$ vim /lib/systemd/system/getty@.service
### Add "-a root" into ExecStart for agetty
ExecStart=-/sbin/agetty -a root --keep-baud 115200,38400,9600 %I $TERM
$ reboot
$ vim /lib/systemd/system/serial-getty@.service
### Add "-a root" into ExecStart for agetty
ExecStart=-/sbin/agetty -a root --keep-baud 115200,38400,9600 %I $TERM
$ reboot