Difference between revisions of "XenFAQ2"

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(Migrated to Xen_FAQ_DomU)
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If the drivers are installed correctly there should be a Xen device under 'System Devices' in device manager.
If the drivers are installed correctly there should be a Xen device under 'System Devices' in device manager.
== Domain0 ==
=== Why cannot I see all my RAM on my Dom0? ===
Domain 0 is a paravirt VM in reality, so the amount of ram you allocate to it is what you will see when using local tools like free, /proc/meminfo, top, etc.
To see the full system ram, you need to use the xm tools... and in this case, 'xm info' which will show you all the system resources, as opposed to the resources available to dom0.
Also, you have 16GB ram on the system... you probably already know this, but be aware that without a PAE enabled kernel (if you're using 32bit Xen) you'll only see 4GB of this. PAE will allow you to use up to 16, or maybe 32 (I don't remember what the upper limit for PAE enabled Xen is off the top of my head).
=== Is there any way of checking DomU´s I/O from Dom0? ===
iostat (Debian: sysstat-package)
=== Can I allocate one CPU to the Dom0 exclusively? ===
Add this to the kernel boot line - dom0_max_vcpus=1 & dom0_vcpus_pin
Edit /etc/xen/xend-config.sxp - set “(dom0-cpus 1)” Reboot Dom0
To try on an active system without a Reboot -
xm vcpu-set 0 1 xm vcpu-pin 0 0 0
=== Running xm info I see the following memory available; what does the free memory mean? ===
total_memory : 2046 free_memory : 5
Free_memory from "xm info" shows memory not allocated to any domain (inlcuding dom0). "free", "top" (or whatever) shows free memory on that particular domain (in your case, dom0). You can adjust memory allocation per domain using "xm mem-set".

Revision as of 17:45, 12 November 2011

Icon todo.png Needs Refactor

This document would benefit from being broken up into smaller documents alongside topics and merged with split up documents from XenFAQ

Icon todo.png Needs Review

Not quite clear how up-to-date these questions and answers are.

This document has been created from http://www.xen.org/files/Support/XenUsersCommonlyAskedQuestions.pdf as a life version. Also see XenFAQ: this page needs correcting and merging into XenFAQ

Guest Related Questions

Guest Conversion

How do I convert a Centos HVM Guest to a PV Guest?

Creating a Centos HVM domU with working PV drivers : http://pastebin.com/fb6fe631 Converting HVM guest to PV guest : http://pastebin.com/f6a5022bf

If you follow both parts correctly you should have a working PV domU. If anything goes wrong during conversion process, you should still be able to boot the previous HVM domU config if you select the non-xen kernel (second entry) from grub menu.list.

I have an Xen image that was built for a graphical console (VNC). Is there any way to change it to the non-graphical console (xen console)?

For HVM guest, you need to enable serial port on domU config file (example here: http://pastebin.com/fb6fe631), and setup domU to use serial port (ttyS0 on Linux) by modifying (for Linux domU) /boot/grub/menu.lst, /etc/inittab, and /etc/securetty.

If it's PV guest, you need to set up domU to use xen console (which is xvc0 on current xen version, hvc0 on pv_ops kernel). It's similar to setting up domU for serial console, you just need to change ttyS0 to hvc0. An example of domU setup that can use both xvc0 and vnc console is here : http://pastebin.com/f6a5022bf

How do I remove an active virtual machine?

xm shutdown or xm delete

How do I run xm console to a WindowsXP DomU?

You can't xm console to that (I'm not sure you can xm console to any hvm, but I know you can't to one that doesn't have a console).

I start a new DomainU (Guest) and some text scrolls by for launching the guest but then it just sits there with Continue and no actions takes place?

The console for this new DomainU is not properly available for you; fix this by adding xtra="xencons=tty" in the configuration file. This will bring up a login screen directly for your new DomainU.

One of our CentOS 5.3 randomly reboots, at different times of the day, and I can't see why it's doing it. I have looked through the logs, but don't see any thing in there that shows me why it has rebooted. How can I debug this?

The problem is that when the box panics, it stops syslogd, so you don't get the panic output in /var/log. The best way to fix this is to setup a logging serial console.


What are the GPLPV Drivers and where can I get them?

A collection of open source Window PV drivers that allow Windows to be para-virtualized. They are currently being implemented under the leadership of James Harper. More information on these drivers at:

How can I tell if the GPLPV Drivers are loaded correctly?

If the drivers are installed correctly there should be a Xen device under 'System Devices' in device manager.