joinc man page on DigitalUNIX

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joinc(8)							      joinc(8)

       joinc - Daemon for DHCP client configuration

       /usr/sbin/joinc [-f] [-dn] [-ln]

       Sets  debug  level  to  n. If debug is turned on, log messages are also
       enabled.	 Runs in the  foreground  instead  of  as  a  daemon  process.
       Enables	warning	 (n > 0) and log (n > 1) messages. If n is not explic‐
       itly given, the value one is assumed (warnings are turned on).

       The joinc daemon implements the client half of the Dynamic Host Config‐
       uration Protocol (DHCP) with hardware extensions.

       (JOIN is a trademark of Competitive Automation.)

       The DHCP protocol, among other things, permits a client to establish an
       endpoint for communication with a network by delivering an  IP  address
       for  each  of  the  client's  network interfaces, and a “lease” on that
       address. The lease specifies the interval for which the address remains
       valid:  it may be infinite or of fixed duration. If it appears that the
       client wishes to continue using the IP address  after  its  expiration,
       the DHCP protocol must negotiate an extension. For this reason the DHCP
       client code must run as a daemon, only terminating when the client pow‐
       ers down.

       Communication  with  the joinc daemon is effected through the agency of
       an auxiliary program called dhcpconf.  The joinc daemon may be  invoked
       as  a  user process (requiring root privileges), but this is not neces‐
       sary as the dhcpconf program will start it implicitly.

       When started, joinc reads its startup  file,  /etc/join/client.pcy  and
       either  proceeds to act on the instruction(s) passed to it by the dhcp‐
       conf program, or enters a passive state while awaiting a	 new  command.
       When joinc receives a command to configure an interface the DHCP proto‐
       col starts. If successful the interface is configured.  The  configura‐
       tion  received is stored in the interface.dhc file located (by default)
       under the /etc/join directory.  The client daemon sleeps until it needs
       to  renew the lease, which happens well before the lease expires.  Upon
       wakeup, if the interface is found to be down  or	 has  a	 different  IP
       address, joinc considers that the interface is no longer under its con‐
       trol and drops it from future consideration, until an explicit  request
       arrives from dhcpconf. If the lease cannot be renewed, joinc takes down
       the interface when it expires as required by the	 DHCP  protocol.   See
       RFC 1541 for details.

       The  DHCP protocol also acts as a mechanism to configure other informa‐
       tion needed by the client such as name domain and router addresses. The
       joinc daemon does not configure this information but acts as a database
       which may be interrogated by other programs, particularly by  dhcpconf.
       This  approach  is more flexible in that it allows third party software
       access to the data through a published API, and allows system  adminis‐
       trators	to control client configuration by customizing startup scripts
       to permit various aspects of the client and its software to be  custom‐
       ized  in	 a specific order.  On clients with a single interface this is
       straightforward; clients with multiple interfaces may present difficul‐
       ties because some information arriving on different interfaces may need
       to be merged, or may be inconsistent. Furthermore, the configuration of
       the  interfaces	is asynchronous; requests may arrive while some or all
       of the interfaces are still unconfigured.  The  joinc  daemon  resolves
       these  problems	as  follows.  When  a  request	for a global parameter
       arrives, joinc searches all interfaces that were	 successfully  config‐
       ured, and returns to the requester the name of the first one it find to
       contain the pertinent data. The client program may then access the data
       by  an API which reads the appropriate interface.dhc file. If no inter‐
       faces are successfully configured when the request is received,	or  if
       the  none  of  those  which  are	 configured have the data, the request
       fails. The dhcpconf program allows this behavior to  be	overridden  by
       insisting  that	the global data sought be associated with a particular
       interface. See dhcpconf(8) for details.

       The joinc daemon writes informational and error messages in four	 cate‐
       gories:	Errors	are  severe,  usually  unrecoverable,  events  due  to
       resource exhaustion and other unexpected failure of  system  calls.  An
       error  is  also	generated if the client's lease on an IP address is in
       danger of expiring.  Warnings  are  less	 severe,  and  in  most	 cases
       describe	 unusual  or  incorrect	 datagrams  received  from clients, or
       requests for service that cannot be provided.   Informational  messages
       provide	a readable transcription of (correct) actions performed by the
       server on behalf of client hosts.  Debug messages may be	 generated  at
       various	levels	of  verbosity  from zero (not at all) through nine, as
       controlled by the -d option.

       Warning, informational, and debug messages are  discarded.  Errors  are
       written	to /dev/console and are sent to the system logger syslog(3) at
       priority LOG_ERR and with a facility identifier LOG_DAEMON. If warnings
       are enabled they also are written to the system console and syslog with
       the same facility, but at priority LOG_WARNING. The creation and dispo‐
       sition  of  messages  is	 controlled by the -f, -d, and -l command line
       options, and the JOINLOG environment variable.	When present,  JOINLOG
       names  a	 file  to  which messages are sent in preference to the system
       console. Note that until the root file system is mounted read-write  no
       ordinary file can be used for this purpose.

       A  cluster  member  should never be a DHCP client. It should always use
       static addressing.

       If a cluster is to support a DHCP server, there can be  only  one  DHCP
       server  for  all	 the  cluster  members	using  a  common database with

       The joinc daemon can configure clients with two or more interfaces giv‐
       ing  each  an IP address. However, each interface so configured must be
       on a different physical network and subnet.

       Upon receipt of SIGUSR1 signals, the joinc daemon dumps the contents of
       its  scheduling	table  and the status of each interface under its con‐

       By default, the joinc daemon expects to read its policy file  and  read
       and  write  its configuration databases in the /etc/join directory. The
       JOINCONFIG environment variable may  be	used  to  select  a  different
       directory.   Contains parameters that govern the behavior of joinc, and
       general policies concerning network administration.  Contains the  con‐
       figuration  for	interface.   The existence of this file does not imply
       that the configuration is correct, since the lease may have expired.

       Commands: dhcpconf(8), dhcpparm(8), joind(8), showdhc(8), shleases(8)

       Files: client.pcy(4)

       RFC 1541


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