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

NAME
     inetd - internet ``super-server''

SYNOPSIS
     inetd [-d] [-l] [-c maximum] [-C rate] [-a address] [-p filename]
           [-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 following options are available:

     -d      Turn on debugging.

     -l      Turn on logging.

     -c maximum
             Specify the default maximum number of services that can be
             invoked.  May be overridden on a per-service basis with the "max-
             child" parameter.

     -C rate
             Specify the default maximum number of times a service can be
             invoked from a single IP address in one minute; the default is
             unlimited.  May be overridden on a per-service basis with the
             "max-connections-per-ip-per-minute" parameter.

     -R rate
             Specify the maximum number of times a service can be invoked in
             one minute; the default is 256.

     -a      Specify a specific IP address to bind to.

     -p      Specify an alternate file in which to store the process ID.

     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}[/max-child[/max-connections-per-ip-per-minute]]
           user[:group][/login-class]
           server program
           server program arguments

     To specify an ONC RPC-based service, the entry would contain these
     fields:

           service name/version
           socket type
           rpc/protocol
           user[:group][/login-class]
           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.  TCPMUX requests are only accepted
     when the multiplexor service itself is enabled, above and beyond and
     specific TCPMUX-based servers; see the discussion of internal services
     below.

     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).  When used to specify an ONC RPC-based service, this
     field is a valid RPC service name in the file /etc/rpc.  The part on the
     right of the ``/'' is the RPC version number. This can simply be a single
     numeric argument or a range of versions.  A range is bounded by the low
     version to the high version - ``rusers/1-3''.  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''.  If it is desired that the service
     is reachable via T/TCP, one should specify ``tcp/ttcp''.  Rpc based
     services are specified with the ``rpc/tcp'' or ``rpc/udp'' service type.
     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
     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
     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 maximum number of outstanding child processes (or ``threads'') for a
     ``nowait'' service may be explicitly specified by appending a ``/''
     followed by the number to the ``nowait'' keyword. Normally (or if a value
     of zero is specified) there is no maximum. Otherwise, once the maximum is
     reached, further connection attempts will be queued up until an existing
     child process exits. This also works in the case of ``wait'' mode,
     although a value other than one (the default) might not make sense in
     some cases.  You can also specify the maximum number of connections per
     minute for a given IP address by appending a ``/'' followed by the number
     to the maximum number of outstanding child processes. Once the maximum is
     reached, further connections from this IP address will be dropped until
     the end of the minute.

     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.  Optional group part separated by ``:'' allows to specify
     group name different than default group for this user.  Optional
     login-class part separated by ``/'' allows to specify login class
     different than default ``daemon'' login class.

     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 available in
     both TCP and UDP versions; the UDP versions will refuse service if the
     request specifies a reply port corresponding to any internal service.
     (This is done as a defense against looping attacks; the remote IP address
     is logged.)  For details of these services, consult the appropriate RFC
     document.

     The TCPMUX-demultiplexing service is also implemented as an internal
     service.  For any TCPMUX-based service to function, the following line
     must be included in inetd.conf:

           tcpmux  stream  tcp     nowait  root    internal

     When given the -l option inetd will log an entry to syslog each time an
     accept(2) is made, which notes the service selected and the IP-number of
     the remote requestor.

     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.  Except when started in debugging mode,
     inetd records its process ID in the file /var/run/inetd.pid to assist in
     reconfiguration.

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
     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.

FILES
     /etc/inetd.conf     configuration file.
     /etc/rpc            translation of service names to RPC program numbers.
     /etc/services       translation of service names to port numbers.
     /var/run/inetd.pid  the pid of the currently running inetd.

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/bin/phonebook phonebook
     rstatd/1-3   dgram   rpc/udp wait root  /usr/libexec/rpc.rstatd  rpc.rstatd

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 many 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.

           4.   The invoked service program has an error that causes clients
                to retry quickly.

     Use the -R rate 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(5) database. 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 uid
     service: can't set gid gid
     The user or group ID for the entry's user field is invalid.

     setsockopt(SO_PRIVSTATE): Operation not supported
     The inetd program attempted to renounce the privileged state associated
     with a socket but was unable to.

SEE ALSO
     login.conf(5), passwd(5), rpc(5), services(5), comsat(8), fingerd(8),
     ftpd(8), portmap(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.  Support for ONC RPC based services is
     modeled after that provided by SunOS 4.1.

BSD 4.4                        February 7, 1996                        BSD 4.4

NAME | SYNOPSIS | DESCRIPTION | TCPMUX | FILES | EXAMPLES | ERROR MESSAGES | SEE ALSO | HISTORY

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