Udhcpc: Difference between revisions

Revision as of 14:12, 28 October 2018

You may want to customize the behavior of the default DHCP client (udhcpc from busybox), which is called by /sbin/ifup by having "dhcp" in /etc/network/interfaces.

The default behavior is driven by the script /usr/share/udhcpc/default.script

Its default configuration may be overwritten by /etc/udhcpc/udhcpc.conf

Authorized key:value pairs are:

key	default value	possible values
NO_GATEWAY	-	<list of iface names>
IF_METRIC	-	<metric value>
IF_PEER_DNS	yes	<anything but yes>
RESOLV_CONF	/etc/resolv.conf	no ; NO ; -
NO_DNS	-	<list of iface names>

Example /etc/udhcpc/udhcpc.conf:

RESOLV_CONF="no" # Prevents overwriting of /etc/resolv.conf

Custom scripts can be added as /etc/udhcpc/pre-* and /etc/udhcpc/post-* to be run before/after deconfig/renew/bound DHCP events.

As an example, /etc/udhcpc/post-bound/mtu could contain, to change the interface MTU from the default (1500) to 1492, which is useful if on ADSL (which uses 8 bytes):

r=$(/sbin/ip route | grep ^default | head -n 1)
# Needs iproute2 package, rather than busybox's "ip", to change mtu
/sbin/ip route replace $r mtu 1492

@@ Line 1: / Line 1: @@
-You may want to customize behavior of default dhcp client (udhcpc from busybox).
+You may want to customize the behavior of the default DHCP client (udhcpc from busybox), which is called by /sbin/ifup by having "dhcp" in /etc/network/interfaces.
-The default behavior is drived by the script /usr/share/udhcpc/default.script
+The default behavior is driven by the script /usr/share/udhcpc/default.script
-It's default configuration may be overwritten by a /etc/udhcpc/udhcpc.conf file.
+Its default configuration may be overwritten by /etc/udhcpc/udhcpc.conf
-Authorized key:value pair are available:
+Authorized key:value pairs are:
 {| cellpadding="15" border="1" class="wikitable"
@@ Line 34: / Line 34: @@
 |}
-You may also add custom scripts /etc/udhcpc/pre-* and /etc/udhcpc/post-* to be run before and after deconfig|renew|bound dhcp events.
+Example /etc/udhcpc/udhcpc.conf:
+ RESOLV_CONF="no" # Prevents overwriting of /etc/resolv.conf
+Custom scripts can be added as /etc/udhcpc/pre-* and /etc/udhcpc/post-* to be run before/after deconfig/renew/bound DHCP events.
+As an example, /etc/udhcpc/post-bound/mtu could contain, to change the interface MTU from the default (1500) to 1492, which is useful if [https://en.wikipedia.org/wiki/Maximum_transmission_unit on ADSL] (which uses 8 bytes):
+ r=$(/sbin/ip route | grep ^default | head -n 1)
+ # Needs iproute2 package, rather than busybox's "ip", to change mtu
+ /sbin/ip route replace $r mtu 1492
 [[Category:Networking]]
 [[Category:Embedded Systems]]