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

[Jerry]

On Wed, May 17, 2017 at 2:17 PM, Nerijus Baliunas <
neri...@users.sourceforge.net> wrote:

> On Wed, 17 May 2017 14:09:57 -0700 Jerry  wrote:
>
> > Setting both hvc0 and tty is working as desired.  Thanks again to
> everyone
> > that replied.  I'm updating my kickstart script to include adding
> > console=tty in addition to the other.
>
> Should it be set by default then?
>
> Regards,
> Nerijus
>

I'd say so.  The addition of console=hvc0 to the grub configuration seems
to be a pretty new thing (didn't have this issue with Xen on CentOS 6, so
possibly limited to CentOS 7).

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

[Nerijus Baliunas]

On Wed, 17 May 2017 14:09:57 -0700 Jerry  wrote:

> Setting both hvc0 and tty is working as desired.  Thanks again to everyone
> that replied.  I'm updating my kickstart script to include adding
> console=tty in addition to the other.

Should it be set by default then?

Regards,
Nerijus
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Re: [CentOS-virt] What is the purpose setting console=hvc0 in the dom0 grub config?

[Jerry]

On Wed, May 17, 2017 at 8:54 AM, Jerry  wrote:

>
>
> On Wed, May 17, 2017 at 8:44 AM, George Dunlap  wrote:
>
>> On Wed, May 17, 2017 at 4:20 PM, Jerry  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.
>>
>> It's the CentOS Xen package setting this.  But the Xen option
>> "console=com1,tty" should make it such that Xen sends its output
>> *both* to the serial line, *and* the monitor.
>>
>> I take it you're not seeing any Xen output at all on your IPMI console?
>>
>>  -George
>>
>
> The boot messages are suppressed, but if it boots successfully the login
> prompt shows up. If I remove console=hvc0 both the boot messages and login
> prompt show up.
>
> Note: the IPMI console I'm looking at is just the local monitor being
> redirected.  It isn't a special device/driver.
>
> I'll try what Konrad is suggesting, setting this:
>
> console=hvc0 console=tty
>
> And will see what happens.  It'll be a few hours until I can try it out.
>
> Thank you to every one that has responded, I appreciate the help.
>
> Jerry.
>
>

Setting both hvc0 and tty is working as desired.  Thanks again to everyone
that replied.  I'm updating my kickstart script to include adding
console=tty in addition to the other.

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

[Jerry]

On Wed, May 17, 2017 at 8:44 AM, George Dunlap  wrote:

> On Wed, May 17, 2017 at 4:20 PM, Jerry  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.
>
> It's the CentOS Xen package setting this.  But the Xen option
> "console=com1,tty" should make it such that Xen sends its output
> *both* to the serial line, *and* the monitor.
>
> I take it you're not seeing any Xen output at all on your IPMI console?
>
>  -George
>

The boot messages are suppressed, but if it boots successfully the login
prompt shows up. If I remove console=hvc0 both the boot messages and login
prompt show up.

Note: the IPMI console I'm looking at is just the local monitor being
redirected.  It isn't a special device/driver.

I'll try what Konrad is suggesting, setting this:

console=hvc0 console=tty

And will see what happens.  It'll be a few hours until I can try it out.

Thank you to every one that has responded, I appreciate the help.

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

[George Dunlap]

On Wed, May 17, 2017 at 4:20 PM, Jerry  wrote:
> On Wed, May 17, 2017 at 2:39 AM, George Dunlap  wrote:
>>
>> On Wed, May 17, 2017 at 4:26 AM, Jerry  wrote:
>> > I always disable "rhgb quiet" on a fresh install because I don't like
>> > boot
>> > messages being hidden from me, and now this other thing does it.  I like
>> > details, I need the details, don't hide them from me.
>>
>> I feel the same way about 'rhgb quiet'.  :-)
>>
>> The 'console=hvc0' setting doesn't hide them from you, it just sends
>> them somewhere you're not looking.
>
>
> I'm looking at the system's console during installation. Sending it
> somewhere else is hiding it from me.
>
>>
>> On bare metal, the console output can typically go two places:
>> 1. The screen
>> 2. A serial port
>>
>> For server applications serial has several advantages over the screen:
>> * You can capture the output to more easily report bugs
>> * If you're capturing it you can keep things that would have scrolled
>> off-screen, or been erased due to a reboot
>> * In a datacenter it's faster, more convenient, and cheaper than an
>> IP-based KVM switch
>
>
> I get what these things are, but not what hvc0 is doing.

See below -- it sends the output to Xen; Xen will then forward it to
the serial, the screen, or both.

> This system has built-in IPMI, the installation was done remotely using it.
>
>>
>> Xen has the same two options above; but when Linux is running as a
>> dom0 under Xen, there are three places to put it:
>> 1. The screen
>> 2. A serial line
>> 3. Send it to Xen to put wherever Xen is putting it
>>
>> #1 is easy, but #2 is tricky because Xen is likely to be already using
>> the serial port you want to use.
>>
>> "console=hvc0" is #3.
>>
>> What's your Xen command-line look like?  The default should be
>> "console=com1,tty", so Xen's output should show up both places (and so
>> should Linux's if it's set to console=hvc0).
>
>
> 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.

It's the CentOS Xen package setting this.  But the Xen option
"console=com1,tty" should make it such that Xen sends its output
*both* to the serial line, *and* the monitor.

I take it you're not seeing any Xen output at all on your IPMI console?

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

[Konrad Rzeszutek Wilk]

On Wed, May 17, 2017 at 08:37:13AM -0700, Jerry wrote:
> On Wed, May 17, 2017 at 8:25 AM, Konrad Rzeszutek Wilk <
> konrad.w...@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
> nomodeset"

console=hvc0 console=tty

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

You add the 'console' and it will pipe date to it.
If you add more, then it will duplicate it to those.
> 
> 
> > But Linux is pretty quiet unless you add 'loglevel=10' or 'debug' on the
> > Linux command line.
> >
> >

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

[Jerry]

On Wed, May 17, 2017 at 8:25 AM, Konrad Rzeszutek Wilk <
konrad.w...@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
nomodeset"

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

[Konrad Rzeszutek Wilk]

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

[Jerry]

On Wed, May 17, 2017 at 2:39 AM, George Dunlap  wrote:

> On Wed, May 17, 2017 at 4:26 AM, Jerry  wrote:
> > I always disable "rhgb quiet" on a fresh install because I don't like
> boot
> > messages being hidden from me, and now this other thing does it.  I like
> > details, I need the details, don't hide them from me.
>
> I feel the same way about 'rhgb quiet'.  :-)
>
> The 'console=hvc0' setting doesn't hide them from you, it just sends
> them somewhere you're not looking.
>

I'm looking at the system's console during installation. Sending it
somewhere else is hiding it from me.


> On bare metal, the console output can typically go two places:
> 1. The screen
> 2. A serial port
>
> For server applications serial has several advantages over the screen:
> * You can capture the output to more easily report bugs
> * If you're capturing it you can keep things that would have scrolled
> off-screen, or been erased due to a reboot
> * In a datacenter it's faster, more convenient, and cheaper than an
> IP-based KVM switch
>

I get what these things are, but not what hvc0 is doing.

This system has built-in IPMI, the installation was done remotely using it.


> Xen has the same two options above; but when Linux is running as a
> dom0 under Xen, there are three places to put it:
> 1. The screen
> 2. A serial line
> 3. Send it to Xen to put wherever Xen is putting it
>
> #1 is easy, but #2 is tricky because Xen is likely to be already using
> the serial port you want to use.
>
> "console=hvc0" is #3.
>
> What's your Xen command-line look like?  The default should be
> "console=com1,tty", so Xen's output should show up both places (and so
> should Linux's if it's set to console=hvc0).
>

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.

Thanks,
Jerry
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Re: [CentOS-virt] What is the purpose setting console=hvc0 in the dom0 grub config?

[Jerry]

On Wed, May 17, 2017 at 3:02 AM, Mark L Sung  wrote:

> Jerry,
> Refer to console=hvc0 from (https://wiki.xen.org/wiki/
> Xen_FAQ_Console)which is dedicated for domO after Xen kernel loaded, so
> if it hangs it means somewhere the booting process with xen is not right.
>

I might be missing something, but that article makes no mention of
using hvc0 on dom0.

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

[Jerry]

On Wed, May 17, 2017 at 3:43 AM, PJ Welsh  wrote:

> On Tue, May 16, 2017 at 10:26 PM, Jerry  wrote:
>
>> Howdy,
>>
>> I recently went through a frustrating experience trying to get Xen 4
>> running on a CentOS 7 system.  After a fresh install, fully updating the
>> system, rebooting, then trying to install Xen4CentOS it would fail to boot
>> into the 4.9 kernel, sitting there with a blinking cursor indefinitely.
>>
> ...
>
> Check the BIOS to see if Hyperthreading is disabled. If so, enable it. I
> had some Dell server (Dell R710s and R610s) that I finally figured out
> would not boot like you describe when HT is off for some reason.
> PJ
>

I found what my issue was with it not booting, when the 4.9 kernel was
installed it didn't include the mpt3sas driver.  I posted the solution to
the mailing list earlier with the subject:

4.9 kernel fails to boot because it didn't have the mpt3sas module

This post is just asking what the purpose of console=hvc0 is.

Thanks,
Jerry
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Re: [CentOS-virt] What is the purpose setting console=hvc0 in the dom0 grub config?

[PJ Welsh]

On Tue, May 16, 2017 at 10:26 PM, Jerry  wrote:

> Howdy,
>
> I recently went through a frustrating experience trying to get Xen 4
> running on a CentOS 7 system.  After a fresh install, fully updating the
> system, rebooting, then trying to install Xen4CentOS it would fail to boot
> into the 4.9 kernel, sitting there with a blinking cursor indefinitely.
>
...

Check the BIOS to see if Hyperthreading is disabled. If so, enable it. I
had some Dell server (Dell R710s and R610s) that I finally figured out
would not boot like you describe when HT is off for some reason.
PJ
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Re: [CentOS-virt] What is the purpose setting console=hvc0 in the dom0 grub config?

[Mark L Sung]

Jerry,
Refer to console=hvc0 from (https://wiki.xen.org/wiki/Xen_FAQ_Console)which
is dedicated for domO after Xen kernel loaded, so if it hangs it means
somewhere the booting process with xen is not right.

Suggest you to close look at the dmsg or log for debugging. Hope that helps
and cheers.

Xlord

On Wed, May 17, 2017 at 11:26 AM, Jerry  wrote:

> Howdy,
>
> I recently went through a frustrating experience trying to get Xen 4
> running on a CentOS 7 system.  After a fresh install, fully updating the
> system, rebooting, then trying to install Xen4CentOS it would fail to boot
> into the 4.9 kernel, sitting there with a blinking cursor indefinitely.
>
> I thought it was a failure with grub, but it turns out this was set in the
> grub config:
>
> GRUB_CMDLINE_LINUX_XEN_REPLACE_DEFAULT="console=hvc0 ..."
>
> So the kernel was loading successfully, but it was failing boot properly
> (hanging because it couldn't find the / file system, but that's a different
> story). Boot messages were not being displayed on my console because of the
> console=hvc0 setting, hampering the troubleshooting process.
>
> What is the purpose of setting console=hvc0?  I removed it so I could
> trouble shoot this problem, but I didn't re-add it and the system booted
> fine, Xen is working.  Is there something that depends on this?
>
> I always disable "rhgb quiet" on a fresh install because I don't like boot
> messages being hidden from me, and now this other thing does it.  I like
> details, I need the details, don't hide them from me.
>
> Thanks,
> Jerry
>
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