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time-dependent, automatic boot switch?

Is the following possible?

If the time of day is within a certain range, then boot to CD. Otherwise, boot to HD. Do this *without* any user intervention (e.g. user removing the CD or going into BIOS).

Assumptions:
BIOS can be set to adjust boot order.
bootable CD (my customized Knoppix 3.4) is always in the CD-ROM (never ejects).
a floppy drive exists.

Restrictions:
Can't modify the HD in any way.

As far as I can see the options are 1) modifying isolinux on the Knoppix CD -- but how? 2) putting a bootloader on floppy and booting initially from that -- but if I put lilo or grub on a floppy they can't see the CDROM.

I have been puzzling over this for a while and would be very grateful for any ideas!
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dv440
Asked:
dv440
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1 Solution
 
jlevieCommented:
I can think of two ways to do this:

1) Modify Grub to do a time sensitive boot of the desired device and place that on the Knoppix CD.

2) Set the BIOS to boot from CD first and cobble up a time switch for the power to the CD drive.
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dv440Author Commented:
For 1), Knoppix 3.4 uses isolinux as the bootloader.  How do you get it to be "subordinate" to grub?  

2), I hadn't thought of that one... although this would work, the PCs in question are critical servers, so I should have included "Can't modify the hardware in any way" to the "Restrictions" part of the original question.
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jlevieCommented:
> Knoppix 3.4 uses isolinux as the bootloader

Uh, right (smacks self on the forehead). I'd forgotten that. Dunnon if you could get that to work from a floppy or not.

Maybe we could solve this a different way. Could you tell me why you want to do this?
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dv440Author Commented:
I've made a remastered Knoppix CD that does daily maintenance tasks.  User puts my CD in & reboots, causing maintenance tasks to run, this part works just fine.  After Knoppix is finished, though, the user must manually remove the CD before rebooting, otherwise the system boots to CD again.  

If I could figure out how to get a time-sensitive boot decision, then I would keep the CD in the machine permanently, and set up the server to reboot automatically every night, sometime after hours when downtime is acceptable;  at this "magic" time, it reboots to CD, Knoppix boots, runs the maintenance tasks, reboots after finishing, and since the tasks take some time, the next time it reboots, it isn't the "magic" time period anymore;  thus the PC would boot to the HD instead of going on an infinite Knoppix loop.

No matter how I slice the problem, what I end up needing is a bootloader that has if..then conditionals.  Another issue is where the bootloader lives (floppy or CD), although it seems that things would be simpler by starting from CD, then I don't have to worry about the BIOS understanding el torito and all that.  I think I need to look into isolinux, I'm not familiar with what it can do, right now.
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jlevieCommented:
Why do you need to boot from CD for these tasks? What "maintenance tasks" do you run? My bet would be that these could be done without having to reboot the system, and probably scripted from cron.
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dv440Author Commented:
The system runs Windows NT 4.0 Server.  No cron.  ;)

I could do the tasks in Windows, sure, but that would require installing software, which I'm forbidden to do.  Knoppix allows me to bypass this restriction of no-software-installation.
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jlevieCommented:
I see. Running NT from the disk does make the problem more difficult.

From what little I know about I don't see how you could boot NT from isolinux, like you can with Grub. And now that I look at it further I don't think you can boot the CD from Grub. Might it be possible to boot from a tftp server that's only enabled at the desired times? Then all you'd need do is schedule the auto reboot from Windows (how do you plan to do that without a cron or scheduler on NT?) after the tftp server goes active.
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