[ale] Rebooting remotely without a usable /

[mrideout at windserve.com (Matt Rideout)]

Michael B. Trausch wrote, On 09/21/2009 07:19 AM:
> On Mon, 2009-09-21 at 06:29 -0400, Matt Rideout wrote:
>   
>> I have a server that's having issues with its / which prevent shutdown, 
>> reboot, init, etc from being accessible. This could be a hardware or 
>> firmware issue, so I'd like to reboot, and diagnose it remotely so that 
>> I'll know whether to order any hardware before going on-site.
>>
>> I can SSH in, and have an IP KVM hooked up, but have no remote power 
>> management. The SysRq trick isn't working through the KVM. It seems like 
>> there should be a way to reboot through /proc, but I'm drawing a blank. 
>> Any ideas?
>>     
>
> What CPU is the server, and at what bit-width does it run?
>
> Do you have access to gcc and/or as on that server?  If so, you can use
> the reboot(2) syscall to force the system to reboot.  This should do it,
> if you have access to gcc, you can use the pasted code below.  If you do
> not have access to gcc (or cannot write an assembly system call and use
> as to assemble it), the answer to the questions above would (likely)
> permit me (or anyone else on this list) to create an ELF binary using
> the code below for whatever system you're running.
>
> If you do not have GLIBC, but instead an older Linux libc, use the
> command:
>
> gcc -DNO_GLIBC -o force-reboot force-reboot.c
>   
Good thinking! It's running 64-bit Intel Xeon MP 3.66GHz CPUs. Nothing 
located on the disk that isn't already loaded into RAM is usable, so 
compiling on the box isn't an option. I wouldn't be able to scp a binary 
over, or execute the commands to mount a memory filesystem in the 
traditional sense either, since those would access files on the drive. 
Would there be anyway to make that syscall purely from memory?