VMware ESXi and vSphere Cluster Management

Install a Guest Operating System on a VMware ESXi Virtual Machine

Learn how to mount a datastore ISO in vSphere, boot a VMware ESXi virtual machine, install its guest OS, and complete post-installation validation.

A newly created virtual machine (VM) contains virtual hardware such as virtual CPUs, memory, a virtual disk, a network adapter, and possibly a virtual CD/DVD drive. It normally does not contain an installed operating system. This lesson explains how to install a guest operating system from an ISO stored on an ESXi-accessible datastore.

A guest operating system is the operating system installed and running inside a VM. ESXi is VMware's bare-metal hypervisor: it runs on the physical server and provides virtual hardware to VMs. The guest OS is separate from the ESXi host operating environment. Installing a guest OS in a VM is similar to installing an OS on a physical computer, except the computer's hardware is software-defined.

Key terms

Virtual machine: A software-defined computer with virtual hardware that runs on a hypervisor.
vCenter Server: VMware's centralized platform for administering inventory, hosts, and virtual machines.
vSphere Web Client: The browser-based interface used to manage VM settings and open VM consoles.
Datastore: Storage presented to ESXi for VM files, ISO images, and related infrastructure files.
ISO image: One file containing the contents of optical installation media.
Virtual CD/DVD drive: A VM hardware device that can be connected to an ISO or physical optical media.
VM console: Interactive screen and keyboard access to a VM, similar to using a physical system console.
Boot order: The sequence in which the VM firmware tries available bootable devices.

Choose installation media

The installer can be supplied through an ISO image, physical CD/DVD media, or another virtual-media method supported by the VMware environment. For routine ESXi administration, a datastore ISO file is usually the simplest choice. The ISO is uploaded once to storage and can then be mounted by an authorized VM.

Media source	Typical use case	Benefits	Limitations
Datastore ISO file	Normal server and desktop VM deployment	Centralized, reusable, and accessible without a local optical drive	Requires datastore space, permissions, and host access to the datastore
Client or local device, where supported	One-time installation from an administrator workstation	Useful when an ISO is not yet on a datastore	May be slower or dependent on the browser session and management client
Physical host CD/DVD device, where supported	Legacy media or environments that require physical discs	Uses an available physical disc	Requires compatible host hardware, a disc, and appropriate device access

The ISO must be reachable by the ESXi host that will run the VM. A file visible on an administrator's computer is not automatically visible to ESXi. Shared storage is convenient when the VM can move between hosts, while host-local storage is suitable only when the VM remains on a host that can access it.

Prepare the ISO and the virtual machine

Obtain the intended operating system ISO from a trusted, approved source. Confirm its edition, version, architecture, licensing terms, and any integrity information provided by the publisher.
Identify the VM and the ESXi host on which it will run. Confirm that the selected guest OS is supported by the VM hardware version and VMware environment.
Verify that the VM has an empty or appropriately sized virtual disk. The installer needs a target disk unless the OS is being installed for a special diskless or network-boot design.
Upload or copy the ISO into a datastore accessible to the target host. Use a clearly named folder so the file can be found later.
Browse the datastore before editing VM settings. Confirm the upload completed, the file path is correct, and the datastore has enough free space.

Attach a datastore ISO to the virtual CD/DVD drive

Sign in to the vSphere Web Client and open the inventory view.
Select the target VM under the relevant host or cluster.
Open the VM actions menu and choose Edit Settings.
Locate the existing Virtual CD/DVD Drive hardware entry. If the VM has no such device, add a virtual CD/DVD drive if your VM configuration and permissions allow it.
Set the device backing or media source to Datastore ISO File.
Choose the datastore browser control, select the datastore, browse to the intended folder, select the ISO, and confirm the selection.
Enable Connect At Power On. This causes the virtual optical drive to connect automatically when the VM starts.
Save the settings.

Merely having a CD/DVD device present does not provide installation media. The device must have an ISO or another media source selected, and it must be connected. The connection can be made manually while the VM is running or automatically through Connect At Power On.

Virtual CD/DVD drive backing: Datastore ISO File
Media: /path/to/approved-operating-system.iso
Connect At Power On: Enabled

Boot the VM into the installer

Power on the VM.
Open the VM's console from the vSphere Web Client. The console provides the keyboard and display interaction needed by the firmware and installer.
Watch the startup screen. Some installers boot immediately from the connected ISO; others display a prompt such as a request to press a key to boot from the virtual optical drive.
Respond to the boot prompt if it appears.

If the VM starts from an empty virtual disk instead, the firmware may be prioritizing the hard disk over the virtual optical drive. Confirm that the CD/DVD device is connected, then use the VM's boot menu or firmware setup to select the virtual optical drive temporarily. If necessary, adjust the boot order in the VM's firmware settings.

Complete the guest operating system installation

The exact installer screens depend on the operating system and its edition. Follow the vendor's installation guidance, while paying particular attention to these common decisions:

Choose the language, locale, keyboard layout, and time zone.
Select the correct edition and accept licensing terms when required.
Select the virtual disk intended for the guest OS. Verify its size and identity before creating partitions or allowing automatic disk changes.
Choose automatic partitioning or create partitions manually according to the system design. Do not select a datastore or the ESXi host disk; those are not guest installation targets.
Create administrator or root credentials according to organizational policy. Prefer strong, unique credentials and use separate administrative accounts where supported.
Configure networking when requested, including hostname, IP addressing, DNS, gateway, and domain or directory membership.
Apply initial updates and security settings when the installer or first-run wizard provides that option.

The VM may reboot one or more times during installation. A reboot is expected, but the VM must eventually boot from the newly installed virtual disk rather than restarting the installer.

Guest OS installation workflow

Stage	Administrator action	vSphere location or setting	Expected result
Prepare ISO	Obtain approved media and upload it to accessible datastore storage	Datastore browser or datastore file management	ISO is present and readable by the target host
Select datastore ISO file	Choose the VM's virtual CD/DVD drive and browse to the ISO	VM Edit Settings, Virtual CD/DVD Drive	Virtual optical media points to the intended ISO
Enable connection at power-on	Enable automatic device connection	Virtual CD/DVD Drive, Connect At Power On	ISO is connected when the VM starts
Power on VM	Start the VM	VM actions, Power On	VM firmware begins its boot sequence
Open console	Open the interactive display and respond to boot prompts	VM actions, Open Console	Installer interface is visible
Install guest OS	Choose language, disk, partitions, credentials, licensing, network, and updates	Guest OS installer in the VM console	Operating system is installed on the virtual disk
Disconnect installation media	Disconnect the ISO or disable automatic connection	VM Edit Settings, Virtual CD/DVD Drive	Future boots do not return to the installer
Install VMware Tools	Install guest integration components after the base OS works	VM actions and guest OS package or installer tools	Improved device support, performance, time synchronization, and manageability

Disconnect the ISO after installation

After the guest completes installation and successfully starts from its virtual disk, disconnect the installation media. Edit the VM settings and either clear the ISO selection, disconnect the virtual CD/DVD device, or disable Connect At Power On. This prevents a later restart from entering the installation program again.

For a one-time boot choice, leaving the ISO mounted temporarily can be useful, but it increases the risk of accidental reinstallation or repeated entry into setup. Confirm that the virtual disk is the normal boot target before placing the VM into service.

Validate the new guest

Restart the VM if appropriate and verify that it boots from the installed virtual disk.
Confirm that the VM console displays the expected login screen or desktop.
Verify that the guest OS can see the expected virtual disk and that its partitions have the intended sizes.
Check the virtual network adapter inside the guest. Test link status, IP configuration, DNS resolution, and access to approved network destinations.
Test basic OS functions such as login, storage access, time zone, hostname, and required services.
Install VMware Tools or the supported guest-distribution equivalent. VMware Tools provides guest-side drivers and integration components for device support, performance, time synchronization, and manageability.
Apply current OS patches, configure endpoint protection, enable monitoring, and establish a backup plan before production use.

Common boot and media problems

Symptom	Likely cause	Verification	Resolution
No bootable device message	The ISO is not connected, is not bootable, or boot order prioritizes an empty disk	Review CD/DVD backing and connection state; inspect firmware boot order	Connect the device, verify the ISO, and use firmware setup or a boot menu to select the optical drive
ISO cannot be selected	The file was not uploaded, permissions are insufficient, or the host cannot access the datastore	Browse the datastore, check upload status and permissions, and identify the VM's host	Use an accessible datastore, correct permissions, refresh the view, and confirm the file is a valid ISO
Installer restarts repeatedly	The ISO remains connected and the VM connects it at every startup	Inspect the CD/DVD device after reboot	Disconnect or unmount the ISO, disable Connect At Power On, and boot from the virtual disk
VM boots to a blank or unexpected screen	Firmware mode, ISO architecture, boot order, or VM compatibility does not match the OS	Confirm OS version, architecture, firmware settings, and ISO integrity	Use supported VM settings and media, then select the correct boot device
Guest OS cannot access expected virtual hardware	Missing guest drivers or an incompatible virtual storage controller or device configuration	Check the guest device manager or hardware logs and compare the VM configuration with OS requirements	Install required drivers or VMware Tools, and use a controller type supported by the guest OS

The ISO is not visible in the datastore browser

Confirm that the ISO was uploaded to the selected datastore and that the upload completed.
Check whether the file is in a different folder or has an unexpected filename.
Verify that the user can browse the datastore and read the file.
Confirm that the host running the VM can access that datastore, especially when storage is host-local.
Refresh the datastore view and validate that the file is a complete, valid ISO image.

The installer cannot find a target disk

Verify that the VM includes a virtual disk and that it has sufficient capacity.
Check that the virtual disk is attached to the expected virtual storage controller.
Confirm that the guest OS supports the selected controller type, or provide the storage driver requested by the installer.
Do not confuse a datastore file with a disk available inside the guest. The installer must see the VM's virtual disk as guest hardware.

Operational and security considerations

Use trusted, approved installation media and maintain records of OS versions and licenses.
Meet activation, subscription, and other licensing requirements before deployment.
Limit datastore permissions and VM configuration privileges. Unauthorized changes to an ISO or virtual hardware can disrupt a system or introduce unapproved software.
Remove or restrict access to sensitive installation files and credentials used during setup.
Plan patching, endpoint protection, monitoring, backups, and recovery testing after the base installation.
Document the VM's OS version, firmware mode, disk layout, network identity, datastore, and post-installation settings.

Practical examples

Install a server operating system from a datastore ISO

Identify a VM with suitable CPU, memory, networking, and an empty virtual disk.
Upload the approved server OS ISO to shared or host-accessible datastore storage.
Edit the VM's virtual CD/DVD drive, select Datastore ISO File, and choose the uploaded ISO.
Enable Connect At Power On.
Power on the VM, open its console, and follow the server OS installer.
After the first successful boot from the virtual disk, disconnect the ISO and install VMware Tools or the supported equivalent.

Desktop VM does not boot into the installer

Confirm that the intended ISO is selected and that the CD/DVD drive is connected.
Restart the VM and enter firmware setup or open the supported boot menu.
Select the virtual optical drive as the temporary boot device.
Resume the normal desktop OS installation process.

A VM keeps reopening the installer

Recognize the pattern: the ISO is still attached or the CD/DVD device reconnects at every power-on.
Disconnect the ISO or clear Connect At Power On.
Restart the VM and confirm that it boots from the installed virtual disk.

Exam-relevant notes

A datastore ISO is a file stored on infrastructure storage; it is not automatically available to every ESXi host.
Datastore ISO File selects the media source, while Connect At Power On controls whether the virtual drive connects when the VM starts.
A VM can have a virtual CD/DVD device without having bootable media attached.
If a VM boots from the wrong device, check both device connection state and firmware boot order.
Disconnect installation media after setup so later boots reach the installed guest OS.
VMware Tools is a post-installation component, not a replacement for the guest operating system.

For the related procedure, see Install A Guest Operating System.