inetd(8) - NetBSD Manual Pages

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


NAME

     inetd, inetd.conf - internet ``super-server''


SYNOPSIS

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


DESCRIPTION

     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 available for inetd:

     -d      Turns on debugging.

     -l      Turns on libwrap connection logging.

     Upon execution, inetd reads its configuration information from a configu-
     ration file which, by default, is /etc/inetd.conf.  There must be an en-
     try 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 (except for
     one special case, described below).  The fields of the configuration file
     are as follows:

           [addr:]service-name
           socket-type
           protocol[,sndbuf=size][,rcvbuf=size]
           wait/nowait[.max]
           user[.group]
           server-program
           server program arguments

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

           service-name/version
           socket-type
           rpc/protocol[,sndbuf=size][,rcvbuf=size]
           wait/nowait[.max]
           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
     indiciates what local address inetd should use when listening for that
     service, or the single character ``*'' to indicate INADDR_ANY, meaning
     `all local addresses'.  To avoid repeating an address that occurs fre-
     quently, 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 further 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.

     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 single
     numeric argument or a range of versions.  A range is bounded by the low
     version to the high version - ``rusers/1-3''.

     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 ``tcp'' or ``udp''.  Rpc based services are specified with
     the ``rpc/tcp'' or ``rpc/udp'' service type.

     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-
     lows:

           tcp,rcvbuf=16384
           tcp,sndbuf=64k
           tcp,rcvbuf=64k,sndbuf=1m

     A literal value may be specified, or modified using `k' to indicate kilo-
     bytes or `m' to indicate megabytes.  Socket buffer sizes may be specified
     for all services and protocols except for tcpmux services.

     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 sock-
     et.  If a datagram server connects to its peer, freeing the socket so in-
     etd 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 in-
     etd 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 40.

     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 eventual-
     ly 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.  identd(8) is usually the only stream
     server marked as wait.

     The user entry should contain the user name of the user as whom the serv-
     er 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 associ-
     ated 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 in-
     etd 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.

     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).  For details of these services, consult the ap-
     propriate 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.


BUGS

     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.)


SEE ALSO

     comsat(8), fingerd(8), ftpd(8), rexecd(8), rlogind(8), rshd(8),
     telnetd(8), tftpd(8), hosts_access(5), hosts_options(5)


HISTORY

     The inetd command appeared in 4.3BSD.  Support for Sun-RPC based services
     is modeled after that provided by SunOS 4.1.  Support for specifying the
     socket buffer sizes was added in NetBSD 1.4.


SECURITY CONSIDERATIONS

     Enabling the ``echo'', ``discard'', and ``chargen'' built-in trivial ser-
     vices is not recommended because remote users may abuse these to cause a
     denial of network service to or from the local host.

NetBSD 1.4                      March 16, 1991                               3