joinc(8) System Manager's Manual joinc(8)
NAME
joinc - Daemon for DHCP client configuration
SYNOPSIS
/usr/sbin/joinc [-f] [-dn] [-ln]
OPTIONS
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
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 dhcp-
conf program, or enters a passive state while awaiting a new command. When joinc receives a command to configure an interface the DHCP pro-
tocol 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 sys-
tem 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 behav-
ior 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 con-
trolled 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
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
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
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
Commands: dhcpconf(8), dhcpparm(8), joind(8), showdhc(8), shleases(8)
Files: client.pcy(4)
RFC 1541
joinc(8)