The listen process ``listens'' to a network for service requests, accepts requests when they arrive, and invokes servers in response to those service requests. The network listener process may be used with any connection-oriented network (more precisely, with any connection-oriented transport provider) that conforms to the Transport Layer Interface (TLI) Specification.
The listener internally generates a pathname for the minor device for each connection; it is this pathname that is used in the utmpx entry for a service, if one is created. By default, this pathname is the concatenation of the prefix /dev/netspec with the decimal representation of the minor device number. In either case, the representation of the minor device number will be at least two digits (for example, 05 or 27), or longer when it is necessary to accommodate minor device numbers larger than 99.
When a connection indication is received, the listener creates a new transport endpoint and accepts the connection on that endpoint. Before giving the file descriptor for this new connection to the server, any designated STREAMS modules are pushed and the configuration script is executed, (if one exists). This file descriptor is appropriate for use with either TLI (see t_sync(3NSL) ) or the sockets interface library.
By default, a new instance of the server is invoked for each connection. When the server is invoked, file descriptor 0 refers to the transport endpoint, and is open for reading and writing. File descriptors 1 and 2 are copies of file descriptor 0; no other file descriptors are open. The service is invoked with the user and group IDs of the user name under which the service was registered with the listener, and with the current directory set to the HOME directory of that user.
Alternatively, a service may be registered so that the listener will pass connections to a standing server process through a FIFO or a named STREAM, instead of invoking the server anew for each connection. In this case, the connection is passed in the form of a file descriptor that refers to the new transport endpoint. Before the file descriptor is sent to the server, the listener interprets any configuration script registered for that service using doconfig(3NSL), although doconfig is invoked with both the NORUN and NOASSIGN flags. The server receives the file descriptor for the connection in a strrecvfd structure using an I_RECVFD ioctl(2).
For more details about the listener and its administration, see nlsadmin(1M).
See attributes(5) for descriptions of the following attributes:
|ATTRIBUTE TYPE||ATTRIBUTE VALUE|
When passing a connection to a standing server, the user and group IDs contained in the strrecvfd structure will be those for the listener (that is, they will both be 0); the user name under which the service was registered with the listener is not reflected in these IDs.
When operating multiple instances of the listener on a single transport provider, there is a potential race condition in the binding of addresses during initialization of the listeners, if any of their services have dynamically assigned addresses. This condition would appear as an inability of the listener to bind a static-address service to its otherwise valid address, and would result from a dynamic-address service having been bound to that address by a different instance of the listener.