I really like Twitter. I think it’s a great, fun, service, that helps enable interesting online communities, and is a surprisingly effective way to spread news and information to lots of people online. One of the things that I’ve loved about Twitter is their API, and how open and welcoming they’ve b...

I’m at Dragon*Con this weekend, my second time here now. I decided that if I was going to Dragon*Con again, I needed to do something in terms of costuming, and I wanted it to be something unique – I wasn’t going to come anywhere near as epic as some of the costumes people pull off, but I wanted some...

Basically anyone who’s used Linux for any amount of time eventually comes to know and love the strace command. strace is the system-call tracer, which traces the calls that a program makes into the kernel in order to interact with the outside world. If you’re not already familiar with this incredibl...

In response to my query last time, ezyang asked for any tips or tricks I have for finding my way around the Linux kernel. I’m not sure I have much in the way of systematic advice for tracking down the answers to questions about the Linux kernel, but thinking about what I do when posed with a patch t...

I haven’t been feeling very motivated to blog lately – I’ve missed the last two weeks of Iron Blogger, and I’m not totally enthusiastic about any of the items on my “to blog” list. But, I do enjoy blogging when I actually get into posts, and I’d like to keep updating this blog. So, in a bit of a cop...

I’m pretty sure every developer who has ever worked with a modern database-backed application, particularly a web-app, has a love/hate relationship with their ORM, or object-relational mapper. On the one hand, ORMs are vastly more pleasant to work with than code that constructs raw SQL, even, genera...

Last time, I announced Check Plus, a declarative language for defining Check tests in C. This time, I want to talk about the tricks I used to implement a declarative minilanguage using the C preprocessor (and some GCC extensions). The Problem We want to write some toplevel declarations that look lik...

Check is an excellent unit-testing framework for C code, used by a number of relatively well-known projects. It includes features such as running all tests in separate address spaces (using fork(2)), which means that the test suite can properly report segfaults or similar crashes without the test ru...

A few weeks ago, I wrote that software engineers should keep lab notebooks as they work, in addition to just documenting things after the fact. Today, I’m going to share the techniques that I’ve found useful to try to get in the habit of lab-notebooking my work, even though I still feel like I could...

One of the major reasons I can’t stand webapps is because I’m a serious emacs junkie, and I can’t edit text in anything that doesn’t have decent emacs keybindings. Fortunately, on Linux, at least, GTK provides basic emacs keybindings if you add gtk-key-theme-name = "Emacs" to your .gtkrc-2.0. Howeve...

Most of the projects I've been working on today have fairly strict code review policies. My work requires code review on most of our code, and as we bring on an army of interns for the summer, I've been responsible for reviewing lots of code. Additionally, about five months ago BarnOwl, the console-...

If you’re reading this blog, I probably don’t have to explain why I love GNU screen. I can keep a long-running session going on a server somewhere, and log in and resume my session without losing any state. I also love X-forwarding. I love being able to log into a remote server and work in a shell t...

Recently, I’ve been working on some BarnOwl branches that move more of the core functionality of BarnOwl into perl code, instead of C (BarnOwl is written in an unholy mix of C and perl code that call each other back and forth obsessively). Moving code into perl has many advantages, but one problem i...

Since I first discovered ratpoison in 2005 or so, I've basically exclusively used tiling window managers, going through, over the years, StumpWM, Ion 3, and finally XMonad. They've all had various strengths and weaknesses, but I've never been totally happy with any of them. This blog entry is a writ...

Software engineers, as a rule, suck at writing things down. Part of this is training – unlike chemists and biologists who are trailed to obsessively document everything they do in their lab notebooks, computer scientists are taught to document the end results of their work, but aren't, in general, t...

With the announcement this week that Quora had taken $11 million in VC at an $86 million valuation, there’s been an awful lot of attention on Quora. I’ve had an account there and wanted to write up some of my initial thoughts. If you haven’t heard about Quora, it’s yet another question/answer site o...

About two months ago, Linux saw CVE-2010-0307, which was a trival denial-of-service attack that could crash essentially any 64-bit Linux machine with 32-bit compatibility enabled. LWN has an excellent writeup of the bug, which turns out to be a subtle error related to the details of the execve syste...

The fundamental tool of any engineering discipline is the notion of abstraction. If we can build a set of useful, easily-described behaviors out of a complex system, we can build other systems on top of those pieces, without having to understand to worry about the full complexity of the underlying s...

After my previous post got posted to reddit, there was a bunch of interesting discussion there about some details I’d handwaved over. This is a quick followup on some the investigation that various people carried out, and the conclusions they reached. In the reddit thread, lacos/lbzip2 objected that...

6.033, MIT’s class on computer systems, has as one of its catchphrases, “Complex systems fail for complex reasons”. As a class about designing and building complex systems, it’s a reminder that failure modes are subtle and often involve strange interactions between multiple parts of a system. In my ...

So, you may have noticed that I suddenly started updating this blog for the first time in a while. The reason is that I’ve recently started an ongoing event with a whole bunch of friends around here to encourage us to blog more. Like so many good ideas, it all started with a fundamentally simple pre...

I’ve been looking for a good solution for versioning and synchronizing my dotfiles between machines for some time. I experimented with keeping all of ~ in subversion for a while, but it never worked out well for me. I’ve finally settled on a solution that I like using git, and so this is a writeup o...

CVE-2007-4573 is two years old at this point, but it remains one of my favorite vulnerabilities. It was a local privilege-escalation vulnerability on all x86_64 kernels prior to v2.6.22.7. It’s very simple to understand with a little bit of background, and the exploit is super-simple, but it’s still...

In my previous blog post, I discussed how git is distinctive among version control system in the way in which it makes the backend model that is being used to store data the most important element of the tool, and that experts use it by having the complete model in their head, and thinking in terms ...

I’ve been helping a number of people get started working with git over the last couple of weeks, as Ksplice has brought on some new interns, and we’ve had to get them up to speed on our internal git repositories. (As you might expect from a bunch of kernel hackers, we use git for absolutely everythi...

(This is part three of a multi-part introduction to termios and terminal emulation on UNIX. Read part 1 or part 2 if you’re new here) For my final entry on termios, I will be looking at job control in the shell (i.e. backgrounding and foreground jobs) and the very closely related topic of signal gen...

(This is part two of a multi-part introduction to termios and terminal emulation on UNIX. Read part 1 if you’re new here) In this entry, we’ll look at the interfaces that are used to control the behavior of the “termios” box sitting between the master and slave pty. The behaviors I described last ti...

If you’re a regular user of the terminal on a UNIX system, there are probably a large number of behaviors you take mostly for granted without really thinking about them. If you press ^C or ^Z it kills or stops the foreground program – unless it’s something like emacs or vim, in which case it gets ha...

I’ve made two new interesting discoveries about wpa_supplicant since writing my last blog post on the subject. (Actually, I pretty much made both of them while reading documentation in order to write it, and have been lame about writing them up). Using wpa_gui It turns out that wpa_gui not only allo...

As most of you probably know, X has several different mechanisms for copy-paste, used by different applications in different ways. I know some people who use them deliberately, juggling two pieces of text in different clipboards at once, but for me, it’s always just been annoying. When I copy someth...