i3/docs/debugging

Debugging i3: How To
====================
Michael Stapelberg <michael@i3wm.org>
January 2014

This document describes how to debug i3 to send us useful bug
reports, even if you have no knowledge of C programming.

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
process and/or need further help, do not hesitate to contact us!

== Verify you are using i3 ≥ 4.7

Only the latest major version of i3 is supported, i.e. version 4.7 currently.
To verify which version you are running, use:

---------------
$ i3 --moreversion 2>&- || i3 --version
Binary i3 version:  4.7 (2013-12-22, branch "tags/4.7")
Running i3 version: 4.7-84-gac74a63 (2014-01-01, branch "next") (pid 1995)
---------------

Your version can look like this:

4.7 (release version)::
You are using a release version. In many cases, bugs are already
fixed in the development version of i3. Even if the bug is not a known fixed
one, 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.

4.7-85-g9c15b95 (development version)::
Your version is 85 commits newer than 4.7, and the git revision of your
version is +9c15b95+. 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
------------------------------

If you cannot restart i3 for some reason, you can enable debug logging on the
fly:

---------------------------------------
i3-msg 'debuglog on; shmlog on; reload'
---------------------------------------

== 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 | bzip2 -c > /tmp/i3.log.bz2
--------------------------------------------------------------------

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

== On crashes: Obtaining a backtrace

When i3 crashes, it will display a dialog stating “i3 just crashed”, offering
you to save a backtrace to a text file.

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 check whether 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.

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.