Use coredumpctl to find and fix bugs

An unfortunate fact is that all software has bugs, and some bugs can cause the system to crash. When it occurs, it often leaves a data file on disk called a "core dump." This file contains relevant data about when your system crashed and may help determine why the crash occurred. Often developers ask for data in the form of a "traceback" showing the flow of instructions that led to the crash. Developers can use it to fix bugs to improve the system. If your system crashes, here's how to easily generate a traceback.

Start using coredumpctl

Most Fedora systems use the Automatic Error Reporting Tool (ABRT) [1] to automatically capture crash files and log bugs. However, this method may help if you disabled the service or removed the package.

If you experience a system crash, first make sure you are running the latest software. Updates often contain fixes for bugs that have been discovered to cause serious errors and crashes. After you update, try to reproduce the situation that caused the error.

If the crash still occurs, or you are already running the latest software, there is the helpful coredumpctl tool. This program helps find and handle crashes. To view a list of all core dumps on the system, run the following command:

coredumpctl list

Don't be surprised if you see a longer list than expected. Sometimes system components crash silently in the background and recover on their own. An easy way to quickly find today's dump is to use the -since option:

coredumpctl list --since=today

The "PID" column contains the process ID used to identify the dump. Please pay attention to this number because you will need it later. Or, if you don't want to remember it, assign it to a variable using:

MYPID=<PID>

To view information about the core dump, use this command (use the $MYPID variable or replace the PID number):

coredumpctl info $MYPID

Install debuginfo package

Debug symbol escapes between data in the core dump and instructions in the original code. This symbolic data can be quite large. Unlike the packages most users run on Fedora systems, symbols are installed as the "debuginfo" package. To determine which debuginfo packages you must install, first run the following command:

coredumpctl gdb $MYPID

This may display a lot of information on the screen. The last line may tell you to use dnf to install more debuginfo packages. Run this command with sudo [2] to install:

sudo dnf debuginfo-install <packages...>

Then try the coredumpctl gdb $MYPID command again. You may need to do this repeatedly as other symbols will be expanded in the traceback.

Capture traceback

Run the following command in the debugger to log information:

set logging file mybacktrace.txt
set logging on

You may find that turning off pagination helps. For long tracebacks, this saves time.

set pagination off

Now run the traceback:

thread apply all bt full

Now you can type quit to exit the debugger. mybacktrace.txt Contains trace information that can be attached to a bug or issue. Or, if you're collaborating with someone in real time, you can upload text to pastebin. Either way, you can now provide developers with more help resolving issues.

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