Spring Equinox Solar Eclipse

(Click on the photo for added detail.)
(Click on the photo for added detail.)

Today’s photo took a bit of work. Much of this was anticipated, but some was not. I can safely say that this was a technically challenging photo, and I learned a few things processing it. It’s good to stretch one’s abilities every so often.

Obviously this is the photo of the eclipse that I mentioned last week. I wanted to create a photo with the solar trajectory during the eclipse (that I knew would take about two hours from first contact to fourth contact), with something interesting in the foreground. Initially I planned to go to Lapsi, but later decided that Dingli was a better choice. As usual with such things, The Photographer’s Ephemeris helped immeasurably in the planning stage. Given the sun’s elevation in late morning, I knew I’d need to use a very wide lens, which would also mean the sun would be a very small disk in the photo. Not much to do about that. And of course, given the sun’s intensity, I’d need to cover a huge exposure range between the sun, sky, and foreground.

On the day we drove up to Dingli, found a congenial spot behind the chapel dedicated to St Mary Magdalene, and set up. I covered the exposure difference between sun and sky as usual with grad filters. I also used a polariser to increase contrast (the glare down here is phenomenal, even this early in the year). To get the sun to be anything other than a starburst I had to bracket exposures. And based on the result, I should have bracketed even further. The end result is obviously a composite of multiple images: one for each time the sun appears, a few for the sky, and one for the foreground. I hope you like the result.

Adding client nodes to a Torque/PBS system on Ubuntu 14.04 LTS

A few weeks ago I wrote a blog post on installing a single-node Torque/PBS job scheduler on an Ubuntu 14.04 LTS system. The node served as scheduler, queue manager, compute node, and submission node. For my application, this node was installed in a machine room, and was primarily meant to act as a shared compute node; users would need to submit their jobs remotely from their workstations. So an additional part of the job involved the addition of a number of such nodes as job submission nodes. It proved to be rather simpler than I expected, and I’m finally writing about how I did that.

As in my earlier post, the following commands need to be issued as root, either on the machine to be added as a job submission node (I’ll call this the client from now on) or on the machine that’s already installed as scheduler, queue manager, compute node, and submission node (I’ll call this the server from now on).

First, of course, the client machine needs to have the necessary packages installed. This is easily done.

apt-get install torque-client torque-mom

We’ll be installing the client as both a job submission node and a compute node; we won’t necessarily want it to act as a compute node but this makes it easier if we do. So, we first need to stop the compute node process.

/etc/init.d/torque-mom stop

Next, we configure the client to point to the already configured server.

echo SERVER.DOMAIN > /etc/torque/server_name

This does two things: it lets the client know where any submitted jobs need to go for scheduling, and it also lets the compute node process know where to get work from. All we need to do after this is to start the compute node process again

/etc/init.d/torque-mom start

Now, we simply need to let the server know that it should accept any jobs coming from this client. So, on the server, we tell the queue manager that our new client is a valid job submission node.

qmgr -c 'set server submit_hosts += CLIENT'

Note that, as when we added the server machine as a job submission node, this client address cannot be a FQDN (see the previous post for an explanation). Note that if the server cannot resolve the client name from its IP (i.e. if you don’t have reverse DNS lookup on the client’s domain) then you’ll need to add the client IP and name (qualified, if you want) to /etc/hosts on the server. This allows the server to do the necessary name lookup from the client IP.

That’s basically it. To test, just submit a job from the client machine, and it should work.

Overlooking the Lower Cliffs at Dingli

(Click on the photo for added detail.)
(Click on the photo for added detail.)

I meant to post something else today. Specifically, I hoped I’d have processed the photo from the eclipse by now, but that’s taking longer. So instead I’m sharing a photo I took at the end of that session, when the eclipse was almost over. By that time, the sun had moved out of frame, so I recomposed to show the upper and lower cliff lines, with the fields in the terrace between them. The tiny island of Filfla is in the distance.

This section of cliffs is in two levels: the upper cliffs drop by 20-30m, then there’s terraced fields over a drop of about 80-100m, and a further 120m drop in the lower cliffs, straight to the sea. It’s all rather dramatic, but it can be tricky to keep a sense of the whole thing on a 2D picture.

I knew I wanted a person on the rocky outcrop, for scale, so I figured I’d get myself in the photo for once. R was with me, so I set up the camera, explained what I wanted, and left the trigger in her hands. Soon after that, we packed up and went for lunch at a lovely place in Dingli.

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