30 July, 2011

HTML Slidy

HTML Slidy is a neat style sheet for making powerpoint-like presentations that are: i) written in HTML, and ii) appear in a browser. I've used it for one presentation and quite liked it. My presentation was entirely text. I can imagine it being more awkward for graphics-intensive presentations where the automatic reflowing of content to fit the current window turns into a downside rather than an upside.

23 July, 2011

dnssec revisited

well I was pleased that my dnssec notes remained sufficiently intelligble after a few months to set up a new zone. but the machine I was just using took almost 5h to generate keys for a new zone. oh the entropy.

16 July, 2011

browserid in-browser shell logins

I've previously wired up my shell server barwen.ch to allow browser-based logins using OpenID and shellinabox. I've written about that on this blog before. I saw a few articles about Mozilla's BrowserID. The code snippets there looked like they would integrate well with the code I had already. So my evening project (which ended up only taking about half an hour) was to prototype BrowserID-based shell login.

It works basically the same as for the OpenID login on barwen.ch:

To get set up: you need to sign up for a barwen.ch account which will cost you 50 cents on PayPal; you need to send me the email that you use for BrowserID (instead of / in addition to an SSH key).

To actually log in, go to the login page http://s0.barwen.ch/~benc/browserid.html and log in. A terminal will appear in your browser. You do shell stuff.

This code is pretty crappy so I don't really want to release it until I've had a thought about the security for at least an hour (though you can find fragments of it elsewhere on this blog). I especially think that there might be some attacks possible by using freaky email addresses vs my unsanitised string handling. (I'm looking at you, Bobby Tables).

bbc 500

During the wedding of the Duke and Duchess of Cambridge in April, the BBC website was for a while overwhelmed and giving http 500 errors. I was amused by the graphic they presented:

which UK viewers above a certain age will find familiar.

09 July, 2011

blue traffic light

when I was a little boy, it always struck me that traffic lights should have a blue light in addition to the red and the green (and the amber), though I could never decide what it should be for.

anyway I discovered that in Hong Kong, the MTR East Rail line *does* have a blue light on its signals, so my childhood desire is finally satisfied. it even seems a sensible use:

Passenger trains have been running under an overlaid Automatic Train Protection (ATP) system since 1998. A blue aspect is displayed at signals when a train fitted with working ATP is approaching. A signal showing a blue aspect can be ignored by the driver, who will drive according to the information shown on the cab display.

02 July, 2011

mrtg user counts

I had a graph in mrtg of two variables: number of login sessions (the blue line, the count of users from the unix users command), and number of unique users logged in (the green solid area - formed by deduping the output of users).

I decided that the number of login sessions was a bit useless especially with people using screen. A more interesting graph is perhaps something else based on the number of users doing things rather than the number of things a user is doing. So I chose to count the number of (normal, not system) users who have at least one process running.

I count it this way:


# first, unique users logged in
echo $(users | sed 's/ /\n/g' | sort | uniq | wc -l)

# number of users who have 3xxx user numbers and have a process running 
# 3xxx is the "normal user" range, though perhaps I could distinguish in other ways
U=$(ps -A --format user= | sort | uniq | while read a ; do id -u $a ; done | grep -e '3...' | wc -l)

echo $U
echo 0
echo 0

and here's the output: (green is logged-in users, blue is users with processes running)

If you click through to the full page, you might see the change happening in the middle of week 17 of 2011, which is the beginning of May.