[nycbug-talk] FreeBSD jails and custom kernels

pete wright nomadlogic
Wed Aug 31 11:08:12 EDT 2005

On 8/31/05, max <max at neuropunks.org> wrote:
> Hello,
> I have a jail question. Can I make custom kernel per jail?
> Basically, I need COMPAT_LINUX, but I dont feel really good about recompiling the kernel on the host itself, since its a production machine, but it has some jails that I can happily destroy if anything goes wrong.
> I looked on google, nothing too relevant, and from jail howto's that ive seen, we always link /kernel to /dev/null and use the main host's kernel.
> I can see why it would be pretty hard to implement, to have a full kernel instance per jail, but  im still wondering if its possible.
> Thanks!

No you can not make a custom kernel per jail.  You can, and often
should, make a custom userland per jail as this run's ontop of the
host Kernel+Userland.

This paper provides a good background on the thoery behind the
operation of jails in FreeBSD:


In short, jail's are not a virtual machine they are an extension of
the concept of chroot.


Pete Wright
NYC's *BSD User Group

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