Cloning revisited.
We purchased new Dell workstations (Dimension 7500), which had dual hexa-core Xeons (it seems that Intel calls them strangely hexad-core). Because it was only three nodes, I decided it is too much effort to setup them up properly and decided to do a disk cloning from a quad-core node. However, when I did this, OS would not boot (it said /dev/root was not present, which means it did not set up the devices in /dev correctly).
So what I did was to install CentOS 5.4 in the minimal configuration, kept /boot, /dev, /proc and /sys and then I replaced all other root directories (/usr etc) by the ones from CentOS 5.1 in a quad-core. The difference in versions escaped my attention until the system complained during boot that /lib/modules did not have the core components for the newer version (which I hid away but thoughtfully did not delete)! So I merged that directory (core components come in separate subdirectories, so that was clean) between the old and new versions. Because of this cheating with using older preset OS, I saved a lot of time in installing xinetd, setting up NFS etc - everything was already installed. So this method of merging seems to work.
There was one horrible event though. Knoppix 5.1 would freeze during boot (this is an old OS) on this new hardware. Knoppix 6.0 booted but found only 8 cores. This was suspicious but fine, however, its network would only work outwards (no connexions to this node). Almost dispaired, I compared byte by byte what ifconfig printed. And it showed that netmask was different. After setting
ifconfig eth0 192.168.1.1 netmask 255.255.0.0
network started to work. But it showed its terrible character again and again. For some strange reason this command had to be excecuted several times (first I did ifconfig eth0 192.168.1.1) before it started to work. Computers are like humans?! (Apart from the "mystique", the boring explanation is that the network setup for some reason was delayed after Knoppix booted; and it overwrote (?) my ifconfig setting on its own malicious self! This is confirmed by a warning message shown some time after my first ifconfig command telling that network is unavailable. Then the second ifconfig would knock the presumptious Knoppix to obedience.)