VMware ESXi and vSphere Cluster Management

Install a Guest Operating System in a VMware ESXi Virtual Machine

Learn how to upload an operating system ISO to an ESXi-accessible datastore, attach it to a VM, boot from it, complete installation, and validate VMware Tools and guest networking.

A newly created virtual machine (VM) provides virtual hardware such as a processor, memory, virtual disk, network adapter, and CD/DVD device. It does not yet have a usable operating system. Installing the guest operating system turns that empty virtual computer into a functional server or workstation.

This process is similar to preparing a physical computer with an empty disk: you need installation media, you boot from that media, and you install the operating system onto the computer's disk.

Key Terms

• Guest operating system: The operating system installed and running inside a VM. Windows Server and Linux are examples.
• Virtual machine: A software-defined computer with virtual CPU, memory, storage, networking, and other devices.
• ESXi host: The VMware hypervisor server that runs VMs. The guest OS is separate from the ESXi host operating environment.
• vCenter Server: VMware management software used to centrally manage ESXi hosts and VMs.
• vSphere Client: The browser-based interface used to administer vCenter-managed infrastructure.
• Datastore: Storage presented to ESXi for VM files, ISO images, templates, and related data.
• ISO image: A disk-image file containing bootable operating system installation media.
• Virtual CD/DVD drive: A VM hardware device that can use an ISO file or, where supported, physical media.
• Remote console: An interactive screen and keyboard session for observing the VM boot process and operating the installer.

Prerequisites

• Access to vCenter Server through the vSphere Client or the applicable current vSphere management interface.
• An existing VM with a virtual disk, suitable firmware, and enough CPU and memory for the chosen operating system.
• A supported and properly licensed operating system ISO from a trusted vendor or approved internal software repository.
• A datastore with enough free space for the ISO and access from the ESXi host that will run the VM.
• Permission to edit VM settings, browse the datastore, power on the VM, and open its remote console.

If the VM has not been created yet, review adding virtual hardware to a VM and your organization's VM creation procedure first.

Choose Installation Media

An ISO image is the standard installation source for a VM. It behaves like a bootable optical disc, but it avoids handling physical media and is easy to reuse for multiple installations.

Obtain the ISO from a trusted operating-system vendor or an approved internal repository. Check the vendor's checksum when one is provided, particularly for production systems. Do not use an image whose source or integrity is uncertain.

Prepare and Store the ISO

1. Identify the ESXi host that will run the VM and the datastore it can access.
2. Confirm that the datastore has enough free capacity for the ISO and normal VM operation.
3. Upload the ISO to the datastore, or use an ISO that is already stored there.
4. Verify the filename, operating system edition, release, architecture, and checksum if available.
5. Confirm that the target host can see the datastore and that your vCenter permissions allow you to browse and use the file.

Shared storage is preferable when the VM may move between hosts. An ISO stored only on host-local storage can become unavailable after a migration or host change if the destination host cannot access that storage.

Datastore layout and access depend on the storage type. For related storage administration, see datastores in vSAN and access controls in NFS.

Attach the ISO to the VM

1. Sign in to vCenter Server using the vSphere Client or current equivalent.
2. Open Hosts and Clusters from the inventory view.
3. Locate and select the target VM.
4. Open Edit Settings.
5. Expand CD/DVD Drive 1, or select the VM's available virtual CD/DVD drive.
6. Set the backing source to Datastore ISO File.
7. Browse the datastore and select the intended operating system ISO.
8. Select Connect at power on. This setting attaches the virtual device automatically when the VM starts.
9. Save the VM hardware configuration.

VM settings: Edit Settings -> CD/DVD Drive 1 -> Datastore ISO File -> Select ISO -> Connect at power on

Check the selected path carefully. A VM can have multiple CD/DVD devices, and selecting the wrong device or an older ISO can cause the VM to boot into an unintended installer.

Boot from the Installation ISO

1. Power on the VM.
2. Open the VM remote console immediately so you can observe firmware and installer activity.
3. Confirm that the VM detects the mounted ISO and begins loading the operating system installer.
4. If a boot prompt appears, choose the option to boot from the CD/DVD device.

The VM firmware follows a boot order, which is the sequence used to try virtual devices. If the virtual disk is empty, the firmware should continue to the ISO, but an incorrect boot order, a disconnected device, or a non-bootable ISO can prevent installation from starting.

Some operating systems require a particular firmware type, such as BIOS or UEFI. Select the firmware and virtual hardware recommended for the operating system before installation when possible. Changing firmware after installation can make an existing installation unbootable.

Complete the Guest Operating System Installer

Use the remote console to work through the vendor-specific installer. The exact screens differ between operating systems, but the main decisions are similar.

• Select the language, locale, keyboard layout, and time zone.
• Choose the VM's intended virtual disk as the installation destination.
• Configure the storage layout or partitions. Confirm the disk identity before selecting an option that erases data.
• Set the hostname, administrator or root credentials, and any required local users.
• Configure networking when the installer supports it, or plan to configure it after the first boot.
• Apply organization-specific security, partitioning, naming, and licensing requirements.
• Allow the installer to copy files and reboot when it reports that installation is complete.

Example: Windows Server Installation

1. Upload the Windows Server ISO to a datastore accessible to the target ESXi host.
2. Open the target VM's settings and configure its CD/DVD drive to use that datastore ISO.
3. Enable Connect at power on, save the settings, power on the VM, and open the console.
4. In Windows Setup, select the language and keyboard options, then choose the appropriate Windows Server edition and installation type.
5. Select the VM's virtual disk as the destination and complete the installation.
6. Set the administrator password and initial hostname and network configuration according to local standards.
7. Install VMware Tools, disconnect the ISO, and reboot.
8. Verify that Windows starts from the installed virtual disk rather than returning to Windows Setup.

Example: Linux Server Installation

1. Place a supported Linux distribution ISO on an accessible datastore.
2. Attach the ISO to the VM's virtual CD/DVD drive and connect it at power on.
3. Boot the VM and use the console to start the Linux installer.
4. Configure locale, keyboard, time zone, disk partitioning, users, hostname, and network settings.
5. Install the system on the intended virtual disk and reboot when prompted.
6. Disconnect the ISO so the VM boots from the installed system.
7. Install open-vm-tools or the VMware-supported tools package for the selected distribution, using the distribution's supported package-management method.

Disconnect the ISO After Installation

After the first successful installation reboot, disconnect or unmount the ISO. In the VM hardware settings, clear the CD/DVD connection or change the backing so that the device is not connected at power on. You can also disconnect the device from the running VM when the guest no longer needs it.

Leaving the ISO connected can cause the VM to start the installer again on the next reboot. If the installer keeps appearing, disconnect the ISO and verify that the virtual hard disk is ahead of the CD/DVD device in the boot order.

Install VMware Tools and Finish Guest Configuration

VMware Tools is guest-side software that improves integration between the operating system and the virtualization platform. Depending on the guest OS and package, it can provide:

• Improved display behavior and mouse interaction.
• Time synchronization between the guest and virtualization platform.
• Graceful guest shutdown and restart support.
• Improved network and storage drivers where applicable.
• Guest information reporting, including the guest IP address and tools status.

For Linux distributions, open-vm-tools is commonly the supported choice. For Windows and other supported guests, use the VMware Tools package and installation method appropriate to that operating system. Confirm that the service is running after installation.

Then apply current guest operating system updates, activate licensing where required, configure the network, and apply your organization's security baseline. A baseline snapshot may be appropriate before a controlled change, but a snapshot is not a backup and should not be retained as a substitute for a backup strategy.

Guest OS Installation Workflow

Validate the Installation

Troubleshooting

The VM does not boot into the installer

• Verify that the CD/DVD drive uses the intended datastore ISO.
• Confirm that the device is connected while the VM is powered on.
• Review the VM firmware boot order. The virtual disk or network device may be ahead of the CD/DVD drive.
• Check that the ISO is bootable and was not corrupted. Validate its checksum or test a known-good image.

The ISO cannot be selected or is unavailable

• Confirm that the ISO was uploaded to the datastore and that the filename and path are correct.
• Check that the datastore is mounted and accessible by the ESXi host running the VM.
• If the VM moved to another host, verify that the new host can access the ISO storage. Shared storage avoids this host-local dependency.
• Check vCenter permissions, datastore health, and host connectivity.

The VM repeatedly starts the installer

• Disconnect the CD/DVD device or clear its ISO backing after installation.
• Confirm that Connect at power on is disabled for the installation media.
• Reboot and verify that the virtual hard disk is selected as the boot device.

The guest has poor console responsiveness or limited integration

• Check whether VMware Tools is installed and running.
• Install or upgrade VMware Tools using the guest OS's supported method.
• For Linux, confirm that the supported open-vm-tools package and its service are installed.
• Restart the guest or affected services when required, then check the tools status in vSphere.

The installer cannot see the virtual disk or network adapter

• Confirm that the guest OS supports the selected VM hardware version, storage controller, and virtual network adapter.
• Review the operating system's hardware requirements for CPU, memory, firmware, and disk capacity.
• Provide vendor-required storage or network drivers during installation if applicable.
• Check that the VM has the expected virtual devices and that they are connected.

Exam-Relevant Notes

• The guest OS runs inside the VM; it is not the same as the ESXi host operating environment.
• An ISO must be accessible to the ESXi host that runs the VM, not merely present on the administrator's local computer.
• Connect at power on controls whether the virtual CD/DVD device is attached automatically at startup.
• A datastore ISO is usually more reliable and repeatable than physical media.
• Shared datastore storage is important when a VM can run on multiple ESXi hosts.
• Disconnect installation media after setup so firmware boots from the installed virtual disk.
• VMware Tools improves guest integration, but snapshots are not backups.

For broader administration practice, see the VMware ESXi online course, adding an ESXi host to vCenter inventory, and assigning permissions.