A Process ID (PID) uniquely identifies a UNIX process. On D3, each D3 process is a UNIX process, and, therefore, is assigned a PID by UNIX. D3 processes are usually identified by their D3 port number (from 0 to the maximum number of ports), as usual. It is sometimes necessary to identify the PID of a D3 process. The PIDs are displayed by the TCL commands list-users, pid, psr and by the UNIX command d3.