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📝 Add Q&A entry about private futex warning

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Since this problem can be pin-pointed to kernel versions that are older
than 2.6.22, a Q&A entry separate from the more general "Kernel too
old" problem may be justified.

This Q&A entry discusses the origin of the problem, some of the
symptoms (no symptoms for "simple" programs like vim, but warnings and
crashes for others), and concludes with a remark about possible (but
complicated) workarounds.
This commit is contained in:
Christian Friesicke 2017-03-11 17:45:54 +01:00
parent 978ab8d408
commit bee9e2df54
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README.md
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@ -276,6 +276,34 @@ Troubleshooting
> The output shows the minimum recommended Linux kernel version.
## Kernel doesn't support private futexes ##
> **Q**: Why do I get the warning: "kompat: this kernel doesn't support private
> futexes and PRoot can't emulate them."?
> **A**: This happens on older host OS kernels when the trick of showing a fake
> kernel version to the JuNest chroot is applied (see above:
> [Kernel too old](#kernel-too-old)).
> The consequence of showing a fake kernel version to the JuNest chroot is that
> in the background, PRoot needs to translate requests from applications in the
> chroot to the old kernel of the host OS. Some of the newer kernel
> functionality can be emulated, but private futexes cannot be translated.
> Private Futexes were introduced in Linux kernel 2.6.22. Therefore, the above
> problem likely appears on old Linux systems, for example RHEL5 systems, which
> are based on Linux kernel 2.6.18. Many of the core tools like `which`, `man`,
> or `vim` run without problems while others, especially XOrg-based programs,
> are more likely to show the warning. These are also more likely to crash
> unexpectedly.
> Currently, there is no (easy) workaround for this. In order to be fully
> compatible with kernels below 2.6.22, both the precompiled package from
> JuNest and all software that is installed later needs to be compiled for this
> kernel. Most likely this can only be achieved by building the needed software
> packages from source, which kind of contradicts JuNest's distro-in-a-distro
> philosophy.
## SUID permissions ##
> **Q**: Why I do not have permissions for ping?