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I always compile my own kernel, and therefore I am not reliant on the distribution kernel (in my case Debian). I have always wondered, whether there is an optimal combination of userspace and kernelspace versions. Let's say I am using Debian stable (Wheezy), which by default comes with an 3.2 kernel.

I have compiled my own custom kernel 3.9, because it has features which I want (X.509 module signing). Can this potentially have any drawbacks?

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I've had 3.2 running on Debian Squeeze (6.0) for a long time, and I just got the newest 3.4 longterm stable, and 3.9 stable working on an ancient athlon64 x2-4400. The only problem so far, one old PCI NIC driver segfaulted when the box tried to go into some sort of sleep mode. Other than that, no issues. – Marcin May 29 '13 at 11:39

In my experience the userland tools have no problems with newer kernel versions.

However, applications that rely on particular kernel interfaces (and thus ship with a corresponding kernel module) tend to break. An example is VirtualBox. This might be tricky if you use the stock version, which would not receive an update in this case, since it works with the stock kernel.

My suggestion is to install both, the stock and the custom kernel. Run your custom kernel and check if you encounter any problems. If something fails, you can simply reboot and load the stock kernel.

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The userland interface of the kernel is quite backward compatible, so you usually get no problems if you install a newer kernel.

Some (minor) drawbacks:

  • possibly not all features from the newer kernel usable because of older userspace tools.
  • warning messages because of deprecated use of interfaces/features.
  • often problems with out-of-the-tree kernel modules (usually in *-dkms or *-source packages)
  • no security support from the distribution

If you get any problems, you can try to installer newer userspace tools / dkms packages from Debian testing/sid/experimentar or backports if available.

BTW: As far as I have tested it, Debian Wheezy runs fine with Debian's 3.8 kernel.

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