mohamadaliakbari/ubuntu-run-dhclient-on-startup.md

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Run dhclient on Startup in Ubuntu 18.04

Raw

dhclient is the Dynamic Host Configuration Protocol (DHCP) Client one would use to allow a client to connect to a DHCP server.

$ sudo nano /etc/rc.local

#!/bin/bash
dhclient
exit 0

$ sudo chmod 755 /etc/rc.local

$ sudo systemctl enable rc-local

$ sudo systemctl restart rc-local

$ sudo systemctl status rc-local

p1-ra commented Feb 26, 2020 •

edited

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Ubuntu 18.04 (server) is using systemd-networkd as default, if the service is enable systemctl status systemd-networkd, the proper way to enable dhcp is to use the systemd network configuration files (/etc/systemd/network/*)
https://www.freedesktop.org/software/systemd/man/systemd.network.html

As exemple, the following configuration file will enable DHCP to any nic that have a name that's matching enp*

cat /etc/systemd/network/20-dhcp.network
[Match]
Name=enp*

[Network]
DHCP=ipv4

SolarGranola commented Mar 4, 2020

Ubuntu 18.04 (server) is using systemd-networkd as default, if the service is enable systemctl status systemd-networkd, the proper way to enable dhcp is to use the systemd network configuration files (/etc/systemd/network/*)
https://www.freedesktop.org/software/systemd/man/systemd.network.html

As exemple, the following configuration file will enable DHCP to any nic that have a name that's matching enp*
cat /etc/systemd/network/20-dhcp.network
[Match]
Name=enp*

[Network]
DHCP=ipv4

How would you do this in Ubuntu 16.04? This is what systemctl status returns for me:

systemd-networkd.service - Network Service
   Loaded: loaded (/lib/systemd/system/systemd-networkd.service; disabled; vendor preset: enabled)
   Active: inactive (dead)
   Docs: man:systemd-networkd.service(8)

p1-ra commented Mar 4, 2020 via email •

edited

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Looks that the service is actually disabled. You can start it and enable it at boot with: - sudo systemctl start systemd-networkd - sudo systemctl enable systemd-networkd

…

On Wed, Mar 4, 2020, 8:33 PM Justin ***@***.***> wrote: Ubuntu 18.04 (server) is using systemd-networkd as default, if the service is enable systemctl status systemd-networkd, the proper way to enable dhcp is to use the systemd network configuration files (/etc/systemd/network/*) https://www.freedesktop.org/software/systemd/man/systemd.network.html As exemple, the following configuration file will enable DHCP to any nic that have a name that's matching enp* cat /etc/systemd/network/20-dhcp.network [Match] Name=enp* [Network] DHCP=ipv4 How would you do this in Ubuntu 16.04? This is what systemctl status returns for me: systemd-networkd.service - Network Service Loaded: loaded (/lib/systemd/system/systemd-networkd.service; disabled; vendor preset: enabled) Active: inactive (dead) Docs: man:systemd-networkd.service(8) — You are receiving this because you commented. Reply to this email directly, view it on GitHub <https://gist.github.com/1cb9400984094541581fff07143e1c9d?email_source=notifications&email_token=AELDPIVP7ROWQ6GC4S6KSP3RF2UG5A5CNFSM4JI76BFKYY3PNVWWK3TUL52HS4DFVNDWS43UINXW23LFNZ2KUY3PNVWWK3TUL5UWJTQAGDKSY#gistcomment-3200300>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AELDPIQNUGNQBVQ2L5Q5YHTRF2UG5ANCNFSM4JI76BFA> .

andrewroth commented Mar 17, 2020

Nobody seems to mention how ridiculous it is that ubuntu doesn't "just work" with auto dhcp like it used to. Odd.

wilkinsmr commented May 5, 2020

Making a rc.local file to run dhclient is not the correct solution. You will most likely end-up with multiple network renders doing DHCP client operations and cause problems with future upgrades.

Ubuntu switched to netplan in release 17.10 (see Migrating to Netplan) which by default uses

NetworkManager for Ubuntu Desktop
systemd-networkd for Ubuntu Server

You can change the network "renderer" (networkd or NetworkManager) for any/all interfaces in the yaml config files under /etc/netplan (see netplan reference). You can also configure DHCP client options in netplan, but @p1-ra provided a better approach for cases using systemd-networkd which gives you more control (see Network Configuration for systemd.networkd)

In cases where NetworkManager is running, there is no need to abandon it, it's actually pretty good these days (unlike the old days when the first thing we did on a new install was to disable it) and it does DHCP client by default! However, OOTB it runs its own internal DHCP client which ignores /etc/dhcp/dhclient.conf and any hooks you may have added.
If you want NetworkManager to run dhclient instead, just edit /etc/NetworkManager/NetworkManager.conf and add a new line for "dhcp=dhclient" under the main section.

/etc/NetworkManager/NetworkManager.conf

[main]
dhcp=dhclient

(see NetworkManager.conf for details and other options)

When NetworkManager is restarted with systemctl restart NetworkManager it merges /etc/dhcp/dhclient.conf with its own interface specific configuration under /var/lib/NetworkManager. You can see dhclient running and the locations for conf, leases, etc. in your process list e.g.

ps -fC dhclient
	/sbin/dhclient -d -q \
		-sf /usr/lib/NetworkManager/nm-dhcp-helper \
		-pf /run/NetworkManager/dhclient-wlp58s0.pid \
		-lf /var/lib/NetworkManager/dhclient-02d2ec1b-e3f4-40f4-abbc-679afea5041b-wlp58s0.lease \
		-cf /var/lib/NetworkManager/dhclient-wlp58s0.conf wlp58s0
	/sbin/dhclient -d -q -6 -N \
		-sf /usr/lib/NetworkManager/nm-dhcp-helper \
		-pf /run/NetworkManager/dhclient6-wlp58s0.pid \
		-lf /var/lib/NetworkManager/dhclient6-02d2ec1b-e3f4-40f4-abbc-679afea5041b-wlp58s0.lease \
		-cf /var/lib/NetworkManager/dhclient6-wlp58s0.conf wlp58s0

(wlp58s0 in this example is my wifi interface)

ttbek commented Jun 11, 2020 •

edited

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This is inane complexity for the sake of complexity. No one needs a "network renderer" We need straightforward configuration for the things we want. Not 20 different "network rendering" components all throwing a fit because you did something outside of their auspices. Even Avahi decided it was a good idea to mess with my bridge configuration. I'm pretty sure I didn't even choose to install it, it was a nasty gift that came with my upgrade to 20.04.
But yes, rc.local is probably not the place to do this. Should probably create a systemd unit for it once you finally get all the interfering stuff out of the way.
Look, probably if I were starting from scratch it would be easy to just make the Netplan config, but I'm not starting from scratch, I'm starting with a complicated manually created network and it would be working perfectly fine if this newly installed insanity didn't keep butting in.

ChicagoJay commented Nov 4, 2020

I had this same problem with Ubuntu Server 20.04 LTS. The fix works, so you are a deity, and you have my sincerest gratitude - but WHY do I need it? I have other VMs that are running Ubuntu 20.04, that don't need this fix. They needed IPv6 turned off, to avoid the 2 minute boot delay, but that was it. DHCPv4 works fine.

Thanks!

mark-e-deyoung commented Dec 11, 2020 •

edited

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Helped me get DHCP working for IP over InfiniBand (ipoib) interfaces in a MAAS cluster. The DHCP process in systemd-networkd used by netplan doesn't seem to work with ipoib while dhclient does.

See: netplan not sending DHCP request of IPoIB interfaces.

ac101m commented Mar 14, 2021

I have a bunch of machines running 16.04 (which will be going EOL in a month and a half) that need to be upgraded.
I have run into this issue with ipoib on another machine running 20.04 and am now dreading the upgrade.

In all the years since I started using linux, I never encountered a situation where /etc/network/interfaces either bugged out or wasn't capable of doing what I needed it to. I just don't understand why this needed to be changed! Its things like this that give me second thoughts about ubuntu.

mickaelbaron commented Feb 24, 2022

Hi,

In my case, DHCP server was provided by a Windows Server. To fix the problem, you need to apply this workaround (https://netplan.io/examples/#integration-with-a-windows-dhcp-server).

Details with Ubuntu 20.04 LTS

Edit /etc/netplan/00-installer-config.yaml
Add dhcp-identifier key into current network configuration

network:
  ethernets:
    eth0:
      dhcp-identifier: mac
      dhcp4: true
  version: 2

Restart Netplan configuration

$ sudo netplan generate
$ sudo netplan apply

leeanh2612 commented Mar 31, 2022

Hi,

In my case, DHCP server was provided by a Windows Server. To fix the problem, you need to apply this workaround (https://netplan.io/examples/#integration-with-a-windows-dhcp-server).

Details with Ubuntu 20.04 LTS

Edit /etc/netplan/00-installer-config.yaml

Add dhcp-identifier key into current network configuration
network:
  ethernets:
    eth0:
      dhcp-identifier: mac
      dhcp4: true
  version: 2
Restart Netplan configuration
$ sudo netplan generate
$ sudo netplan apply

Thanks man you are boss <3

jialeif commented Oct 26, 2022

[Match]
Name=enp*

[Network]
DHCP=ipv4

Great helps

gbc921 commented Sep 19, 2023 •

edited

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Ubuntu 18.04 (server) is using systemd-networkd as default, if the service is enable systemctl status systemd-networkd, the proper way to enable dhcp is to use the systemd network configuration files (/etc/systemd/network/*) https://www.freedesktop.org/software/systemd/man/systemd.network.html

As exemple, the following configuration file will enable DHCP to any nic that have a name that's matching enp*
cat /etc/systemd/network/20-dhcp.network
[Match]
Name=enp*

[Network]
DHCP=ipv4

Awesome!
Had to do that for the Cloud Image of Ubuntu Server 22.04 LTS (Jammy)

Then later sudo systemctl daemon-reload && sudo systemctl enable systemd-networkd --now