Wait until we're connected to the Internet.
The Internet may be behind a captive portal, so let's wait for that.
If you are using Arch Linux, just makepkg and use pacman to install.
If not, you're on your own (patches welcome).
Run sudo systemctl enable --now wait-online after installation to activate.
This service will be ordered before network-online.target, so your services needing Internet access will be started at the correct time.
There is also a wait-online-onresume.service that you can enable for restarting wait-online.service after resuming from a sleep so that the wait-online command works well.
check-online will check if we are connected to the Internet and notify wait-online. This is the service script.
wait-online will wait until we are connected to the Internet (need check-online running).