I'm a doctor, not a mechanic
UMOD installers (or "Unreal Modules") are the Unreal engine's native format for game content distribution and automated installation. A UMOD installer is basically an (uncompressed) archive of files stored along with information about where those files are to be installed to and about neccessary INI file changes. You could even create shortcuts or registry entries with UMOD files.
In UT2003 UMOD installers have the file extension UT2MOD ("UT 2003 Module"), but that's the only difference. (Well, the installer doesn't work correctly until build 2166, but that's a different thing. Read UMOD/Problems for more information.)
UMOD vs. ZIP
Keep in mind that many people vastly prefer plain zipped distributions over UMOD installers for a variety of reasons, some of them being described in UMOD/Problems, another one being that they just prefer having complete control over the installation process (server admins tend to like that, for instance).
Creating a zipped distribution can be automatized just as well as Legacy:UMOD/Creating a UMOD distribution, but you need a command line archiving tool for that. Info-ZIP.org distributes zip and unzip, two powerful Open Source tools for creating and extracting .zip files.
There's a huge discussion going on on whether it's advisable or not to add subdirectory information to .zip files. In a nutshell, subdirectory information allows users to simply extract the entire .zip file into their Unreal Tournament or UT2003 base directory. While that's very convenient, the downside is that many people don't expect it to happen (and don't bother to check whether subdirectory information is present or not), extract the individual files in their respective target directories manually and thus inadvertently create a second-level subdirectory structure below their Unreal Tournament base directory. That defeats the purpose of making the installation process as convenient as possible for those users, of course.
- umod Wizard – Graphical tool for creating basic UMOD installers
- Legacy:UMOD/Creating – How to create UMOD installers
- Legacy:UMOD/Source – The format of the files used to compile a UMOD file (can't think of a better name for the page)
- Legacy:UMOD/Reference – UMOD configuration files sections and directives.
- Legacy:UMOD/Problems – What to do if it doesn't work
- Legacy:UMOD/File Format – The internal file structure of UMOD files (advanced topic)
- Legacy:UMOD/Removing – How to remove installed UMOD files
JCBDigger: I have created a VBScript installer which you can download from my web site. http://games.DiscoverThat.co.uk It even adds the ServerPackage name if you want it to. Only any good for Windows. My Unix scripting is very out of date, but if someone could create a Linux shell script we'd have a complete set and no longer need UMod.