[ale] Serial consoles

[Eric Z. Ayers]

Part of my job is to maintain machines attached with serial consoles. Having
the serial consoles setup make it possible for me to maintain and
diagnose a remote system. 

Now, a PC is unlike many other UNIX workstations/servers in that there
isn't a command line console burned into firmware.  We have Alpha
stations with serial console ports attached to a terminal server. 

First of all, the serial port is active even when you are down in the
firmware mode.  This means you can watch the entire boot process from
the serial port.   This command line console also has some hardware
diagnostic commands and allows you to boot of of different disks or into
a different operating system.  Also, there is a special escape sequence
that breaks out of the operating system into the command line console
interface.  This is helpful when the machine has crashed or for some
reason up, but not responding.

-Eric.

Todd Graham Lewis writes:
 > On Sat, 18 Jan 1997, Byron A Jeff wrote:
 > 
 > > Now that's interesting. Exactly how does that happen? Each machine has
 > > a modem and phone line? Dialing up on the phone line reboots the machine and
 > > connects the modem to the serial line? Like I said interesting...
 > 
 > Well, you can use these things called "portmasters", or "multi-port serial
 > cards", to allow you to access a number of machines from _another_
 > machine, all right over the network.  If you run a multi-port serial card
 > on an old 386, then you can have encrypted, etc. access to your machines
 > at the boot prompt, allowing you to switch kernels remotely, see where the
 > machine is hanging on reboot, etc.
 > 
 > > Tell me more. I do have a couple of machines that I'd like to be able to
 > > boot remotely. However there are no phone lines available to signal the
 > > reboot.
 > 
 > You can signal the reboot with "ssh -l root machine \"shutdown -r now\"".
 > 
 > Without serial consoles, you just have to pray that they do come back up
 > properly, which many times, especially in the face of abnormal failure in
 > the first place, is not the case.
 > 
 > __
 > Todd Graham Lewis             Linux!                 Core Engineering
 > Mindspring Enterprises  tlewis at mindspring.com   (800) 719 4664, x2804