Syslinux - Mar 2008 - passing parameters to the newly booted kernel

is it possible to pass parameters from a .cfg file to the newly  
booted kernel?

my setup is pxelinux where the relevent config is

label fbsd63
	kernel memdisk
	append initrd=/freebsd6.3.hd harddisk

what i would like to do is pass in some parameter so the booted  
kernel can behave differently.
i've looked in teh archives without success, although i did see an  
elliptic reference
to /proc/cmdline from within /linuxrc.

i boot both freebsd and linux kernels, so answers for both would be  
welcome.

------------------
Andrew Hume  (best -> Telework) +1 732-886-1886
andrew at research.att.com  (Work) +1 973-360-8651
AT&T Labs - Research; member of USENIX and LOPSA

On Wed, Mar 26, 2008 at 09:07:40AM -0400, Andrew Hume
wrote:
> is it possible to pass parameters from a .cfg file to the newly  
> booted kernel?
> 
> my setup is pxelinux where the relevent config is
> 
> label fbsd63
> 	kernel memdisk
> 	append initrd=/freebsd6.3.hd harddisk
> 
> what i would like to do is pass in some parameter so the booted  
> kernel can behave differently.
> i've looked in teh archives without success, although i did see an  
> elliptic reference
> to /proc/cmdline from within /linuxrc.
All arguments to the kernel are accessible via /proc/cmdline. Also,
unrecognized var=val arguments are passed in the environment to the boot
process (/sbin/init, /init).

Usually, I parse /proc/cmdline like this:

cmd=" $(cat /proc/cmdline) "

getval()
{
  local val

  val="${cmd##* $1=}"
  [ "$val" != "$cmd" ] || return 1
  echo "${val%% *}"
}

Then:
root=$(getval root)
> i boot both freebsd and linux kernels, so answers for both would be  
> welcome.
Can't help you with freebsd, sorry.

-- 
lfr
0/0

Andrew Hume wrote:
> is it possible to pass parameters from a .cfg file to the newly  
> booted kernel?
> 
> my setup is pxelinux where the relevent config is
> 
> label fbsd63
> 	kernel memdisk
> 	append initrd=/freebsd6.3.hd harddisk
> 
> what i would like to do is pass in some parameter so the booted  
> kernel can behave differently.
> i've looked in teh archives without success, although i did see an  
> elliptic reference to /proc/cmdline from within /linuxrc.
> 
> i boot both freebsd and linux kernels, so answers for both would be  
> welcome.
> 
Yes, although you don't want to use MEMDISK for it.  If you boot the 
kernel "natively", you can pass arguments to it.

I believe FreeBSD kernels are Multiboot images, so you can boot them via 
mboot.c32.

Passing arguments to MEMDISK is possible too, but then the OS has to 
know about MEMDISK specifically.

	-hpa