#32 UML related bug in Linux host kernels before 2.6.17

[Fermín Galán]

From https://lists.dit.upm.es/pipermail/vnuml-users/2006-November/000554.html

I recently found a problem using VNUML in the following enviroment:

- Host kernel: 2.6.13-skas3-v8.2
- UML kernel: 2.6.16.27-bs2-xt-1m
- Root_fs: 0.4.1

(It may affect other kernels/filesystem combinations but I haven't checked
it myself).

Symptom: when building topologoy (vnumlparser.pl -t) virtual machine booting
hangs with the following trace:

[...]
Checking that ptrace can change system call numbers...OK
Checking syscall emulation patch for ptrace...OK
Checking advanced syscall emulation patch for ptrace...OK
Checking for tmpfs mount on /dev/shm...OK
Checking PROT_EXEC mmap in /dev/shm/...failed: Operation not permitted
/dev/shm/ must be not mounted noexec

It seems a bug related with host kernels before 2.6.17 (*) (see
http://lists.alioth.debian.org/pipermail/pkg-uml-pkgs/2006-November/000395.html
for details)

Quick solution:

- Add the following line to host /etc/fstab:

shm /dev/shm tmpfs nodev,nosuid 0 0

- Execute 'mount /dev/shm'

Best solution:

- Use host kernel 2.6.17 or later (*)

Best regards

------
Fermín

(*) I'm not fully sure, but I guess so because of the patch that fix the
issue (http://lkml.org/lkml/2006/4/10/255) appears in the kernel changelog
for 2.6.17 (http://www.kernel.org/pub/linux/kernel/v2.6/ChangeLog-2.6.17
commit 966a082f80a073af1564c5ed6313ef2f0587dde3)