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Citrix Hypervisor
8.2 CU1 XenServer 8
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Linux VMs

December 16, 2024
Contributed by: 
X X

When you want to create a Linux VM, create the VM using a template for the operating system you want to run on the VM. You can use a template that Citrix Hypervisor provides for your operating system, or one that you created previously. You can create the VM from either XenCenter or the CLI. This section focuses on using the CLI.

Note:

To create a VM of a newer minor update of a RHEL release than is supported for installation by Citrix Hypervisor, complete the following steps:

  • Install from the latest supported media
  • Use yum update to bring the VM up-to-date

This process also applies to RHEL derivatives such as CentOS and Oracle Linux.

We recommend that you install the Citrix VM Tools for Linux immediately after installing the operating system. For more information, see Install Citrix VM Tools for Linux.

The overview for creating a Linux VM is as following:

  1. Create the VM for your target operating system using XenCenter or the CLI.

  2. Install the operating system using vendor installation media.

  3. Install the Citrix VM Tools for Linux (recommended).

  4. Configure the correct time and time zone on the VM and VNC as you would in a normal non-virtual environment.

Citrix Hypervisor supports the installation of many Linux distributions as VMs.

Warning:

The Other install media template is for advanced users who want to attempt to install VMs running unsupported operating systems. Citrix Hypervisor has been tested running only the supported distributions and specific versions covered by the standard supplied templates. Any VMs installed using the Other install media template are not supported.

For information regarding specific Linux distributions, see Installation notes for Linux distributions.

Supported Linux distributions

For a list of supported Linux distributions, see Guest operating system support.

Other Linux distributions are not supported. However, distributions that use the same installation mechanism as Red Hat Enterprise Linux (for example, Fedora Core) might be successfully installed using the same template.

Create a Linux VM

This section includes procedures for creating a Linux VM by installing the OS from a physical CD/DVD or from a network-accessible ISO.

Create a Linux VM by using the xe CLI

This section shows the CLI procedure for creating a Linux VM by installing the OS from a physical CD/DVD or from a network-accessible ISO.

  1. Create a VM from the appropriate template. The UUID of the VM is returned:

    xe vm-install template=template-name new-name-label=vm-name
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  2. Add a virtual CD-ROM to the new VM:

    • If you are installing from a CD or DVD, get the name of the physical CD drive on the Citrix Hypervisor server:

       xe cd-list
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      The result of this command gives you something like SCSI 0:0:0:0 for the name-label field.

      Use this value parameter as the cd-name parameter:

       xe vm-cd-add vm=vm_name cd-name="host_cd_drive_name_label" device=3
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    • If you are installing from a network-accessible ISO, use the name of the ISO from the ISO library-label as the value for the cd-name parameter:

       xe vm-cd-add vm=vm_name cd-name="iso_name.iso" device=3
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  3. Insert the operating system installation CD into the CD drive on the Citrix Hypervisor server.

  4. Open a console to the VM with XenCenter or an SSH terminal and follow the steps to perform the OS installation.

  5. Start the VM. It boots straight into the operating system installer:

    xe vm-start uuid=UUID
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  6. Install the guest utilities and configure graphical display. For more information, see Install the Citrix VM Tools for Linux.

Create a Linux VM by using XenCenter

  1. On the XenCenter toolbar, click the New VM button to open the New VM wizard.

    The New VM wizard allows you to configure the new VM, adjusting various parameters for CPU, storage, and networking resources.

  2. Select a VM template and click Next.

    Each template contains the setup information that is required to create a VM with a specific guest operating system (OS), and with optimum storage. This list reflects the templates that Citrix Hypervisor currently supports.

    Note:

    If the OS that you are installing on your VM is compatible only with the original hardware, check the Copy host BIOS strings to VM box. For example, you might use this option for an OS installation CD that was packaged with a specific computer.

    After you first start a VM, you cannot change its BIOS strings. Ensure that the BIOS strings are correct before starting the VM for the first time.

    To copy BIOS strings using the CLI, see Install HVM VMs from Reseller Option Kit (BIOS-locked) Media. The option to set user-defined BIOS strings are not available for HVM VMs.

  3. Enter a name and an optional description for the new VM.

  4. Choose the source of the OS media to install on the new VM.

    Installing from a CD/DVD is the simplest option for getting started.

    1. Choose the default installation source option (DVD drive)
    2. Insert the disk into the DVD drive of the Citrix Hypervisor server

    Citrix Hypervisor also allows you to pull OS installation media from a range of sources, including a pre-existing ISO library.

    To attach a pre-existing ISO library, click New ISO library and indicate the location and type of the ISO library. You can then choose the specific operating system ISO media from the list.

  5. Select a home server for the VM.

    A home server is the server which provides the resources for a VM in a pool. When you nominate a home server for a VM, Citrix Hypervisor attempts to start the VM on that server. If this action is not possible, an alternate server within the same pool is selected automatically. To choose a home server, click Place the VM on this server and select a server from the list.

    Notes:

    • In WLB-enabled pools, the nominated home server isn’t used for starting, restarting, resuming, or migrating the VM. Instead, Workload Balancing nominates the best server for the VM by analyzing Citrix Hypervisor resource pool metrics and by recommending optimizations.
    • If a VM has one or more virtual GPUs assigned to it, the home server nomination doesn’t take effect. Instead, the server nomination is based on the virtual GPU placement policy set by the user.
    • During rolling pool upgrade, the home server is not considered when migrating the VM. Instead, the VM is migrated back to the server it was on before the upgrade. If you do not want to nominate a home server, click Don’t assign this VM a home server. The VM is started on any server with the necessary resources.

    Click Next to continue.

  6. Allocate processor and memory resources for the VM. Click Next to continue.

  7. Assign a virtual GPU.

    If vGPU is supported, the New VM wizard prompts you to assign a dedicated GPU or one or more virtual GPUs to the VM. This option enables the VM to use the processing power of the GPU. With this feature, you have better support for high-end 3D professional graphics applications such as CAD/CAM, GIS, and Medical Imaging applications.

  8. Allocate and configure storage for the new VM.

    Click Next to select the default allocation (24 GB) and configuration, or you might want to do the following extra configuration:

    • Change the name, description, or size of your virtual disk by clicking Edit.
    • Add a new virtual disk by selecting Add.

  9. Configure networking on the new VM.

    Click Next to select the default NIC and configurations, including an automatically created unique MAC address for each NIC. Alternatively, you might want to do the following extra configuration:

    • Change the physical network, MAC address, or Quality of Service (QoS) priority of the virtual disk by clicking Edit.
    • Add a new virtual NIC by selecting Add.

  10. Review settings, and then click Create Now to create the VM and return to the Search tab.

    An icon for your new VM appears under the host in the Resources pane.

    On the Resources pane, select the VM, and then click the Console tab to see the VM console.

  11. Follow the OS installation screens and make your selections.

  12. After the OS installation completes and the VM reboots, install the Citrix VM Tools for Linux.

Create a Linux VM by using PXE boot

You can use PXE boot to install the operating system of your Linux VM. This approach can be useful when you have to create many Linux VMs.

To install by using PXE boot, set up the following prerequisites in the network where your Linux VMs are located:

  • DHCP server that is configured to direct any PXE boot installation requests to the TFTP server
  • TFTP server that hosts the installation files for the Linux operating system

When creating the Linux VM, run the following commands:

  1. Create a VM from the appropriate template. The UUID of the VM is returned:

    xe vm-install template=template-name new-name-label=vm-name
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  2. Set the boot order to boot from the disk and then from the network:

    xe vm-param-set uuid=<UUID> HVM-boot-params:order=cn
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  3. Start the VM to begin the PXE boot installation:

    xe vm-start uuid=<UUID>
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  4. Install the guest utilities and configure graphical display. For more information, see Install the Citrix VM Tools for Linux.

For more information about using PXE boot to install Linux operating systems, see the operating system documentation:

Install Citrix VM Tools for Linux

Although all supported Linux distributions are natively paravirtualized (and don’t need special drivers for full performance), Citrix VM Tools for Linux provide a guest agent. This guest agent provides extra information about the VM to the host. Install the guest agent on each Linux VM to benefit from the following features:

  • View VM performance data in XenCenter.

    For example, the following memory performance values are visible in XenCenter only when the XenServer VM Tools are installed: “Used Memory”, “Disks”, Network” and “Address”.

  • In XenCenter, view the Linux guest operating system information.

  • In the XenCenter Networking tab, view the IP address of the VM.

  • Launch an SSH Console to the VM from XenCenter.

  • Adjust the number of vCPUs on a running Linux VM.

  • Enable Dynamic Memory Control (DMC).

    Note:

    You cannot use the Dynamic Memory Control (DMC) feature on Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Rocky Linux 8, Rocky Linux 9, or CentOS Stream 9 VMs as these operating systems do not support memory ballooning with the Xen hypervisor.

It is important to keep the Linux guest agent up-to-date as you upgrade your Citrix Hypervisor server. For more information, see Update Linux kernels and guest utilities.

Note:

Before installing the guest agent on a SUSE Linux Enterprise Desktop or Server 15 guest, ensure that insserv-compat-0.1-2.15.noarch.rpm is installed on the guest.

To install the Citrix VM Tools for Linux:

  1. Download the Citrix VM Tools for Linux file from the Citrix Hypervisor downloads page.

  2. Copy the LinuxGuestTools-xxx.tar.gz file to your Linux VM or to a shared drive that the Linux VM can access.

  3. Extract the contents of the tar file: tar -xzf LinuxGuestTools-xxx.tar.gz

  4. Run the installation script as the root user:

    /<extract-directory>/install.sh
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  5. If the kernel has been upgraded, or the VM was upgraded from a previous version, reboot the VM now.

Installation notes for Linux distributions

This following section lists vendor-specific, configuration information to consider before creating the specified Linux VMs.

For more detailed release notes on all distributions, see Linux VM Release Notes.

Red Hat Enterprise Linux* 7 (32-/64-bit)

The new template for these guests specifies 2 GB RAM. This amount of RAM is a requirement for a successful install of v7.4 and later. For v7.0 - v7.3, the template specifies 2 GB RAM, but as with previous versions of Citrix Hypervisor, 1 GB RAM is sufficient.

Note:

This information applies to both Red Hat and Red Hat derivatives.

Apt repositories (Debian)

For infrequent or one-off installations, it is reasonable to use a Debian mirror directly. However, if you intend to do several VM installations, we recommend that you use a caching proxy or local mirror. Either of the following tools can be installed into a VM.

  • Apt-cacher: An implementation of proxy server that keeps a local cache of packages
  • debmirror: A tool that creates a partial or full mirror of a Debian repository

Prepare to clone a Linux VM

Typically, when cloning a VM or a computer, unless you generalize the cloned image, attributes unique to that machine are duplicated in your environments. Some of the unique attributes that are duplicated when cloning are the IP address, SID, or MAC address.

As a result, Citrix Hypervisor automatically changes some virtual hardware parameters when you clone a Linux VM. When you copy the VM using XenCenter, XenCenter automatically changes the MAC address and IP address for you. If these interfaces are configured dynamically in your environment, you might not need to modify the cloned VM. However, if the interfaces are statically configured, you might need to modify their network configurations.

The VM may need to be customized to be made aware of these changes. For instructions for specific supported Linux distributions, see Linux VM Release Notes.

Machine name

A cloned VM is another computer, and like any new computer in a network, it must have a unique name within the network domain.

IP address

A cloned VM must have a unique IP address within the network domain it is part of. Generally, this requirement is not a problem when DHCP is used to assign addresses. When the VM boots, the DHCP server assigns it an IP address. If the cloned VM had a static IP address, the clone must be given an unused IP address before being booted.

MAC address

There are two situations when we recommend disabling MAC address rules before cloning:

  1. In some Linux distributions, the MAC address for the virtual network interface of a cloned VM is recorded in the network configuration files. However, when you clone a VM, XenCenter assigns the new cloned VM a different MAC address. As a result, when the new VM is started for the first time, the network does recognize the new VM and does not come up automatically.

  2. Some Linux distributions use udev rules to remember the MAC address of each network interface, and persist a name for that interface. This behavior is intended so that the same physical NIC always maps to the same ethn interface, which is useful with removable NICs (like laptops). However, this behavior is problematic in the context of VMs.

    For example, consider the behavior in the following case:

    1.  Configure two virtual NICs when installing a VM
1.  Shut down the VM
1.  Remove the first NIC

    When the VM reboots, XenCenter shows just one NIC, but calls it eth0. Meanwhile the VM is deliberately forcing this NIC to be eth1. The result is that networking does not work.

For VMs that use persistent names, disable these rules before cloning. If you do not want to turn off persistent names, you must reconfigure networking inside the VM (in the usual way). However, the information shown in XenCenter does not match the addresses actually in your network.

Update Linux kernels and guest utilities

The Linux guest utilities can be updated by rerunning the install.sh script from the Citrix VM Tools for Linux (see Install the Citrix VM Tools for Linux).

For yum-enabled distributions, CentOS and RHEL, xe-guest-utilities installs a yum configuration file to enable subsequent updates to be done using yum in the standard manner.

For Debian, /etc/apt/sources.list is populated to enable updates using apt by default.

When upgrading, we recommend that you always rerun install.sh. This script automatically determines if your VM needs any updates and installs if necessary.

Upgrade from PV to HVM guests

PV mode guests are not supported in Citrix Hypervisor 8.2. Before upgrading your server to Citrix Hypervisor 8.2, follow these steps to upgrade your existing PV Linux guests to supported versions.

  1. Upgrade the guest operating system to a version that is supported by Citrix Hypervisor. Perform the upgrade by using the mechanism provided by that Linux distribution.

    After this step, the upgraded guest is still PV mode, which is not supported and has known issues.

  2. Use the pv2hvm script to convert the newly upgraded guest to the supported HVM mode.

    On the Citrix Hypervisor server, open a local shell, log on as root, and enter the following command:

    /opt/xensource/bin/pv2hvm vm_name
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    Or

    /opt/xensource/bin/pv2hvm vm_uuid
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  3. Restart the VM to complete the process.

Linux VM release notes

Most modern Linux distributions support Xen paravirtualization directly, but have different installation mechanisms and some kernel limitations.

RHEL graphical install support

To use the graphical installer, in XenCenter step through the New VM wizard. In the Installation Media page, in the Advanced OS boot parameters section, add vnc to the list parameters:

graphical utf8 vnc
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A screenshot of the New VM wizard. On the Installation Media page, the value `graphical utf8 vnc` is entered in the Advanced OS Boot Parameters field.

You are prompted to provide networking configuration for the new VM to enable VNC communication. Work through the remainder of the New VM wizard. When the wizard completes, in the Infrastructure view, select the VM, and click Console to view a console session of the VM. At this point, it uses the standard installer. The VM installation initially starts in text mode, and may request network configuration. Once provided, the Switch to Graphical Console button is displayed in the top right corner of the XenCenter window.

Red Hat Enterprise Linux 7 (deprecated)

After migrating or suspending the VM, RHEL 7 guests might freeze during resume. For more information, see Red Hat issue 1141249.

Red Hat Enterprise Linux 8

You cannot use the Dynamic Memory Control (DMC) feature on Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Rocky Linux 8, Rocky Linux 9, or CentOS Stream 9 VMs as these operating systems do not support memory ballooning with the Xen hypervisor.

Red Hat Enterprise Linux 9

You cannot use the Dynamic Memory Control (DMC) feature on Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Rocky Linux 8, Rocky Linux 9, or CentOS Stream 9 VMs as these operating systems do not support memory ballooning with the Xen hypervisor.

CentOS 7 (deprecated)

For the list of CentOS 7 release notes, see Red Hat Enterprise Linux 7.

CentOS Stream 9

If you attempt to shut down a CentOS Stream 9 VM by using XenCenter or the xe CLI, the shutdown process pauses and times out after 1200s. This behaviour is caused by a kernel issue in kernel-5.14.0-362.el9.

The following workarounds are available:

  • To work around a single instance of the issue, you can shut down the VM from inside the guest operating system.

  • To prevent the issue from occuring for your VM, downgrade your VM to use kernel-5.14.0-354.el9 by running the following commands in the VM:

     # yum install kernel-5.14.0-354.el9
 # grubby --set-default /boot/vmlinuz-5.14.0-354.el9.x86_64

You cannot use the Dynamic Memory Control (DMC) feature on Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Rocky Linux 8, Rocky Linux 9, or CentOS Stream 9 VMs as these operating systems do not support memory ballooning with the Xen hypervisor.

Rocky 9 and CentOS Stream 9 VMs require that the host has a CPU compatible with x86-64-v2 instruction set or higher. For more information, see https://access.redhat.com/solutions/6833751.

Oracle Linux 7

For the list of Oracle Linux 7 release notes, see Red Hat Enterprise Linux 7.

Scientific Linux 7 (deprecated)

For the list of Scientific Linux 7 release notes, see Red Hat Enterprise Linux 7.

Rocky Linux 9

You cannot use the Dynamic Memory Control (DMC) feature on Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Rocky Linux 8, Rocky Linux 9, or CentOS Stream 9 VMs as these operating systems do not support memory ballooning with the Xen hypervisor.

Rocky 9 and CentOS Stream 9 VMs require that the host has a CPU compatible with x86-64-v2 instruction set or higher. For more information, see https://access.redhat.com/solutions/6833751.

Debian 10 (deprecated)

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. For more information, see Debian issues 944106 and 944125.

Debian 11

When installing Debian 11 32-bit on a VM using a QEMU emulated network device, the installation might fail. This issue is caused by the Xen PV drivers being missing from the installer kernel.. For more information, see https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=818481.

This issue is not present in the 64-bit Debian 11.

Debian 12

Debian 12 (Bookworm) does not support GPU passthrough or vGPUs.

SUSE Linux Enterprise 12

Prepare a SLES guest for cloning

Note:

Before you prepare a SLES guest for cloning, ensure that you clear the udev configuration for network devices as follows:

cat< /dev/null > /etc/udev/rules.d/30-net_persistent_names.rules

To prepare a SLES guest for cloning:

  1. Open the file /etc/sysconfig/network/config

  2. Edit the line that reads:

    FORCE_PERSISTENT_NAMES=yes
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    To

    FORCE_PERSISTENT_NAMES=no
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  3. Save the changes and reboot the VM.

For more information, see Prepare to Clone a Linux VM.

Ubuntu 24.04

Due to a known issue with Mesa drivers on Ubuntu 24.04, after installing an Ubuntu 24.04 (desktop) VM on an AMD platform host with the Wayland protocol enabled by default, you might experience repeated re-login prompts.

We recommend to work around this issue by disabling Wayland or upgrading your Mesa drivers:

  • Disable Wayland

    Open a command prompt and run the following command:

     sudo nano /etc/gdm3/custom.conf
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    Set the following value to disable Wayland:

     WaylandEnable=false
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    Restart the VM to complete the process.

  • Update your Mesa drivers

    Run the following commands:

     sudo add-apt-repository ppa:kisak/kisak-mesa
 sudo apt update
 sudo apt upgrade
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    Restart the VM to complete the process.

Linux VMs
December 16, 2024
Contributed by: 
X X
December 16, 2024
Contributed by: 
X X

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