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.)