Backup of https://stackoverflow.com/a/77365896/4305230 fixes https://bugs.launchpad.net/netplan/+bug/2039083 https://bugs.launchpad.net/ubuntu/+source/netplan.io/+bug/1906646
i have solved this problem
netplan apply says ovsdb-server.service is not running, then i just install this openvswitch
since i run ubuntu server in raspberry pi, i need to install extra lib:
# run this first
$ sudo apt-get install linux-modules-extra-raspi
# run this then
$ sudo apt-get install openvswitch-switch-dpdk
you may need to check installation by run these command again
after the installation complete, no annoying WARNING shows again:
$ sudo netplan try
however, systemd-networkd-wait-online.service still timeout, no matter how many times you restart it
i have consulted the man page for systemd-networkd-wait-online.service usage
this service is just to wait all interface managed by systemd-networkd are ready
in fact, i only use ethernet interface and wlan interface, these interfaces work well
$ ip a
# status of my interfaces
so i asked chatgpt about how to wait specific interfaces for systemd-networkd-wait-online.service
it told my to add args in /lib/systemd/system/systemd-networkd-wait-online.service
$ vim /lib/systemd/system/systemd-networkd-wait-online.service
[Service]
Type=oneshot
# flag `--interface` is used to wait specific interface
# in this case, i need to wait wlan interface and ethernet interface
ExecStart=/lib/systemd/systemd-networkd-wait-online --interface=wlan0 --interface=eth0
RemainAfterExit=yes
# this parameter is used to set timeout, 30s is enough for my pi
TimeoutStartSec=30sec
after edition, you need to reload this script and restart service
$ systemctl daemon-reload
$ systemctl restart systemd-networkd-wait-online.service
that is all, everything gonna be fine (maybe)