[systemd-devel] Serial console flow control will stuck systemd

[Lennart Poettering]

On Fr, 12.04.24 09:33, 细石泉 (nichelnich at gmail.com) wrote:

> systemd will write log to console directly when bootup. A unexpected serial
> console flow control maybe block systemd at embedded systems. I guess
> systemd doesn't do a good job of initializing the serial console.

It doesn't do any job of it. We try hard to not reconfigure the serial
port at all, and we tell getty to not do this either. The assumption
is that whatever you configure on the kernel cmdline should remain in
effect all the way through.

> If a noise XOFF(HEX13) generate when systemd bootup, systemd stucked.
> Should systemd turn off any flow control stuff when initializing the serial
> console?

Tell the kernel what kind of flow control you want, we should not
reconfigure things then.

Note that iirc XON/XOFF handling is enabled on by default on most
linux ttys, i.e. "stty" will generally report "ixon" on terminals,
including graphical ones. And C-S/C-Q is generally understood to just
work to suspend terminal output. Hence, turning this off would
probably be quite confusing to most.

Lennart

--
Lennart Poettering, Berlin