PhysicalUncertainty

I’ve used sed for a long time, and maybe at one time I was aware of the -i option, but it has long since been forgotten until recently. The -i option is allows you to apply a substitution ‘inplace’, i.e. to overwrite text in the file you are processing. This is really something that should have been in my linux toolbox before now. Hopefully, this time I won’t forget it.

I have a long-standing interest in leadership. I find it really interesting that some people are particularly effective at motivating and directing people, whereas others are not. I have also wanted to write an article about leadership for a while, but I have never been sure where to start or what to cover. I am certainly no expert on leadership, more of an interested observer. Nonetheless, I saw something today that affected me today and I feel the need to get some thoughts out of my head.

I like to play soccer, and although I don’t play competitively any more, I like to go out on the weekends and kick a ball around. It is early fall and it was wet and noticeably colder than last month. There was a childrens team practicing on the other side of the field and it was hard to not hear what the coaches were saying. There were three adults (parents I guess) and one of them was The Talker. Unfortunately, he wasn’t terribly effective at getting the children to do what he wanted. The expression, ‘herding cats’ seems appropriate, but then that’s children for you. So he became frustrated and ended up shouting at the kids, berating them, and putting them down. It’s not an easy job teaching children, but this was an avoidable situation.

I recently finished reading the book ‘flow’ which is essentially about creating a happy existence by trying to be engaged in whatever activity you are performing. So this is something that I have been thinking about recently and couldn’t help applying it to the situation I was witnessing with the children playing soccer. One situation in particular stood out: they were practicing crosses from the corner where the Talker adult would kick the ball from the edge of the field to the children who were in front of the goal — the attackers trying to get a goal and the defenders trying to stop them. Now, these were children. Maybe 8 — 10 years of age. When an adult kicks a soccer ball at you from about 30 — 40 feet away it can be a bit intimidating to try to stop it. Clearly these children were not excited about the prospect, and it didn’t help that Talker adult wasn’t particular accurate. The result was that Talker adult became frustrated as the ball usually flew over the children or the children leaped out of the way of the ball. So he ended up shouting and berating them, and they mostly stood around doing nothing in the cold and wet just getting bored. Any wonder that they started acting up?

Practicing crosses in the goal area is a great thing when the players are not afraid of the ball and know how to head the ball at the goal. But these children were not at that point. The coaches should have started with something more basic. First, the children need to be doing something so they are not getting cold and bored. Second they need to feel that they are working at something that is challenging, but not too difficult or intimidating. Perhaps the coaches could have had the children line up in front of the goal and simply thrown the ball in the air for each child to head. This makes it less intimidating for the children and they get to run around. Once they start to understand the routine maybe add to it by having child that last headed the ball be the person to throw the ball in the air next to build on the teamwork. But the idea is to present a challenge that you know they are capable of, and when they become confident increase the difficulty a little to make sure they are doing something achievable but challenging.

Being a teacher means being a leader. The goal is to motivate and teach by engaging the interest and building the confidence of the student through realistic challenges that allow the student to succeed through work and effort.

Recently I was playing around with EC2 and wanted to rsync a whole bunch of data on an instance. Because Amazon uses ssh-keys to provide secure logins you provide the identity file when you login. This is simple when simply logging onto the server to noodle around, but how to provide the key when trying to rsync via SSH? The answer turns out to be pretty easy,


eval $(ssh-agent)
ssh-add ~/.ssh/[my-public-key]


This starts up an agent and passes your identity file (SSH key) to the agent, which forwards the file (during the current session) whenever using SSH. So once you have perform this small invocation, you can simply use rsync to copy to the target server,


rsync -avz [some-place-on-your-machine] [user]@[server]:[some-place-on-server]


I remember that one of the things that frustrated and confused me a lot when I first started using linux was what happened when was running a program and pressed CTRL-Z. This suspends the program but it does not terminate it, which is what I thought it did. And then of course I wondered my computer would start grinding to a halt after a couple of hours of use…

Well, suspending a program is actually a really powerful feature when you know how to interact with a suspended process. Suppose you are writing some code in vim and you get to something that you want to look up in a man page. One nice way of doing this is to suspend vim (CTRL-Z), search for whatever you need to know, and then restart vim from where you were by using the fg command. For whatever reason you need to interrupt what you are doing, this gives you a nice way to get back to where you were without any messing around.

The next command is bg. Sometimes you find that you have started a program that is doing something that takes a while, and really you don’t need to watch it to completion. In that case, you can suspend the program using CRTL-Z and then type bg to run the process in the background as if you had originally run the program with a trailing ampersand.

So fg and bg are handy but there are a couple of more commands that help to expand the utility of this workflow. The first is the jobs command. Using jobs you can get a list of the current jobs, which includes suspended processes. You may have noticed when you suspend a process that the first part of the output on the command line is a number in square brackets: this is the job id of the suspended process. If you have more than one process suspended you can use jobs to get the list, and then pass the id to fg, for example, to resume that particular process. Similarly with bg.

However, the way that I most often find myself using the job id is to kill a process. Sometimes you have a program running that you need to terminate but CTRL-C isn’t working for whatever reason. You can CTRL-Z and then terminate the process using kill -9 %id, where ‘id’ is the job id of the suspended process. NB: the % is a literal in this command, so e.g. this is actually what you type to kill the first suspended process kill -9 %1.