Udhcpc - Revision history

John3-16: 1. /* Configuration / - Added observation that 'udhcpc.conf' would not be overwritten, if amended, whenever its source package busybox is subsequently updated, but a new file created: 'udhcpc.conf.apk-new'; 2. / Configuration */ Moved the advanced 'default.script' help after the introductory 'key:value pairs' help; 3. Style and grammar amendments.

2025-11-21T18:29:46Z

1. Configuration: - Added observation that 'udhcpc.conf' would not be overwritten, if amended, whenever its source package busybox is subsequently updated, but a new file created: 'udhcpc.conf.apk-new'; 2. Configuration: Moved the advanced 'default.script' help after the introductory 'key:value pairs' help; 3. Style and grammar amendments.

← Older revision		Revision as of 18:29, 21 November 2025
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	== Configuration ==		== Configuration ==

	The default DHCP client <code>udhcpc</code> from ~~busybox~~ gets invoked by the networking scripts {{path\|/sbin/ifup}} and {{path\|/sbin/ifdown}} when "<code>dhcp</code>" is added to the interface name in the file {{path\|/etc/network/interfaces}}.		The default DHCP client <code>udhcpc</code> from [[BusyBox]] gets invoked by the networking scripts {{path\|/sbin/ifup}} and {{path\|/sbin/ifdown}} when "<code>dhcp</code>" is added to the interface name in the file {{path\|/etc/network/interfaces}}.

	The default behavior of udhcpc is driven by the script {{path\|/usr/share/udhcpc/default.script}}		The default behavior of udhcpc is driven by the script {{path\|/usr/share/udhcpc/default.script}}

	Entries in {{path\|/etc/network/interfaces}} for DHCP interfaces will drive the <code>udhcpc</code> command line. For example {{cat\|/etc/network/interfaces\|auto eth0		Entries in {{path\|/etc/network/interfaces}} for DHCP interfaces will drive the <code>udhcpc</code> command line. For example, {{cat\|/etc/network/interfaces\|auto eth0
	iface eth0 inet dhcp		iface eth0 inet dhcp
	hostname myhostname		hostname myhostname
Line 16:		Line 16:
	The hostname will send the DHCP option to the server to tell the server the name of this client.		The hostname will send the DHCP option to the server to tell the server the name of this client.

	By default, the inbuilt ~~Busybox~~ DHCP client [[udhcpc]] requests a static set of options from the DHCP server. If you need to extend this set, you can do so by setting some additional command line options for the DHCP client, via the <code>udhcpc_opts</code> in your interface configuration. The following example requests <code>domain-search</code> option:		By default, the inbuilt BusyBox DHCP client [[udhcpc]] requests a static set of options from the DHCP server. If you need to extend this set, you can do so by setting some additional command line options for the DHCP client, via the <code>udhcpc_opts</code> in your interface configuration. The following example requests the <code>domain-search</code> option:
	{{cat\|/etc/network/interfaces\|...		{{cat\|/etc/network/interfaces\|...
	auto eth0		auto eth0
Line 23:		Line 23:
	For a complete list of command line options for udhcpc, see [https://busybox.net/downloads/BusyBox.html#udhcpc this document].		For a complete list of command line options for udhcpc, see [https://busybox.net/downloads/BusyBox.html#udhcpc this document].

	The default configuration of <code>udhcpc</code> may be overridden by {{path\|/etc/udhcpc/udhcpc.conf}}. ~~Please see~~ {{path\|~~/usr/share/~~udhcpc~~/default~~.~~script~~}} ~~for how~~ the ~~values are used~~.		The default configuration of <code>udhcpc</code> may be overridden by {{path\|/etc/udhcpc/udhcpc.conf}}. Also, if this file were ever customized, e.g. for any values discussed below, whenever its parent package {{Pkg\|busybox}} is updated, '''apk''' will note that the file had been modified and will [[Alpine_Package_Keeper#Handling_apk-new_files\|opt not to overwrite it]] but rather will place its own newly-supplied {{path\|udhcpc.conf}} file renamed as {{path\|udhcpc.conf.apk-new}} . Be sure to compare both files and to preserve the required changes.

	{{path\|udhcpc.conf}} accepts the following key:value pairs:		{{path\|udhcpc.conf}} accepts the following key:value pairs:
Line 64:		Line 64:
	{{cat\|/etc/udhcpc/udhcpc.conf\|RESOLV_CONF{{=}}"no" # Prevents overwriting of /etc/resolv.conf}}		{{cat\|/etc/udhcpc/udhcpc.conf\|RESOLV_CONF{{=}}"no" # Prevents overwriting of /etc/resolv.conf}}

	Custom scripts can be added as {{path\|/etc/udhcpc/pre-}} and {{path\|/etc/udhcpc/post-}} to be run before/after deconfig/renew/bound DHCP events. The custom scripts must be set as '''executable''' by root, ~~e.g.~~ <code>chmod 744</code>. Refer ~~an example~~ [[#Change MTU for ADSL\|custom script]]		Please see {{path\|/usr/share/udhcpc/default.script}} for details on how the values are used.

			Custom scripts can be added as {{path\|/etc/udhcpc/pre-}} and {{path\|/etc/udhcpc/post-}} to be run before/after deconfig/renew/bound DHCP events. The custom scripts must be set as '''executable''' by root, using <code>chmod 744</code>. Refer below for a sample [[#Change MTU for ADSL\|custom script]].

	As another example for fine tuning, consider uncommenting and amending the {{ic\|#NO_DNS{{=}}"eth1 wlan1"}} line there with the relevant interfaces, described so as to "''Prevent overwriting of resolv.conf on a per-interface basis''".		As another example for fine tuning, consider uncommenting and amending the {{ic\|#NO_DNS{{=}}"eth1 wlan1"}} line there with the relevant interfaces, described so as to "''Prevent overwriting of resolv.conf on a per-interface basis''".

John3-16: 1. Added troubleshooting section 'can't rename '/etc/resolv.conf.*': Operation not permitted'; 2. Added "/tmp/resolv.conf" as a possible default value in the udhcpc.conf key:value pair table; 3. Added possibility of fine tuning /etc/udhcpc/udhcpc.conf with NO_DNS as another example; 4. Amended grammar.

2025-10-28T02:55:43Z

1. Added troubleshooting section 'can't rename '/etc/resolv.conf.*': Operation not permitted'; 2. Added "/tmp/resolv.conf" as a possible default value in the udhcpc.conf key:value pair table; 3. Added possibility of fine tuning /etc/udhcpc/udhcpc.conf with NO_DNS as another example; 4. Amended grammar.

← Older revision		Revision as of 02:55, 28 October 2025
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	\| RESOLV_CONF		\| RESOLV_CONF
	\| {{path\|/etc/resolv.conf}}		\| {{path\|/etc/resolv.conf}}
	\| no ; NO ; -		\| no ; NO ; /tmp/resolv.conf ; -
	\| do not overwrite or alternative path for {{path\|resolv.conf}}		\| do not overwrite or alternative path for {{path\|resolv.conf}}
	\|-		\|-
Line 65:		Line 65:

	Custom scripts can be added as {{path\|/etc/udhcpc/pre-}} and {{path\|/etc/udhcpc/post-}} to be run before/after deconfig/renew/bound DHCP events. The custom scripts must be set as '''executable''' by root, e.g. <code>chmod 744</code>. Refer an example [[#Change MTU for ADSL\|custom script]]		Custom scripts can be added as {{path\|/etc/udhcpc/pre-}} and {{path\|/etc/udhcpc/post-}} to be run before/after deconfig/renew/bound DHCP events. The custom scripts must be set as '''executable''' by root, e.g. <code>chmod 744</code>. Refer an example [[#Change MTU for ADSL\|custom script]]

			As another example for fine tuning, consider uncommenting and amending the {{ic\|#NO_DNS{{=}}"eth1 wlan1"}} line there with the relevant interfaces, described so as to "''Prevent overwriting of resolv.conf on a per-interface basis''".

	== Troubleshooting ==		== Troubleshooting ==

	{{Todo\|The below ~~section need~~ testing and confirmation.}}		{{Todo\|The section below needs testing and confirmation.}}

	=== Change MTU for ADSL ===		=== Change MTU for ADSL ===
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	The reload drops all firewall rules, re-acquires the Internal and external IPs, and re-writes the rules. I'm sure there is a better way.		The reload drops all firewall rules, re-acquires the Internal and external IPs, and re-writes the rules. I'm sure there is a better way.

			=== 'can't rename '/etc/resolv.conf.****': Operation not permitted' ===

			Such notifications at bootup or when (re-)starting the networking service from a shell refer to a '''udhcpc''' script that attempts to overwrite {{Path\|/etc/resolv.conf}} with a transitory {{Path\|resolv.conf.**}} file that it had created, but which fails due to the original file having been made immutable e.g. with {{ic\|doas chattr +i /etc/resolv.conf}}. The four digits in the .** suffix refer to the ''pid'' number of the {{Path\|/usr/share/udhcpc/default.script}}, as in the following case:
			<pre>
			$ doas rc-service networking restart
			* Starting networking ...
			* lo ... [ ok ]
			* eth0 ...
			udhcpc: started, v1.37.0
			udhcpc: broadcasting discover
			udhcpc: broadcasting discover
			udhcpc: broadcasting select for 192.168.1.2, server 192.168.1.1
			udhcpc: lease of 192.168.1.2 obtained from 192.168.1.1, lease time 86400
			mv: can't rename '/etc/resolv.conf.4175': Operation not permitted
			</pre>
			Immutability was likely set manually by an administrator seeking to prevent one or more preferred DNS nameserver(s) from being overwritten in that file.

			To preempt such reports, consider whether the use of immutability for {{Path\|/etc/resolv.conf}} is necessary, while conserving its contents: although the issue in itself is innocuous albeit leading '''udhcpc''' to [https://gitlab.alpinelinux.org/alpine/aports/-/issues/15198 leave behind such transitory files], it may also obstruct legitimate future updates of its stock file design locally. To forego such concerns for standard installations, instead of employing immutability, [[Udhcpc#Configuration\|consider configuring]] the {{Path\|/etc/udhcpc/udhcpc.conf}} file, supplied since Alpine Linux v3.19, by setting {{ic\|RESOLV_CONF{{=}}"no"}} so that udhcpc will not overwrite the file, or by setting which specific interfaces are not to overwrite it e.g. {{ic\|NO_DNS{{=}}"eth1 wlan1"}}. Immutability could then be removed with {{ic\|doas chattr -i /etc/resolv.conf}} .

			Since {{Path\|/etc/resolv.conf.***}} files accumulate unnecessarily is set each time that the udhcpc script is run, such files may be deleted, as in the following instruction. '''Be sure to add the full stop character ('.') before the asterisk ('')''' so as to not delete the required {{Path\|/etc/resolv.conf}} file:

			{{cmd\|doas rm /etc/resolv.conf.*}}

	== See also ==		== See also ==

Prabuanand: moved content from Configure Networking page

2025-07-18T08:08:17Z

moved content from Configure Networking page

← Older revision		Revision as of 08:08, 18 July 2025
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	The default behavior of udhcpc is driven by the script {{path\|/usr/share/udhcpc/default.script}}		The default behavior of udhcpc is driven by the script {{path\|/usr/share/udhcpc/default.script}}

	Entries in {{path\|/etc/network/interfaces}} for DHCP interfaces will drive the <code>udhcpc</code> command line. For example~~:<br>~~		Entries in {{path\|/etc/network/interfaces}} for DHCP interfaces will drive the <code>udhcpc</code> command line. For example {{cat\|/etc/network/interfaces\|auto eth0

	{{cat\|/etc/network/interfaces\|auto eth0
	iface eth0 inet dhcp		iface eth0 inet dhcp
	hostname myhostname		hostname myhostname
	}}		}}

	will set these parameters on the command line:~~<br>~~		will set these parameters on the command line: {{cmd\|udhcpc -i eth0 -x hostname:myhostname}}

	~~{{cmd\|udhcpc -i eth0 -x~~ hostname~~:myhostname}}~~		The hostname will send the DHCP option to the server to tell the server the name of this client.

	~~The hostname will send~~ the DHCP ~~option to~~ the server to ~~tell the server the name of~~ this ~~client.~~		By default, the inbuilt Busybox DHCP client [[udhcpc]] requests a static set of options from the DHCP server. If you need to extend this set, you can do so by setting some additional command line options for the DHCP client, via the <code>udhcpc_opts</code> in your interface configuration. The following example requests <code>domain-search</code> option:
			{{cat\|/etc/network/interfaces\|...
	~~You~~ can ~~add arbitrary~~ command line ~~parameters to~~ the <code>udhcpc_opts</code> ~~setting~~ in {{~~path~~\|/etc/network/interfaces}}. ~~See the example of <code>udhcpc_opts<~~/~~code> in [[Configure Networking~~#~~IPv4 DHCP Configuration\|the main networking article]~~].		auto eth0
			iface eth0 inet dhcp
			udhcpc_opts -O search}}
			For a complete list of command line options for udhcpc, see [https://busybox.net/downloads/BusyBox.html#udhcpc this document].

	The default configuration of <code>udhcpc</code> may be overridden by {{path\|/etc/udhcpc/udhcpc.conf}}. Please see {{path\|/usr/share/udhcpc/default.script}} for how the values are used.		The default configuration of <code>udhcpc</code> may be overridden by {{path\|/etc/udhcpc/udhcpc.conf}}. Please see {{path\|/usr/share/udhcpc/default.script}} for how the values are used.
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	== Troubleshooting ==		== Troubleshooting ==

	{{Todo\|The below section need testing and confirmation~~. Please help contributing~~.}}		{{Todo\|The below section need testing and confirmation.}}

	=== Change MTU for ADSL ===		=== Change MTU for ADSL ===

Prabuanand: updated wikilink, fixed category

2025-07-18T07:51:19Z

updated wikilink, fixed category

← Older revision		Revision as of 07:51, 18 July 2025
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	{{DISPLAYTITLE:udhcpc}}		{{DISPLAYTITLE:udhcpc}}This page documents the working of default DHCP client <code>udhcpc</code> from [[Busybox]].
	~~{{Main\|Configure Networking}}~~
	This page documents the working of default DHCP client <code>udhcpc</code> from Busybox.

	== Configuration ==		== Configuration ==
Line 86:		Line 84:
	The reload drops all firewall rules, re-acquires the Internal and external IPs, and re-writes the rules. I'm sure there is a better way.		The reload drops all firewall rules, re-acquires the Internal and external IPs, and re-writes the rules. I'm sure there is a better way.

	== See ~~Also~~ ==		== See also ==
	[https://udhcp.busybox.net/README.udhcpc Busybox udhcpc Readme]
			* [[Configure Networking\|Main Networking page]]
			* [https://udhcp.busybox.net/README.udhcpc Busybox udhcpc Readme]

	[[Category:Networking]]		[[Category:Networking]]
	~~[[Category:Embedded Systems]]~~

Prabuanand: changed heading and removed empty line

2024-10-17T14:56:47Z

changed heading and removed empty line

← Older revision		Revision as of 14:56, 17 October 2024
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	{{DISPLAYTITLE:udhcpc}}		{{DISPLAYTITLE:udhcpc}}

	{{Main\|Configure Networking}}		{{Main\|Configure Networking}}
	This page documents the working of default DHCP client <code>udhcpc</code> from Busybox.		This page documents the working of default DHCP client <code>udhcpc</code> from Busybox.
Line 66:		Line 65:
	{{cat\|/etc/udhcpc/udhcpc.conf\|RESOLV_CONF{{=}}"no" # Prevents overwriting of /etc/resolv.conf}}		{{cat\|/etc/udhcpc/udhcpc.conf\|RESOLV_CONF{{=}}"no" # Prevents overwriting of /etc/resolv.conf}}

	Custom scripts can be added as {{path\|/etc/udhcpc/pre-}} and {{path\|/etc/udhcpc/post-}} to be run before/after deconfig/renew/bound DHCP events. The custom scripts must be set as '''executable''' by root, e.g. <code>chmod 744</code>. Refer an example [[#Change ~~default~~ MTU for ADSL\|custom script]]		Custom scripts can be added as {{path\|/etc/udhcpc/pre-}} and {{path\|/etc/udhcpc/post-}} to be run before/after deconfig/renew/bound DHCP events. The custom scripts must be set as '''executable''' by root, e.g. <code>chmod 744</code>. Refer an example [[#Change MTU for ADSL\|custom script]]

	== Troubleshooting ==		== Troubleshooting ==
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	{{Todo\|The below section need testing and confirmation. Please help contributing.}}		{{Todo\|The below section need testing and confirmation. Please help contributing.}}

	=== Change ~~default~~ MTU for ADSL ===		=== Change MTU for ADSL ===

	As an example, {{path\|/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 that uses PPPoE] (which uses 8 bytes for its own header):		As an example, {{path\|/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 that uses PPPoE] (which uses 8 bytes for its own header):

Prabuanand: Added reference to Main Networking article, headings and moved the content related to ADSL MTU to troubleshooting section.

2024-10-17T14:27:18Z

Added reference to Main Networking article, headings and moved the content related to ADSL MTU to troubleshooting section.

← Older revision		Revision as of 14:27, 17 October 2024
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	{{DISPLAYTITLE:udhcpc}}		{{DISPLAYTITLE:udhcpc}}
	~~{{Expand\|Please help us expand this article by contributing.}}~~

	~~You may want to customize~~ the ~~behavior~~ of ~~the~~ default DHCP client (<code>udhcpc</code> from ~~busybox), which is called by {{path\|/sbin/ifup}} by having "<code>dhcp</code>" in {{path\|/etc/network/interfaces}}~~.		{{Main\|Configure Networking}}
			This page documents the working of default DHCP client <code>udhcpc</code> from Busybox.

	The default behavior is driven by the script {{path\|/usr/share/udhcpc/default.script}}		== Configuration ==

			The default DHCP client <code>udhcpc</code> from busybox gets invoked by the networking scripts {{path\|/sbin/ifup}} and {{path\|/sbin/ifdown}} when "<code>dhcp</code>" is added to the interface name in the file {{path\|/etc/network/interfaces}}.

			The default behavior of udhcpc is driven by the script {{path\|/usr/share/udhcpc/default.script}}

	Entries in {{path\|/etc/network/interfaces}} for DHCP interfaces will drive the <code>udhcpc</code> command line. For example:<br>		Entries in {{path\|/etc/network/interfaces}} for DHCP interfaces will drive the <code>udhcpc</code> command line. For example:<br>
Line 18:		Line 22:

	The hostname will send the DHCP option to the server to tell the server the name of this client.		The hostname will send the DHCP option to the server to tell the server the name of this client.

	~~The documentation for <code>udhcpc</code> can be found in [https://udhcp.busybox.net/README.udhcpc the busybox udhcpc readme file]<br>~~

	You can add arbitrary command line parameters to the <code>udhcpc_opts</code> setting in {{path\|/etc/network/interfaces}}. See the example of <code>udhcpc_opts</code> in [[Configure Networking#IPv4 DHCP Configuration\|the main networking article]].		You can add arbitrary command line parameters to the <code>udhcpc_opts</code> setting in {{path\|/etc/network/interfaces}}. See the example of <code>udhcpc_opts</code> in [[Configure Networking#IPv4 DHCP Configuration\|the main networking article]].
Line 64:		Line 66:
	{{cat\|/etc/udhcpc/udhcpc.conf\|RESOLV_CONF{{=}}"no" # Prevents overwriting of /etc/resolv.conf}}		{{cat\|/etc/udhcpc/udhcpc.conf\|RESOLV_CONF{{=}}"no" # Prevents overwriting of /etc/resolv.conf}}

	Custom scripts can be added as {{path\|/etc/udhcpc/pre-}} and {{path\|/etc/udhcpc/post-}} to be run before/after deconfig/renew/bound DHCP events. ~~They~~ must be set as '''executable''' by root, e.g. <code>chmod 744</code>		Custom scripts can be added as {{path\|/etc/udhcpc/pre-}} and {{path\|/etc/udhcpc/post-}} to be run before/after deconfig/renew/bound DHCP events. The custom scripts must be set as '''executable''' by root, e.g. <code>chmod 744</code>. Refer an example [[#Change default MTU for ADSL\|custom script]]

			== Troubleshooting ==

			{{Todo\|The below section need testing and confirmation. Please help contributing.}}

			=== Change default MTU for ADSL ===

	As an example, {{path\|/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 that uses PPPoE] (which uses 8 bytes for its own header):		As an example, {{path\|/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 that uses PPPoE] (which uses 8 bytes for its own header):

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

	~~<b>Hack alert:</b>~~
	I needed to restart my firewall (which replaces the <code>iptables</code> script from Alpine) when the client binds to a new IP, so I added the following line in the function <code>bound()</code>, right after '<code>resolvconf</code>':		I needed to restart my firewall (which replaces the <code>iptables</code> script from Alpine) when the client binds to a new IP, so I added the following line in the function <code>bound()</code>, right after '<code>resolvconf</code>':

Line 79:		Line 86:

	The reload drops all firewall rules, re-acquires the Internal and external IPs, and re-writes the rules. I'm sure there is a better way.		The reload drops all firewall rules, re-acquires the Internal and external IPs, and re-writes the rules. I'm sure there is a better way.

			== See Also ==
			[https://udhcp.busybox.net/README.udhcpc Busybox udhcpc Readme]

	[[Category:Networking]]		[[Category:Networking]]
	[[Category:Embedded Systems]]		[[Category:Embedded Systems]]

Sertonix: replace /etc/init.d with rc-service

2023-11-17T10:26:53Z

replace /etc/init.d with rc-service

← Older revision		Revision as of 10:26, 17 November 2023
Line 76:		Line 76:
	I needed to restart my firewall (which replaces the <code>iptables</code> script from Alpine) when the client binds to a new IP, so I added the following line in the function <code>bound()</code>, right after '<code>resolvconf</code>':		I needed to restart my firewall (which replaces the <code>iptables</code> script from Alpine) when the client binds to a new IP, so I added the following line in the function <code>bound()</code>, right after '<code>resolvconf</code>':

	{{cmd\|# ~~/etc/init.d/~~iptables reload}}		{{cmd\|# rc-service iptables reload}}

	The reload drops all firewall rules, re-acquires the Internal and external IPs, and re-writes the rules. I'm sure there is a better way.		The reload drops all firewall rules, re-acquires the Internal and external IPs, and re-writes the rules. I'm sure there is a better way.

Zcrayfish: Title case corrected.

2023-09-22T00:32:00Z

Title case corrected.

← Older revision		Revision as of 00:32, 22 September 2023
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			{{DISPLAYTITLE:udhcpc}}
	{{Expand\|Please help us expand this article by contributing.}}		{{Expand\|Please help us expand this article by contributing.}}

Sertonix: use path, cmd & cat template

2023-09-16T21:55:43Z

use path, cmd & cat template

← Older revision		Revision as of 21:55, 16 September 2023
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	{{Expand\|Please help us expand this article by contributing.}}		{{Expand\|Please help us expand this article by contributing.}}

	You may want to customize the behavior of the default DHCP client (<code>udhcpc</code> from busybox), which is called by ~~<code>~~/sbin/ifup~~</code>~~ by having "<code>dhcp</code>" in ~~<code>~~/etc/network/interfaces~~</code>~~.		You may want to customize the behavior of the default DHCP client (<code>udhcpc</code> from busybox), which is called by {{path\|/sbin/ifup}} by having "<code>dhcp</code>" in {{path\|/etc/network/interfaces}}.

	The default behavior is driven by the script ~~<code>~~/usr/share/udhcpc/default.script~~</code>~~		The default behavior is driven by the script {{path\|/usr/share/udhcpc/default.script}}

	Entries in ~~<code>~~/etc/network/interfaces~~</code>~~ for DHCP interfaces will drive the <code>udhcpc</code> command line. For example:<br>		Entries in {{path\|/etc/network/interfaces}} for DHCP interfaces will drive the <code>udhcpc</code> command line. For example:<br>

	~~<pre>~~auto eth0		{{cat\|/etc/network/interfaces\|auto eth0
	iface eth0 inet dhcp		iface eth0 inet dhcp
	hostname myhostname~~</pre>~~		hostname myhostname
			}}

	will set these parameters on the command line:<br>		will set these parameters on the command line:<br>

	~~<pre>~~-i eth0 -x hostname:myhostname~~</pre>~~		{{cmd\|udhcpc -i eth0 -x hostname:myhostname}}

	The hostname will send the DHCP option to the server to tell the server the name of this client.		The hostname will send the DHCP option to the server to tell the server the name of this client.
Line 19:		Line 20:
	The documentation for <code>udhcpc</code> can be found in [https://udhcp.busybox.net/README.udhcpc the busybox udhcpc readme file]<br>		The documentation for <code>udhcpc</code> can be found in [https://udhcp.busybox.net/README.udhcpc the busybox udhcpc readme file]<br>

	You can add arbitrary command line parameters to the <code>udhcpc_opts</code> setting in ~~<code>~~/etc/network/interfaces~~</code>~~. See the example of <code>udhcpc_opts</code> in [[Configure Networking#IPv4 DHCP Configuration\|the main networking article]].		You can add arbitrary command line parameters to the <code>udhcpc_opts</code> setting in {{path\|/etc/network/interfaces}}. See the example of <code>udhcpc_opts</code> in [[Configure Networking#IPv4 DHCP Configuration\|the main networking article]].

	The default configuration of <code>udhcpc</code> may be overridden by ~~<code>~~/etc/udhcpc/udhcpc.conf~~</code>~~. Please see ~~<code>~~/usr/share/udhcpc/default.script~~</code>~~ for how the values are used.		The default configuration of <code>udhcpc</code> may be overridden by {{path\|/etc/udhcpc/udhcpc.conf}}. Please see {{path\|/usr/share/udhcpc/default.script}} for how the values are used.

	~~<code>~~udhcpc.conf~~</code>~~ accepts the following key:value pairs:		{{path\|udhcpc.conf}} accepts the following key:value pairs:

	{\| cellpadding="15" border="1" class="wikitable"		{\| cellpadding="15" border="1" class="wikitable"
Line 33:		Line 34:
	\|-		\|-
	\| RESOLV_CONF		\| RESOLV_CONF
	\| /etc/resolv.conf		\| {{path\|/etc/resolv.conf}}
	\| no ; NO ; -		\| no ; NO ; -
	\| do not overwrite or alternative path for resolv.conf		\| do not overwrite or alternative path for {{path\|resolv.conf}}
	\|-		\|-
	\| NO_DNS		\| NO_DNS
	\| -		\| -
	\| <list of iface names>		\| <list of iface names>
	\| Prevent overwriting of resolv.conf on a per-interface basis		\| Prevent overwriting of {{path\|resolv.conf}} on a per-interface basis
	\|-		\|-
	\| NO_GATEWAY		\| NO_GATEWAY
Line 58:		Line 59:
	\|}		\|}

	Example ~~<code>~~/etc/udhcpc/udhcpc.conf~~</code>~~:		Example {{path\|/etc/udhcpc/udhcpc.conf}}:

	RESOLV_CONF="no" # Prevents overwriting of /etc/resolv.conf		{{cat\|/etc/udhcpc/udhcpc.conf\|RESOLV_CONF{{=}}"no" # Prevents overwriting of /etc/resolv.conf}}

	Custom scripts can be added as ~~<code>~~/etc/udhcpc/pre-~~</code>~~ and ~~<code>~~/etc/udhcpc/post-~~</code>~~ to be run before/after deconfig/renew/bound DHCP events. They must be set as '''executable''' by root, e.g. <code>chmod 744</code>		Custom scripts can be added as {{path\|/etc/udhcpc/pre-}} and {{path\|/etc/udhcpc/post-}} to be run before/after deconfig/renew/bound DHCP events. They must be set as '''executable''' by root, e.g. <code>chmod 744</code>

	As an example, ~~<code>~~/etc/udhcpc/post-bound/mtu~~</code>~~ 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 that uses PPPoE] (which uses 8 bytes for its own header):		As an example, {{path\|/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 that uses PPPoE] (which uses 8 bytes for its own header):

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

	<b>Hack alert:</b>		<b>Hack alert:</b>
	I needed to restart my firewall (which replaces the <code>iptables</code> script from Alpine) when the client binds to a new IP, so I added the following line in the function <code>bound()</code>, right after '<code>resolvconf</code>':		I needed to restart my firewall (which replaces the <code>iptables</code> script from Alpine) when the client binds to a new IP, so I added the following line in the function <code>bound()</code>, right after '<code>resolvconf</code>':

	/etc/init.d/iptables reload		{{cmd\|# /etc/init.d/iptables reload}}

	The reload drops all firewall rules, re-acquires the Internal and external IPs, and re-writes the rules. I'm sure there is a better way.		The reload drops all firewall rules, re-acquires the Internal and external IPs, and re-writes the rules. I'm sure there is a better way.

CarloMonte at 06:42, 16 August 2023

2023-08-16T06:42:39Z

← Older revision		Revision as of 06:42, 16 August 2023
Line 23:		Line 23:
	The default configuration of <code>udhcpc</code> may be overridden by <code>/etc/udhcpc/udhcpc.conf</code>. Please see <code>/usr/share/udhcpc/default.script</code> for how the values are used.		The default configuration of <code>udhcpc</code> may be overridden by <code>/etc/udhcpc/udhcpc.conf</code>. Please see <code>/usr/share/udhcpc/default.script</code> for how the values are used.

	~~Authorized key:value pairs for~~ <code>udhcpc.conf</code> ~~are~~:		<code>udhcpc.conf</code> accepts the following key:value pairs:

	{\| cellpadding="15" border="1" class="wikitable"		{\| cellpadding="15" border="1" class="wikitable"