In the handbook (http://www.freebsd.org/doc/en/books/developers-handbook/kerneldebug-online-ddb.html): > There is an option available for serial consoles that allows the use of a serial line BREAK on the console line to enter DDB (options BREAK_TO_DEBUGGER in the kernel config file). This option has been modified to control the default value of the debug.kdb.break_to_debugger tunable, which controls both serial and video console debugger behaviour. ddb(4) may benefit from a mention kernel config NOTES files have incorrect information (jmg@ is looking at that)
Hi Ed, thanks for filing the report. I'd love to see more activity from developers on "their" handbook. ;) I've re-categorized it as a documentation bug. Could you provide a writeup (doesn't have to be in XML, we doc folks can do that) for the changes you're proposing? You can also send us a review on Phabricator if that is easier for you. Cheers Benedict
Hi Benedict, I still need to figure out exactly what the update should be; I submitted this ticket while working with jmg upon discovery that the handbook doesn't match the implementation. Developers should indeed be updating the documentation as they make these changes. Anyhow, I will update this or submit a Phabricator review once I have a handle on what the change should be.
We have these sysctls to control behaviour: ebug.debugger_on_trap: Run debugger on kernel trap before panic debug.debugger_on_recursive_panic: Run debugger on recursive kernel panic debug.debugger_on_panic: Run debugger on kernel panic debug.kdb.panic: set to panic the kernel debug.kdb.enter: set to enter the debugger debug.kdb.break_to_debugger: Enable break to debugger debug.kdb.alt_break_to_debugger: Enable alternative break to debugger and these kernel options: # # Don't enter the debugger for a panic. Intended for unattended operation # where you may want to enter the debugger from the console, but still want # the machine to recover from a panic. # options KDB_UNATTENDED # Options for serial drivers that support consoles: options BREAK_TO_DEBUGGER # A BREAK/DBG on the console goes to # ddb, if available. # Solaris implements a new BREAK which is initiated by a character # sequence CR ~ ^b which is similar to a familiar pattern used on # Sun servers by the Remote Console. There are FreeBSD extensions: # CR ~ ^p requests force panic and CR ~ ^r requests a clean reboot. options ALT_BREAK_TO_DEBUGGER