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Suraj Patil
Suraj Patil

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Fine-Tuning LUKS on Fedora Atomic Desktops: Performance, TRIM, and Key Derivation Upgrades

Fedora Atomic Desktops (like Silverblue, Kinoite, and Sway) offer a revolutionary, immutable operating system experience built for stability and containerized workflows. But when it comes to low-level disk encryption tweaks—especially for those running LUKS on SSDs—a few things behave differently compared to traditional Fedora Workstation installations.

This article outlines how to manually adjust LUKS settings on Atomic desktops, specifically to:

  • Improve SSD performance under heavy I/O
  • Enable TRIM support for encrypted devices
  • Future-proof your encryption by upgrading the key derivation function (KDF)

These changes are especially helpful for existing installs and are drawn from ongoing community efforts in the Fedora Silverblue issue tracker.

🐢 The Problem: "Application Not Responding" Under Load

Fedora users on Atomic desktops have reported unresponsive behavior when the system is under disk-heavy operations. One root cause is sub-optimal defaults in how dm-crypt handles SSDs.

You may be affected if:

  • You use full-disk encryption (LUKS)
  • Your root partition resides on an SSD
  • You notice UI hangs during heavy disk activity (e.g., updates, copying files)

✅ Solution 1: Improve dm-crypt Performance on SSD

The issue stems from lack of proper queue/discard tuning. Here's how to set it up manually.

1. Identify Your Root Device 

lsblk -o NAME,MOUNTPOINT
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Look for the cryptroot or luks-* device (your encrypted root).

lsblk output showing LUKS device

2. Check Current Settings 

cat /sys/block/dm-0/queue/discard_granularity
cat /sys/block/dm-0/queue/rotational
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If discard_granularity is 0, or rotational is 1, you're likely missing SSD optimizations.

Checking dm-crypt discard and rotational values

3. Create a Udev Rule

Create a new file:

sudo nano /etc/udev/rules.d/10-dmcrypt-ssd.rules
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Paste:

ACTION=="add", KERNEL=="dm-*", ATTR{queue/discard_granularity}=="0", ATTR{queue/discard_granularity}="4096"
ACTION=="add", KERNEL=="dm-*", ATTR{queue/rotational}=="1", ATTR{queue/rotational}="0"
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Then reload:

sudo udevadm control --reload-rules
sudo udevadm trigger
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Creating and reloading Udev rule

✅ Solution 2: Enable TRIM for Encrypted Devices

TRIM helps SSDs maintain performance over time by telling the drive which blocks are no longer used.

1. Enable Periodic TRIM 

sudo systemctl enable fstrim.timer
sudo systemctl start fstrim.timer
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2. Confirm It Works

After 24 hours, check the logs:

journalctl -u fstrim.timer
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Checking fstrim.timer status

You should see successful TRIM operations, even on encrypted volumes.

✅ Solution 3: Upgrade LUKS Key Derivation Function (KDF)

Modern cryptography best practices recommend stronger and more memory-hard KDFs, like argon2id, instead of the older PBKDF2. New Fedora installations may default to argon2id, but upgrades might not.

1. Check Current KDF 

sudo cryptsetup luksDump /dev/nvme0n1p3 | grep PBKDF
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luksDump output showing PBKDF2

2. Upgrade KDF (Careful!)

First, backup your data. Then:

sudo cryptsetup luksConvertKey --pbkdf=argon2id /dev/nvme0n1p3
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Replace /dev/nvme0n1p3 with your actual LUKS device.

This will preserve your current password but upgrade the internal key handling.

💡 Why This Matters

Atomic desktops are built for resilience, but performance tuning is still in the user’s hands. These three improvements:

  • Reduce system freezes
  • Improve SSD lifespan and speed
  • Future-proof your disk encryption setup

Together, they make your Fedora Atomic desktop more responsive, secure, and modern.

❤️ Community Resources

📝 Final Tip

If you’re running Fedora Kinoite, Silverblue, Sericea, or Sway — or even Fedora CoreOS — these tweaks can make a big difference. It’s a great reminder that even in an immutable world, you still have powerful tools for tuning what matters most.

Happy hacking! 🐧

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