NAME

     inetd — internet “super-server”

SYNOPSIS

     inetd [-d] [-E] [-i] [-l] [-q length] [-R rate] [configuration_file]

DESCRIPTION

     inetd 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 finished, 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.

     -E      Prevents inetd from laundering the environment.  Without this option a selection of
             potentially harmful environment variables, including PATH, will be removed and not
             inherited by services.

     -i      Makes the program not daemonize itself.

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

     -q length
             Specify the length of the listen(2) connections queue; the default is 128.

     -R rate
             Specify the maximum number of times a service can be invoked in one minute; the
             default is 256.  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
             wait/nowait configuration fields below.

     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.  The fields of the configuration file are as follows:

           service name
           socket type
           protocol[,sndbuf=size][,rcvbuf=size]
           wait/nowait[.max]
           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
           rpc/protocol[,sndbuf=size][,rcvbuf=size]
           wait/nowait[.max]
           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
     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 configuration 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 or a port
     number.  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”.  For UNIX-domain sockets 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 or “unix”.  Examples might
     be “tcp” or “udp”.  RPC based services are specified 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-domain.

     In addition to the protocol, the configuration file may specify the send and receive socket
     buffer sizes for the listening socket.  This is especially 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 performance may be
     realized in some situations.  The socket buffer sizes are specified by appending their
     values to the protocol specification as follows:

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

     A literal value may be specified, or modified using ‘k’ to indicate kilobytes 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.  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 256.  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.

     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 eventually 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 “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 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.

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

   libwrap
     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 separate lines in inetd.conf, for
     “tcp4” and “tcp6”.

     Under various combinations of IPv4/v6 daemon settings, inetd will behave as follows:
     •   If you have only one server on “tcp4”, IPv4 traffic will be routed to the server.  IPv6
         traffic will not be accepted.
     •   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”.
     •   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.

SEE ALSO

     fingerd(8), ftpd(8), identd(8), talkd(8)

HISTORY

     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.

BUGS

     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.

     Server programs used with “dgram” “udp” “nowait” must read from the network socket, or inetd
     will spawn processes until the maximum is reached.

     Host address specifiers, while they make conceptual sense for RPC services, 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.)