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


[править] NAME

    inetd -- internet ``super-server

[править] SYNOPSIS

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


    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
    -W      Turn on TCP Wrapping for internal services which are built in to
    -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
            the hostname corresponds to that of the jail(8) environment.
            When the hostname specification is used and both IPv4 and IPv6
            bindings are desired, one entry with the appropriate protocol
            type for each binding is required for each service in
            /etc/inetd.conf.  For example, a TCP-based service would need two
            entries, one using ``tcp4 for the protocol and the other using
            ``tcp6.  See the explanation of the /etc/inetd.conf protocol
            field below.
    -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:
    To specify an ONC RPC-based service, the entry would contain these
    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
    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 listed 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 TCPMUX ser-
    vices, 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-
    vices must use ``stream.
    The protocol must be a valid protocol or ``unix.  Examples are ``tcp
    or ``udp, both of which imply IPv4 for backward compatibility.  The
    names ``tcp4 and ``udp4 specify IPv4 only.  The names ``tcp6 and
    ``udp6 specify IPv6 only.  The names ``tcp46 and ``udp46 specify
    that the entry accepts both IPv4 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) and talkd(8) utilities are
    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
    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.  The optional group part separated by ``: allows a group
    name other than the default group for this user to be specified.  The
    optional login-class part separated by ``/ allows specification of a
    login class other than the default ``daemon login class.
    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
    The server-program-arguments entry lists the arguments to be passed to
    the server-program, starting with argv[0], which usually is the name of
    the program.  If the service is provided internally, the service-name of
    the service (and any arguments 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
    -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
    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
    appropriate RFC document.
    The TCPMUX-demultiplexing service is also implemented as an internal ser-
    vice.  For any TCPMUX-based service to function, the following line must
    be included in inetd.conf:
          tcpmux  stream  tcp     nowait  root    internal
    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,
    or configured otherwise with the -p option, inetd records its process ID
    in the file /var/run/ to assist in reconfiguration.


  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.
    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 the TCPMUX ser-
    vices which are enabled in inetd.conf.
    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).
    Each policy specifier is applied to all the following lines in inetd.conf
    until the next policy specifier.  An empty policy specifier resets the
    IPsec policy.
    If an invalid IPsec policy specifier appears in inetd.conf, inetd will
    provide an error message via the syslog(3) interface and abort execution.
  UNIX Domain Sockets
    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:
    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 a UNIX domain socket, inetd must change the own-
    ership 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; use /var/run or a similar directory instead.
    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.  For example, specifying a
    socket named /var/run/chargen would invoke the ``chargen service when a
    connection is received on that socket.

[править] FILES

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

[править] EXAMPLES

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


    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.
          2.   A broken client program is requesting the service too fre-
          3.   A malicious user is running a program to invoke the service in
               a denial-of-service attack.
          4.   The invoked service program has an error that causes clients
               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.
    unknown rpc/udp or rpc/tcp
    No entry was found for either udp or tcp in the netconfig(5) database.
    unknown rpc/udp6 or rpc/tcp6
    No entry was found for either udp6 or tcp6 in the netconfig(5) database.

[править] SEE ALSO

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

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

[править] 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 9.0 January 12, 2008 FreeBSD 9.0

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