Do we need this crap on LWN? [LWN.net]

Do we need this crap on LWN?

Posted Feb 22, 2007 20:01 UTC (Thu) by bojan (subscriber, #14302)
In reply to: Do we need this crap on LWN? by markc
Parent article: ESR's goodbye note

> Great, but not on a dedicated host 10,000 miles away.

You missed the unattended upgrade bit above. The one with kickstart.

Let me repeat again. This particular limitation (of not being able to upgrade CentOS 3 to CentOS 4 while running) has nothing to do with RPM. It has to do with the fact that CentOS 4 (i.e. RHEL4) uses udev and CentOS 3 (i.e. RHEL3) uses a dev package. When dev gets removed by upgrading to udev, your system is hosed (you have nothing left in /dev).

Otherwise, I've done plenty of hot upgrades by doing "yum upgrade" on many different versions of Fedora.

> which is the point that ESR seems to have finally stumbled upon in the head article

He stumbled upon his on inability to manage his own system and/or ask others how to do it.

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Do we need this crap on LWN?

Posted Feb 22, 2007 20:15 UTC (Thu) by loening (guest, #174) [Link]

Speaking of remote upgrades with RPM. I personally have done
RH8->RH9->FC1->FC2->FC3->FC4->FC5->FC6

On a workstation that sits 300 miles away from me that I haven't seen in years.

dev => udev

Posted Feb 25, 2007 14:54 UTC (Sun) by smurf (subscriber, #17840) [Link]

So please enlighten us poor souls who have *no*idea* why you'd need to "clean out" /dev when moving to an udev-based system. Why not leave the old package-supplying-/dev-nodes installed?

You can mount a tempfs onto /mnt/whatever, create the bare essential device nodes there, move-mount that to /dev, and start up udev. (In fact, this is how a udev-based system boots in the first place.)

Total downtime for programs attempting to open /dev/null (or whatever): Zero.

Afterwards, if you do want to remove the old /dev-supplying package, well ... RPM has a --justdb option.

dev => udev

Posted Feb 26, 2007 4:27 UTC (Mon) by bojan (subscriber, #14302) [Link]

> why you'd need to "clean out" /dev when moving to an udev-based system

Well, if you run "yum upgrade", it is a fact that that's is what's going to happen: upgrade to udev will remove dev, which will remove all entries in /dev.

As you explained, it is not necessarily what needs to happen - but it does by default. So, unless you're prepared for some creative surgery (as per you explanation), you will get screwed.

Coming back the original question of supported upgrades from CentOS 3 to 4 (or RHEL 3 to 4), it is obviuos why this is not a recommeded thing to do - people don't normally want to recommend a complicated and risky process that would in the end require a reboot anyway (new kernel). RHEL packages were designed to be upgraded using the upgrade process, not "yum upgrade" (remember: RHEL 3 and 4 don't even ship yum, it's a CentOS addition).

You can find some more info here (search for udev):

http://www.redhat.com/docs/manuals/enterprise/RHEL-4-Manu...

Note how you have to be on 2.6 kernel before starting this. CentOS 3 (i.e. RHEL 3) is based on 2.4 kernel.

Instead, one cuts a small kickstart file, starts an upgrade and after some minutes has a fully upgraded system with far less risk of stuffing things up.