libc6 vs libc6-xen problems with applications segfaulting

We recieved the following email this morning which may be a problem from time to time with other users, so i thought I would share this.

Subject: Seg faults on apache mysql and a couple of other less import programs. Probably need a fresh install.

Hi I have a serious problem with my VPS

Apache, and Mysql seg fault when you try to start them. Started happening after a reboot yesterday. However it had been a few months since the last reboot so it is hard to say what caused the problem. I can't find the problem and unless you guys see something I missed it looks like I need to install a fresh image.

It is currently running Ubuntu 8.04LTS. It is fine to stick with that.

Its fairly well documented that using a standard libc6 in your Xen VPS can cause a few problems with the tls and applications segfaulting without errors.

There is an easy fix for most, and that's to install libc6-xen which will require a reboot of your VPS.  One gotcha however is for people running Ubuntu 8.04 (LTS) where there is broken packages. Now i can see that they logged a bug back in 2008 however it doesnt appear to have been fixed.

root@hostname:~# apt-get install libc6-xen
The following packages have unmet dependencies:
libc6-xen: PreDepends: libc6 (= 2.7-10ubuntu3) but 2.7-10ubuntu5 is to be installed
E: Broken packages

The simple fix is in the dmesg however in this one.

************************************************** *************
************************************************** *************
** WARNING: Currently emulating unsupported memory accesses **
** in /lib/tls glibc libraries. The emulation is **
** slow. To ensure full performance you should **
** install a 'xen-friendly' (nosegneg) version of **
** the library, or disable tls support by executing **
** the following as root: **
** mv /lib/tls /lib/tls.disabled **
** Offending process: init (pid=2594) **
************************************************** *************
************************************************** *************

Just do as requested,

mv /lib/tls /lib/tls.disabled

And reboot.  Once the newer Ubuntu comes out at the end of the month, then you can update to the latest LTS and it should hopefully be fixed.

If you get stuck for any reason at all, just drop in an email into the support, we are only too happy to help out.

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