# Environment variables

This is the traditional variable type in PDI. You define an environment variable through the Set Environment Variables dialog box in the **Edit** menu, or by hand by passing it as an option to the Java Virtual Machine (JVM) with the -D flag.

Environment variables are an easy way to specify the location of temporary files in a platform-independent way; for example, the\*\*${java.io.tmpdir}\*\* variable points to the `/tmp/` directory on Unix/Linux/OS X and to the `C:\Documents and Settings\<username\Local Settings\Temp\` directory on Windows.

The only problem with using environment variables is that they cannot be used dynamically. For example, if you run two or more transformations or jobs at the same time on the same application server, you may get conflicts. Changes to the environment variables are visible to all software running on the virtual machine.


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