Index - U
| unblockSignals | System.Posix.Signals, System.Posix.Signals.Exts, System.Posix.ByteString, System.Posix | 
| undl | System.Posix.DynamicLinker.ByteString, System.Posix.DynamicLinker, System.Posix.ByteString, System.Posix | 
| unionFileModes | System.Posix.Files.ByteString, System.Posix.Files, System.Posix.ByteString, System.Posix | 
| Unlock | System.Posix.IO.ByteString, System.Posix.IO, System.Posix.ByteString, System.Posix | 
| unsetEnv | |
| 1 (Function) | System.Posix.Env, System.Posix | 
| 2 (Function) | System.Posix.Env.ByteString, System.Posix.ByteString | 
| urgentDataAvailable | System.Posix.Signals, System.Posix.Signals.Exts, System.Posix.ByteString, System.Posix | 
| userDefinedSignal1 | System.Posix.Signals, System.Posix.Signals.Exts, System.Posix.ByteString, System.Posix | 
| userDefinedSignal2 | System.Posix.Signals, System.Posix.Signals.Exts, System.Posix.ByteString, System.Posix | 
| UserEntry | |
| 1 (Type/Class) | System.Posix.User, System.Posix.ByteString, System.Posix | 
| 2 (Data Constructor) | System.Posix.User, System.Posix.ByteString, System.Posix | 
| userGecos | System.Posix.User, System.Posix.ByteString, System.Posix | 
| userGroupID | System.Posix.User, System.Posix.ByteString, System.Posix | 
| UserID | System.Posix.ByteString, System.Posix | 
| userID | System.Posix.User, System.Posix.ByteString, System.Posix | 
| userName | System.Posix.User, System.Posix.ByteString, System.Posix | 
| userPassword | System.Posix.User, System.Posix.ByteString, System.Posix | 
| userShell | System.Posix.User, System.Posix.ByteString, System.Posix | 
| userTime | System.Posix.Process.ByteString, System.Posix.Process, System.Posix.ByteString, System.Posix | 
| usleep | System.Posix.Unistd, System.Posix.ByteString, System.Posix |