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[Xen-users] Is it possible to have two serial consoles?

  • To: xen-users@xxxxxxxxxxxxx
  • From: Andy Smith <andy@xxxxxxxxxxxxxx>
  • Date: Thu, 12 Nov 2015 11:17:23 +0000
  • Delivery-date: Thu, 12 Nov 2015 11:18:41 +0000
  • List-id: Xen user discussion <xen-users.lists.xen.org>
  • Openpgp: id=BF15490B; url=http://strugglers.net/~andy/pubkey.asc


Is it possible to have the hypervisor output to, and accept input
from two serial consoles at the same time?

For example let's assume there is a real serial port on ttyS0.
Here's how I'd normally configure that in Xen + grub 2 on Debian:


GRUB_CMDLINE_XEN="dom0_mem=1024M loglvl=all guest_loglvl=all com1=115200,8n1 
GRUB_CMDLINE_LINUX="console=tty0 console=hvc0 earlyprintk=xen"

That gets me console on both the serial port and VGA, both get all
the boot output and have a getty running on them at the end of the

Now let's assume there is *also* an IPMI serial console on ttyS1,
and for now I do not change any settings.

What happens now is, ttyS1 is not usable. It get no output during
boot, dom0 OS doesn't see it as an available serial device and can't
make a getty listen on it.

I think that is because dom0 OS doesn't know about it, only knows of
tty0 and is relying on Xen to deal with serial ports. Obviously as I
haven't touched the "com1" setting in Xen, nothing different is
going to happen.

So, I read http://wiki.xen.org/wiki/Xen_Serial_Console and tried:

GRUB_CMDLINE_XEN="dom0_mem=1024M loglvl=all guest_loglvl=all 
com1=115200,8n1,0x2f8,10 console=com1,vga"

That gets me a serial console on the IPMI serial (ttyS1), but
nothing on the real serail port (ttyS0).

It seems to me like Xen can only deal with one serial port at a
time. Is that the case?

Note that my first assumption that com1 would mean ttyS0 so to
address ttyS1 you'd use com2, com3 and so on, proved to be
incorrect. There is only com1 in Xen from what I can see, and you
tell Xen which serial port com1 corresponds to by configuring the
address (and possibly IRQ) hence "com1=115200,8n1,0x2f8,10".

So, has anyone ever got it to talk to two serial ports at once, or
is that not possible?


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