LinuxSA Mailing list archives

  From: Michael Neuling <mneuling@radlogic.com.au>
  To  : Richard Russell <richard@austrics.com.au>
  Date: Fri, 12 Nov 1999 13:44:25 +1030

Re: /proc/sys/kernel/sysrq

> On booting, I get an error complaining about a missing
> /proc/sys/kernel/sysrq file. As far as I can tell, it is caused by the
> following lines of code in  /etc/rc.d/rc.sysinit 
> 
> -----------------------------------------
> if [ "$MAGIC_SYSRQ" = "no" ]; then
>         echo "0" > /proc/sys/kernel/sysrq
> fi
> -----------------------------------------
> 
> It seems to have no effect whatsoever on the running of my system --
> it's just an annoying error on boot (which, BTW, I can't find evidence
> of in any logs... -- if anyone could point me to the log which would
> have this, I'd appreciate it...)
> 
> I think this has to do with Kernel debugging features, which are
> switched off in my Kernel... (the last question in the config thing --
> referring to a magic sysrq key for debugging...)
> 
> Is there any reason why this error should occur? I'm not all that
> familiar with /proc, but it would appear to me that the above echo
> command would create the file if it doesn't exist... or maybe the error
> is being caused elsewhere, but I can't find it...

/proc is a figment of the operating sytems imagination.  It was stolen
from the PLAN9 OS (everything in plan9 is concidered to be a
file). You cannot create/delete files like any other file system.  Is
it is NOT like a RAM Disk.  Reads and writes to particular files cause
system calls defined in the kernel eg.  cat /proc/net/ip_fwchains
calls a function in FS part of the kernel to print out all of the
current mount points.

Writes can control certain parameters of the kernel.  eg 'echo 1 >
/proc/sys/net/ipv4/ip_forward' turns on IP ip forwarding (ie. the
write to that file causes certain routing paramters to be changed)

BTW the SYSRQ option is a very useful option as you can unmount root
when your machine is screwed therefore avoiding an fsck on
reboot ....... not that Linux ever screws you machine :-)

Regards
Michael
--
Michael Neuling                        mneuling@radlogic.com.au (o_ 
RADLogic Pty Ltd, Adelaide, South Australia ph: +61 8 8373-3990 //\ 
http://www.radlogic.com.au                  fx: +61 8 8373-3251 V_/_

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