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The Rackspace cloud server tech tells my CentOS 5.4 VPS (Xen) runs "CentOS with an Ubuntu kernel"

Could someone explain, in plain terms, what "CentOS with an Ubuntu kernel" means and if there are any disadvantages (performance, mgmt) between that and running CentOS with a CentOS kernel?


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up vote 3 down vote accepted

This sounds like a miscommunication. Maybe the host machine and the virtual machine use different distributions.

As you describe, in most cases, you are going to encounter compatibility issues precompiled between distribution kernels and different distributions. It could be it was compiled using a different glibc or has the wrong version of user land utilities. The variables are numerous and tedious.

If someone paid intimate attention to detail or was simply lucky, they may have been successful in finding a precompiled distribution kernel that is cross compatible.

I guess they could have technically used the package source and compiled on a different distribution. However, if the distribution had a feature-set desired and you could not locate a precompiled package for your distribution, it could be compiled from the main kernel source.

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According to rackspace: "The "Ubuntu kernel" part of that is just a Linux kernel package that Ubuntu maintains. It's still Linux. We chose that one because it works with all distributions we offer in Rackspace Cloud Servers. In more words, the first answer at ( was correct: It's still a Linux kernel." – Gaia May 5 '10 at 17:41

I would assume that it means that the kernel, the actual operating system core itself, is a modified Ubuntu kernel, while the distro itself is CentOS. That would be kind of odd since usually the kernel is built as part of the distro so all the management tools and utilities are built with the same libraries and such, though, but I guess it's feasible.

It could be that the tech was just mistaken, or someone told him that they made some customizations to the kernel to add a feature like Ubuntu's default kernel has. You should be able to recompile a kernel to customize it (add/subtract support for features that are unneeded, maybe make the kernel smaller or reduce memory footprint or add support for something in their cloud that the default doesn't have) and so he just got used to saying that when customers called.

The advantage disadvantage question is moot without knowing what alterations were made or customized. If I had to guess, I'd say it isn't an ubuntu kernel, as I'm not entirely sure you can just drop it in as a replacement. 99.9% of people out there replacing the kernel would do so with either a repository alteration from the distro or through a recompile with their distro's toolchain.

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