[CentOS] Xen, Amazon, and /proc/cmdline

Stephen Harris lists at spuddy.org
Tue Jan 26 23:25:54 UTC 2010

On Tue, Jan 26, 2010 at 03:48:45PM -0600, Kurt Newman wrote:
> What I'm trying to figure out is at what point in the booting process is
> something looking at /proc/cmdline INSTEAD of /etc/inittab for the
> default run level.

Aren't these passed by the kernel to init as cmdline arguments and environment
variables?  Check out the kernel sources for init/main.c

> I've already looked at modifying /etc/rc.d/rc (since it's the one that
> uses /sbin/runlevel to execute various /etc/rcX.d scripts.  I was hoping
> to have a more elegant way so that I don't have to maintain
> CentOS-specific bootstrap code.

Well, it's not CentOS specific; it's Amazon specifc.

But, anyway, what differences are there between rc3 and rc4 ?  On my
machine they're minimal:
% diff -r rc3.d rc4.d
Only in rc4.d: K95firstboot
Only in rc3.d: S99firstboot

If you build your rc files correctly so that they're chkconfig compatible
then you just make your script get added to rc3 and rc4
  # chkconfig: 2345 09 91
  # description: my startup script

Alternatively, how about this inittab entry:
 4:4:once:/sbin/init 3

May work.  I've never tested!



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