INETD(8)						      System Manager'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 program 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: standard and TCPMUX.  A standard service has a well-known port assigned to it; it may
       be a service that implements an official Internet standard or is a BSD-specific service.  As described in RFC  1078,  TCPMUX  services  are
       nonstandard  services  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.

       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 consists 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 organi-
       zation'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 message, 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  ser-
       vices  operate  in  this  manner.  Stream-based servers that use ``wait'' are started with the listening service socket, and must accept at
       least one connection request before exiting.  Such a server would normally 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 internally, 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'',  ``dis-
       card'',	``chargen'' (character generator), ``daytime'' (human readable time), and ``time'' (machine readable time, in the form of the num-
       ber of seconds since midnight, January 1, 1900).  All of these services are tcp based.  For details of these services, consult  the  appro-
       priate 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 connects 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 posi-
       tive (+) or negative (-) acknowledgment, immediately followed by an optional message 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 connection 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.

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 terminated.
       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 service too frequently, 3) a malicious user is running a program
       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 message 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.

4.4 Berkeley Distribution					 November 7, 1996							  INETD(8)