cloud-init: stop persisting zram swap into /etc/fstab (slow cloud boot)

[igorpecovnik]

On the arm64 cloud images, boot takes ~90 s longer than it should. Root cause:

• armbian-zram-config.service sets up zram swap at boot.
• cloud-init's mounts module sees that active swap and persists it to /etc/fstab: /dev/zram0 none swap sw,comment=cloudconfig 0 0.
• On the next boot systemd turns that line into a dev-zram0.swap unit that blocks ~90 s on the device timeout waiting for /dev/zram0 (which only appears once armbian-zram-config runs), failing swap.target until it recovers.

Confirmed on two production cloud hosts (armbian-aarch64-1/2), both with the identical fstab line and a 90 s dev-zram0.device timeout in dmesg.

Fix

A cloud.cfg.d drop-in (99-armbian-no-zram-swap.cfg) that sets cloud-init's swap mount to null:

mounts:
  - [ swap, null ]

This removes cloud-init's default swap mount so it leaves zram/swap management to Armbian, while keeping the rest of the mounts module. Verified against cc_mounts.py (26.1): handle() runs sanitize_mounts_configuration before add_default_mounts_to_cfg, so the sanitized swap→/dev/zram0 entry suppresses the auto-added default swap entry, and the null mountpoint keeps it out of fstab.

Deployed cloud hosts were already fixed by removing the stale fstab line (armbian-zram-config still provides the swap); this stops new images from shipping the bug.

Summary by CodeRabbit

• Bug Fixes
  • Prevented cloud-init from persisting dynamically configured Armbian zram swap in /etc/fstab.
  • Preserved processing for other mount configurations.

[coderabbitai]

📝 Walkthrough

Walkthrough

The PR adds a cloud-init configuration that prevents Armbian zram swap from being persisted in /etc/fstab while leaving other mount processing enabled.

Changes

Cloud-init swap handling

Layer / File(s)	Summary
Override swap mount persistence extensions/cloud-init/config/99-armbian-no-zram-swap.cfg	Adds documentation and sets the cloud-init mounts swap entry to null.

Estimated code review effort: 1 (Trivial) | ~2 minutes

Possibly related PRs

• armbian/build#10065: Changes swapfile creation in armbian-install, while this PR changes cloud-init swap persistence.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: preventing cloud-init from persisting zram swap entries to /etc/fstab.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch cloudinit-no-zram-swap-fstab

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