Starting a kernel out of a running kernel...

Starting a kernel out of a running kernel...

[Volker Jung]

Hello,

is there a solution for starting a new Linux kernel out of a running Linux 
kernel using GRUB or a changed GRUB? First I thought I could use LILO. But LILO 
runs in real mode, not having any idea about protected mode. GRUB runs in 
protected mode itself - in order to boot an OS it has to switch back to real 
mode or to prepare the protected mode control registers of the CPU to start the 
OS. So GRUB may be able to pass control from one kernel to the other.

The idea: Instead of using GRUBs abilities to do various things inside a shell 
one could use it to boot a complete Linux. Then one can do everything one wants 
and afterwards one could start the desired system WITHOUT rebooting.

Perhaps this sounds crazy but there is a problem where this idea would be 
helpful: So you could implement a read only failsafe system that starts again 
whenever you reset your remote server and out of this system (remotely 
controlled via SSH or similar) you could start the desired system WITHOUT having 
to reboot which would again start the failsafe system which isn't the thing one 
wants. You can call this "GRUB with a fully featured OS"...

In LILO this behaviour could be implemented using the -R option - but this 
assumes a read write medium...

Any suggestions?

Thanks in advance
Volker

Re: Starting a kernel out of a running kernel...

[Jan C. Kleinsorge]

Volker Jung wrote:
> Hello,
>
> is there a solution for starting a new Linux kernel out of a running
> Linux kernel using GRUB or a changed GRUB? First I thought I could use
> LILO. But LILO runs in real mode, not having any idea about protected
> mode. GRUB runs in protected mode itself - in order to boot an OS it
> has to switch back to real mode or to prepare the protected mode
> control registers of the CPU to start the OS. So GRUB may be able to
> pass control from one kernel to the other.
>
> The idea: Instead of using GRUBs abilities to do various things inside
> a shell one could use it to boot a complete Linux. Then one can do
> everything one wants and afterwards one could start the desired system
> WITHOUT rebooting.
>
> Perhaps this sounds crazy but there is a problem where this idea would
> be helpful: So you could implement a read only failsafe system that
> starts again whenever you reset your remote server and out of this
> system (remotely controlled via SSH or similar) you could start the
> desired system WITHOUT having to reboot which would again start the
> failsafe system which isn't the thing one wants. You can call this
> "GRUB with a fully featured OS"...
>
> In LILO this behaviour could be implemented using the -R option - but
> this assumes a read write medium...
>
> Any suggestions?
That is not possible. 'Protected Mode' clearly denotes some form of
protection. Unless you grant the software extra privileges (that is,
write kernel-code)
it's virtually impossible. Apropos 'virtually': Use some virtualization
technology instead and you never will have to reboot any machine again,
ever.
>
> Thanks in advance
> Volker
>
>
> _______________________________________________
> Grub-devel mailing list
> Grub-devel@gnu.org
> http://lists.gnu.org/mailman/listinfo/grub-devel
>

-jan

Re: Starting a kernel out of a running kernel...

[Brian Sammon]

> is there a solution for starting a new Linux kernel out of a running Linux 
> kernel using GRUB or a changed GRUB? First I thought I could use LILO. But LILO 

It's not based on grub, but "kexec"/"kboot" does that sort of thing:
  http://www.xmission.com/~ebiederm/files/kexec/README
  http://lists.osdl.org/mailman/listinfo/fastboot/
  http://kboot.sourceforge.net/