gri3-wm/docs/debugging

Debugging i3: How To
====================
Michael Stapelberg <michael@i3wm.org>
December 2012

This document describes how to debug i3 suitably for sending us useful bug
reports, even if you have no clue of C programming.

First of all: Thank you for being interested in debugging i3. It really means
something to us to get your bug fixed. If you have any questions about the
debugging and/or need further help, do not hesitate to contact us!

== Verify you are using the latest (development) version

Please verify that you are using the latest version of i3:

---------------
$ i3 --version
i3 version 4.1.2-248-g51728ba (2012-02-12, branch "next")
---------------

Your version can look like this:

4.1.2 (release version)::
You are using a release version. In many cases, bugs are already
fixed in the development version of i3. If they aren’t, we will still ask you
to reproduce your error with the most recent development version of i3.
Therefore, please upgrade to a development version if you can.

4.1.2-248-g51728ba (development version)::
Your version is 248 commits newer than 4.1.2, and the git revision of your
version is +51728ba+. Go to http://code.i3wm.org/i3/commit/?h=next and see if
the line "commit" starts with the same revision. If so, you are using the
latest version.

Development versions of i3 have logging enabled by default and are compiled
with debug symbols.

== Enabling logging

If you are using a development version (see previous section), you don’t need
to do anything -- skip to section 3.

If you are using a release version with a custom +~/.xsession+ (or xinitrc)
file, execute i3 with a line like this:

----------------------------------
# Use 25 MiB of RAM for debug logs
exec i3 --shmlog-size=26214400
----------------------------------

If you are *NOT* using an +~/.xsession+ file but you just chose "i3" from the
list of sessions in your desktop manager (gdm, lxdm, …), edit
+/usr/share/xsessions/i3.desktop+ and replace the +Exec=i3+ line with:

------------------------------
Exec=i3 --shmlog-size=26214400
------------------------------

== Obtaining the debug logfile

No matter whether i3 misbehaved in some way without crashing or whether it just
crashed, the logfile provides all information necessary to debug the problem.

To save a compressed version of the logfile (suitable for attaching it to a
bugreport), use:
--------------------------------------------------------------------
DISPLAY=:0 i3-dump-log | gzip -9c > /tmp/i3.log.gz
--------------------------------------------------------------------

This command does not depend on i3 (it also works while i3 displays
the crash dialog), but it requires a working X11 connection.

== Compiling with debug symbols

To actually get useful backtraces, you should make sure that your version of i3
is compiled with debug symbols:

------------------------------------------------------------------------------
$ file `which i3`
/usr/bin/i3: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically
linked (uses shared libs), for GNU/Linux 2.6.18, not stripped
------------------------------------------------------------------------------

Notice the +not stripped+, which is the important part. If you have a version
which is stripped, please have a look if your distribution provides debug
symbols (package +i3-wm-dbg+ on Debian for example) or if you can turn off
stripping. If nothing helps, please build i3 from source.

== Obtaining a backtrace

Once you have made sure that your i3 is compiled with debug symbols and the C
debugger +gdb+ is installed on your machine, you can let i3 generate a
backtrace in the crash dialog.

After pressing "b" in the crash dialog, you will get a file called
+/tmp/i3-backtrace.%d.%d.txt+ where the first +%d+ is replaced by i3’s process
id (PID) and the second one is incremented each time you generate a backtrace,
starting at 0.

== Sending bug reports/debugging on IRC

When sending bug reports, please attach the *whole* log file. Even if you think
you found the section which clearly highlights the problem, additional
information might be necessary to completely diagnose the problem.

When debugging with us in IRC, be prepared to use a so called nopaste service
such as http://nopaste.info or http://pastebin.com because pasting large
amounts of text in IRC sometimes leads to incomplete lines (servers have line
length limitations) or flood kicks.