[READ THIS FIRST!!! Update 6/13/2009: If you’ve come here looking to get plugin updates to work and you’re using WordPress 2.8, you really want to start with this more recent post on the topic and then come back for the permission information.]
One of the neat features of WordPress 2.5 is the click to install plugin upgrades, assuming the plugin is registered in the WordPress Plugin Directory. If certain conditions are correct on the server it can do it in place, otherwise it tries to do it via FTP.
To make it so wordpress could upgrade them on the server without FTP requires doing some permission changes. You should be aware, the changes I made allow the web server (Apache) to be able to write to the plugin directory. This creates some security exposure. Since I do nightly backups, for me this is an acceptable risk. You may make a different call.
The way I’ve done it also assumes you have admin rights on the unix box or you’re friendly with (s)he who does. Without admin rights to do the group ownership changes, you’re stuck having to make files writable by the world, and that’s not something I’d do. Luckily, I hold the power on the box(es) I care about. Continue reading Fix/Tricks for plugin auto-update on WordPress 2.5