SOLUTION - systemctl hangs and gives "Connection timed out" in every call when using serial-getty@.service

systemctl_serial-getty.txt

I've stumbled upon this problem after migrating from sysvinit to systemd.

To get the serial console working on systemd I had to set up a service called serial-getty@.service. It uses
agetty as a way to open ports, ask for login name and password.

The problem started after I noticed that my custom program, called with /sbin/agetty -i -n -l <program>, would not recognize the
Enter inserted as a End Of Line (EOL) special char. Then, I had to change from agetty to /bin/busybox getty to get the key recognized.

*latter I learned that this problem could be resolved using the command 'stty cooked'*

However, after using busybox with systemd, I noticed that, if a serial console port was enables but not connected to a client, every
call to systemctl would hang until receives a "Connection timed out" and not execute the command at all.

It took me a while to realize that the problem was busybox.

So, do not use busybox getty with systemd... At least not with serial-ports. Some hardwares have serial ports enabled by default at
BIOS, so your calls to systemctl may hang.

Use /sbin/agetty and then set the terminal environment with stty cooked or something.

https://linux.die.net/man/8/agetty
https://linux.die.net/man/1/stty