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diff --git a/doc/troubleshooting.rst b/doc/troubleshooting.rst new file mode 100644 index 0000000..6cd7218 --- /dev/null +++ b/doc/troubleshooting.rst @@ -0,0 +1,110 @@ +.. highlight:: console +.. _Troubleshooting: + +*************** +Troubleshooting +*************** + +First of all, check the logs. Enabling at least the ``warning`` message +severity may help you to identify some problems. See the :ref:`Logging section` +for details. + +.. _Submitting a bugreport: + +Reporting bugs +============== + +If you are unable to solve the problem by yourself, you can submit a +bugreport to the Knot DNS developers. For security or sensitive issues +contact the developers directly on +`knot-dns@labs.nic.cz <mailto:knot-dns@labs.nic.cz>`_. +All other bugs and questions may be directed to the public Knot DNS users +mailing list +(`knot-dns-users@lists.nic.cz <mailto:knot-dns-users@lists.nic.cz>`_) or +may be entered into the +`issue tracking system <https://gitlab.nic.cz/knot/knot-dns/issues>`_. + +Before anything else, please try to answer the following questions: + +* Has it been working? +* What has changed? System configuration, software updates, network + configuration, firewall rules modification, hardware replacement, etc. + +The bugreport should contain the answers for the previous questions and in +addition at least the following information: + +* Knot DNS version and type of installation (distribution package, from source, + etc.) +* Operating system, platform, kernel version +* Relevant basic hardware information (processor, amount of memory, available + network devices, etc.) +* Description of the bug +* Log output with the highest verbosity (category ``any``, severity ``debug``) +* Steps to reproduce the bug (if known) +* Backtrace (if the bug caused a crash or a hang; see the next section) + +If possible, please provide a minimal configuration file and zone files which +can be used to reproduce the bug. + +.. _Generating backtrace: + +Generating backtrace +==================== + +Backtrace carries basic information about the state of the program and how +the program got where it is. It helps determining the location of the bug in +the source code. + +If you run Knot DNS from distribution packages, make sure the debugging +symbols for the package are installed. The symbols are usually distributed +in a separate package. + +There are several ways to get the backtrace. One possible way is to extract +the backtrace from a core dump file. Core dump is a memory snapshot generated +by the operating system when a process crashes. The generating of core dumps +must be usually enabled:: + + $ ulimit -c unlimited # Enable unlimited core dump size + $ knotd ... # Reproduce the crash + ... + $ gdb knotd <core-dump-file> # Start gdb on the core dump + (gdb) info threads # Get a summary of all threads + (gdb) thread apply all bt full # Extract backtrace from all threads + (gdb) quit + +To save the backtrace into a file, the following GDB commands can be used:: + + (gdb) set pagination off + (gdb) set logging file backtrace.txt + (gdb) set logging on + (gdb) info threads + (gdb) thread apply all bt full + (gdb) set logging off + +To generate a core dump of a running process, the `gcore` utility can be used:: + + $ gcore -o <output-file> $(pidof knotd) + +Please note that core dumps can be intercepted by an error-collecting system +service (systemd-coredump, ABRT, Apport, etc.). If you are using such a service, +consult its documentation about core dump retrieval. + +If the error is reproducible, it is also possible to start and inspect the +server directly in the debugger:: + + $ gdb --args knotd -c /etc/knot.conf + (gdb) run + ... + +Alternatively, the debugger can be attached to a running server +process. This is generally useful when troubleshooting a stuck process:: + + $ knotd ... + $ gdb --pid $(pidof knotd) + (gdb) continue + ... + +If you fail to get a backtrace of a running process using the previous method, +you may try the single-purpose ``pstack`` utility:: + + $ pstack $(pidof knotd) > backtrace.txt |