If the calling process is not already a session leader, setpgrp
    sets the process group ID of the calling process to the process
    ID of the calling process. If setpgrp creates a new session, then
    the new session has no controlling terminal.

    The setpgrp function has no effect when the calling process is a
    session leader.

    This function requires that long (32-bit) UID/GID support be
    enabled. See 32-Bit UID and GID Macro (Integrity servers, Alpha)
    for more information.