Run dhclient on Startup in Ubuntu 18.04

ubuntu-run-dhclient-on-startup.md

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

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.

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.

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

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

[Match]
Name=enp*

[Network]
DHCP=ipv4

Great helps

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