Debugging

First Steps

For capturing the data required for filing bug reports, you can use the bug reporting tool which is available from most dialog screens and from the system tray menu - it takes care of collecting a lot of the information required for bugs reports. The session info dialog window is also useful for diagnostics.

Always try to narrow it down as much as possible, by turning off as many features as possible (clipboard, audio, OpenGL, etc) and trying various encodings.
If possible, try another operating system or another client (ie: the builtin HTML5 client), try a different version, etc

xpra info is always good to have.

The xpra toolbox, which is also accessible from the main launch screen, can be used both natively on the client or through an xpra session on the server. The test tools from this toolbox should run pretty much the same in both cases, comparing the results can be useful.

Debug Logging is the most commonly used debugging technique, enable logging for the subsystem categories relevant to your problem.

Domain specific debugging

Some areas of the system may have dedicated pages which may be more useful for debugging:

• keyboard
• encodings

GDB

When dealing with crashes ("core dumped"), the best way to debug is to fire gdb to get a backtrace.

Attaching to an existing xpra process

Find the pid of the xpra process with:

ps -ef | grep xpra

Then attach gdb to this process:

gdb python $PID_OF_XPRA_PROCESS_TO_DEBUG

wait for it to load all the debug symbols then:

(gdb) continue

Starting xpra in gdb

gdb /usr/bin/python3
run /usr/bin/xpra start ...

or simply:

gdb --args /usr/bin/python /usr/bin/xpra start ...
run

Getting the backtrace

Then once you manage to hit the crash, gdb should show you its prompt again and you can extract the python stacktrace with py-bt and the full stacktrace with bt. Having both is useful.

Note: installing the required "debug" symbol packages for your distribution is out of scope, please refer to your vendor's package manager for details (ie: debian and yum debuginfo-install).

Signal Handling

Xpra handles SIGINT, SIGTERM and SIGUSR1 + SIGUSR2.

To prevent gdb from intercepting SIGINT so you can send this signal to the xpra process, use handle SIGINT nostop pass. ie:

gdb -ex "handle SIGINT nostop pass" \
--args /usr/bin/python3 /usr/bin/xpra start :20 --no-daemon --start=xterm