| Unlock | System.Posix.IO, System.Posix |
| UserEntry |
| 1 (Type/Class) | System.Posix.User, System.Posix |
| 2 (Data Constructor) | System.Posix.User, System.Posix |
| UserID | System.Posix |
| undl | System.Posix.DynamicLinker |
| unionFileModes | System.Posix.Files, System.Posix |
| unsetEnv | System.Posix.Env, System.Posix |
| userGecos | System.Posix.User, System.Posix |
| userGroupID | System.Posix.User, System.Posix |
| userID | System.Posix.User, System.Posix |
| userName | System.Posix.User, System.Posix |
| userPassword | System.Posix.User, System.Posix |
| userShell | System.Posix.User, System.Posix |
| userTime | System.Posix.Process, System.Posix |
| usleep | System.Posix.Unistd, System.Posix |
