Known issues

This article contains advisories and minor issues in the XenServer 8 release and any workarounds that you can apply.


  • When attempting to use the serial console to connect to a XenServer host, 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 slower to read from the parent snapshot than from the leaf. (CP-32853)

  • When attempting to log in to the dom0 console with an incorrect password, you receive the following error message: When trying to update a password, this return status indicates that the value provided as the current password is not correct. This error message is expected even though it relates to a password change, not a login. Try to log in with the correct password.


  • When NVIDIA T4 added in pass-through mode to a VM on some specific server hardware, that VM might not power on. (CA-360450)

Windows guests

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

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

  • On Windows VMs, when updating the xenbus driver to version, ensure that you complete both of the requested VM restarts. If both restarts are not completed, the VM might revert to emulated network adapters and use different settings, such as DHCP or different static IP addressing.

    To complete the second restart, you might be required to use a local account to log into the Windows VM. When you log in, you are prompted to restart.

    If you are unable to log in to the Windows VM after the first restart, you can use XenCenter to restart the VM and complete the xenbus driver installation. (CP-34181)

  • When you create a UEFI VM, the Windows installation requires a key press to start. If you do not press a key during the required period, the VM console switches to the UEFI shell.

    To work around this issue, you can restart the installation process in one of the following ways:

    • In the UEFI console, type the following commands.

    • Reboot the VM

    When the installation process restarts, watch the VM console for the installation prompt. When the prompt appears, press any key. (CA-333694)

  • When attempting to update a Windows 10 VM from 1909 to 20H2 or later, the update might fail with a blue screen showing the error: INACCESSIBLE BOOT DEVICE. (XSI-1075)

    To make it less likely that this failure occurs, you can take the following steps before attempting to update:

    1. Update the XenServer VM Tools for Windows on your VM to the latest version.
    2. Snapshot the VM.
    3. In the VM registry, delete the following values from the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\XENFILT\Parameters key: ActiveDeviceID, ActiveInstanceID, and ActiveLocationInformation
  • When creating a Windows VM from a template that is set to not automatically update its drivers, the created VM is incorrectly set to update its drivers. To work around this issue, run the following command: xe pool-param-set policy-no-vendor-device=true uuid=<pool-uuid>. This command ensures that future VMs created from the template are correctly set to not automatically update drivers. VMs that were previously generated from the template are not changed. (CA-371529)

  • vTPM operations performed by the user or by Windows in the background might fail in the following situations:

    • If the toolstack or the XenServer host crash before the operation is synchronized to the disk. Errors when writing to disk are ignored.
    • If the pool coordinator is not running or the toolstack is being restarted.

    In the case of this type of failure the vTPM returns an error to the operating system. Windows logs these errors to the System Event log.

Linux guests

  • You cannot use the Dynamic Memory Control (DMC) feature on Red Hat Enterprise Linux 8 VMs as Red Hat does not support memory ballooning with the Xen hypervisor. (CA-378797)

  • On some Linux VMs, especially busy systems with outstanding disk I/O, attempts to suspend or live migrate the VM might fail. To work around this issue, try increasing the value of /sys/power/pm_freeze_timeout, for example, to 300000. If this work around is not successful, you can upgrade the Linux kernel of the VM to the latest version. (CP-41455)

  • 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)

  • After a CentOS 8 VM with only one CPU is migrated to a new XenServer host, the first time a CPU-bound command runs on the VM, it times out. To work around this issue, you can assign more than one CPU to the VM and restart it. (XSI-864)

  • Some minor versions of Ubuntu 18.04 (for example 18.04.2 and 18.04.3) use an 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 XenServer. (XSI-527)


  • When upgrading to or installing XenServer 8 from an ISO located on an IIS server, the install or upgrade can fail and leave your hosts unable to restart. The remote console shows the GRUB error: “File ‘/boot/grub/i3860pc/normal.mod’ not found. Entering rescue mode”. This issue is caused by the IIS configuration causing package files to be missing. To work around this issue, ensure that double escaping is allowed on IIS before extracting the installation ISO on it. (XSI-1063)


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

  • In a Windows VM with XenServer VM Tools for Windows 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 hosts in your clustered pool, your cluster can lose quorum and fence during an upgrade. To avoid this situation, either add a host to or remove a host from your cluster. Ensure that you have either one or three hosts 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 a GFS2 SR has less than 500 MB of space on it, when you attempt to delete disks stored on this SR, the operation can fail. (CA-379589)

  • After removing an HBA LUN from a SAN, you might see log messages and I/O failures when querying Logical Volume information. To work around this issue, reboot the XenServer host. (XSI-984)

  • You cannot set or change the name of the tmpfs SR used by the PVS-Accelerator. When the type is tmpfs, the command xe sr-create disregards the value set for name-label and instead uses a fixed value. If you attempt to run the command xe sr-param-set to change the name of the tmpfs SR, you receive the error SCRIPT_MISSING.

  • When attempting to repair a connection to a read-only NFS v3 SR, the operation can fail on the first attempt with the error “SM has thrown a generic python exception”. To work around this issue, attempt the repair operation again. This issue is caused by a write operation in the initial repair attempt. (XSI-1374)

  • You cannot run more than 200 PVS-Accelerator-enabled VMs on a XenServer host. (CP-39386)


  • While the install update is in progress on a pool member, you might see the error “The operation could not be performed because getting updates is in progress.”. To resolve this error, you can retry the operation. (CA-381215)


  • 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)

  • It is not advisable to apply updates to the same pool from concurrent instances of XenCenter because this might disrupt the update process.

    If more than one instance of XenCenter is attempting to install multiple updates on a pool, a host might fail to install with the error: “The update has already been applied to this server. The server will be skipped.” This error causes the whole update process to stop. (CA-359814)

    To workaround this issue:

    1. Ensure that no other XenCenter instance is in the process of updating the pool
    2. Refresh the update list in the Notifications > Updates panel
    3. Start the update from the beginning
  • In XenCenter, when you attempt to import an OVF package or a disk image from a folder containing a hash character (#) in its name, the import fails with a null reference exception. (CA-368918)

  • In XenCenter, if you create a VM using an earlier version of XenServer and then import, migrate, or upgrade that VM to XenServer 8, the maximum number of vCPUs supported on that VM might be incorrectly displayed.

    This applies to:

    • VMs imported into XenServer 8 using OVF/OVA files created from a Citrix Hypervisor 8.2 (or earlier) host.
    • VMs migrated from a Citrix Hypervisor 8.2 (or earlier) host to a XenServer 8 host.
    • VMs created on a Citrix Hypervisor 8.2 (or earlier) host before upgrading it to XenServer 8.

    To workaround this issue, use the xe CLI or the management API to increase the number of vCPUs on your VM.

  • If you create a VM by importing a VHD file, you cannot increase the number of vCPUs above 16.

  • In pools with GFS2 SRs, using XenCenter to generate a server status report (SSR) can fail. To work around this issue, generate your SSRs by running the following command in the host console: xenserver-status-report. (CA-375900)

Known issues