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.


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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


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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.


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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.


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