[CentOS-virt] What is the purpose setting console=hvc0 in the dom0 grub config?

Wed May 17 15:37:13 UTC 2017
Jerry <jerryubi at gmail.com>

On Wed, May 17, 2017 at 8:25 AM, Konrad Rzeszutek Wilk <
konrad.wilk at oracle.com> wrote:

> > This is what's defined in /etc/default/grub following the install of the
> > Xen:
> >
> > GRUB_CMDLINE_XEN_DEFAULT="dom0_mem=1024M,max:1024M cpuinfo
> com1=115200,8n1
> > console=com1,tty loglvl=all guest_loglvl=all"
> > GRUB_CMDLINE_LINUX_XEN_REPLACE_DEFAULT="console=hvc0 earlyprintk=xen
> > nomodeset"
> >
> > I didn't set these myself, this is what the xen package (or one of its
> > dependencies) is doing.
> >
> > I'm still not clear on why hvc0 is needed, or why it's being set, but
> what
> > I do know for sure is it was causing the boot messages to be suppressed.
> So the hvc0 is to use the PV console driver to pipe all the messages to
> the Xen one.
> And Xen is configured to use the serial console (com1=115200,8n1).
> Which means that all you Linux bootup info should be piped to that.
So how would I properly configure it to still write to tty without
disabling hvc0?  Perhaps something like this?

GRUB_CMDLINE_LINUX_XEN_REPLACE_DEFAULT="console=hvc0,tty earlyprintk=xen

Looks like I have some learning to do.  Do you happen to know of a good
article explaining how console redirection works?

> But Linux is pretty quiet unless you add 'loglevel=10' or 'debug' on the
> Linux command line.
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