Check if shared library is installed on Mac OS X

One way to check whether a library is installed is to use ld, e.g. check that zlib is installed:

ld -lzlib

If library is installed you’ll get something like this:

ld: warning: -arch not specified
ld: could not find entry point "start" (perhaps missing crt1.o) for inferred architecture x86_64

If library is not installed you’ll get something like this:

ld: library not found for -lzlib

Checking for disc overload on linux

The trick is to use vmstat and look at the number for “wait on acknowledge”.

vmstat -S m 1 100

Look under “cpu” and the “wa” column. If this number is high, it is bad. It should be zero. Some sample output from vmstat looks like this:

procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa
 0  0      0    406     83   3062    0    0     1     5    1    4  0  0 99  1
 0  0      0    406     83   3062    0    0     0     0 2020   49  0  0 100  0
 0  0      0    406     83   3062    0    0     0     0 2020   41  0  0 100  0
 0  0      0    406     83   3062    0    0     0     0 2018   53  0  0 100  0

Look at the column furthest to the right.

OpenStreetMap tiles in EPSG:25832 projection using GeoServer

Warning: This is a description of how to create a OpenStreetMap WMS with GeoServer. It works fine up to the point where the layers published as an unstyled WMS. This is where I’ve not been able to produce a good result, because of lack of a good Styled Layer Descriptor (SLD). If you have hints about a good SLD, feel welcome to submit a comment!

The idea

The idea is/was to first create a good general purpose OpenStreetMap WMS, and then use GeoWebCache to generate tiles from this WMS source in a custom projection, epsg:25832 in our case.

Continue reading “OpenStreetMap tiles in EPSG:25832 projection using GeoServer”

Easy two column layout in latex

Include the packages. The blindtext package is just an easy way to type Lorem ipsum etc.

\usepackage{multicol}
\usepackage{blindtext}

Make a two column section of a page.

\begin{multicols}{2}[\textbf{Example for a two column text}]
\blindtext
\end{multicols}

If only more people wrote like Lamport

I’m half way through the Part-time parliament on Paxos article by Leslie Lamport. It is an article that describes a three-phase consensus protocol by telling a story of a (fictional) parliement on the greek island of Paxos, complete with fat priests, busy businessmen, and a vivid description of the parliament hall. The story illustrates how the members of the parliament, who would walk in and out at any time, could pass decrees and agree on what had been agreed upon, decree-wise.

Continue reading “If only more people wrote like Lamport”