Pervasive Code

Silencing pointless reverse DNS warnings from OpenSSH

Jamie Flournoy — Thu, 22 May 2008 08:51:51 +0000

If you’ve been using SSH for long you’ve probably seen this at least once: Address 11.22.33.44 maps to www.foobar.com, but this does not map back to the address - POSSIBLE BREAK-IN ATTEMPT!

Sometimes this is helpful. Sometimes this is really annoying and incorrect. Assuming you are a moderately well informed sysadmin and know that this message can safely be ignored, you might have been stumped trying to silence it. You may have tried every option in man ssh_options and even some of your own (STFU on?) I think I may be able to help.
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Updated .autotest

Jamie Flournoy — Sun, 18 May 2008 05:36:19 +0000

I just brought a new project into the world of autotest. I’m not using the Leopard FSEvents “fix” because it’s not necessary (note the sleep and add_exception calls below). I am using the fun and helpful sound plugin, but not the playlist version of that plugin. Here’s my .autotest file.
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Making Rcov measure your whole Rails app, even if tests miss entire source files

Jamie Flournoy — Fri, 16 May 2008 22:42:42 +0000

I’ve seen a few Rake tasks for Rcov that work OK, but which fail in an interesting way (if you care about coverage): they give your coverage metrics an unexpected boost if you have 0% coverage in one or more source files.

Huh? Exactly. If you have 500 source files, and your test suite only requires one of them, then you get a free ride on those 499 files that have 0% coverage. Theoretically you could get 100% coverage in your report even though 499 source files are not touched at all. D’oh!
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Rails snippet: require app files only once

Jamie Flournoy — Fri, 16 May 2008 22:24:11 +0000

Ruby’s Kernel.require method will re-require the same source file if you pass it differing arguments that point to the same file. It doesn’t use File.expand_path to make sure it hasn’t already loaded the same file before. This can cause problems if you’re using constants or doing one-time initialization in a source file that’s getting loaded multiple times for one reason; you’ll need to add a wrapper that prevents re-entry.

If this annoys you as much as it does me (why should my application code include workarounds for what I regard to be a Ruby bug?), add this snippet to your config/environment.rb (pre Rails 2.0) or config/preinitializer.rb (Rails 2.0 or later).
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Recommended mount options for ext3

Jamie Flournoy — Fri, 16 May 2008 03:54:30 +0000

The details of the various mount options for the ext3 filesystem are fairly well documented, but as with many things in the Unix world, knowledge is far easier to come by than wisdom. That’s a pithy way of saying that I had to do some digging to find recommendations, as opposed to explanations. So here are my recommendations for ext3 users (which encompasses the majority of the Linux-using world, as far as I can tell).
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Save power and heat: spin down backup drives when idle

Jamie Flournoy — Fri, 16 May 2008 00:48:16 +0000

Here’s a tip for those of you who, like me, back up your data to hard disks instead of tapes. Backing up to the same hard disk doesn’t protect you much (if the disk failed, you’d lose the data and the backup at once), so presumably you’re backing up to a separate physical drive. That means that the backup drive need not spin 24/7. Instead, it only needs to spin at backup time.
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Retroactively Minimizing Installed Packages on CentOS 5.1

Jamie Flournoy — Tue, 15 Apr 2008 01:16:44 +0000

In my CentOS 5.1 Minimal VPS Install Guide I describe how to install a very lean set of OS packages when starting from scratch. But what if the VPS is preinstalled for you by a hosting provider? There will be things preinstalled that you don’t need, which will slow down backups and updates, and waste the relatively tiny amount of disk space that VPS plans offer. So here are some instructions to help you identify and remove packages that you don’t need, when they’ve already been installed.
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Why mod_rails is great for light-duty Rails apps

Jamie Flournoy — Mon, 14 Apr 2008 20:30:25 +0000

The Ruby on Rails story is usually presented to the new developer as a wonderful break from tradition that makes a developer’s life so much better than the frameworks of the past. The clattering of skeletons in the closet you’re hearing? Well, that’s because it makes the sysadmin’s life much worse than PHP or Java. That just improved on Friday, with the release of mod_rails. If you’re looking for a way to do shared (or low traffic) hosting of Rails applications, this is for you.
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Thoughts about using Git for closed source projects

Jamie Flournoy — Mon, 14 Apr 2008 16:11:41 +0000

Git is getting a lot of press in the open source world lately, but hasn’t got much traction in the closed source corporate development world. There’s a reason for this, and it’s more than conservatism on the part of the corporate developers. Git (or any DVCS, really) embodies a development culture that isn’t very enterprise-y.
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Sphinx Search init script for Centos 5.1

Jamie Flournoy — Mon, 14 Apr 2008 06:18:11 +0000

Sphinx search is pretty new, and as a result I was unable to find a nice convenient package for it for CentOS 5.1. This is problematic since there is no init script included with the source tarball, and the issue of updating the index is the sysadmin and developer’s problem, and cannot be configured to simply update the index when the data changes.
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