How do I capture log events from before a crash on AC66?

[e94mli]

Is there a way on a rt-ac66 to get the log events from before a crash reboot? Seems log is only stored in ram by default. Was hoping to get a clue to why it reboots.

 

[RMerlin]

You can't. Kernel oops messages aren't logged in Syslog, you need a serial cable to capture that output.

 

[e94mli]

Is possible to capture any of the syslog from before a crash in case there is any indication of errors before the actual kernel crash?

 

[Adamm]

Is possible to capture any of the syslog from before a crash in case there is any indication of errors before the actual kernel crash?

No because the syslog is stored on a ramdisk (/tmp) and is saved to only /jffs on clean reboots etc.

 

[e94mli]

No because the syslog is stored on a ramdisk (/tmp) and is saved to only /jffs on clean reboots etc.

That is what I was afraid of. Well I'm going to try the external syslog option, which I just discovered, not as good but much better than nothing.

 

[ColinTaylor]

You could save the syslog on an attached USB drive instead of in RAM. It may be different for the AC66, but this is how I do it for my N66U (modify to suit your situation).

/jffs/scripts/post-mount :

#!/bin/sh

logger -t $(basename $0) $1

if [ $1 = "/tmp/mnt/VERBATIM" ]
then
	logger -t $(basename $0) "Moving syslog"
	LOGFILE=$1/syslog.log
	killall syslogd
	cat /tmp/syslog.log >> $LOGFILE
	syslogd -m 0 -S -O $LOGFILE -s 200 -l 7
	mv /tmp/syslog.log /tmp/syslog.old
	ln -s $LOGFILE /tmp/syslog.log
fi

 

[KAD]

why not just restart syslogd and point it to a thumbdrive same for klogd

klogd should capture most of the kernel messages, but not those that cause the crash, if it's crashed, it's not going to log anything

edit: collin beat me to it, but why not add klogd as well since he wants kernel messages

 

[e94mli]

Since I'm only doing this for debugging I skipped the script and just killed syslogd and started it again pointing to the flash drive. I also restarted klogd to be on the safe side. Remote syslog didn't give any hints hopefully this will. Thanks for the help.

 

[ColinTaylor]

edit: collin beat me to it, but why not add klogd as well since he wants kernel messages

I could be wrong but I understood that klogd sends it's messages through syslogd by default.

 

[KAD]

I could be wrong but I understood that klogd sends it's messages through syslogd by default.

that's correct
but both syslogd and klogd should be killed then restarted

 

[ColinTaylor]

that's correct
but both syslogd and klogd should be killed then restarted

It's doesn't seem to be required (although it's probably good practice). Looking a busybox's klogd.c, it just uses syslog() to write its messages so I don't see it being a problem.