Provided by: inetutils-inetd_1.9.4-1build1_amd64 bug


     inetd — internet “super-server”


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


     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.

     -p, --pidfile [filename]
             Specifies the pidfile to use instead of the default.

     -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.

     -V, --version
             Shows the version.

     -?, --help
             Shows the help.

             Shows the usage message.

     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

           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

     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 entry.

     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 inetd.conf.


     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 connection.

     TCPLOCALPORT: the port number on which the TCP connection was established.

     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




     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/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 re-enabled 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 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