# 2.11BSD#431 - /usr/man/cat8/inetd.0

    INETD(8)	    UNIX Programmer's Manual		 INETD(8)

    NAME
         inetd - internet ``super-server''

    SYNOPSIS
         inetd [-d] [-R rate] [configuration file]

    DESCRIPTION
         The inetd program should be run at boot time by /etc/rc (see
         rc(8)).  It then listens for connections on certain internet
         sockets.  When a connection is found on one of its sockets,
         it decides what service the socket corresponds to, and
         invokes a program to service the request.	The server pro-
         gram is invoked with the service socket as its standard
         input, output and error descriptors.  After the program is
         finished, inetd continues to listen on the socket (except in
         some cases which will be described below).  Essentially,
         inetd allows running one daemon to invoke several others,
         reducing load on the system.

         The options available for inetd:

         -d        Turns on debugging.

         -R rate   Specifies the maximum number of times a service
    	       can be invoked in one minute; the default is 1000.

         Upon execution, inetd reads its configuration information
         from a configuration file which, by default, is
         /etc/inetd.conf.  There must be an entry for each field of
         the configuration file, with entries for each field
         separated by a tab or a space.  Comments are denoted by a
         ``#'' at the beginning of a line.	There must be an entry
         for each field.  The fields of the configuration file are as
         follows:

    	  service name
    	  socket type
    	  protocol
    	  wait/nowait
    	  user
    	  server program
    	  server program arguments

         There are two types of services that inetd can start: stan-
         dard and TCPMUX.  A standard service has a well-known port
         assigned to it; it may be a service that implements an offi-
         cial Internet standard or is a BSD-specific service.  As
         described in RFC 1078, TCPMUX services are nonstandard ser-
         vices that do not have a well-known port assigned to them.
         They are invoked from inetd when a program connects to the
         ``tcpmux'' well-known port and specifies the service name.
         This feature is useful for adding locally-developed servers.

    Printed 11/26/99	November 7, 1996			1

    INETD(8)	    UNIX Programmer's Manual		 INETD(8)

         The service-name entry is the name of a valid service in the
         file /etc/services.  For ``internal'' services (discussed
         below), the service name must be the official name of the
         service (that is, the first entry in /etc/services).  For
         TCPMUX services, the value of the service-name field con-
         sists of the string ``tcpmux'' followed by a slash and the
         locally-chosen service name. The service names listed in
         /etc/services and the name ``help'' are reserved.	Try to
         choose unique names for your TCPMUX services by prefixing
         them with your organization's name and suffixing them with a
         version number.

         The socket-type should be one of ``stream'', ``dgram'',
         ``raw'', ``rdm'', or ``seqpacket'', depending on whether the
         socket is a stream, datagram, raw, reliably delivered mes-
         sage, or sequenced packet socket.	TCPMUX services must use
         ``stream''.

         NOTE: ``rdm'' and ``seqpacket'' are not supported in
         2.11BSD.

         The protocol must be a valid protocol as given in
         /etc/protocols.  Examples might be ``tcp'' or ``udp''.
         TCPMUX services must use ``tcp''.

         The wait/nowait entry specifies whether the server that is
         invoked by inetd will take over the socket associated with
         the service access point, and thus whether inetd should wait
         for the server to exit before listening for new service
         requests.	Datagram servers must use ``wait'', as they are
         always invoked with the original datagram socket bound to
         the specified service address.  These servers must read at
         least one datagram from the socket before exiting.  If a
         datagram server connects to its peer, freeing the socket so
         inetd can received further messages on the socket, it is
         said to be a ``multi-threaded'' server; it should read one
         datagram from the socket and create a new socket connected
         to the peer.  It should fork, and the parent should then
         exit to allow inetd to check for new service requests to
         spawn new servers.  Datagram servers which process all
         incoming datagrams on a socket and eventually time out are
         said to be ``single-threaded''.  Comsat(8), biff(1) and
         talkd(8) are examples of the latter type of datagram server.
         Tftpd(8) is an example of a multi-threaded datagram server.

         Servers using stream sockets generally are multi-threaded
         and use the ``nowait'' entry.  Connection requests for these
         services are accepted by inetd , and the server is given
         only the newly-accepted socket connected to a client of the
         service.  Most stream-based services operate in this manner.
         Stream-based servers that use ``wait'' are started with the
         listening service socket, and must accept at least one

    Printed 11/26/99	November 7, 1996			2

    INETD(8)	    UNIX Programmer's Manual		 INETD(8)

         connection request before exiting.  Such a server would nor-
         mally accept and process incoming connection requests until
         a timeout.  TCPMUX services must use ``nowait''.

         The user entry should contain the user name of the user as
         whom the server should run.  This allows for servers to be
         given less permission than root.

         The server-program entry should contain the pathname of the
         program which is to be executed by inetd when a request is
         found on its socket.  If inetd provides this service inter-
         nally, this entry should be ``internal''.

         The server program arguments should be just as arguments
         normally are, starting with argv[0], which is the name of
         the program.  If the service is provided internally, the
         word ``internal'' should take the place of this entry.

         The inetd program provides several ``trivial'' services
         internally by use of routines within itself.  These services
         are ``echo'', ``discard'', ``chargen'' (character genera-
         tor), ``daytime'' (human readable time), and ``time''
         (machine readable time, in the form of the number of seconds
         since midnight, January 1, 1900).	All of these services are
         tcp based.  For details of these services, consult the
         appropriate RFC from the Network Information Center.

         The inetd program rereads its configuration file when it
         receives a hangup signal, SIGHUP.	Services may be added,
         deleted or modified when the configuration file is reread.

    TCPMUX
         RFC 1078 describes the TCPMUX protocol: ``A TCP client con-
         nects to a foreign host on TCP port 1.  It sends the service
         name followed by a carriage-return line-feed <CRLF>.  The
         service name is never case sensitive.  The server replies
         with a single character indicating positive (+) or negative
         (-) acknowledgment, immediately followed by an optional mes-
         sage of explanation, terminated with a <CRLF>.  If the reply
         was positive, the selected protocol begins; otherwise the
         connection is closed.'' The program is passed the TCP con-
         nection as file descriptors 0 and 1.

         If the TCPMUX service name begins with a ``+'', inetd
         returns the positive reply for the program.  This allows you
         to invoke programs that use stdin/stdout without putting any
         special server code in them.

         The special service name ``help'' causes inetd to list
         TCPMUX services in inetd.conf.

    Printed 11/26/99	November 7, 1996			3

    INETD(8)	    UNIX Programmer's Manual		 INETD(8)

    EXAMPLES
         Here are several example service entries for the various
         types of services:

         ftp	   stream  tcp	 nowait root  /usr/libexec/ftpd       ftpd -l
         ntalk	   dgram   udp	 wait	root  /usr/libexec/ntalkd     ntalkd
         tcpmux/+date  stream  tcp	 nowait guest /bin/date               date
         tcpmux/phonebook stream tcp nowait guest /usr/local/phonebook phonebook

    ERROR MESSAGES
         The inetd server logs error messages using syslog(3).
         Important error messages and their explanations are:

         service/protocol server failing (looping), service ter-
         minated.
         The number of requests for the specified service in the past
         minute exceeded the limit. The limit exists to prevent a
         broken program or a malicious user from swamping the system.
         This message may occur for several reasons: 1) there are
         lots of hosts requesting the service within a short time
         period, 2) a 'broken' client program is requesting the ser-
         vice too frequently, 3) a malicious user is running a pro-
         gram to invoke the service in a 'denial of service' attack,
         or 4) the invoked service program has an error that causes
         clients to retry quickly.	Use the -R option, as described
         above, to change the rate limit.  Once the limit is reached,
         the service will be reenabled automatically in 10 minutes.

         service/protocol: No such user 'user', service ignored
         service/protocol: getpwnam: user: No such user
         No entry for user exists in the passwd file. The first mes-
         sage occurs when inetd (re)reads the configuration file. The
         second message occurs when the service is invoked.

         service: can't set uid number
         service: can't set gid number
         The user or group ID for the entry's user is invalid.

    SEE ALSO
         comsat(8), fingerd(8), ftpd(8), rexecd(8), rlogind(8),
         rshd(8), telnetd(8), tftpd(8)

    HISTORY
         The inetd command appeared in 4.3BSD.  TCPMUX is based on
         code and documentation by Mark Lottor.

    Printed 11/26/99	November 7, 1996			4

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