| Value | Meaning |
|---|---|
| IN1 | There is data to read. |
| OUT4 | Data can be written (without blocking). |
| PRI2 | There is urgent data to read. |
| ERR8 | Error condition. |
| HUP16 | Hung up (the connection has been broken, usually for pipes and sockets). |
| NVAL32 | Invalid request. The file descriptor is not open. |
A bitwise combination representing a condition to watch for on an event source.