Can I have linux-headers newer than the running kernel?

Jarjar · Apprentice Joined: 21 Jul 2002 Posts: 265 Location: Sweden

I'm still running 2.6.28, and the ebuild for those (or older) linux-headers has been removed. Along with masking newer kernels for the time being, I masked linux-headers; now emerge tells me

Sadako · Posted: Mon Mar 08, 2010 12:53 pm Post subject:

Yes, it's absolutely safe.

There's a variable you can add to make.conf for glibc, which determines the oldest kernel you can boot the kernel with.
As long as this isn't set to the value of your installed kernel headers version (which is the max value you can use), then there would be no issue.

The variable is "NPTL_KERN_VER", and 2.6.9 has been the default for ages, so technically you could use a kernel that old.
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depontius · Advocate Joined: 05 May 2004 Posts: 3526

Given that we can't even find a kernel that old, are there any advantages to be gained by moving NPTL_KERN_VER to something a bit newer? I would see the big gotcha being if one booted a LiveCD with a really old kernel, and then tried to chroot into an install with a newer NPTL_KERN_VER, but even that's unlikely. Besides, it's an excuse to throw out old install and rescue CDs, and burn a current set.
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Jarjar · Apprentice Joined: 21 Jul 2002 Posts: 265 Location: Sweden

Great, thanks

Why exactly are linux-headers not packaged with the kernel tarball itself, though? :oops:

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Sadako · Posted: Mon Mar 08, 2010 2:29 pm Post subject:

depontius;

I typically do that when doing a new install, setting it to the stable linux-headers version, and haven't encountered any issues.

Once I did get actually caught, were I needed to chroot from a livecd, and the latest kernel on the only cds I had handy was one version behind the NPTL_KERN_VER value, which did kinda suck, but usually the stable linux-headers version lags behind the most current kernel release to provide a decent safety margin.

In theory it should make glibc use a little less kruft for older kernels, and be a little more efficient, but tbh I doubt there are any noticable gains to be had (I'm still gonna continue doing it anyways, because why not?).

Oh, FWIW, when you run `file` on a binary it should tell you what the minimum version kernel that binary will run under, as a result of this setting.
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Sadako · Posted: Mon Mar 08, 2010 2:32 pm Post subject:

depontius · Advocate Joined: 05 May 2004 Posts: 3526