Efficiency of Cooling Servers

One thing I had wondered was why home air-conditioning systems are more efficient than air-conditioning systems for server rooms. I received some advice on this matter from the manager of a small server room (which houses about 30 racks of very powerful and power hungry servers).

The first issue is terminology, the efficiency of a […]

Improving Blog Latency to Benefit Readers

I just read an interesting post about latency and how it affects web sites [1]. The post has some good ideas but unfortunately mixed information on some esoteric technologies such as infiniband that are not generally applicable with material that is of wide use (such as ping times).

The post starts by describing the latency […]

Killing Servers with Virtualisation and Swap

The Problem:

A problem with virtual machines is the fact that one rogue DomU can destroy the performance of all the others by inappropriate resource use. CPU scheduling is designed to allow reasonable sharing of computational resources, it is unfortunately not well documented, the XenSource wiki currently doesn’t document the “credit” scheduler which is used […]

Ownership of the Local SE Linux Policy

A large part of the disagreement about the way to manage the policy seems to be based on who will be the primary “owner” of the policy on the machine. This isn’t a problem that only applies to SE Linux, the same issue applies for various types of configuration files and scripts throughout the process […]

SE Linux Policy Packaging for a Distribution

Caleb Case (Ubuntu contributer and Tresys employee) has written about the benefits of using separate packages for SE Linux policy modules [1].

Firstly I think it’s useful to consider some other large packages that could be split into multiple packages. The first example that springs to mind is coreutils which used to be textutils, shellutils, […]

SpamAssassin During SMTP

For some time people have been telling me about the benefits of SpamAssassin (SA). I have installed it once for a client (at their demand and against my recommendation) but was not satisfied with the result (managing the spam folder was too complex for their users).

The typical configuration of SA has it run after […]

Executable Stacks in Lenny

One thing that I would like to get fixed for Lenny is the shared objects which can reduce the security of a system. Almost a year ago I blogged about the libsmpeg0 library which is listed as requiring an executable stack [1]. I submitted a two-line patch which fixes the problem while making no code […]

Xen CPU use per Domain

The command “xm list” displays the number of seconds of CPU time used by each Xen domain. This makes it easy to compare the CPU use of the various domains if they were all started at the same time (usually system boot). But is not very helpful if they were started at different times.

I […]

A New Strategy for Xen MAC Allocation

When installing Xen servers one issue that arises is how to assign MAC addresses. The Wikipedia page about MAC addresses [1] shows that all addresses that have the second least significant bit of the most significant byte set to 1 are “locally administered”. In practice people just use addresses starting with 02: for this purpose […]

Lenny SE Linux on the Desktop

I have been asked about the current status of Lenny SE Linux on the Desktop.

The first thing to consider is the combinations of policies and configurations. I will number them if only for the purpose of this post, if the numbering is considered generally helpful it could be more widely adopted to describe configurations.