Unix System Services
A full Unix environment built into z/OS, with a shell, directories and files alongside the traditional mainframe world.
Also written USS, z/OS UNIX, OMVS
Unix System Services, usually shortened to USS or z/OS UNIX, is a certified Unix environment that runs as part of z/OS. It gives you a familiar hierarchical filesystem with directories and paths, a shell, and standard commands such as ls, cd, grep and vi.
It exists because a great deal of modern software expects Unix. Java, Python, web servers, git, package managers and most middleware run on the mainframe through USS. So do the file transfer and scripting tools that connect mainframe systems to everything else.
The interesting part is that the two worlds coexist. A single system has both traditional datasets and Unix files, and programs can work with both. A COBOL batch job can read a dataset and write a file into a Unix directory for another system to collect.
If you are arriving from Linux or macOS, USS is often the most comfortable starting point on the platform, and a useful bridge while the dataset side of z/OS becomes familiar.
Related terms
- z/OSThe main operating system that runs on IBM mainframes, in the same way Windows or Linux runs on a laptop or server.
- DatasetWhat a mainframe calls a file: a named collection of records with a defined structure, rather than a loose stream of bytes.
- TSOTime Sharing Option: the interactive login environment on z/OS, where you get a command prompt and a session of your own.
- File transferMoving data between the mainframe and other systems, where character encoding and record structure both need attention.