Re: remote access to boot loader?

[Justin Filoseta <filoseta math gatech edu>]

On Fri, Apr 07, 2006 at 06:50:54AM +0800, John Summerfield wrote:
> Matt Hyclak wrote:
> >You can have grub go out the serial port, so depending on your hardware
> >setup, you could access it that way.
> 
> I think the standard RH build doesn't support that, so you may need to 
> tweak the spec file and rebuild it.

No rebuild required on RHEL4 AS. Probably the same for all of the others
too, this is pretty standard.


Add either of the two lines to /boot/grub/grub.conf in order to make
grub's interface available on the serial port. Obviously change the
parameters to match your equipment, these values are rather default.

# for serial and console
serial --unit=0 --speed=9600 --word=8 --parity=no --stop=1
terminal --timeout=10 serial console 

# just serial
serial --unit=0 --speed=9600 --word=8 --parity=no --stop=1
terminal serial



Just for reference if you want a console on the serial port after
grub (for times sshd isn't working).

Disclaimer: I have been using these notes without revision for many years,
they have worked from 7.3 to RHEL4-U3 but it is quite possible
some steps are no longer necessary or considered the "best" solution.

1) add "console=tty0 console=ttyS0,9600n81 " to the end of your kernel
line in /boot/grub/grub.conf.

2) add "ST:12345:respawn:/sbin/mgetty /dev/ttyS0 -s 9600 -r" to /etc/inittab

3) add the following 5 lines to /etc/mgetty+sendfax/mgetty.config
    # serial console
    port ttyS0
        direct y
        speed 9600
        toggle-dtr n 

4) modify /etc/securetty if needed (add "ttyS0" )

5) Depending on circumstances you may want to also enable the magic
sysreq key in /etc/sysctl.conf to permit remote reboots (among other
things) when the system is too locked up for a regular /sbin/reboot.
Read the documentation before doing this, there is a reason it is
called "magic."


Justin