Ubuntu 用 systemd 了，所以就没有 runlevel 了。
对应的，是一个systemd targets.
Mapping between runlevels and systemd targets
┌─────────┬───────────────────┐
│Runlevel │ Target │
├─────────┼───────────────────┤
│0 │ poweroff.target │
├─────────┼───────────────────┤
│1 │ rescue.target │
├─────────┼───────────────────┤
│2, 3, 4 │ multi-user.target │
├─────────┼───────────────────┤
│5 │ graphical.target │
├─────────┼───────────────────┤
│6 │ reboot.target │
└─────────┴───────────────────┘
Now, to just change the "runlevels" in 16.04, you can use for eg:
sudo systemctl isolate multi-user.target
To make this the default "runlevel", you can use:
sudo systemctl enable multi-user.target sudo systemctl set-default multi-user.target
https://askubuntu.com/questions/788323/change-runlevel-on-16-04