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inetd(8)

NAME

     inetd -- internet ``super-server''

SYNOPSIS

     inetd [-d] [-l] [-w] [-W] [-c maximum] [-C rate] [-a address | hostname]
	   [-p filename] [-R rate] [-s maximum] [configuration file]

DESCRIPTION

     The inetd utility should be run at boot time by /etc/rc (see rc(8)).  It
     then listens for connections on certain internet sockets.	When a connec-
     tion is found on one of its sockets, it decides what service the socket
     corresponds to, and invokes a program to service the request.  The server
     program is invoked with the service socket as its standard input, output
     and error descriptors.  After the program is finished, inetd 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 following options are available:

     -d      Turn on debugging.

     -l      Turn on logging of successful connections.

     -w      Turn on TCP Wrapping for external services.  See the
	     IMPLEMENTATION NOTES section for more information on TCP Wrappers
	     support.

     -W      Turn on TCP Wrapping for internal services which are built in to
	     inetd.

     -c maximum
	     Specify the default maximum number of simultaneous invocations of
	     each service; the default is unlimited.  May be overridden on a
	     per-service basis with the "max-child" parameter.

     -C rate
	     Specify the default maximum number of times a service can be
	     invoked from a single IP address in one minute; the default is
	     unlimited.  May be overridden on a per-service basis with the
	     "max-connections-per-ip-per-minute" parameter.

     -R rate
	     Specify the maximum number of times a service can be invoked in
	     one minute; the default is 256.  A rate of 0 allows an unlimited
	     number of invocations.

     -s maximum
	     Specify the default maximum number of simultaneous invocations of
	     each service from a single IP address; the default is unlimited.
	     May be overridden on a per-service basis with the "max-child-per-
	     ip" parameter.

     -a      Specify one specific IP address to bind to.  Alternatively, a
	     hostname can be specified, in which case the IPv4 or IPv6 address
	     which corresponds to that hostname is used.  Usually a hostname
	     is specified when inetd is run inside a jail(8), in which case

     -p      Specify an alternate file in which to store the process ID.

     Upon execution, inetd reads its configuration information from a configu-
     ration 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.  There must be an entry for each field.  The
     fields of the configuration file are as follows:

	   service name
	   socket type
	   protocol
	   {wait|nowait}[/max-child[/max-connections-per-ip-per-minute[/max-child-per-ip]]]
	   user[:group][/login-class]
	   server program
	   server program arguments

     To specify an ONC RPC-based service, the entry would contain these
     fields:

	   service name/version
	   socket type
	   rpc/protocol
	   user[:group][/login-class]
	   server program
	   server program arguments

     There are two types of services that inetd can start: standard and TCP-
     MUX.  A standard service has a well-known port assigned to it; it may be
     a service that implements an official Internet standard or is a
     BSD-specific service.  As described in RFC 1078, TCPMUX services are non-
     standard services that do not have a well-known port assigned to them.
     They are invoked from inetd when a program connects to the ``tcpmux''
     well-known port and specifies the service name.  This feature is useful
     for adding locally-developed servers.  TCPMUX requests are only accepted
     when the multiplexor service itself is enabled, above and beyond and spe-
     cific TCPMUX-based servers; see the discussion of internal services
     below.

     The service-name entry is the name of a valid service in the file
     /etc/services, or the specification of a UNIX domain socket (see below).
     For ``internal'' services (discussed below), the service name should be
     the official name of the service (that is, the first entry in
     /etc/services).  When used to specify an ONC 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 sin-
     gle numeric argument or a range of versions.  A range is bounded by the
     low version to the high version - ``rusers/1-3''.	For TCPMUX services,
     the value of the service-name field consists of the string ``tcpmux''
     followed by a slash and the locally-chosen service name.  The service
     names listed in /etc/services and the name ``help'' are reserved.	Try to
     choose unique names for your TCPMUX services by prefixing them with your
     organization's name and suffixing them with a version number.

     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.  TCPMUX ser-
     T/TCP, one should specify ``tcp/ttcp'', which implies IPv4 for backward
     compatibility.  The name ``tcp4/ttcp'' specifies IPv4 only, while
     ``tcp6/ttcp'' specifies IPv6 only.  The name ``tcp46/ttcp'' specify that
     the entry accepts both IPv6 and IPv6 connections via a wildcard AF_INET6
     socket.  Rpc based services are specified with the ``rpc/tcp'' or
     ``rpc/udp'' service type.	One can use specify IPv4 and/or IPv6 with the
     4, 6 or 46 suffix, for example ``rpc/tcp6'' or ``rpc/udp46''.  TCPMUX
     services must use ``tcp'', ``tcp4'', ``tcp6'' or ``tcp46''.

     The wait/nowait entry specifies whether the server that is invoked by
     inetd will take over the socket associated with the service access point,
     and thus whether inetd should wait for the server to exit before listen-
     ing for new service requests.  Datagram servers must use ``wait'', as
     they are always invoked with the original datagram socket bound to the
     specified service address.  These servers must read at least one datagram
     from the socket before exiting.  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; it should read one
     datagram from the socket and create a new socket connected to the peer.
     It should fork, and the parent should then exit to allow inetd to check
     for new service requests to spawn new servers.  Datagram servers which
     process all incoming datagrams on a socket and eventually time out are
     said to be ``single-threaded''.  The comsat(8), (biff(1)) and talkd(8)
     utilities are both examples of the latter type of datagram server.  The
     tftpd(8) utility is an example of a multi-threaded datagram server.

     Servers using stream sockets generally are multi-threaded and use the
     ``nowait'' entry.	Connection requests for these services are accepted by
     inetd, and the server is given only the newly-accepted socket connected
     to a client of the service.  Most stream-based services operate in this
     manner.  Stream-based servers that use ``wait'' are started with the lis-
     tening service socket, and must accept at least one connection request
     before exiting.  Such a server would normally accept and process incoming
     connection requests until a timeout.  TCPMUX services must use
     ``nowait''.

     The maximum number of outstanding child processes (or ``threads'') for a
     ``nowait'' service may be explicitly specified by appending a ``/'' fol-
     lowed by the number to the ``nowait'' keyword.  Normally (or if a value
     of zero is specified) there is no maximum.  Otherwise, once the maximum
     is reached, further connection attempts will be queued up until an exist-
     ing child process exits.  This also works in the case of ``wait'' mode,
     although a value other than one (the default) might not make sense in
     some cases.  You can also specify the maximum number of connections per
     minute for a given IP address by appending a ``/'' followed by the number
     to the maximum number of outstanding child processes.  Once the maximum
     is reached, further connections from this IP address will be dropped
     until the end of the minute.  In addition, you can specify the maximum
     number of simultaneous invocations of each service from a single IP
     address by appending a ``/'' followed by the number to the maximum number
     of outstanding child processes.  Once the maximum is reached, further
     connections from this IP address will be dropped.

     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.  Optional group part separated by ``:'' allows to specify
     group name different than default group for this user.  Optional
     login-class part separated by ``/'' allows to specify login class differ-
     starting with argv[0], which is the name of the program.  If the service
     is provided internally, the service-name of the service (and any argu-
     ments to it) or the word ``internal'' should take the place of this
     entry.

     Currently, the only internal service to take arguments is ``auth''.
     Without options, the service will always return ``ERROR : HIDDEN-USER''.
     The available arguments to this service that alter its behavior are:

     -d fallback
	     Provide a fallback username.  If the real ``auth'' service is
	     enabled (with the -r option discussed below), return this user-
	     name instead of an error when lookups fail for either socket cre-
	     dentials or the username.	If the real ``auth'' service is dis-
	     abled, return this username for every request.  This is primarily
	     useful when running this service on a NAT machine.

     -g      Instead of returning the user's name to the ident requester,
	     report a username made up of random alphanumeric characters, e.g.
	     ``c0c993''.  The -g flag overrides not only the user names, but
	     also any fallback name, .fakeid or .noident files.

     -t sec[.usec]
	     Specify a timeout for the service.  The default timeout is 10.0
	     seconds.

     -r      Offer a real ``auth'' service, as per RFC 1413.  All the remain-
	     ing flags apply only in this case.

     -i      Return numeric user IDs instead of usernames.

     -f      If the file .fakeid exists in the home directory of the identi-
	     fied user, report the username found in that file instead of the
	     real username.  If the username found in .fakeid is that of an
	     existing user, then the real username is reported.  If the -i
	     flag is also given then the username in .fakeid is checked
	     against existing user IDs instead.

     -F      same as -f but without the restriction that the username in
	     .fakeid must not match an existing user.

     -n      If the file .noident exists in the home directory of the identi-
	     fied user, return ``ERROR : HIDDEN-USER''.  This overrides any
	     fakeid file which might exist.

     -o osname
	     Use osname instead of the name of the system as reported by
	     uname(3).

     The inetd utility also provides several other ``trivial'' services inter-
     nally by use of routines within itself.  These services are ``echo'',
     ``discard'', ``chargen'' (character generator), ``daytime'' (human read-
     able time), and ``time'' (machine readable time, in the form of the num-
     ber of seconds since midnight, January 1, 1900).  All of these services
     are available in both TCP and UDP versions; the UDP versions will refuse
     service if the request specifies a reply port corresponding to any inter-
     nal service.  (This is done as a defense against looping attacks; the
     remote IP address is logged.)  For details of these services, consult the
     When given the -l option inetd will log an entry to syslog each time a
     connection is accepted, noting the service selected and the IP-number of
     the remote requester if available.  Unless otherwise specified in the
     configuration file, and in the absence of the -W and -w options, inetd
     will log to the ``daemon'' facility.

     The inetd utility rereads its configuration file when it receives a
     hangup signal, SIGHUP.  Services may be added, deleted or modified when
     the configuration file is reread.	Except when started in debugging mode,
     inetd records its process ID in the file /var/run/inetd.pid to assist in
     reconfiguration.

IMPLEMENTATION NOTES

   TCP Wrappers
     When given the -w option, inetd will wrap all services specified as
     ``stream nowait'' or ``dgram'' except for ``internal'' services.  If the
     -W option is given, such ``internal'' services will be wrapped.  If both
     options are given, wrapping for both internal and external services will
     be enabled.  Either wrapping option will cause failed connections to be
     logged to the ``auth'' syslog facility.  Adding the -l flag to the wrap-
     ping options will include successful connections in the logging to the
     ``auth'' facility.

     Note that inetd only wraps requests for a ``wait'' service while no
     servers are available to service requests.  Once a connection to such a
     service has been allowed, inetd has no control over subsequent connec-
     tions to the service until no more servers are left listening for connec-
     tion requests.

     When wrapping is enabled, the tcpd daemon is not required, as that func-
     tionality is builtin.  For more information on TCP Wrappers, see the rel-
     evant documentation (hosts_access(5)).  When reading that document, keep
     in mind that ``internal'' services have no associated daemon name.
     Therefore, the service name as specified in inetd.conf should be used as
     the daemon name for ``internal'' services.

   TCPMUX
     RFC 1078 describes the TCPMUX protocol: ``A TCP client connects to a for-
     eign host on TCP port 1.  It sends the service name followed by a car-
     riage-return line-feed <CRLF>.  The service name is never case sensitive.
     The server replies with a single character indicating positive (+) or
     negative (-) acknowledgment, immediately followed by an optional message
     of explanation, terminated with a <CRLF>.	If the reply was positive, the
     selected protocol begins; otherwise the connection is closed.''  The pro-
     gram is passed the TCP connection as file descriptors 0 and 1.

     If the TCPMUX service name begins with a ``+'', inetd returns the posi-
     tive reply for the program.  This allows you to invoke programs that use
     stdin/stdout without putting any special server code in them.

     The special service name ``help'' causes inetd to list TCPMUX services in
     inetd.conf.

   IPsec
     The implementation includes a tiny hack to support IPsec policy settings
     for each socket.  A special form of comment line, starting with ``#@'',
     is interpreted as a policy specifier.  Everything after the ``#@'' will
     be used as an IPsec policy string, as described in ipsec_set_policy(3).
     In addition to running services on IP sockets, inetd can also manage UNIX
     domain sockets.  To do this you specify a protocol of ``unix'' and spec-
     ify the UNIX domain socket as the service-name.  The service-type may be
     ``stream'' or ``dgram''.  The specification of the socket must be an
     absolute path name, optionally prefixed by an owner and mode of the form
     :user:group:mode:.  The specification:

	   :news:daemon:220:/var/run/sock

     creates a socket owned by user ``news'' in group ``daemon'' with permis-
     sions allowing only that user and group to connect.  The default owner is
     the user that inetd is running as.  The default mode only allows the
     socket's owner to connect.

     WARNING: while creating UNIX domain socket, inetd must change the owner-
     ship and permissions on the socket.  This can only be done securely if
     the directory in which the socket is created is writable only by root.
     Do NOT use inetd to create sockets in world writable directories, such as
     /tmp, instead use /var/run or a similar directory.

     Internal services may be run on UNIX domain sockets, in the usual way.
     In this case the name of the internal service is determined using the
     last component of the socket's pathname.

FILES

     /etc/inetd.conf	 configuration file
     /etc/rpc		 translation of service names to RPC program numbers
     /etc/services	 translation of service names to port numbers
     /var/run/inetd.pid  the pid of the currently running inetd

EXAMPLES

     Here are several example service entries for the various types of ser-
     vices:

     ftp	  stream  tcp	nowait root  /usr/libexec/ftpd	      ftpd -l
     ntalk	  dgram   udp	wait   root  /usr/libexec/ntalkd      ntalkd
     telnet	  stream  tcp6	nowait root  /usr/libexec/telnetd  telnetd
     shell	  stream  tcp46  nowait root  /usr/libexec/rshd rshd
     tcpmux/+date stream  tcp	nowait guest /bin/date		      date
     tcpmux/phonebook stream tcp nowait guest /usr/local/bin/phonebook phonebook
     rstatd/1-3   dgram   rpc/udp wait root  /usr/libexec/rpc.rstatd  rpc.rstatd
     /var/run/echo stream unix	nowait root  internal
     #@ ipsec ah/require
     chargen	  stream  tcp	nowait root  internal
     #@

ERROR MESSAGES

     The inetd server logs error messages using syslog(3).  Important error
     messages and their explanations are:

     service/protocol server failing (looping), service terminated.
     The number of requests for the specified service in the past minute
     exceeded the limit.  The limit exists to prevent a broken program or a
     malicious user from swamping the system.  This message may occur for sev-
     eral reasons:

	   1.	There are many hosts requesting the service within a short
		time period.
		to retry quickly.

     Use the -R rate option, as described above, to change the rate limit.
     Once the limit is reached, the service will be reenabled automatically in
     10 minutes.

     service/protocol: No such user user, service ignored
     service/protocol: getpwnam: user: No such user
     No entry for user exists in the passwd(5) database.  The first message
     occurs when inetd (re)reads the configuration file.  The second message
     occurs when the service is invoked.

     service: can't set uid uid
     service: can't set gid gid
     The user or group ID for the entry's user field is invalid.

     setsockopt(SO_PRIVSTATE): Operation not supported
     The inetd utility attempted to renounce the privileged state associated
     with a socket but was unable to.

SEE ALSO

     ipsec_set_policy(3), hosts_access(5), hosts_options(5), login.conf(5),
     passwd(5), rpc(5), services(5), comsat(8), fingerd(8), ftpd(8),
     rexecd(8), rlogind(8), rpcbind(8), rshd(8), telnetd(8), tftpd(8)

     Michael C. St. Johns, Identification Protocol, RFC1413.

HISTORY

     The inetd utility appeared in 4.3BSD.  TCPMUX is based on code and docu-
     mentation by Mark Lottor.	Support for ONC RPC based services is modeled
     after that provided by SunOS 4.1.	The IPsec hack was contributed by the
     KAME project in 1999.  The FreeBSD TCP Wrappers support first appeared in
     FreeBSD 3.2.

FreeBSD 5.4		       February 7, 1996 		   FreeBSD 5.4

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