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     inetd - internet “super-server”


     inetd [-d] [-R rate] [--environment] [--resolve]
           [configuration_files ...]


     The information in this man page may be inaccurate or incomplete.  The
     authoritative documentation for the inetd utility is contained in document.  To access it from your command line, type

     info inetd

     The online copy of the documentation is available at the following


     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, --debug
             Turns on debugging.

             Pass local and remote address data via environment variables. See
             ENVIRONMENT below.

     -R, --rate rate
             Specifies the maximum number of times a service can be invoked in
             one minute; the default is 40.

             Resolve local and remote IP addresses and pass them to the server
             program via TCPLOCALHOST and TCPREMOTEHOST environment variables.
             See ENVIRONMENT below. This option implies --environment.

             Shows the version.

     --help  Shows the help.

     Upon execution, inetd reads its configuration information from a
     configuration file on the command line, by default, /etc/inetd.conf and
     /etc/inetd.d.  If the configuration pathname is a directory, all the
     files in the directory are read like a configuration file. All of the
     configuration files are read and merged.  There must be an entry for each
     field in 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.  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
     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 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 message, or sequenced packet socket.  TCPMUX services
     must use “stream”.

     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[.max] 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 both
     examples of the latter type of datagram server.  Tftpd(8) is an example
     of a multi-threaded datagram server.  The optional “max” suffix
     (separated from “wait” or “nowait” by a dot) specifies the maximum number
     of times a service can be invoked in one minute; the default is 40.  If a
     service exceeds this limit, inetd will log the problem and stop servicing
     requests for the specific service for ten minutes.  See also the -R
     option above.

     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 connection request
     before exiting.  Such a server would normally accept and process incoming
     connection requests until a timeout.  TCPMUX services must use “nowait”.

     The optional “max” suffix (separated from “wait” or “nowait” by a dot) is
     a decimal number that specifies the maximum number of server instances
     that may be spawned from inetd within an interval of 60 seconds.  It
     overrides the settings of the -R command line option.

     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
     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 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


     If a connection is made with a streaming protocol (TCP) and if
     --environment option has been given, inetd will set the following
     environment variables before starting the program:

     PROTO: always "TCP".

     TCPLOCALIP: the local IP address of the interface which accepted the

     TCPLOCALPORT: the port number on which the TCP connection was

     TCPREMOTEIP: the IP address of the remote client.

     TCPREMOTEPORT: the port number on the client side of the TCP connection.

     In addition, if given the --remote option, inetd will set the following
     environment variables:




     Here are several example service entries for the various types of

     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
     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

     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 environment variables (see ENVIRONMENT) are set only for TCP IPv4
     nowait connections.


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