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diff --git a/docs/contributing/md-debugging.md b/docs/contributing/md-debugging.md new file mode 100644 index 00000000..73b622c6 --- /dev/null +++ b/docs/contributing/md-debugging.md @@ -0,0 +1,191 @@ +(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: + +```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)` +- continue 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: + +```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 running individual migrators for testing, +you need to convert the "magic string" on your own by: + +```none +vyos@vyos:~$ /usr/libexec/vyos/run-config-migration.py --virtual --set-vintage vyos /tmp/config.boot +``` + +### Configuration Error on System Boot + +Being 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 down 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 should 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 following +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 highest +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. + + +```{include} /_include/common-references.txt +``` + + +[bootchart.conf]: https://github.com/vyos/vyos-build/blob/current/data/live-build-config/includes.chroot/etc/systemd/bootchart.conf +[vyatta-cfg]: https://github.com/vyos/vyatta-cfg |