inetd man page on 4.4BSD

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INETD(8)		  BSD System Manager's Manual		      INETD(8)

     inetd — internet “super-server”

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

     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 connec‐
     tion 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 configu‐
     ration 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
	   server program
	   server program arguments

     There are two types of services that inetd can start: standard and TCP‐
     MUX.  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-spe‐
     cific 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 organization's name and suf‐
     fixing 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”.

     The protocol must be a valid protocol as given in /etc/protocols.	Exam‐
     ples 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 listen‐
     ing for new service requests.  Datagram servers must use “wait”, as they
     are always invoked with the original datagram socket bound to the speci‐
     fied 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 both 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 lis‐
     tening 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

     The inetd program provides several “trivial” services internally by use
     of routines within itself.	 These services are “echo”, “discard”,
     “chargen” (character generator), “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.

     RFC 1078 describes the TCPMUX protocol: ``A TCP client connects to a for‐
     eign host on TCP port 1.  It sends the service name followed by a car‐
     riage-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 message
     of explanation, terminated with a <CRLF>.	If the reply was positive, the
     selected protocol begins; otherwise the connection is closed.''  The pro‐
     gram is passed the TCP connection as file descriptors 0 and 1.

     If the TCPMUX service name begins with a ``+'', inetd returns the posi‐
     tive 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

     Here are several example service entries for the various types of ser‐

     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/bin/phonebook phonebook

     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 sev‐
     eral 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 pro‐
     gram 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.

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

     The inetd command appeared in 4.3BSD.  TCPMUX is based on code and docu‐
     mentation by Mark Lottor.

4.4BSD				 June 1, 1994				4.4BSD

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