Re: is booting an OS without power cycling a host possible?

[Drake Donahue]

On Sat, 2012-03-17 at 14:24 -0700, Peter Van Wieren wrote:
> The running system indeed could change grub.cfg to default to
> distribution "B", and I could reboot.  "B" should start OK. 
> 
> My concern is that if "B" fails to boot, for whatever reason, or upon
> booting "B" I find that it lacks the tools to modify the MBR /
> grub.cfg then I will never ever be to revert the change to return the
> default distribution be "A", instead of "B".  
> 
> In order to avoid risking this worst-case scenario, I was hoping to
> find some alternative.
> 
> Pete
> 
> 
> --- On Sat, 3/17/12, Leslie S Satenstein <address@hidden>
> wrote:
>         
>         From: Leslie S Satenstein <address@hidden>
>         Subject: Re: is booting an OS without power cycling a host
>         possible?
>         To: "Arbiel Perlacremaz" <address@hidden>,
>         "Peter Van Wieren" <address@hidden>, "address@hidden"
>         <address@hidden>
>         Date: Saturday, March 17, 2012, 5:14 PM
>         
>         I am a little confused. Currently I have a grub.cfg that has
>         three operating systems in the list.  If I reboot, the default
>         value setting boots that operating system.
>         So, if I am right, all that is required is for the system that
>         is handing over control, to change the default setting in the
>         grub.cfg file.
>         
>         
>         Is that not what is wanted and what solves the problem^
>         
>          
>         ------------------
>         
>         Regards
>         
>          Leslie
>         
>         Mr. Leslie Satenstein
>         50 years in IT and going strong.
>         Yesterday was a good day, today is a better day,
>         and tomorrow will be even better.
>          
>         mailto:address@hidden
>         alternative: address@hidden 
>         www.itbms.biz  
>         
>         
>                 
>                 ______________________________________________________
>                 From: Arbiel Perlacremaz
>                 <address@hidden>
>                 To: Peter Van Wieren <address@hidden>;
>                 address@hidden 
>                 Sent: Saturday, March 17, 2012 4:58 PM
>                 Subject: Re: is booting an OS without power cycling a
>                 host possible?
>                 
>                 
>                 I do not quite understand what you want to do. Is that
>                 that, in a first 
>                 stage, you want to boot distribution A, and then, in a
>                 second stage, 
>                 switch to distribution B, as though you had directly
>                 booted distribution B.
>                 
>                 This is definitely not possible.
>                 
>                 Now, there is no difficulty to have grub2 (for Grub
>                 Legacy, you may be 
>                 speaking of, I really don't know) residing on a drive
>                 to boot a 
>                 distribution located on another drive.
>                 
>                 So, please, clarify the situation you are in.
>                 
>                 Arbiel
>                 
>                 Le 17/03/2012 19:33, Peter Van Wieren a écrit :
>                 > I have a host with linux distribution "A".  The host
>                 is presently running "A", and has already been started
>                 by grub.  There exists, on a second hard disk drive,
>                 linux distribution "B" is installed but not mounted.
>                 >
>                 > I hoped I could transition from "A" to "B", without
>                 power cycling the host or editing the MBR, by running
>                 grub from the command line as root.  In a root shell I
>                 started grub and planned to issue the commands:
>                 >
>                 >    1) root (hd1,0)
>                 >    2) kernel .... vmlinuz
>                 >    3) initrd ....
>                 >    4) boot
>                 >
>                 > My hope was that distribution "B" would boot, and
>                 "A" would somehow be abolished.  I do not know for
>                 sure if the above is supposed to even be possible or
>                 not.  Can it be done?
>                 >
>                 > I made it to step #3.  The trouble is the "initrd"
>                 command returns "Error 16: inconsistent filesystem"
>                 >
>                 >
>                 >
>                 > P.S. Why would I want to do this?  Answer: I threw
>                 my old USB keyboard in the trash, and replaced it with
>                 a new one.  It was all well and good, until I found
>                 that the new keyboard doesn't work at all during the
>                 BIOS or GRUB stages -- the new keyboard only works
>                 after the OS has been booted.  Thus if I change the
>                 default option in grub.conf to "B" and something
>                 doesn't work, my host will become completely useless
>                 until such a time as I can locate a 2002 era USB
>                 keyboard -- which in theory should work in the BIOS
>                 and GRUB stages.
>                 >
>                 > Thanks,
>                 > Pete
>                 >
>                 > _______________________________________________
>                 > Help-grub mailing list
>                 > address@hidden
>                 > https://lists.gnu.org/mailman/listinfo/help-grub
>                 
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>                 
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If the new default choice fails, boot a cd, mount the grub partition,
change the default in grub.cfg.

ps2 keyboards for $10 and below are common.