An LSB conforming system must adhere to the FHS 2.2.
The FHS allows many components or subsystems to be optional. An application must check for the existence of an optional component before using it, and should behave in a reasonable manner if the optional component is not present.
The following device nodes must exist under /dev. Other devices may also exist in /dev.
All data written to this device is discarded. A read from this device will return an EOF condition.
This device is a source of zeroed out data. All data written to this device is discarded. A read from this device will return as many bytes containing the value zero as was requested.
This device is a synonym for the controlling terminal of a process. Once this device is opened, all reads and writes will behave as if the actual controlling terminal device had been opened.