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diff --git a/docs/contributing/debugging.rst b/docs/contributing/debugging.rst new file mode 100644 index 00000000..fec73257 --- /dev/null +++ b/docs/contributing/debugging.rst @@ -0,0 +1,206 @@ +.. _debugging: + +######### +Debugging +######### + +There are two flags available to aid in debugging configuration scripts. +Since configuration loading issues will manifest during boot, the flags are +passed as kernel boot parameters. + +ISO image build +=============== + +When having trouble compiling your own ISO image or debugging Jenkins issues +you can follow the steps at :ref:`iso_build_issues`. + +System Startup +============== + +The system startup can be debugged (like loading in the configuration +file from ``/config/config.boot``. This can be achieve by extending the +Kernel command-line in the bootloader. + +Kernel +------ + +* ``vyos-debug`` - Adding the parameter to the linux boot line will produce + timing results for the execution of scripts during commit. If one is seeing + an unexpected delay during manual or boot commit, this may be useful in + identifying bottlenecks. The internal flag is ``VYOS_DEBUG``, and is found + in vyatta-cfg_. Output is directed to ``/var/log/vyatta/cfg-stdout.log``. + +* ``vyos-config-debug`` - During development, coding errors can lead to a + commit failure on boot, possibly resulting in a failed initialization of the + CLI. In this circumstance, the kernel boot parameter ``vyos-config-debug`` + will ensure access to the system as user ``vyos``, and will log a Python + stack trace to the file ``/tmp/boot-config-trace``. + File ``boot-config-trace`` will generate only if config loaded with a failure + status. + +Live System +=========== + +A number of flags can be set up to change the behaviour of VyOS at runtime. +These flags can be toggled using either environment variables or creating +files. + +For each feature, a file called ``vyos.feature.debug`` can be created to +toggle the feature on. If a parameter is required it can be placed inside +the file as its first line. + +The file can be placed in ``/tmp`` for one time debugging (as the file +will be removed on reboot) or placed in '/config' to stay permanently. + +For example, ``/tmp/vyos.ifconfig.debug`` can be created to enable +interface debugging. + +It is also possible to set up the debugging using environment variables. +In that case, the name will be (in uppercase) VYOS_FEATURE_DEBUG. + +For example running, ``export VYOS_IFCONFIG_DEBUG=""`` on your vbash, +will have the same effect as ``touch /tmp/vyos.ifconfig.debug``. + +* ``ifconfig`` - Once set, all commands used, and their responses received + from the OS, will be presented on the screen for inspection. + +* ``command`` - Once set, all commands used, and their responses received + from the OS, will be presented on the screen for inspection. + +* ``developer`` - Should a command fail, instead of printing a message to the + user explaining how to report issues, the python interpreter will start a + PBD post-mortem session to allow the developer to debug the issue. As the + debugger will wait from input from the developer, it has the capacity to + prevent a router to boot and therefore should only be permanently set up + on production if you are ready to see the OS fail to boot. + +* ``log`` - In some rare cases, it may be useful to see what the OS is doing, + including during boot. This option sends all commands used by VyOS to a + file. The default file is ``/tmp/full-log`` but it can be changed. + +.. note:: In order to retrieve the debug output on the command-line you need to + disable ``vyos-configd`` in addition. This can be run either one-time by + calling ``sudo systemctl stop vyos-configd`` or make this reboot-safe by + calling ``sudo systemctl disable vyos-configd``. + +FRR +--- + +Recent versions use the ``vyos.frr`` framework. The Python class is located +inside our ``vyos-1x:python/vyos/frr.py``. It comes with an embedded debugging/ +(print style) debugger as vyos.ifconfig does. + +To enable debugging just run: ``$ touch /tmp/vyos.frr.debug`` + +Debugging Python Code with PDB +------------------------------ + +Sometimes it might be useful to debug Python code interactively on the live +system rather than a IDE. This can be achieved using pdb. + +Let us assume you want to debug a Python script that is called by an op-mode +command. After you found the script by looking up the op-mode-defitions you +can edit the script in the live system using e.g. vi: +``vi /usr/libexec/vyos/op_mode/show_xyz.py`` + +Insert the following statement right before the section where you want to +investigate a problem (e.g. a statement you see in a backtrace): +``import pdb; pdb.set_trace()`` +Optionally you can surrounded this statement by an ``if`` which only triggers +under the condition you are interested in. + +Once you run ``show xyz`` and your condition is triggered you should be dropped +into the python debugger: + + +.. code-block:: none + + > /usr/libexec/vyos/op_mode/show_nat_translations.py(109)process() + -> rule_type = rule.get('type', '') + (Pdb) + +You can type ``help`` to get an overview of the available commands, and +``help command`` to get more information on each command. + +Useful commands are: + +* examine variables using ``pp(var)`` +* contine execution using ``cont`` +* get a backtrace using ``bt`` + +Config Migration Scripts +------------------------ + +When writing a new configuration migrator it may happen that you see an error +when you try to invoke it manually on a development system. This error will +look like: + +.. code-block:: none + + vyos@vyos:~$ /opt/vyatta/etc/config-migrate/migrate/ssh/0-to-1 /tmp/config.boot + Traceback (most recent call last): + File "/opt/vyatta/etc/config-migrate/migrate/ssh/0-to-1", line 31, in <module> + config = ConfigTree(config_file) + File "/usr/lib/python3/dist-packages/vyos/configtree.py", line 134, in __init__ + raise ValueError("Failed to parse config: {0}".format(msg)) + ValueError: Failed to parse config: Syntax error on line 240, character 1: Invalid syntax. + +The reason is that the configuration migration backend is rewritten and uses +a new form of "magic string" which is applied on demand when real config +migration is run on boot. When runnint individual migrators for testing, +you need to convert the "magic string" on your own by: + +.. code-block:: none + + vyos@vyos:~$ /usr/libexec/vyos/run-config-migration.py --virtual --set-vintage vyos /tmp/config.boot + +Configuration Error on System Boot +---------------------------------- + +Beeing brave and running the latest rolling releases will sometimes trigger +bugs due to corner cases we missed in our design. Those bugs should be filed +via Phabricator_ but you can help us to narrow doen the issue. Login to your +VyOS system and change into configuration mode by typing ``configure``. Now +re-load your boot configuration by simply typing ``load`` followed by return. + +You shoudl now see a Python backtrace which will help us to handle the issue, +please attach it to the Phabricator_ task. + +Boot Timing +----------- + +During the migration and extensive rewrite of functionality from Perl into +Python a significant increase in the overall system boottime was noticed. The +system boot time can be analysed and a graph can be generated in the end which +shows in detail who called whom during the system startup phase. + +This is done by utilizing the ``systemd-bootchart`` package which is now +installed by default on the VyOS 1.3 (equuleus) branch. The configuration is +also versioned so we get comparable results. ``systemd-bootchart`` is configured +using this file: bootchart.conf_ + +To enable boot time graphing change the Kernel commandline and add the folowing +string: ``init=/usr/lib/systemd/systemd-bootchart`` + +This can also be done permanently by changing ``/boot/grub/grub.cfg``. + +Priorities +========== + +VyOS CLI is all about priorities. Every CLI node has a corresponding +``node.def`` file and possibly an attached script that is executed when the +node is present. Nodes can have a priority, and on system bootup - or any +other ``commit`` to the config all scripts are executed from lowest to higest +priority. This is good as this gives a deterministic behavior. + +To debug issues in priorities or to see what's going on in the background +you can use the ``/opt/vyatta/sbin/priority.pl`` script which lists to you +the execution order of the scripts. + +.. stop_vyoslinter + +.. _vyatta-cfg: https://github.com/vyos/vyatta-cfg +.. _bootchart.conf: https://github.com/vyos/vyos-build/blob/current/data/live-build-config/includes.chroot/etc/systemd/bootchart.conf +.. include:: /_include/common-references.txt + +.. start_vyoslinter |