Debugging i3: How To
====================
-Michael Stapelberg <michael+i3@stapelberg.de>
-July 2011
+Michael Stapelberg <michael@i3wm.org>
+February 2012
This document describes how to debug i3 suitably for sending us useful bug
reports, even if you have no clue of C programming.
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!
-== Enabling logging
+== Verify you are using the latest (development) version
-i3 logs useful information to stdout. To have a clearly defined place where log
-files will be saved, you should redirect stdout and stderr in your
-+~/.xsession+. While you’re at it, putting each run of i3 in a separate log
-file with date/time in its filename is a good idea to not get confused about
-the different log files later on.
+Please verify that you are using the latest version of i3:
---------------------------------------------------------------------
-exec /usr/bin/i3 >~/i3log-$(date +'%F-%k-%M-%S') 2>&1
---------------------------------------------------------------------
-
-To enable verbose output and all levels of debug output (required when
-attaching logfiles to bugreports), add the parameters +-V -d all+, like this:
-
---------------------------------------------------------------------
-exec /usr/bin/i3 -V -d all >~/i3log-$(date +'%F-%k-%M-%S') 2>&1
---------------------------------------------------------------------
-
-== Enabling core dumps
+---------------
+$ i3 --version
+i3 version 4.1.2-248-g51728ba (2012-02-12, branch "next")
+---------------
-When i3 crashes, often you have the chance of getting a 'core dump' (an image
-of the memory of the i3 process which can be loaded into a debugger). To get a
-core dump, you have to make sure that the user limit for core dump files is set
-high enough. Many systems ship with a default value which even forbids core
-dumps completely. To disable the limit completely and thus enable core dumps,
-use the following command (in your +~/.xsession+, before starting i3):
+Your version can look like this:
--------------------
-ulimit -c unlimited
--------------------
+4.1.2::
+You are using a release version. Please
+upgrade to a development version first, or read
+link:debugging-release-version[Debugging i3: How To (release version)].
-Furthermore, to easily recognize core dumps and allow multiple of them, you
-should set a custom core dump filename pattern, using a command like the
-following:
+4.1.2-248-g51728ba::
+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.
----------------------------------------------
-sudo sysctl -w kernel.core_pattern=core.%e.%p
----------------------------------------------
+Development versions of i3 have several properties which make debugging easier:
-This will generate files which have the executable’s file name (%e) and the
-process id (%p) in it. You can save this setting across reboots using
-+/etc/sysctl.conf+.
+1. Shared memory debug logging is enabled by default. You do not have to enable
+ logging explicitly.
+2. Core dumps are enabled by default.
+3. If you are using a version from the Debian/Ubuntu autobuilder, it is
+ compiled without optimization. Debug symbols are available in the i3-wm-dbg
+ package. When compiling i3 yourself, debug mode is the default.
-== Compiling with debug symbols
+== Obtaining the debug logfile
-To actually get useful core dumps, you should make sure that your version of i3
-is compiled with debug symbols, that is, that the symbols are not stripped
-during the build process. You can check whether your executable contains
-symbols by issuing the following command:
+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.
-----------------
-file $(which i3)
-----------------
-
-You should get an output like this:
-------------------------------------------------------------------------------
-/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.
+To save a compressed version of the logfile (suitable for attaching it to a
+bugreport), use:
+--------------------------------------------------------------------
+i3-dump-log | gzip -9c > /tmp/i3.log.gz
+--------------------------------------------------------------------
-== Generating a backtrace
+This command does not depend on i3 (it also works when i3 currently displays
+the crash dialog), but it requires a working X11 connection. When running it
+from a virtual console (Ctrl-Alt-F1), use:
-Once you have made sure that your i3 is compiled with debug symbols and that
-core dumps are enabled, you can start making sense out of the core dumps.
+--------------------------------------------------------------------
+DISPLAY=:0 i3-dump-log | gzip -9c > /tmp/i3.log.gz
+--------------------------------------------------------------------
-Because the core dump depends on the original executable (and its debug
-symbols), please do this as soon as you encounter the problem. If you
-re-compile i3, your core dump might be useless afterwards.
+== Obtaining a backtrace
-Please install +gdb+, a debugger for C. No worries, you don’t need to learn it
-now. Start gdb using the following command (replacing the actual name of the
-core dump of course):
+When i3 displays its crash dialog, do the following:
-----------------------------
-gdb $(which i3) core.i3.3849
-----------------------------
+1. Switch to a virtual console (Ctrl-Alt-F1) or login from a different computer
+2. Generate a backtrace (see below)
+3. Switch back to the crash dialog (Ctrl-Alt-F7)
+4. Restart i3 in-place (you will keep your session), continue working
-Then, generate a backtrace using:
+This is how you get a backtrace from a running i3 process:
---------------
-backtrace full
---------------
+-----------------
+I3PID=$(pidof i3)
+gdb /proc/$I3PID/exe $I3PID \
+ --batch --quiet \
+ --ex 'backtrace full' > /tmp/i3-backtrace.txt 2>&1
+-----------------
== Sending bug reports/debugging on IRC
-When sending bug reports, please paste the relevant part of the log (if in
-doubt, please send us rather too much information than too less) and the whole
-backtrace (if there was a core dump).
+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
projects / i3 / i3 / blobdiff