inetd

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

NAME
     inetd, inetd.conf — 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
     getaddrinfo().  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.

   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.)

BSD                             November 14, 2015                            BSD