Suppose, not hypothetically, that you have some standard physical servers. As is typical, the servers have more than one network interface (two is usually the basics even for 1U servers, and maybe you put in a 10G-T card in some), but you're only using one network interface on one network; the others are just sort of there. Recently you've started putting Ubuntu 26.04 LTS on them, and to your surprise (and displeasure) these machines stall for two minutes on boot, which they report as waiting for systemd-networkd-wait-online .

The direct culprit is that you haven't told Canonical Netplan to ignore the state of network carrier for all of the network interfaces that you aren't using and don't have plugged in to anything. This is the ' ignore-carrier ' property, listed in Properties for all device types , and you need to set it on every network interface that is listed in /etc/netplan/*.yaml. However, why this happens and how we got here is a little bit convoluted (and it can happen in versions other than 26.04, under the right circumstances).

Famously, Netplan doesn't actually configure your networks itself. Instead it creates a configuration for something else (a 'backend'), and on servers this is systemd-networkd . For every network listed in your Netplan configuration, Netplan will write a ' 10-netplan-<name>.network ' file to /run/systemd/network/ , with the appropriate contents taken from whatever your configuration says. As sort of covered in systemd-networkd-wait-online's documentation (when carefully combined with the description of network states in networkctl ), this will cause systemd-networkd-wait-online to wait for every such interface to have carrier (up to its timeout ), unless the .network file specifies ConfigureWithoutCarrier=yes , which Netplan sets only if you put the ignore-carrier property on the interface in your Netplan configuration.

(Under some circumstances Netplan will also write .link files for one or more interfaces.)

At install time, the Ubuntu server installer gives you options for what to do with each network interface it detects. If you explicitly configure an IP address or set an interface to do DHCP (or the installer sets it to do DHCP and you don't explicitly turn that off), the interface will of course appear in your installed system's Netplan configuration because it has to. However, if you explicitly disable an interface (or in some versions of the installer, the installer disables it because it detected no carrier and/or no DHCP), the Ubuntu server installer has traditionally not written any information about that interface to your installed server Netplan configuration. Since these additional interfaces weren't mentioned in Netplan at all, Netplan never wrote out .network files for them and systemd-networkd-wait-online never waited for carrier for them. Your server's Netplan file contained only the interfaces you actually used and you were happy even if there were no ' ignore-carrier: true ' settings.

What's changed in Ubuntu 26.04 is that the Ubuntu server installer appears to write out an ' accept-ra: false ' property for every interface it detects, even if you disabled the interface during network configuration in the installer. Since the installer itself now mentions every interface in your generated Netplan configuration, Netplan writes .network files for all of them to /run/systemd/network and you wind up 'waiting' for carrier on every interface on boot, causing a two minute delay, which is the default timeout used by systemd-networkd-wait-online (it's the --timeout option's default value ). You can fix this either by setting ' ignore-carrier: true ' on every such interface or by deleting all of those interfaces from your Netplan configuration.

(To confuse you, systemd will report during boot that systemd-networkd-wait-online has no timeout and it's technically correct. What systemd really means is that the systemd-networkd-wait-online.service file doesn't specify a TimeoutStartSec= setting and as ' Type=oneshot service, it doesn't get a default one. Instead the timeout is inside the systemd-networkd-wait-online program and is opaque to systemd (the PID 1 daemon that is trying to 'start' this weird service).)

Because I had to wrangle this, here is how to list every network interface and then set them to ignore carrier, assuming you're using Ubuntu 26.04 where they are already all listed in your Netplan configuration:

ifnames="$(ip --json link show | jq -r '.[] | select(.link_type == "ether") | .ifname')"
for i in $ifnames; do
    netplan set "ethernets.$i.ignore-carrier=true"
done

This isn't perfect and will match some virtual interfaces, but I leave dealing with that as an exercise to the reader, along with excluding interfaces that currently have carrier. For our purposes at install time, this is good enough. And yes, we turn off detecting carrier even on our active interface because we would rather have the machine come up to the extent that maybe we can log in on the console or the like.

(It would be nice to have a way to delete a particular interface entirely, but Netplan's command line interface doesn't provide any good way to do that.)