LISTEN(8) Maintenance Procedures LISTEN(8)


listen - network listener daemon


/usr/lib/saf/listen [-m devstem] net_spec


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)

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


The listener will use devstem as the prefix for the




ioctl(2), doconfig(3NSL), nlsgetcall(3NSL), nlsprovider(3NSL),
t_sync(3NSL), streamio(4I), attributes(7), nlsadmin(8), pmadm(8), sac(8),


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

April 3, 1997 LISTEN(8)