Tag Archives: citrix

Screen Flicker in Internet Explorer within XenDesktop Sessions



When scrolling and doing mouse-overs in Internet Explorer (IE) frames or pages, within a Windows XP XenDesktop session, screen flicker is seen.



You need to enable the following key in the registry:

HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main

Value Name: "Force Offscreen Composition"

Data Type: DWORD

Value: 1

The following registry tweak forces off screen composition within Microsoft Internet Explorer 5 and above. This tweak will prevent against screen flicker when you view a web page that contains animated content.

For more information, see the following Citrix article:




Memory Recommendations for Citrix Provisioning Servers (PVS)



How much memory should I install in my Provisioning Servers?


The basic formula Citrix recommends is this:

2 GB + (2 GB * #vDisks)

For more detailed information regarding memory allocation & recommendations, see the document "Advanced Memory and Storage Considerations for Provisioning Services"


Recommended Reading:



Virtual Machine in XenServer Will Not Shut Down or Start; Stuck/Frozen Starting/Stopping


If you’ve worked with XenServer for any length of time, you have no doubt experienced having a VM turn “orange” or “amber” or otherwise become unmanageable.  Here are couple of similar problem scenarios and solutions that might help.


Problem Scenario #1:

You notice that a VM has numerous lifecycle events on a XenServer.  It has continuously attempted to shutdown, but remains in the green/on state.  The VM will not display a console, or POST information.   Manual shutdowns in XenCenter do not work (Shutdown or Force Shutdown).


You may have success trying some of these ideas, or it may take a combination of these to obtain control of the stuck VM.

  1. Start by trying an ‘xe-toolstack-restart’ on the pool master server.   This is the easiest fix, and will work a majority of the time.   You will lose connection to your pool momentarily.  If this doesn't work, go onto the next steps listed below.
  2. If this is a XenDesktop hosted VM, put the VM in maintenance mode, if you cannot force a Start/Shutdown from the DDC
  3. From the XenServer console, try the following command to force a shutdown:  ‘xe vm-shutdown –force vm=VMNAME’.  If VM does not shutdown with this command, proceed to next step
  4. In XenCenter, once the above two items are done, attempt to "Reboot" the VM. It may restart now.

Related Issue:

I experienced a similar issue where all members were down in a XenServer pool, but the pool Master remained up and functional.  The 'toolstack' processes were not running on pool members. An ‘xe-toolstack-restart’ was required on each pool member XenServer before the server would appear functional and participate in the XenServer Pool.


Problem Scenario #2:

This is the most common scenario you will see.  A virtual machine will go into an “amber” or “orange” state and you are unable to shutdown, reboot, or even forcefully reset the VM.



  1. Find the UUID of the hung VM.
    You can do this via the command line with ‘xe vm-list’ or via XenCenter.
  2. Find the Domain ID of the hung VM.
    Run ‘list_domains’ from the command line, and match the UUID with the ID number



    id |                                 uuid |  state
    0  | 2fe455fe-3185-4abc-bff6-a3e9a04680b0 |    R
    47 | 267227f3-a59e-dafe-b183-82210cf51ec4 |    B
    59 | 298817fb-8a3e-7501-11e0-045a8aa860ff |    B
    60 | 46e3d5aa-2f02-dfdc-b053-9a8ac56ec5d1 |    B
    61 | 16cf3204-eb17-5a12-e8d0-c72087bda690 |    B
    62 | 1f9053b5-c6ca-40bb-504e-3017c37e7281 |    H
    63 | ddaec491-097a-e271-362b-f2f985e26e4a |    R
    65 | 55f3b225-4f65-d1ea-aa19-add44c5acce7 |    B
    66 | 7adef6fd-9171-5426-b333-6fb1b57b8e60 |    B H
    67 | 6046dc13-f70b-8398-56fb-069c22440a7c |    B
    68 | f201cd94-a501-00c2-d21e-8c2f03ea167b |    B H

  3. Run destroy_domain on the Domain ID.


    # /opt/xensource/debug/destroy_domain -domid 62

  4. The VM will still show itself as running, so now, we need to reboot it.


    # xe vm-reboot name-label='name of the VM' –force

  5. The VM is now rebooted, and you can bring it up as if you had just pulled the plug.  That is, check for some disk corruption, etc.






XenServer NIC Status Shows "Disconnected" in XenCenter Despite Known Physically Active/Connected State


When viewing a XenCenter host's NICs in the NIC tab, you may notice that some network interface cards display themselves as "Disconnected". You believe these interfaces are indeed connected to the physical network.  What to do?


1) Double check physical network connection, ensure physical connection/link at the switch level – ensure this is not a bad patch cable, or physical cabling issue

2) You can easily view Ethernet interfaces in XSconsole to verify which interfaces are listed as "disconnected" eg. "eth4", "eth1", etc.

3) At the XenServer command shell, run 'xe pif-list' to display a list of pifs and see if the related "eth" interfaces are listed as connected=false.

4) Obtain the UUID from the above output and run the following command 'xe pif-plug uuid=<UUID>' (inserting the UUID you have obtained from the above list).  You may find several entries for the above interfaces – try each one until the pif-plug works. This should forcefully re-attach the interface.  Once done, check back in XenCenter and you should see the Ethernet interface correctly reporting as "Connected".