200 lines
9.5 KiB
Groff
200 lines
9.5 KiB
Groff
.\" dhclient-script.8
|
|
.\"
|
|
.\" Copyright (c) 1996-1999 Internet Software Consortium.
|
|
.\" Use is subject to license terms which appear in the file named
|
|
.\" ISC-LICENSE that should have accompanied this file when you
|
|
.\" received it. If a file named ISC-LICENSE did not accompany this
|
|
.\" file, or you are not sure the one you have is correct, you may
|
|
.\" obtain an applicable copy of the license at:
|
|
.\"
|
|
.\" http://www.isc.org/isc-license-1.0.html.
|
|
.\"
|
|
.\" This file is part of the ISC DHCP distribution. The documentation
|
|
.\" associated with this file is listed in the file DOCUMENTATION,
|
|
.\" included in the top-level directory of this release.
|
|
.\"
|
|
.\" Support and other services are available for ISC products - see
|
|
.\" http://www.isc.org for more information.
|
|
.TH dhclient-script 8
|
|
.SH NAME
|
|
dhclient-script - DHCP client network configuration script
|
|
.SH DESCRIPTION
|
|
The DHCP client network configuration script is invoked from time to
|
|
time by \fBdhclient(8)\fR. This script is used by the dhcp client to
|
|
set each interface's initial configuration prior to requesting an
|
|
address, to test the address once it has been offered, and to set the
|
|
interface's final configuration once a lease has been acquired. If no
|
|
lease is acquired, the script is used to test predefined leases, if
|
|
any, and also called once if no valid lease can be identified.
|
|
.PP
|
|
This script is not meant to be customized by the end user. If local
|
|
customizations are needed, they should be possible using the enter and
|
|
exit hooks provided (see HOOKS for details). These hooks will allow the
|
|
user to override the default behaviour of the client in creating a
|
|
.B /etc/resolv.conf
|
|
file.
|
|
.PP
|
|
No standard client script exists for some operating systems, even though
|
|
the actual client may work, so a pioneering user may well need to create
|
|
a new script or modify an existing one. In general, customizations specific
|
|
to a particular computer should be done in the
|
|
.B /etc/dhclient.conf
|
|
file. If you find that you can't make such a customization without
|
|
customizing
|
|
.B /etc/dhclient.conf
|
|
or using the enter and exit hooks, please submit a bug report.
|
|
.SH HOOKS
|
|
When it starts, the client script first defines a shell function,
|
|
.B make_resolv_conf ,
|
|
which is later used to create the
|
|
.B /etc/resolv.conf
|
|
file. To override the default behaviour, redefine this function in
|
|
the enter hook script.
|
|
.PP
|
|
On after defining the make_resolv_conf function, the client script checks
|
|
for the presence of an executable
|
|
.B /etc/dhclient-enter-hooks
|
|
script, and if present, it invokes the script inline, using the Bourne
|
|
shell '.' command. The entire environment documented under OPERATION
|
|
is available to this script, which may modify the environment if needed
|
|
to change the behaviour of the script. If an error occurs during the
|
|
execution of the script, it can set the exit_status variable to a nonzero
|
|
value, and
|
|
.B /etc/dhclient-script
|
|
will exit with that error code immediately after the client script exits.
|
|
.PP
|
|
After all processing has completed,
|
|
.B /etc/dhclient-script
|
|
checks for the presence of an executable
|
|
.B /etc/dhclient-exit-hooks
|
|
script, which if present is invoked using the '.' command. The exit status
|
|
is passed in the exit_status shell variable, and will always be zero if the
|
|
script succeeded at the task for which it was invoked.
|
|
.SH OPERATION
|
|
When dhclient needs to invoke the client configuration script, it
|
|
writes a shell script into /tmp which defines a variety of variables.
|
|
In all cases, $reason is set to the name of the reason why the script
|
|
has been invoked. The following reasons are currently defined:
|
|
MEDIUM, PREINIT, BOUND, RENEW, REBIND, REBOOT, EXPIRE, FAIL and TIMEOUT.
|
|
.PP
|
|
.SH MEDIUM
|
|
The DHCP client is requesting that an interface's media type
|
|
be set. The interface name is passed in $interface, and the media
|
|
type is passed in $medium.
|
|
.SH PREINIT
|
|
The DHCP client is requesting that an interface be configured as
|
|
required in order to send packets prior to receiving an actual
|
|
address. For clients which use the BSD socket library, this means
|
|
configuring the interface with an IP address of 0.0.0.0 and a
|
|
broadcast address of 255.255.255.255. For other clients, it may be
|
|
possible to simply configure the interface up without actually giving
|
|
it an IP address at all. The interface name is passed in $interface,
|
|
and the media type in $medium.
|
|
.PP
|
|
If an IP alias has been declared in dhclient.conf, its address will be
|
|
passed in $alias_ip_address, and that ip alias should be deleted from
|
|
the interface, along with any routes to it.
|
|
.SH 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. The media type is passed in $medium. Any
|
|
options acquired from the server are passed using the option name
|
|
described in \fBdhcp-options\fR, 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.
|
|
.PP
|
|
Before actually configuring the address, dhclient-script should
|
|
somehow ARP for it and exit with a nonzero status if it receives a
|
|
reply. In this case, the client will send a DHCPDECLINE message to
|
|
the server and acquire a different address. This may also be done in
|
|
the RENEW, REBIND, or REBOOT states, but is not required, and indeed
|
|
may not be desirable.
|
|
.PP
|
|
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,
|
|
seperated by spaces). A default route should be set using
|
|
$new_routers, and static routes may need to be set up using
|
|
$new_static_routes.
|
|
.PP
|
|
If an IP alias has been declared, it must be set up here. The alias
|
|
IP address will be written as $alias_ip_address, and other DHCP
|
|
options that are set for the alias (e.g., subnet mask) will be passed
|
|
in variables named as described previously except starting with
|
|
$alias_ instead of $new_. Care should be taken that the alias IP
|
|
address not be used if it is identical to the bound IP address
|
|
($new_ip_address), since the other alias parameters may be incorrect
|
|
in this case.
|
|
.SH 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.
|
|
.SH 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.
|
|
.SH REBOOT
|
|
The DHCP client has successfully reacquired its old address after a
|
|
reboot. This can be processed as with BOUND.
|
|
.SH 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.
|
|
.SH 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.
|
|
.SH 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.
|
|
.PP
|
|
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.
|
|
.SH FILES
|
|
Each operating system should generally have its own script file,
|
|
although the script files for similar operating systems may be similar
|
|
or even identical. The script files included in the Internet
|
|
Software Consortium DHCP distribution appear in the distribution tree
|
|
under client/scripts, and bear the names of the operating systems on
|
|
which they are intended to work.
|
|
.SH 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.
|
|
.SH SEE ALSO
|
|
dhclient(8), dhcpd(8), dhcrelay(8), dhclient.conf(5) and
|
|
dhclient.leases(5).
|
|
.SH AUTHOR
|
|
.B dhclient-script(8)
|
|
has been written for the Internet Software Consortium
|
|
by Ted Lemon <mellon@fugue.com> in cooperation with Vixie
|
|
Enterprises. To learn more about the Internet Software Consortium,
|
|
see
|
|
.B http://www.vix.com/isc.
|
|
To learn more about Vixie
|
|
Enterprises, see
|
|
.B http://www.vix.com.
|