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

Wed May 17 15:25:30 UTC 2017
Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>

> 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.

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

> Thanks,
> Jerry

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