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Re: [Xen-devel] Question: Redirect guest kernel's message via serial port to a file on dom0

2015-08-25 3:42 GMT-04:00 Andrew Cooper <andrew.cooper3@xxxxxxxxxx>:
> On 25/08/2015 03:48, Meng Xu wrote:
>> Hi Andrew,
>> Thank you so much for your suggestion! I tried but have some questions.
>> 2015-08-24 4:10 GMT-04:00 Andrew Cooper <andrew.cooper3@xxxxxxxxxx>:
>>> On 24/08/2015 04:01, Meng Xu wrote:
>>> Hi,
>>> I'm trying to use a PV guest VM on Xen to help debug Linux.
>>> I was using VirtualBox to help debug Linux kernel by redirecting the output 
>>> of the serial port of the VM to a file in the host. I can do it in 
>>> VirtualBox.
>>> [Why do I want to achieve this?]
>>> It is much faster to reboot a VM than rebooting the physical machine.
>>> I don't need another machine to physically connect to the serial port of 
>>> the development machine.
>>> I want to use Xen for as many things as possible. ;-)
>>> I tried to google a tutorial or manual about how to configure it, but 
>>> didn't find any. :-(
>>> In my understanding, I need to do the following things:
>>> 1) I need to add a line (something like "serial=") in the guest's 
>>> configuration file to specify the serial port device to the VM;
>>> 2) I need some configuration to redirect the output of the serial device to 
>>> a file in domU;
>>> 3) After that, I can configure the kernel command line in the VM to dump 
>>> the kernel message via the serial port of the VM. (I know how to do this 
>>> step.)
>>> Did anyone have tried this before and have some configuration I can refer 
>>> to? or
>>> Could anyone give me some references that describes how to configure the 
>>> above three steps?
>>> I really appreciate any help or suggestion or comment.
>>> Configure xenconsoled to log guest consoles to file "--log=guest" at which 
>>> point anything sent to hvc0 will be logged to files in 
>>> /var/log/xen/guest/console (configurable with "--log-dir=")
>> I set "XENCONSOLED_TRACE=guest" under /etc/default/xencommons ,
>> because in /etc/init.d/xencommons, it has: test -z
>> So I think this is what you mean by "--log=guest"; After I set this
>> variable and restart the xencommons by "service xencommons restart" on
>> dom0 (Ubuntu 12.04LTS), I still couldn't find the file in
>> /var/log/xen/guest/console when I reboot the VM.
>> Actually, "find /var -name console" returns no result.
>> **My question is:**
>> Is there anything else I need to configure to get the
>> /var/log/xen/guest/console?
>> I don't see the folder under /var/log/xen. :-(
> You probably need to mkdir it then, or extend the args list with
> --log-dir=/var/log/xen

I tried both, but neither of them works. :-(

I'm wondering if anyone has some document about how to do this?
If there is some document about how to debug this configuration issue,
it could also be helpful...
But I didn't find it after googling and trying for 2 hours...:-(

Below is the detail of what I tried:

I tried to mkdir /var/log/xen/guest and restart the xencommons by
"service xencommons restart", I still didn't see the console file.
I create the console file under /var/log/xen/guest, there is nothing
inside console when I reboot the VM.

I also tried to specify --log-dir=/var/log/xen by changing the line 98
at /etc/init.d/xencommons to
--log=$XENCONSOLED_TRACE --log-dir=/var/log/xen""
I output the $XENCONSOLED_ARGS to confirm that its value is
--log=guest --log-dir=/var/log/xen.

Thank you very much!



Meng Xu
PhD Student in Computer and Information Science
University of Pennsylvania

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