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.
Kernel boot parameters
Adding the parameter vyos-debug 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.
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 /tmp/boot-config-trace.