dbaranski.net

This technique requires the “Extra Packages for Enterprise Linux” repo.. So this is not a .rpm install from some untrusted site. It’s from the RedHat repos themselves.

Firstly, install the EPEL package. More information on EPEL is available from their site. Then, install git and you’re done!

See the EPEL FAQ for more details.

Following any of the usual how-to’s didn’t leave me with a successfully speedy login.. I eventually tracked down the problem to a particularly monumental bug in RedHat’s OpenSSH server (apparently fixed up stream.. it does us all now no good)..

The fix

1. edit /etc/ssh/sshd_config
2. Find and change the lines (or add if missing):
   GSSAPIAuthentication yes
   ...
   #UseDNS yes

   to

   GSSAPIAuthentication no
   ...
   UseDNS no
3. Enjoy

Side Note

If you use CentOS you’re probably unable to reboot your SSH server and you don’t know it.

I also experienced this problem while attempting to restart the ssh server. Everything seemed to work but when checking the logs it showed serious errors. It complained about being unable to bind to port 22. To see if you have the same problem follow these steps..

If you find something like the following:

then you’ve got problems.. It’s basically saying that the localhost IPv6 address (represented as “::”) is hogging port 22 instead of 0.0.0.0 (means ANY IPv4 address). If that’s what you want, then great! If not..

edit

and change it to look as follows from

to

Hope this helps!

References

• http://www.ubuntugeek.com/fix-for-ssh-slow-to-ask-for-password-in-ubuntu-feisty-fawn.html
• http://bugs.centos.org/view.php?id=3234
• http://www.openssh.com/faq.html#3.3

My search for a simple solution to a 1000Hz Xen Kernel lead to dead ends all around despite having heard of success stories from others on the Xen mailing list.

I’m still unsure as to why Xen decided to run at 250Hz instead of the default 1000Hz. Though I’ve heard there are software “problems” with specific packages when shifted over to a 1000Hz environment. I myself am stuck and require 1000Hz for proper operation of my gaming servers. I’m currently capped for performance because of this (don’t ask me why… ask Valve..) and am not looking forward to recompiling the kernel every time there is an update to Xen or the kernel… Though its looking like the only option.

I’ll document my findings as they come (probably along with a guide on how to do this as well, since there is none).

Well, after a few weeks of trouble I’ve finally got my DomU image working at 1000Hz.. The interesting thing is that I didn’t even have to reboot my server running dom0 to achieve this success!

Initially I ran into trouble because I was attempting to compile the xenified kernel from the xen.org site. This code lead to kernel panics during boot because that kernel couldn’t detect LVM volumes which CentOS uses by default. I was unable to find the “exact” reason for this problem and therefore moved onto other solutions.

I eventually came to CentOS’s own wiki and found that their kernel-recompile tutorial would work perfectly since the xen configs were included with the source! (awesome stuff).. Though, originally I had thought that I would need to replace the dom0 kernel and therefore worried a bit if problems arose. (I have servers far away that are not at arms reach for human intervention)… So I used a test box at home..

After a kernel recompile locally I installed the kernels (after configuring for 1000Hz) on dom0 and booted up a DomU.. To my surprise it was still using the original kernel that was installed which lead me to my conclusion… I ended up installing the recompile kernel only on the DomU that required it! And it works perfectly to boot with no need to sweat over dom0 not booting.

I’ll make a guide for this shortly however if anyone is interested in following the steps I took (very well written) head over to the CentOS wiki article CenOS Custom Kernel. Well written indeed.