Access to shell during or after kernel panic?

[Mick mtn]

On Fri, Nov 11, 2016 at 1:18 AM, Polytropon <freebsd at edvax.de> wrote:

> On Fri, 11 Nov 2016 00:18:39 -0700, Mick mtn wrote:
> > FreeBSD 11R on macbook pro.
> > does not see dvd, yet the system was installed via
> > FreeBSD-11.0-RELEASE-amd64-dvd1.iso
> > ----------------------------------------------------------------
> > partial panic printout:
> > module visa failed to register: 17
> > kbd0 at kbdmux0
> > Panic Module_register_init
> > CPUID=0
> > ...
> > ...
> > ...
> > #1 0 . . . kdb backtrace           at 0x67
> > #2 ...      vpanic                       at 0x182
> > #3          panic                         at 0x43
> > #4          module_register_init at 0x11c
> > #5          mi_startup                 at 0x118
> > #6          btext                          at 0x2c
> >
> > uptime 1s
> > -----------------------------------------------------------------
> > I can see the files in the rescue directory, but can not move to that
> > directory or issue commands like rescue/vi -v boot/loader.conf
>
> After a kernel panic, you usually cannot access the shell anymore,
> not locally, not remotely. But you can press Ctrl+Alt+Esc to enter
> the kernel debugger (which probably won't be much help at this
> point).
>
> I will try Ctrl+Alt+Esc
renders OK prompt, back to square one.

>
>
> > ANY HINTS on possible keyboard combinations to force boot from dvd?
> > Holding "C" on boot is not getting the result i expected.
>
> Is pressing C at boot a Mac-specific action?
>
YES, pressing C prior/during initial boot should direct the process to boot
from alternate media, typically looking at optical drive media. But can be
used to find USB devices as well if the mac boot partition has not been
destroyed.

In this case that partition has been destroyed.
The entire disk was repartitioned to boot FreeBSD only.

>
> When you can access the FreeBSD loader prompt, entering the
> command "boot -C" will usually try to boot from optical media.
> This is the same prompt where you can unload unwanted kernel
> modules, set a different kernel, or enter "boot -s" to continue
> into single user mode (where mounting / r/w and editing files
> using /rescue/vi would be possible).
>
>
>
>
> --
> Polytropon
> Magdeburg, Germany
> Happy FreeBSD user since 4.0
> Andra moi ennepe, Mousa, ...
>