Known issues

This article contains advisories and minor issues in Citrix Hypervisor 8.1 release and any workarounds that you can apply.


  • If your Citrix Hypervisor servers run on hardware containing Intel Sandy Bridge family CPUs, you might need to shutdown and restart your VMs as part of updating or upgrading to Citrix Hypervisor 8.1. For more information, see (CP-32460)

  • A pool’s CPU feature set can change while a VM is running. (For example, when a new host is added to an existing pool, or when the VM is migrated to a host in another pool.) When a pool’s CPU feature set changes, the VM continues to use the feature set which was applied when it was started. To update the VM to use the pool’s new feature set, you must power off and then start the VM. Rebooting the VM, for example, by clicking ‘Reboot’ in XenCenter, does not update the VM's feature set. (CA-188042)

  • The increase in the amount memory allocated to dom0 in Citrix Hypervisor 8.0 can mean there is slightly less memory available for running VMs. On some hardware, you might not be able to run the same number of VMs with Citrix Hypervisor 8.1 as you could on the same hardware with XenServer 7.6 and earlier versions. (CP-29627)

  • When attempting to use the serial console to connect to a Citrix Hypervisor server, the serial console might refuse to accept keyboard input. If you wait until after the console refreshes twice, the console then accepts keyboard input. (CA-311613)

  • When read caching is enabled it is significantly slower to read from the parent snapshot than from the leaf. This has been improved for sequential reads, but not for other types of read. (CA-329760)

  • If you have previously been hosting the Citrix License Server Virtual Appliance version 11.14 or earlier on your Citrix Hypervisor server, you are warned when upgrading or updating to Citrix Hypervisor 8.1 that this virtual appliance is a PV VM that is no longer supported.

  • On Citrix Hypervisor 8.1 systems that were updated from Citrix Hypervisor 8.0, after XAPI restart you might see errors from the following services:

    • usb-scan.service
    • storage-init.service
    • xapi-domains.service
    • mpathcount.service
    • create-guest-templates.service

    The errors in these services can present a number of different issues, for example, VMs that have been configured to start automatically might not start.

    This is caused by the xapi-wait-init-complete.service not being enabled. To work around this issue, you can run the following command at the dom0 command-line to enable the required services:

      systemctl preset-all --preset-mode=enable-only



  • When you start in parallel many VMs with AMD MxGPU devices attached, some VMs might fail with a VIDEO_TDR_FAILURE. This might be due to a hardware limitation. (CA-305555)

  • VMs with AMD MxGPU enabled are not supported with UEFI Secure Boot. (CP-32288)


  • On rare occasions, suspending or migrating a Linux VM with outstanding xenstore transactions can hang due to an issue in the VM’s Linux kernel. If your VM experiences this issue, force the VM to shut down and restart it. (CP-30551)

  • If you install Debian 10 (Buster) by using PXE network boot, do not add console=tty0 to the boot parameters. This parameter can cause issues with the installation process. Use only console=hvc0 in the boot parameters. (CA-329015)

  • Some minor versions of Ubuntu 18.04 (for example 18.04.2 and 18.04.3) use a HWE kernel by default that can experience issues when running the graphical console. To work around these issues, you can choose to run these minor versions of Ubuntu 18.04 with the GA kernel or to change some of the graphics settings. For more information, see CTX265663 - Ubuntu 18.04.2 VMs can fail to boot on Citrix Hypervisor. (XSI-527)

  • If you attempt to revert a VM to a scheduled VSS snapshot that was created with Citrix Hypervisor 8.0 or earlier, the VM does not boot. The boot fails with the following error: “This operation cannot be performed because the specified virtual disk could not be found”. This is because the VSS snapshot capability has been removed from Citrix Hypervisor 8.1. (CA-329435)

  • For domain-joined Windows 10 VMs (1903 and later) with the FireEye Agent installed, repeated successful RDP connections can cause the VM to freeze with 100% CPU usage in ntoskrnl.exe. You must perform a hard reboot on the VM to recover from this state. (CA-323760)

  • The guest UEFI boot capability provided in Citrix Hypervisor 8.0 was an experimental feature. Citrix Hypervisor 8.1 does not support migrating UEFI boot VMs created in Citrix Hypervisor 8.0 to Citrix Hypervisor 8.1. You must shutdown UEFI boot VMs before upgrading to Citrix Hypervisor 8.1. (CA-330871)

  • UEFI boot or UEFI Secure Boot VMs can report that they are I/O optimized, even if Citrix VM Tools are not installed. (CA-328093)

  • When UEFI-boot VMs start, they show a Tianocore logo. (CP-30146)

  • A VM reboot might be required before installation of the Citrix VM Tools provided with Citrix Hypervisor 8.1 succeeds. (CA-331215)

  • When installing Citrix VM Tools on a Windows VM from the guest-tools.iso, the installation might fail with the error message “Service ‘Citrix XenServer Windows Management Agent’ (XenSvc) could not be installed. Verify that you have sufficient privileges to install system services.” Work around this issue by uninstalling the Citrix VM Tools, rebooting the VM, and then installing the new tools. (CA-330751)

  • On rare occasions, when installing the latest version of the Citrix VM Tools on a Windows 10 VM, the VM might hang during installation and show a black screen. Force a reboot of the VM to get away from the black screen. You can then work around the issue by reinstalling the xennet Windows I/O driver on the VM. (CA-325026)


  • If you have previously upgraded your Citrix Hypervisor 8.0 installation from XenServer 6.5 or earlier, with virtual machines using the server’s “Local Storage” storage repository, or if a vendor utility partition is present on your disk, you are using a legacy disk layout. The legacy disk layout means the control domain has significantly less space available to it than the current layout (4GB vs 18GB)

    When attempting to apply the Citrix Hypervisor 8.1 update to the Citrix Hypervisor 8.0 installation, you receive the error message “the server does not have enough space”. This happens because installation of the Citrix Hypervisor 8.1 update requires sufficient free space to avoid filling the disk, which is not possible with the legacy layout.

    If you receive this error, you cannot update to Citrix Hypervisor 8.1, and you must perform a fresh installation instead. (CA-268846)

  • When updating from Citrix Hypervisor 8.0 to Citrix Hypervisor 8.1, you might see the following error: “Internal error: xenopsd internal error: Xenops_migrate.Remote_failed(“unmarshalling error message from remote”)”. TThis error is seen if viridian flags were modified for a Windows VM existing at the time of applying the hotfix XS80E003, but the VM was not shutdown and then restarted.

    To avoid this issue, before you try to update to Citrix Hypervisor 8.1, complete all of the steps in the “After installing this hotfix” section of the hotfix article for all Windows VMs hosted on a Citrix Hypervisor 8.0 server that has XS80E003 applied. (XSI-571)


  • Non-ASCII characters, for example, characters with accents, cannot be used in the host console. (CA-40845)

  • In a Windows VM with Citrix VM Tools installed, copy and paste of double-byte characters can fail if using the default desktop console in XenCenter. The pasted characters appear as question marks (?). To work around this issue, you can use the remote desktop console instead. (CA-281807)


  • If you use GFS2 SRs and have two servers in your clustered pool, your cluster can lose quorum and fence during upgrade. To avoid this situation, either remove or add a server from your cluster to ensure that you have either one or three servers in your pool during the upgrade process. (CA-313222)

  • If you are using a GFS2 SR, ensure that you enable storage multipathing for maximum resiliency. If storage multipathing is not enabled, file system block writes might not fully complete in a timely manner. (CA-312678)

  • If you use HPE 3PAR hardware for your storage repository and, with a previous release of XenServer, you use ALUA1 for your host persona, when you upgrade to Citrix Hypervisor 8.0 multipathing no longer works. To work around this issue, migrate your host persona to ALUA2. For more information, see

  • When running Reclaim Space on a thinly provisioned LUN with more than 2 TB of free space, the operation fails with an ioctl not supported error. (CA-332782)

  • If you attempt to enable multipage support on a VM that does not support this feature, you see the following error message: xen_blkfront: Unknown parameter 'max_ring_page_order'. If this causes your VM to drop into the dracut shell, you can recover the VM by following these steps:

    1. Run the following commands:

      rm /etc/modprobe.d/xen_blkfront.conf
      modprobe xen_blkfront
      lvm vgchange -a y
      ln -s /dev/mapper/*root /dev/root
    2. When the VM finishes booting, log in.

    3. Run the following commands in the VM shell:

      rm /etc/modprobe.d/xen_blkfront.conf
      dracut -f -v
    4. Reboot the VM.

vSwitch Controller

  • The vSwitch controller can experience a possible memory leak in the stunnel service. You might see the following message in the vSwitch Controller syslog: “Possible memory leak at…” (XSI-592)


  • Changing the font size or dpi on the computer on which XenCenter is running can result in the user interface appearing incorrectly. The default font size is 96 dpi; Windows 8 and Windows 10 refer to this font size as 100%. (CA-45514) (CAR-1940)

  • When XenCenter is installed on Windows Server 2008 SP2, it can fail to connect to a Citrix Hypervisor host with the message “Could not create SSL/TLS secure channel”. To resolve this issue, ensure that one of the following Windows Updates is installed on the Windows Server 2008 SP2 system: KB4056564 or KB4019276. For more information, see (CA-298456)

  • On Windows 10 (1903 and later) VMs, there can be a delay of a few minutes after installing the Citrix VM Tools before the Switch to Remote Desktop option is available for the VM in XenCenter. You can restart the toolstack to make this option appear immediately. (CA-322672)