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     inetd - internet “super-server”


     inetd [-d] [-E] [-i] [-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
     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 environent variables,
             including PATH, will be removed and not inherited by services.

     -d      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.

     -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

           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 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


     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.  tftpd(8) is an exception; 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 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

     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/
     that contains 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
     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
     ·   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), 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.

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

     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.)