/var/lib/cloud

The /var/lib/cloud directory is a key location used by cloud-init, the standard tool for early initialization of cloud instances. This directory stores persistent state, metadata, instance configuration, and logs related to how an instance was provisioned by cloud-init.

Purpose of /var/lib/cloud

This directory helps cloud-init track the instance lifecycle across reboots, ensuring that initialization scripts and user-data are only run when appropriate. It distinguishes between first boot and subsequent boots.

Directory Structure

Typical structure of /var/lib/cloud/ includes:

/var/lib/cloud/
├── data/
│   ├── result.json            # Final cloud-init result in JSON format
│   └── status.json            # Contains execution status
├── handlers/                  # For custom handler scripts
├── instance/                  # Symlink to current instance directory
├── instances/
│   └── <instance-id>/         # Stores metadata and user-data for this instance
├── scripts/
│   ├── per-boot/              # Scripts run on every boot
│   ├── per-instance/          # Scripts run once per instance
│   ├── per-once/              # Scripts run only once ever
│   └── vendor/                # Scripts provided by the image vendor
├── sem/                       # Semaphore files to track script execution

Key Files and Directories

  • data/status.json: Indicates whether cloud-init ran successfully.

  • instances/<instance-id>/: Contains metadata, user-data, and seed information specific to the current instance.

  • scripts/*: Custom scripts executed by cloud-init at different lifecycle stages.

  • sem/: Tracks whether specific modules or stages have completed to avoid re-execution.

Usage Example

If you want to debug or verify what happened during the boot process:

cat /var/lib/cloud/data/status.json

To examine the user-data provided to the instance:

cat /var/lib/cloud/instances/<instance-id>/user-data.txt

To check logs:

less /var/log/cloud-init.log

Cleanup for Re-Provisioning

If you're reusing a VM image and want cloud-init to rerun on first boot:

sudo cloud-init clean --logs

This clears /var/lib/cloud/ and resets the instance metadata and state.

Security Considerations

  • Protect access to /var/lib/cloud as it may contain sensitive instance metadata.

  • Be cautious when copying VM images with populated /var/lib/cloud; use cloud-init clean.

Conclusion

The /var/lib/cloud directory is essential for managing instance initialization via cloud-init. It provides transparency and control over instance lifecycle configuration, allowing cloud platforms to automate deployment and configuration securely and efficiently.

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