First, your system must be running the Solaris 9 operating environment.
You can then install the Solaris 9 MU4, if you meet both of the following conditions:
You are applying patches that were released in the Solaris 9 8/03 operating environment.
You are retaining patches that you previously applied to your system.
If your system is running the Solaris 9 operating environment, or a Solaris 9 Update release, and you want to fully upgrade to new features and hardware support, install the Solaris 9 8/03 operating environment. The patches that were applied by installing the Solaris 9 8/03 operating environment replace previously installed Solaris 9 patches. The newly installed patches cannot be backed out of the release.
Maintenance Updates are primarily designed to update the Solaris operating environment to a known, tested patch level. If you want to apply a particular patch, and only that patch, do so through your normal support channels.
The name of this product is Solaris 9 MU4. Code or package path names might use Solaris 2.9 or SunOSTM 5.9. Always follow the code or path as it is written in this document.