I was about the re-install Snow Leopard the other day because I did something real dumb and couldn’t figure out how to fix it. I was trying to install a postgreSQL client on my computer and was having trouble with permissions on certain folders in my root directory during installation.

So, stupidly, I recursively set all permissions in the /usr folder to read/write/execute, thinking I could set them back afterwards. Bad idea.

DON’T MESS WITH THESE.

The real kicker here is that if you screw up these settings, you also mess with your ability to use sudo to reset them from the terminal. I found a number of blog posts like this one or this one that basically said: you’re screwed. Wipe your hard drive.

Okay, assuming now that everyone knows what not to do, here’s how to fix it. Run Disk Utility and click “Repair Disk Permissions”:

Simple.