DHCLIENT-SCRIPT(8)

NAME
dhclient-script - DHCP client network configuration script

DESCRIPTION
The DHCP client network configuration script is invoked from time to time by dhclient(8).

In general, customizations specific to a particular computer should be done in the /etc/dhclient.conf file.

OPERATION
When dhclient(8) needs to invoke the client configuration script, it sets up a number of environment variables and runs dhclient-script. In all cases, $reason is set to the name of the reason why the script has been invoked. The following reasons are currently defined: BOUND, RENEW, REBIND, REBOOT, EXPIRE, FAIL and TIMEOUT.

BOUND
    The DHCP client has done an initial binding to a new address. The new IP address is passed in $new_ip_address, and the interface name is passed in $interface. Any options acquired from the server are passed using the option name described in dhcp-options(5), except that dashes (‘-’) are replaced by underscores (‘_’) in order to make valid shell variables, and the variable names start with new_. So for example, the new subnet mask would be passed in $new_subnet_mask.

    When a binding has been completed, a lot of network parameters are likely to need to be set up. A new /etc/resolv.conf needs to be created, using the values of $new_domain_name and $new_domain_name_servers (which may list more than one server, separated by spaces). A default route should be set using $new_routers, and static routes may need to be set up using $new_static_routes.

    Note: since dhclient-script effectively overwrites /etc/resolv.conf, any information contained therein is lost. If options must be passed to the resolver, they may be contained in /etc/resolv.conf.tail, which is appended to the generated /etc/resolv.conf by dhclient-script. See resolv.conf.tail(5) for further information.

RENEW
    When a binding has been renewed, the script is called as in BOUND, except that in addition to all the variables starting with $new_, there is another set of variables starting with $old_. Persistent settings that may have changed need to be deleted - for example, if a local route to the bound address is being configured, the old local route should be deleted. If the default route has changed, the old default route should be deleted. If the static routes have changed, the old ones should be deleted. Otherwise, processing can be done as with BOUND.

REBIND
    The DHCP client has rebound to a new DHCP server. This can be handled as with RENEW, except that if the IP address has changed, the ARP table should be cleared.

REBOOT
    The DHCP client has successfully reacquired its old address after a reboot. This can be processed as with BOUND.

EXPIRE
    The DHCP client has failed to renew its lease or acquire a new one, and the lease has expired. The IP address must be relinquished, and all related parameters should be deleted, as in RENEW and REBIND.

FAIL
    The DHCP client has been unable to contact any DHCP servers, and any leases that have been tested have not proved to be valid. The parameters from the last lease tested should be deconfigured. This can be handled in the same way as EXPIRE.

TIMEOUT
    The DHCP client has been unable to contact any DHCP servers. However, an old lease has been identified, and its parameters have been passed in as with BOUND. The client configuration script should test these parameters and, if it has reason to believe they are valid, should exit with a value of zero. If not, it should exit with a nonzero value.

The usual way to test a lease is to set up the network as with REBIND (since this may be called to test more than one lease) and then ping the first router defined in $routers. If a response is received, the lease must be valid for the network to which the interface is currently connected. It would be more complete to try to ping all of the routers listed in $new_routers, as well as those listed in $new_static_routes, but current scripts do not do this.

SEE ALSO
dhclient.conf(5), dhclient.leases(5), resolv.conf.tail(5), dhclient(8), dhcpd(8), dhcrelay(8)

AUTHORS
-nosplit The original version of dhclient-script was written for the Internet Software Consortium by Ted Lemon <mellon@fugue.com> in cooperation with Vixie Enterprises.

The OpenBSD implementation of dhclient-script was written by Kenneth R. Westerback <krw@openbsd.org>.

BUGS
If more than one interface is being used, there's no obvious way to avoid clashes between server-supplied configuration parameters - for example, the stock dhclient-script rewrites /etc/resolv.conf. If more than one interface is being configured, /etc/resolv.conf will be repeatedly initialized to the values provided by one server, and then the other. Assuming the information provided by both servers is valid, this shouldn't cause any real problems, but it could be confusing.