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

     inetd -- internet ``super-server''

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

     inetd 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.  After the program is fin-
     ished, it 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 are as follows:

     -d      Turns on debugging.

     -l      Turns on libwrap connection logging. Internal services cannot be
             wrapped.  When enabled, /usr/sbin/tcpd is silently not executed
             even if present in /etc/inetd.conf.

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

     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.  The fields of the configuration file are as

           service name
           socket type
           user[.group] or user[:group]
           server program
           server program arguments

     To specify a Sun-RPC based service, the entry would contain these fields.

           service name/version
           socket type
           user[.group] or user[:group]
           server program
           server program arguments

     For internet services, the first field of the line may also have a host
     address specifier prefixed to it, separated from the service name by a
     colon.  If this is done, the string before the colon in the first field
     indicates what local address inetd should use when listening for that
     service.  Multiple local addresses can be specified on the same line,
     separated by commas.  Numeric IP addresses in dotted-quad notation can be
     used as well as symbolic hostnames.  Symbolic hostnames are looked up
     using gethostbyname().  If a hostname has multiple address mappings,
     inetd creates a socket to listen on each address.

     The single character ``*'' indicates INADDR_ANY, meaning ``all local
     addresses''.  To avoid repeating an address that occurs frequently, a
     line with a host address specifier and colon, but no further fields,
     causes the host address specifier to be remembered and used for all fur-
     ther lines with no explicit host specifier (until another such line or
     the end of the file).  A line
     is implicitly provided at the top of the file; thus, traditional configu-
     ration files (which have no host address specifiers) will be interpreted
     in the traditional manner, with all services listened for on all local
     addresses.  If the protocol is ``unix'', this value is ignored.

     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 a Sun-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 sin-
     gle numeric argument or a range of versions.  A range is bounded by the
     low version to the high version - ``rusers/1-3''.  For UNIX domain sock-
     ets this field specifies the path name of the socket.

     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.

     The protocol must be a valid protocol as given in /etc/protocols.  Exam-
     ples might be ``unix'', ``tcp'' or ``udp''.  RPC based services are spec-
     ified with the ``rpc/tcp'' or ``rpc/udp'' service type.  ``tcp'' and
     ``udp'' will be recognized as ``TCP or UDP over default IP version''.
     This is currently IPv4, but in the future it will be IPv6.  If you need
     to specify IPv4 or IPv6 explicitly, use something like ``tcp4'' or
     ``udp6''.  A protocol of ``unix'' is used to specify a socket in the UNIX

     In addition to the protocol, the configuration file may specify the send
     and receive socket buffer sizes for the listening socket.  This is espe-
     cially useful for TCP as the window scale factor, which is based on the
     receive socket buffer size, is advertised when the connection handshake
     occurs, thus the socket buffer size for the server must be set on the
     listen socket.  By increasing the socket buffer sizes, better TCP perfor-
     mance may be realized in some situations.  The socket buffer sizes are
     specified by appending their values to the protocol specification as fol-


     A literal value may be specified, or modified using 'k' to indicate kilo-
     bytes or 'm' to indicate megabytes.

     The wait/nowait entry is used to tell inetd if it should wait for the
     server program to return, or continue processing connections on the
     socket.  If a datagram server connects to its peer, freeing the socket so
     inetd can receive further messages on the socket, it is said to be a
     ``multi-threaded'' server, and should use the ``nowait'' entry.  For
     datagram servers which process all incoming datagrams on a socket and
     eventually time out, the server is said to be ``single-threaded'' and
     should use a ``wait'' entry.  comsat(8) (biff(1)) and talkd(8) are both
     examples of the latter type of datagram server.  tftpd(8) is an excep-
     tion; it is a datagram server that establishes pseudo-connections.  It
     must be listed as ``wait'' in order to avoid a race; the server reads the
     first packet, creates a new socket, and then forks and exits to allow
     inetd to check for new service requests to spawn new servers.  The
     optional ``max'' suffix (separated from ``wait'' or ``nowait'' by a dot)
     specifies the maximum number of server instances that may be spawned from
     inetd within an interval of 60 seconds.  When omitted, ``max'' defaults
     to 256.

     Stream servers are usually marked as ``nowait'' but if a single server
     process is to handle multiple connections, it may be marked as ``wait''.
     The master socket will then be passed as fd 0 to the server, which will
     then need to accept the incoming connection.  The server should eventu-
     ally time out and exit when no more connections are active.  inetd will
     continue to listen on the master socket for connections, so the server
     should not close it when it exits.

     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.  An optional group name can be specified by appending a dot to
     the user name followed by the group name.  This allows for servers to run
     with a different (primary) group ID than specified in the password file.
     If a group is specified and user is not root, the supplementary groups
     associated with that user will still be set.

     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

     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.

     inetd 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 mid-
     night, January 1, 1900).  All of these services are TCP based.  For
     details of these services, consult the appropriate RFC from the Network
     Information Center.

     inetd rereads its configuration file when it receives a hangup signal,
     SIGHUP.  Services may be added, deleted or modified when the configura-
     tion file is reread.  inetd creates a file /var/run/inetd.pid that con-
     tains its process identifier.

     Support for TCP wrappers is included with inetd to provide built-in tcpd-
     like access control functionality.  An external tcpd program is not
     needed.  You do not need to change the /etc/inetd.conf server-program
     entry to enable this capability.  inetd uses /etc/hosts.allow and
     /etc/hosts.deny for access control facility configurations, as described
     in hosts_access(5).

   IPv6 TCP/UDP behavior
     If you wish to run a server for IPv4 and IPv6 traffic, you'll need to run
     two separate processes for the same server program, specified as two sep-
     arate lines in inetd.conf, for ``tcp4'' and ``tcp6''.

     Under various combinations of IPv4/v6 daemon settings, inetd will behave
     as follows:
     o   If you have only one server on ``tcp4'', IPv4 traffic will be routed
         to the server.  IPv6 traffic will not be accepted.
     o   If you have two servers on ``tcp4'' and ``tcp6'', IPv4 traffic will
         be routed to the server on ``tcp4'', and IPv6 traffic will go to
         server on ``tcp6''.
     o   If you have only one server on ``tcp6'', only IPv6 traffic will be
         routed to the server.

         The special ``tcp46'' parameter can be used for obsolete servers
         which require to receive IPv4 connections mapped in an IPv6 socket.
         Its usage is discouraged.

     fingerd(8), ftpd(8), identd(8), rshd(8), talkd(8), telnetd(8), tftpd(8)

     The inetd command appeared in 4.3BSD.  Support for Sun-RPC based services
     is modelled after that provided by SunOS 4.1.  IPv6 support was added by
     the KAME project in 1999.

     Marco d'Itri ported this code from OpenBSD in summer 2002 and added
     socket buffers tuning and libwrap support from the NetBSD source tree.

     On Linux systems, the daemon cannot reload its configuration and needs to
     be restarted when the host address for a service is changed between ``*''
     and a specific address.

     Host address specifiers, while they make conceptual sense for RPC ser-
     vices, do not work entirely correctly.  This is largely because the
     portmapper interface does not provide a way to register different ports
     for the same service on different local addresses.  Provided you never
     have more than one entry for a given RPC service, everything should work
     correctly.  (Note that default host address specifiers do apply to RPC
     lines with no explicit specifier.)

     ``rpc'' on IPv6 is not tested enough.  Kerberos support on IPv6 is not

BSD                             March 16, 1991                             BSD