24 Jul 2014
When using third party package repositories, you occassionally might need to
update expired repository keys. An expired key leads to an error message
sudo apt-get update similar to the following:
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used.
GPG error: http://build.i3wm.org raring Release:
The following signatures were invalid: KEYEXPIRED 1396011159 KEYEXPIRED 1396011159 KEYEXPIRED 1396011159
To find any expired repository keys and their IDs, use
apt-key as follows:
apt-key list | grep expired
You will get a result similar to the following:
pub 4096R/BE1DB1F1 2011-03-29 [expired: 2014-03-28]
The key ID is the bit after the
BE1DB1F1 in this case.
To update the key, run
sudo apt-key adv --recv-keys --keyserver keys.gnupg.net BE1DB1F1
The repository will then be updated with the next
sudo apt-get update.
06 Oct 2013
On the weekend of 4-6th October I was part of #hack4good in London
working with Chris Adams, Corinne Pritchard and Nick Stanton
tackling multi-agency reporting at refugee camps for International Medical
Corps UK with the Taarifa platform.
We approached the problem from two angles: One was developing a workflow for a
paper-based reporting system, where report forms are automatically generated
for a specific area like a refugee camp. Refugees would be able make a report
by filling in the form themselves with the help of a simple iconography to
overcome the language barrier, mark the location on a map and drop it into a
collection box. The forms are machine readable and can be digitized in an
The other was the technical challenge of providing a platform that could
process a variety of different reports that various agencies working at a
refugee camp need to deal with from santiation over general feedback to sexual
exploitation. These can be aggregated in one place by the Taarifa API
which I’ve extended to be able to handle any report schema. Creating a new
report type is a simple as sending a POST request describing the schema to the
API in JSON format. Reports can then be submitted immediately via the JSON
API or via an automatically generated web form. All of that is live and
operational at http://api.taarifa.org.
There was quite a bit of media coverage around #hack4good: Channel
4, SkyNews and a video of the London event by Big Bang
12 Aug 2013
Interoperability between C and Fortran codes is often complicated by Fortran’s
support for “true” multi-dimensional arrays. In addition, Fortran 90 supports
assumed shape (also referred to as deferred shape) arrays, where the extent
sizes are determined at runtime. Actual arguments for array dummy arguments
can be array slices that may be of non-unit stride. In short, an assumed size
Fortran array can reference non-contiguous chunks of memory.
Therefore, the compiler will reject an attempt to obtain a raw data pointer of
a Fortran array to pass to a C function like in the following module:
gfortran 4.7 emits the following error message:
Error: Assumed-shape array 'v' at (1) cannot be an argument to the procedure 'c_loc' because it is not C interoperable
What if you know that the assumed-shaped array passed to your function is
actually contiguous (or you choose to leave it the caller’s responsibility)?
Surely the compiler should be able to give you a pointer to the first array
element like so:
gfortran doesn’t and generates the same error as before. The
gfortran developers have recognized this as a bug, which will be fixed in
the 4.9 release.
In the meantime you can work around it by defining a pure function that simply
returns the first argument of an assumed shape array.
gfortran is happy with
that since now the type of the argument passed to
c_loc is a scalar and
However, this workaround confuses Intel’s and PGI’s Fortran compilers, so
simply escape it using the a preprocessor