redhat "rescue mode"?

David Lee David.Lee at ecmwf.int
Fri Dec 16 09:48:41 UTC 2011


Michael DeHaan wrote:
> [...]
> This reads a bit negatively, as nobody's failing to think here.   
> Cobbler covers a wide variety of audiences.   There are people using it 
> in home labs, up to systems with 50k+ nodes in distributed data centers 
> all over the world.   A lot of what Cobbler does is totally about making 
> things simpler and easier to use -- it's the whole reason the project 
> initially existed.  This is the whole reason for automation.  The 
> documentation and help needs for everyone are going to be different, its 
> not just a linear skill level thing, somebody may not know X while 
> someone may not know Y.   In many cases, it's not even something Cobbler 
> related… if you've got an Anaconda or pressed problem, for instance, 
> that's really not Cobbler's problem at all.   (now, if rescue changes to 
> "rescueplease" in Centos 12, we have some work to do)

Firstly my apologies for getting a bit irked about this.  I'm banging ny 
head on a wall here, because something, somewhere isn't working for us, 
and I (still) cannot figure out what it is.  Put that another way: I 
still haven't found the documentation that points me in the right 
direction to be able to help myself.



> If something is missing, it's not because we're not thinking of a 
> beginner audience (or not thinking), it's because we probably thought 
> something was obvious to most people like us.   Ergo, the best person to 
> fix an unclear section of documentation is the person figuring it out 
> (by asking here, IRC, and elsewhere) and then updating the documentation 
> yourself.   The fact that cobbler has an option for automating rescue 
> mode at all (or did, this is mostly discussion about a regression) is a 
> sign it's trying to make things simple.    

Re "updating the docuemntation [my]self": that's fine.  In fact, if you 
take a look at the wiki, you'll see I've been quite active in the last 
couple of days!

But with this current issue I seem to be in a "chicken or egg" problem: 
I can't find any documentation (whether good or not-so-good) to point me 
down a self-help route both towards my own issue and then towards my 
feeding back into improving the documentation.


> So anyway, there are two problems -- one that rescue as a kernel option 
> doesn't work for you, another that we don't create rescue profiles right 
> now due to a regression, and we could fix it in one of two ways.    For 
> that, I'll take a patch for either, though if we get a patch for 
> --rescue-mode=true, that one will win, because I like not having to 
> remember what the original profile was.

Joergen has made some interesting comments along the way, which have 
been a great help and have actually changed my thinking.

If I understand correctly, he points out that "rescue mode" is highly 
OS-specific, and he questions whether this is scalable and whether it is 
philosophically the right approach.  And I'm beginning to see his point 
of view.

(Indeed, I've always been keen on portability.  My previous 
contributions to Samba (quota, VxFS) and to Linux-HA/heartbeat have been 
in just this same arena of portability!)

So while my immediate issue is wanting to get my Redhat box in rescue 
mode, I can now see that having a "cobbler system edit ... rescue" may 
not be the most appropriate way to achieve this.  (I'm not necessarily 
backing off my request; but i recognise that this is not as clear-cut as 
I had originally thought.)


Perhaps it might be better if I re-cast my end-user query another way:

<query>
Our Cobbler set-up, with RHEL clients, lists every system.  When these 
install, the installation goes straight through, uninterrupted.  But we 
also wish to use this Cobbler set-up occasionally on particular systems 
so that the PXE-boot puts us, in a quasi-DVD-like manner, into the usual 
red screen which would allow us to select rescue mode.

Starting from this Cobbler set-up, what hooks, tweaks and changes do we 
need to employ to achieve this?

P.S.  If this isn't in the existing wiki documentation, I would be happy 
to write it up.
</query>

Note that our existing Cobbler set-up takes the client installation 
through to completion uninterrupted, /without/ presenting the usual red 
countdown screen and boot prompt.

A good start for me would simply to be able to get it to give me that 
boot prompt.  (Although I suspect that further work may still be necessary.)

Michael Mann helpfully provided the link:

http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/5/html/Installation_Guide/s1-rescuemode-boot.html

But that's all about "when you get to the boot prompt...".  My initial 
stumbling block problem is that our existing Cobbler set-up doesn't give 
me such a prompt.

Have I missed a Cobbler setting (or perhaps a kickstart detail?) that 
would toggle this give/hide boot-prompt?


-- 
: David Lee
: ECMWF (Data Handling System)
: Shinfield Park
: Reading  RG2 9AX
: Berkshire
:
: tel:    +44-118-9499 362
: email:  david.lee at ecmwf.int


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