troubleshoot them.

2. '''Assignees''': Bugs that are assigned to a particular individual will be priorities for them to work on. Generally, ask before assigning bugs to a developer, unless you're that developer's manager.


= Bug Research =

For many bugs, a little googling and searching in upstream bug trackers can reveal important additional info.

1. Review all attached log files for error messages.

2. Look for other similar/duplicate bug reports to gain additional perspectives and look for obvious commonalities, like same error messages, driver, hardware, etc. Places to search:

     * google.com
     * bugs.launchpad.net/ubuntu
     * bugs.debian.org/
     * bugs.freedesktop.org/
     * ubuntuforums.org

 If you find the same issue reported in Launchpad, mark the less complete and/or newer bug as a dupe of the other.

 If you find the same issue reported in debian or xorg, mark it as "Also affects project..."

 With Google, it often helps to include "ubuntu" in the search string. Also, you can use "site:freedesktop.org" or "site:debian.org" to narrow the search to a specific domain.

3. Try reproducing the issue, especially if you have similar hardware.

4. Look for a newer version of the package, and review its changes to see if there's a fix for this issue.

 If so, check `apt-get update; apt-cache madison $pkgname` to see if the new version is already packaged. If not, ask a packager to produce a test package of the new release to test for this bug.

5. Upload any patches you run across directly to Launchpad, and be sure to tick the "patch" checkbox, so patches can be queried for later.

6. Have them try an older Ubuntu Live CD, or have them downgrade a specific package. For example, to downgrade the xserver:

{{{
         apt-get install xserver-xorg-core=2:1.3.0.0.dfsg-4ubuntu
}}}

 If an older version fixes the issue, then possibly you can bisect things down to find a specific patch causing the issue. See the Analysis section for how to do this.

7. Unless you've been lucky and found the fix already, finish up the research phase by doing the following:

 * Summarize your findings. Restate the problem, describe progress made, outline remaining suspicions or questions.

 * If appropriate, report the bug upstream to Debian and/or Xorg, attaching all relevant files and a link to the Ubuntu bug report. Summarize the research you did, patches that were tested, and any other details that may be relevant.		 #REFRESH 0 https://wiki.ubuntu.com/X/Troubleshooting

X/Debugging (last edited 2016-01-10 22:13:08 by penalvch)