Skip to content

Building Base VMs

Jump to bottom
Julian Ortega edited this page Jun 11, 2026 · 1 revision

Building Base VMs

A Base VM is a fully provisioned macOS image that serves as the source for cloning. You build one once, then clone it into as many VMs as you need — each clone starts from a known-good state in seconds.

Oven uses Packer with the Tart Packer plugin to build base images.

Overview of the Build Process

IPSW (macOS firmware)
        │
        ▼
  Packer template (.pkr.hcl)
  + optional variables (.pkrvars.hcl)
  + building blocks (provisioners)
        │
        ▼
  packer init → packer validate → packer build
        │
        ▼
  Base VM (local Tart image)
        │
        ▼
  (optional) Push to OCI registry

Creating a Base VM

  1. Navigate to Base VMs in the sidebar.
  2. Click + to open the New Base VM sheet.
  3. Choose a build path:

Path A: From a Packer Template (Recommended)

Select an existing template from the Template Library. Oven ships with vanilla templates from CirrusLabs for:

  • macOS Tahoe (26)
  • macOS Sequoia (15)
  • macOS Sonoma (14)
  • macOS Ventura (13)
  • macOS Monterey (12)

Configure:

  • Display Name — human-readable name for this base image
  • Tart Name — identifier on disk
  • macOS Version — must match the template
  • Template Variables — if the template has a .pkrvars.hcl companion, link it here
  • Building Blocks — add reusable provisioner snippets (see below)

Path B: Manual Build Configuration

For advanced users who want full HCL control:

  1. Choose Manual Build.
  2. Configure hardware (CPU, memory, disk), OS version, and IPSW source.
  3. Toggle provisioning options individually (see Provisioning Options below).
  4. Oven generates the HCL on the fly from your selections.

Provisioning Options

These toggles are available in both template-based and manual builds:

Option What It Does
Passwordless Sudo Configures the build user to run sudo without a password prompt
Auto Login Sets the user account to log in automatically on boot
Install Homebrew Installs the Homebrew package manager
Install Xcode CLI Tools Runs xcode-select --install
Enable SSH Enables the SSH server (Remote Login) in macOS
Disable Screen Lock Turns off the screen lock / screensaver
Disable Sleep Prevents the VM from sleeping
Disable Spotlight Turns off Spotlight indexing
Safari Automation Enables WebDriver support for Safari
Install Tart Guest Agent Installs the Tart guest agent for host↔VM communication
Install Rosetta Installs Rosetta 2 (Apple Silicon VMs only)
Random Computer Name Sets a random hostname on each boot (useful for MDM enrollment)

These correspond to Building Blocks in the template system and can be combined freely.

Building Blocks

Building Blocks are reusable HCL provisioner snippets you can attach to any build. Oven ships 10 seeded blocks:

  1. Passwordless Sudo
  2. Auto Login
  3. Homebrew
  4. Xcode CLI Tools
  5. SSH
  6. Disable Spotlight
  7. Screen Lock
  8. Safari Automation
  9. Random Computer Name
  10. File Upload

You can also create custom building blocks. See Templates & Building Blocks for details.

Boot Commands

Oven automates the macOS Setup Assistant by sending keystroke sequences via Packer's boot_command. You can customize these sequences in the Boot Commands editor within a base VM's configuration.

The default boot command block navigates through the Setup Assistant screens — language selection, network, Apple ID skip, license agreement, account creation — and is tuned for each macOS version.

Running a Build

  1. Open the base VM in the detail pane.
  2. Click Build.
  3. Oven runs packer init, packer validate, then packer build in sequence.
  4. Live output streams into the Build Log panel in real time.
  5. A notification fires when the build completes or fails (if Notifications are configured).

Build Completion Actions

In Preferences → Build, you can configure what happens after a successful build:

  • Do Nothing (default)
  • Lock Screen
  • Shut Down Mac

Validating a Template

Before running a full build, click Validate in the detail pane. Oven runs packer validate and shows any errors inline. This is faster than a full build for catching HCL syntax or variable issues. Only syntax is validated. Boot commands and building blocks can fail as packer validate doesn't catch these issues.

Build History

Each base VM keeps a history of past builds. In the detail pane, open the Build History tab to see:

  • Build date and time
  • macOS version built
  • Duration
  • Success or failure

After the Build

Once built, the base VM appears in the Base VMs list with a status badge. From there you can:

  • Clone it into one or more VMs
  • Push it to an OCI registry to share with teammates — see OCI Registry
  • Rebuild it to pick up a newer macOS patch release

Troubleshooting

Problem Likely Cause Fix
Build fails immediately Missing dependency Check Preferences → Tools; try re-downloading tools
packer validate errors HCL syntax issue Open the template in the HCL editor and look for red markers
Build hangs at Setup Assistant Boot command timing Adjust boot command delays or use a newer template version
IPSW download fails Network or ipsw.me outage Try switching to mist-cli in Preferences → Build
Packer plugin not found Plugin not initialized Run Validate first — it triggers packer init which downloads the plugin

Oven

Using Oven

Integrations

Advanced

Sources

Clone this wiki locally