0661be0b5d
Submitted by: Archie Cobbs (Archie@whistle.com) Changes to allow inted to control the number of servers to start on each service. This is a defence against a denial of service attack in which the system is made unusable by an external party. It also allows the behaviour of small memory systems to be more accuratly predicted, by bounding the extent to which processes can multiply.
496 lines
14 KiB
Groff
496 lines
14 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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.\" from: @(#)inetd.8 8.3 (Berkeley) 4/13/94
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.\" $Id: inetd.8,v 1.9 1996/08/09 22:20:23 julian Exp $
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.\"
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.Dd February 7, 1996
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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 l
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.Op Fl R Ar rate
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.Op Fl a Ar address
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.Op Fl p Ar filename
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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 -compact -width Rratexxx
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.It Fl d
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Turns on debugging.
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.It Fl l
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Turns on logging.
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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 256.
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.It Fl a
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Specify a specific IP address to bind to.
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.It Fl p
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Specify an alternate file in which to store the process ID.
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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}[/max-child]
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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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To specify an
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.No Tn "ONC RPC" Ns -based
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service, the entry would contain these fields:
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.Pp
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.Bd -unfilled -offset indent -compact
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service name/version
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socket type
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rpc/protocol
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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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When used to specify an
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.No Tn "ONC RPC" Ns -based
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service, this field is a valid RPC service name in
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the file
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.Pa /etc/rpc .
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The part on the right of the
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.Dq /
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is the RPC version number. This
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can simply be a single numeric argument or a range of versions.
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A range is bounded by the low version to the high version -
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.Dq rusers/1-3 .
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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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Rpc based services are specified with the
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.Dq rpc/tcp
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or
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.Dq rpc/udp
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service type.
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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 maximum number of outstanding child processes (or ``threads'')
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for a ``nowait'' service may be explicitly specified by appending a
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``/'' followed by the number to the ``nowait'' keyword. Normally
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(or if a value of zero is specified) there is no maximum. Otherwise,
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once the maximum is reached, further connection attempts will be
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queued up until an existing child process exits. This also works
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in the case of ``wait'' mode, although a value other than one (the
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default) might not make sense in some cases.
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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, in the form of the number of seconds since
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midnight, January 1, 1900). All of these services are available in
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both TCP and UDP versions; the UDP versions will refuse service if the
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request specifies a reply port corresponding to any internal service.
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(This is done as a defense against looping attacks; the remote IP address
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is logged.)
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For details of these services, consult the
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appropriate
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.Tn RFC
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document.
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.Pp
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When given the
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.Fl l
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option
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.Nm Inetd
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will log an entry to syslog each time an
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.Xr accept 2
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is made, which notes the
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service selected and the IP-number of the remote requestor.
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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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Except when started in debugging mode,
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.Nm
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records its process ID in the file
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.Pa /var/run/inetd.pid
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to assist in reconfiguration.
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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 "FILES"
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.Bl -tag -width /var/run/inetd.pid -compact
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.It Pa /etc/inetd.conf
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configuration file.
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.It Pa /etc/rpc
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translation of service names to RPC program numbers.
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.It Pa /etc/services
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translation of service names to port numbers.
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.It Pa /var/run/inetd.pid
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the pid of the currently running
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.Nm inetd .
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.El
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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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rstatd/1-3 dgram rpc/udp wait root /usr/libexec/rpc.rstatd rpc.rstatd
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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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.Pp
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.Bl -ohang -compact
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.It Xo
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.Ar service Ns / Ns Ar protocol
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.No " server failing (looping), service terminated."
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.Xc
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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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.Bl -enum -offset indent
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.It
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There are many hosts requesting the service within a short time period.
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.It
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A broken client program is requesting the service too frequently.
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.It
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A malicious user is running a program to invoke the service in
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a denial-of-service attack.
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.It
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The invoked service program has an error that causes clients
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to retry quickly.
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.El
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.Pp
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Use the
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.Fl R Ar rate
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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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.Pp
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.It Xo
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.Ar service Ns / Ns Ar protocol :
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.No \&No such user
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.Ar user ,
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.No service ignored
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.Xc
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.It Xo
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.Ar service Ns / Ns Ar protocol :
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.No getpwnam :
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.Ar user :
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.No \&No such user
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.Xc
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No entry for
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.Ar user
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exists in the
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.Xr passwd 5
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database. 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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.Pp
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.It Xo
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.Ar service :
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.No can't set uid
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.Ar uid
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.Xc
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.It Xo
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.Ar service :
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.No can't set gid
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.Ar gid
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.Xc
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The user or group ID for the entry's
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.Ar user
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field is invalid.
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.Pp
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.It "setsockopt(SO_PRIVSTATE): Operation not supported"
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The
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.Nm
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program attempted to renounce the privileged state associated with a
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socket but was unable to.
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.El
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.Sh SEE ALSO
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.Xr passwd 5 ,
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.Xr rpc 5 ,
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.Xr services 5 ,
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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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.Xr portmap 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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Support for
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.Tn "ONC RPC"
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based services is modeled after that
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provided by
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.Tn SunOS
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4.1.
|