376 lines
11 KiB
Groff
376 lines
11 KiB
Groff
.\" Copyright (c) 1985, 1991, 1993, 1994
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)inetd.8 8.3 (Berkeley) 4/13/94
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.\"
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.Dd April 13, 1994
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.Dt INETD 8
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.Os BSD 4.4
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.Sh NAME
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.Nm inetd
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.Nd internet
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.Dq super-server
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.Sh SYNOPSIS
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.Nm inetd
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.Op Fl d
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.Op Fl R Ar rate
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.Op Ar configuration file
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.Sh DESCRIPTION
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The
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.Nm inetd
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program
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should be run at boot time by
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.Pa /etc/rc
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(see
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.Xr rc 8 ) .
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It then listens for connections on certain
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internet sockets. When a connection is found on one
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of its sockets, it decides what service the socket
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corresponds to, and invokes a program to service the request.
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The server program is invoked with the service socket
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as its standard input, output and error descriptors.
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After the program is
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finished,
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.Nm inetd
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continues to listen on the socket (except in some cases which
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will be described below). Essentially,
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.Nm inetd
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allows running one daemon to invoke several others,
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reducing load on the system.
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.Pp
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The options available for
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.Nm inetd:
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.Bl -tag -width Ds
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.It Fl d
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Turns on debugging.
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.It Fl R Ar rate
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Specifies the maximum number of times a service can be invoked
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in one minute; the default is 1000.
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.El
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.Pp
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Upon execution,
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.Nm inetd
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reads its configuration information from a configuration
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file which, by default, is
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.Pa /etc/inetd.conf .
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There must be an entry for each field of the configuration
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file, with entries for each field separated by a tab or
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a space. Comments are denoted by a ``#'' at the beginning
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of a line. There must be an entry for each field. The
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fields of the configuration file are as follows:
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.Pp
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.Bd -unfilled -offset indent -compact
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service name
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socket type
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protocol
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wait/nowait
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user
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server program
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server program arguments
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.Ed
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.Pp
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There are two types of services that
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.Nm inetd
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can start: standard and TCPMUX.
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A standard service has a well-known port assigned to it;
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it may be a service that implements an official Internet standard or is a
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BSD-specific service.
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As described in
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.Tn RFC 1078 ,
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TCPMUX services are nonstandard services that do not have a
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well-known port assigned to them.
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They are invoked from
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.Nm inetd
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when a program connects to the
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.Dq tcpmux
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well-known port and specifies
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the service name.
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This feature is useful for adding locally-developed servers.
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.Pp
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The
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.Em service-name
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entry is the name of a valid service in
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the file
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.Pa /etc/services .
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For
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.Dq internal
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services (discussed below), the service
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name
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.Em must
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be the official name of the service (that is, the first entry in
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.Pa /etc/services ) .
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For TCPMUX services, the value of the
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.Em service-name
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field consists of the string
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.Dq tcpmux
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followed by a slash and the
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locally-chosen service name.
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The service names listed in
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.Pa /etc/services
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and the name
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.Dq help
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are reserved.
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Try to choose unique names for your TCPMUX services by prefixing them with
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your organization's name and suffixing them with a version number.
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.Pp
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The
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.Em socket-type
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should be one of
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.Dq stream ,
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.Dq dgram ,
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.Dq raw ,
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.Dq rdm ,
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or
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.Dq seqpacket ,
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depending on whether the socket is a stream, datagram, raw,
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reliably delivered message, or sequenced packet socket.
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TCPMUX services must use
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.Dq stream .
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.Pp
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The
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.Em protocol
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must be a valid protocol as given in
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.Pa /etc/protocols .
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Examples might be
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.Dq tcp
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or
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.Dq udp .
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TCPMUX services must use
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.Dq tcp .
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.Pp
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The
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.Em wait/nowait
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entry specifies whether the server that is invoked by inetd will take over
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the socket associated with the service access point, and thus whether
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.Nm inetd
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should wait for the server to exit before listening for new service
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requests.
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Datagram servers must use
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.Dq wait ,
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as they are always invoked with the original datagram socket bound
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to the specified service address.
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These servers must read at least one datagram from the socket
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before exiting.
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If a datagram server connects
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to its peer, freeing the socket so
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.Nm inetd
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can received further messages on the socket, it is said to be
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a
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.Dq multi-threaded
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server;
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it should read one datagram from the socket and create a new socket
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connected to the peer.
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It should fork, and the parent should then exit
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to allow
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.Nm inetd
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to check for new service requests to spawn new servers.
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Datagram servers which process all incoming datagrams
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on a socket and eventually time out are said to be
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.Dq single-threaded .
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.Xr Comsat 8 ,
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.Pq Xr biff 1
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and
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.Xr talkd 8
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are both examples of the latter type of
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datagram server.
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.Xr Tftpd 8
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is an example of a multi-threaded datagram server.
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.Pp
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Servers using stream sockets generally are multi-threaded and
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use the
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.Dq nowait
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entry.
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Connection requests for these services are accepted by
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.Nm inetd ,
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and the server is given only the newly-accepted socket connected
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to a client of the service.
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Most stream-based services operate in this manner.
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Stream-based servers that use
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.Dq wait
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are started with the listening service socket, and must accept
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at least one connection request before exiting.
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Such a server would normally accept and process incoming connection
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requests until a timeout.
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TCPMUX services must use
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.Dq nowait .
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.Pp
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The
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.Em user
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entry should contain the user name of the user as whom the server
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should run. This allows for servers to be given less permission
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than root.
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.Pp
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The
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.Em server-program
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entry should contain the pathname of the program which is to be
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executed by
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.Nm inetd
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when a request is found on its socket. If
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.Nm inetd
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provides this service internally, this entry should
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be
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.Dq internal .
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.Pp
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The
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.Em server program arguments
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should be just as arguments
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normally are, starting with argv[0], which is the name of
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the program. If the service is provided internally, the
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word
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.Dq internal
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should take the place of this entry.
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.Pp
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The
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.Nm inetd
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program
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provides several
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.Dq trivial
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services internally by use of
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routines within itself. These services are
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.Dq echo ,
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.Dq discard ,
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.Dq chargen
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(character generator),
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.Dq daytime
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(human readable time), and
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.Dq time
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(machine readable time,
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in the form of the number of seconds since midnight, January
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1, 1900). All of these services are tcp based. For
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details of these services, consult the appropriate
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.Tn RFC
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from the Network Information Center.
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.Pp
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The
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.Nm inetd
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program
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rereads its configuration file when it receives a hangup signal,
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.Dv SIGHUP .
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Services may be added, deleted or modified when the configuration file
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is reread.
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.Sh TCPMUX
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.Pp
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.Tn RFC 1078
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describes the TCPMUX protocol:
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``A TCP client connects to a foreign host on TCP port 1. It sends the
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service name followed by a carriage-return line-feed <CRLF>. The
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service name is never case sensitive. The server replies with a
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single character indicating positive (+) or negative (\-)
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acknowledgment, immediately followed by an optional message of
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explanation, terminated with a <CRLF>. If the reply was positive,
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the selected protocol begins; otherwise the connection is closed.''
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The program is passed the TCP connection as file descriptors 0 and 1.
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.Pp
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If the TCPMUX service name begins with a ``+'',
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.Nm inetd
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returns the positive reply for the program.
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This allows you to invoke programs that use stdin/stdout
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without putting any special server code in them.
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.Pp
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The special service name
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.Dq help
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causes
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.Nm inetd
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to list TCPMUX services in
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.Pa inetd.conf .
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.Sh "EXAMPLES"
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.Pp
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Here are several example service entries for the various types of services:
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.Bd -literal
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ftp stream tcp nowait root /usr/libexec/ftpd ftpd -l
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ntalk dgram udp wait root /usr/libexec/ntalkd ntalkd
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tcpmux/+date stream tcp nowait guest /bin/date date
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tcpmux/phonebook stream tcp nowait guest /usr/local/bin/phonebook phonebook
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.Ed
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.Sh "ERROR MESSAGES"
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The
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.Nm inetd
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server
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logs error messages using
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.Xr syslog 3 .
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Important error messages and their explanations are:
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.Bd -literal
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\fIservice\fP/\fIprotocol\fP server failing (looping), service terminated.
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.Ed
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The number of requests for the specified service in the past minute
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exceeded the limit. The limit exists to prevent a broken program
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or a malicious user from swamping the system.
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This message may occur for several reasons:
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1) there are lots of hosts requesting the service within a short time period,
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2) a 'broken' client program is requesting the service too frequently,
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3) a malicious user is running a program to invoke the service in
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a 'denial of service' attack, or
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4) the invoked service program has an error that causes clients
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to retry quickly.
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Use the
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.Op Fl R
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option,
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as described above, to change the rate limit.
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Once the limit is reached, the service will be
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reenabled automatically in 10 minutes.
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.sp
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.Bd -literal
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\fIservice\fP/\fIprotocol\fP: No such user '\fIuser\fP', service ignored
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\fIservice\fP/\fIprotocol\fP: getpwnam: \fIuser\fP: No such user
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.Ed
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No entry for
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.Em user
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exists in the
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.Pa passwd
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file. The first message
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occurs when
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.Nm inetd
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(re)reads the configuration file. The second message occurs when the
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service is invoked.
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.sp
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.Bd -literal
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\fIservice\fP: can't set uid \fInumber\fP
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\fIservice\fP: can't set gid \fInumber\fP
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.Ed
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The user or group ID for the entry's
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.Em user
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is invalid.
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.Sh SEE ALSO
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.Xr comsat 8 ,
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.Xr fingerd 8 ,
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.Xr ftpd 8 ,
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.Xr rexecd 8 ,
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.Xr rlogind 8 ,
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.Xr rshd 8 ,
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.Xr telnetd 8 ,
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.Xr tftpd 8
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.Sh HISTORY
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The
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.Nm
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command appeared in
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.Bx 4.3 .
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TCPMUX is based on code and documentation by Mark Lottor.
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