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NAME    [Toc]    [Back]

       joinc - Daemon for DHCP client configuration

SYNOPSIS    [Toc]    [Back]

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

OPTIONS    [Toc]    [Back]

       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 explicitly given, the value  one  is
       assumed (warnings are turned on).

DESCRIPTION    [Toc]    [Back]

       The joinc daemon implements the client half of the Dynamic
       Host Configuration 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 powers 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 necessary 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  dhcpconf  program,  or
       enters  a passive state while awaiting a new command. When
       joinc receives a command to  configure  an  interface  the
       DHCP  protocol starts. If successful the interface is configured.
 The  configuration  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  control  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 information 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 administrators to control client configuration
  by  customizing startup scripts to permit various
       aspects of the client and its software to be customized in
       a specific order.  On clients with a single interface this
       is straightforward; clients with multiple  interfaces  may
       present  difficulties 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 configured,  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 interfaces 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 categories: 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 disposition 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.

RESTRICTIONS    [Toc]    [Back]

       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 failover.

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

DIAGNOSTICS    [Toc]    [Back]

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

FILES    [Toc]    [Back]

       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
       configuration  for  interface.  The existence of this file
       does not imply that the configuration  is  correct,  since
       the lease may have expired.

SEE ALSO    [Toc]    [Back]

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

       Files: client.pcy(4)

       RFC 1541

[ Back ]
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