Development/Tutorials/Debugging/Using Error Messages

When you start a konsole and type the commands to start an application you will see all sorts of statements are printed in the konsole while the application is running. All applications print these messages, to look at them you have to know where to look. The application will have to be compiled with the debugging enabled. So using a precompiled package from a distribution probably will not give you this information. If you compiled the application yourself, make sure the configure option --disable-debug was not used.

In KDE all debugging text-output can be switched on or off based on so called areas. One application can be one or more area. One part of the kde base libraries can be another area. Enabling/disabling these areas from being printed can be done using the kdebugdialog application. For simple debugging selecting all sections is probably wise.

When you are debugging it is best to simply start a konsole and start the application from there. In a konsole you could simply type:

kicker

and in the konsole kicker could return a message like:

ERROR: kicker is already running!

When a lot of output is written to the konsole it might go out of view before you could read it, therefor it is easy to create a text file which contains all this information, to do so type the following:

application 2>&1 | tee debug.log

where 'application' can be replaced with the application you are debugging. Afterwards you could open the file 'debug.log' to look at the messages again.

If you are NOT starting the application from a konsole the messages will be logged somewhere else, or they could have been discarded by the program that started your application.

If your application is started by clicking on an icon your best bet is to check the following log files. Beware; they contain logs for a lot of applications, not just the application you are debugging!

Case 1: Graphical login (i.e. kdm, gdm, xdm, etc.)

The debug messages get redirected into the file ~/.xsession-errors or ~/.X.err in your home directory (that is with a leading dot '.' also watch the Capital).

Case 2: You are using startx:

Use the following command to restart your session:

startx 2>&1 | tee startx.log

so that all the debug messages of applications started at KDE's startup (and any application launched from the panel etc.) go to the file "startx.log"

Links

The debug messages are usually printed in C++ with the kDebug or kWarning statement. Example:

kDebug(1210) << "arbitrary message";
kWarning(1210) << "this rather should not happen";

The number 1210 (so called debug area) in this case represents kicker. You can omit the number.

See also: kDebug/kWarning API documentation and kdebug.areas for list of debug areas numbers. Note that you can use add_definition(-DKDE_DEFAULT_DEBUG_AREA=<number>) in CMakeLists.txt to specify default debug area.

Initial Author: Thomas Zander