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 explicitly given, the value one is
assumed (warnings are turned on).
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.
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.
Upon receipt of SIGUSR1 signals, the joinc daemon dumps
the contents of its scheduling table and the status of
each interface under its control.
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.
Commands: dhcpconf(8), dhcpparm(8), joind(8), showdhc(8),
shleases(8)
Files: client.pcy(4)
RFC 1541
joinc(8)
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