listen(1M) SYSTEM ADMINISTRATION COMMANDS listen(1M)
NAME
listen - network listener daemon
SYNOPSIS
/usr/lib/saf/listen [ -m devstem ] net_spec
DESCRIPTION
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 tran-
sport provider) that conforms to the Transport 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 utmp 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. When the -m devstem option is specified, the
listener will use devstem as the prefix for the pathname.
In either case, the representation of the minor device
number will be at least two digits (e.g., 05 or 27), but
will be longer when necessary to accommodate minor device
numbers larger than 99.
SERVER INVOCATION
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 especially tsync(3N)) 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 ser-
vice 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 connec-
tion is passed in the form of a file descriptor that refers
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listen(1M) SYSTEM ADMINISTRATION COMMANDS listen(1M)
to the new transport endpoint. Before the file descriptor
is sent to the server, the listener interprets any confi-
guration script registered for that service using
doconfig(3N), although doconfig is invoked with both the
NORUN and NOASSIGN flags. The server receives the file
descriptor for the connection in a strrecvfd structure via
an I_RECVFD ioctl(2).
For more details about the listener and its administration,
see nlsadmin(1M).
FILES
/etc/saf/pmtag/*
SEE ALSO
nlsadmin(1M), pmadm(1M), sac(1M), sacadm(1M),
doconfig(3N), nlsgetcall, nlsprovider(3N),
streamio(7).
Network Programmer's Guide
CAVEATS
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 sin-
gle 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 other-
wise valid address, and would result from a dynamic-address
service having been bound to that address by a different
instance of the listener.
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