How to run EMS as a different user on Linux?

Hello, I’m trying use EMS to stream video files that are stored on an external file system that is mounted with NFS, but the local "root" user does not have permission to access the desired files. Instead, the EMS process needs to be run as a specific network user. What is the proper way to run EMS as a different user on a Linux system? I’m using Ubuntu 12.04 to be specific. Thank you, Shane