Open Stack

On Sat, 21 Feb 2015 11:10:23 -0600, Anne Gentle wrote:
> Why's it called serial console? Maybe that background would help me
> understand.

If you want to know what is going on inside a (physical) machine,
there are several options: for instance, you can hook up a monitor
(say, through a VGA or DVI cable) and maybe a keyboard (PS/2, USB)
and look there, you can connect it to a network (Ethernet), or you can
use a serial console (say RS-232). Of all these options, the one thing
that is so old and simple that it is pretty much guaranteed to work
(if present at all), is a console connected over a serial line.

You can tell the (Linux) kernel to log to the serial port (and receive
input from there), connect your machine to some other computer, and
you will get a way to interact with your machine even if it has no
other hardware attached or if all drivers for video, USB, and network
are broken.

Virtualization tech just emulates that physical serial connection. In
earlier OpenStack releases, you could use the serial console only to
receive log data. With Juno, you can use it also to send commands to
the virtual machine. As long as the operating system running inside
the VM is configured to listen on the emulated thing that looks and
behaves just like a serial port, you can interact with it as if you
were sitting in front of it. Hence the "serial console".

Roger