How do I enable kernel boot trace over the serial port?

  • Sorry this is off-topic, but I'm trying to install FreeNAS on a J1900 board and the installer won't even start. I've tried to get some advice on the FreeNAS forum, but I've not got anything so though I would try here as I've always had excellent responses :-)

    Basic problem is that the installer gets stuck in a reboot loop. The kernel starts to load but bombs out and doesn't show anything on the screen long enough for me to see what's going on. Videoing the screen didn't help either!

    I've verified that the board boots ok using a FreeBSB 10 install disk, which is the same version as is used by FreeNAS, so the board should boot.

    I want to enable boot time serial output from the kernel as the system boots so that I can capture the messages and review them. I could do this with Linux, but my FreeBSD foo is not good enough to get it going here. I've tried searching the internet, but the only advice I can find is how to enable it for a running system (so that, e.g., it can be used headless once operational).

    Is is possible to add some boot-time magic to the GRUB command line (e.g. using the 'e' option) to enable kernel boot trace over the serial port when the FreeBSD kernel boots?

  • Netgate Administrator

    If it dumps you at a  prompt you normally invoke the back trace by simply entering 'bt'. I assume it doens't though if you say it's stuck in a loop.

    Does it create a crash log anywhere? Can you boot FreeBSD and mount the drive to look at it?

    If it's a serial console then if you're running putty for example you can just enable logging and then view it afterwards at a rational speed.


  • Thanks for the comments.

    Unfortunately I never get to a prompt and I only have a .iso (on a USB stick) to boot from. This is read only, so there's no crash log either. I should be able to hack the image if required.

    It's the serial boot console that I'm hoping to be able to activate, but I can only do that if there's something I can add to Grub when the system boots.

    The really frustrating bit is that it must be very close to booting - FreeBSD 10 works perfectly and FreeNAS uses the same version, so…

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