Debugging i3: How To
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!
1. 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.
2. 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:
3. 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.
4. 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 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.
5. 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.
6. 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.