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

Kurt Newman knewman at globaldataguard.com
Tue Jan 26 21:48:45 UTC 2010


> Kwan Lowe wrote:
>
> > Kurt Newman wrote:
> > > Amazon (or perhaps Amazon's configuration of Xen) forces a machine to
> > > come up at run level 4, regardless of what's in /etc/inittab.
> > > 
> > > I've looked through /etc/rc.sysinit and /etc/rc.d/rc, to determine which
> > > (if any script) looks at /proc/cmdline and forces a particular run
> > > level, but to no avail.
> > > 
> > > It seems that /sbin/init does the forcing.  Can anyone confirm that
> > > /sbin/init reads /proc/cmdline to overwrite /etc/inittab?  I can't seem
> > > to find any reference in man pages or searching the web.
> > > 
>
> You *can* override the initdefault in inittab via the kernel option,
> but if you're not seeing it in /proc/cmdline it's likely some other rc
> script.  I saw some references to this being controlled via xen:
>
> ...
>
> So it may be being passed through xen which might not show up in
> proc/cmdline (can't test right now).

Perhaps I mis-stated what I was asking.  I'm well aware that Amazon (aka
Xen) is passing run level 4 to the kernel because the number '4' is in
/proc/cmdline.  I can't change that since I cannot configure Xen or even
ask Amazon to.

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.

Is it /sbin/init?  I can't seem to find any reference of that in any man
pages.  Essentially, I'm trying to short-circuit this boot process to
execute a run level of my choosing, and not be forced to use 4.

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.



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