- SWAP tuning for system stability : reducing swap-induced SD card writes ⭐⭐
- Journald to RAM : keeping system logs off the SD card ⭐⭐⭐⭐
- TMPFS for /tmp : avoiding temporary file writes to disk ⭐⭐⭐
- Disable access-time logging : reducing filesystem metadata writes on read ⭐
- Dirty page flush tuning : adjusting kernel write-back timing ⭐⭐⭐⭐
- Enable hardware watchdog auto-reboot : automatic recovery from hard freezes ⭐
- Root filesystem overlay via initramfs switch : eliminating runtime writes to the system partition ⭐⭐⭐⭐⭐
一. SWAP tuning for system stability ⭐⭐
Check current swappiness:
cat /proc/sys/vm/swappiness
(Default is 60 unless previously modified.)
Set swappiness to 10 via sysctl:
sudo vi /etc/sysctl.d/99-swappiness.conf
Add the line:
vm.swappiness=10
Apply and verify:
sudo sysctl -p /etc/sysctl.d/99-swappiness.conf cat /proc/sys/vm/swappiness
Or simply reboot:
sudo reboot
Inspect current swap usage:
cat /proc/swaps swapon --show free -h
(Optional) Recreate swap file
Only needed if your current /swapfile is too small or has been removed.
Disable and remove the old swap file:
sudo swapoff /swapfile sudo rm /swapfile
Create a new 1 GB swap file:
sudo fallocate -l 1G /swapfile sudo chmod 600 /swapfile sudo mkswap /swapfile sudo swapon /swapfile
Enable it at boot:
sudo vi /etc/fstab
Add the line:
/swapfile swap swap defaults 0 0
Confirm:
swapon --show
二. Journald to RAM ⭐⭐⭐⭐
By default, systemd-journald can store logs on disk under /var/log/journal, which creates continuous writes on an SD card. Switching journald to volatile mode keeps logs in RAM (/run/log/journal), so they disappear after reboot and no longer wear the SD card during normal operation.
※ Not needed in full read-only + RAM overlay mode.
Switch journald to RAM-only by modify the file journald.conf:
# sudo vi /etc/systemd/journald.conf # Change or add journal storage setting Storage=volatile # Always store logs in RAM (/run/log/journal) #Storage=auto # Use RAM if /var/log/journal does not exist, otherwise use disk #Storage=persistent # Always store logs on disk (/var/log/journal) SystemMaxFileSize=32M # Limit individual journal file size
Restart journald or reboot:
# Restart journald service sudo systemctl restart systemd-journald # Or reboot to apply sudo reboot
Verify usage and location:
# Check disk usage of journal journalctl --disk-usage # Check actual journal storage location journalctl --verify # → Shows /run/log/journal if stored in RAM (volatile mode) # → Shows /var/log/journal if stored on disk (persistent mode)
三. TMPFS for /tmp ⭐⭐⭐
/tmp is used for short-lived temporary files. Mounting it as tmpfs keeps these writes in RAM instead of on the SD card, reducing wear at the cost of some RAM usage.
※ Not needed if a read-only root filesystem with overlay is already enabled, but useful in normal writable mode.
Configure /tmp as tmpfs
# Mount /tmp in RAM (512MB) # sudo vi /etc/fstab # Add line: /tmpfs /tmp tmpfs defaults,noatime,nosuid,nodev,size=512M,mode=1777 0 0
Apply without reboot (or reboot)
# Mount now without reboot sudo mount -a mount | grep /tmp # Or reboot to apply sudo reboot
Confirm usage
# Confirm /tmp is mounted as tmpfs findmnt /tmp # Show how much space is used in /tmp sudo du -sh /tmp
四. Disable access-time logging on root filesystem ⭐
By default, every file or directory read can update its access time (atime) on disk. Disabling access-time logging stops these updates on read operations, while file modification times are still recorded as usual.
※ Useful in normal writable mode to reduce unnecessary SD card writes. Has no effect when a read-only overlay is active.
Edit root filesystem mount options
# Remove access-time logging on root filesystem # sudo vi /etc/fstab # Replace: /dev/root / ext4 defaults 0 1 # With: /dev/root / ext4 defaults,noatime,nodiratime,errors=remount-ro 0 1
Reboot and verify
# Reboot to apply sudo reboot # Output should show "noatime,nodiratime" in mount options mount | grep 'on / '
五. Dirty page flush tuning ⭐⭐⭐⭐
When an application writes data, the kernel does not immediately write it to disk. Instead, the data is temporarily kept in RAM as dirty pages and written back to disk later in batches. This improves performance, but increases the risk of data loss if power is suddenly cut.
By flushing dirty pages to disk earlier and more frequently, the time window during which written data exists only in RAM is reduced, improving resilience against power loss.
※ Useful in normal writable mode when minimizing data loss on power failure. Has no effect in read-only or overlay modes.
Create a dirty-page tuning config
sudo vi /etc/sysctl.d/99-dirty-flush.conf
Add:
# Start background writeback at 5% dirty memory (default: 10%) vm.dirty_background_ratio=5 # Block new writes at 10% dirty memory (default: 20%) vm.dirty_ratio=10 # Force writeback after 5 seconds (default: 30 seconds) vm.dirty_expire_centisecs=500 # Check for dirty pages every 1 second (default: 5 seconds) vm.dirty_writeback_centisecs=100
Reboot and verify
sudo reboot # Verify dirty page parameters sysctl -a | grep dirty
六. Enable hardware watchdog auto-reboot ⭐
If the system hard-freezes, a hardware watchdog can automatically reboot the device when it stops responding. Jetson Nano provides a built-in watchdog that can be managed by systemd.
In practice, this mainly acts as a last-resort recovery mechanism for complete system hangs, and does not prevent data corruption by itself.
※ Optional. Mostly relevant for unattended or appliance-style systems; limited benefit during active development.
Check watchdog support
zcat /proc/config.gz | grep -Ei 'dog|tegra_wdt'
You should see entries indicating that the Tegra watchdog is enabled in the kernel.
Test the watchdog directly (forces reboot)
sudo sh -c 'echo V > /dev/watchdog'
If working, the system should reboot after roughly one minute.
Do NOT run this on a system with unsaved work.
Configure systemd to use the watchdog
sudo vi /etc/systemd/system.conf
Set:
RuntimeWatchdogSec=30
Reboot and confirm
sudo reboot # Verify watchdog timeout systemctl show --property=RuntimeWatchdogUSec
The reported value should correspond to 30 seconds.
七. Root filesystem overlay via initramfs switch ⭐⭐⭐⭐⭐
All previous sections aim to make a writable, SD-card–based system less fragile. However, for real deployments where power loss is expected, the only robust approach is to stop writing to the system partition entirely.
An initramfs-based root filesystem overlay achieves this by mounting the base root filesystem as read-only and redirecting all runtime writes to a RAM-backed overlay. The system runs normally, but any changes made at runtime are discarded on reboot unless explicitly committed in writable mode.
※ Ideal for deployment, but largely unusable during active development, where a writable root filesystem is required.
※ Any data that must persist at runtime must be stored on a separate, non-system partition; this typically requires explicit disk partitioning and mount configuration.
Clone the overlay setup tool
git clone https://github.com/lehni/root-ro.git cd root-ro
Install the Jetson Nano preset
sudo ./install-nano.sh
This installs a custom initramfs and helper tools that allow booting into either:
-
Read-only root filesystem with a tmpfs overlay (normal safe mode)
-
Fully writable root filesystem (maintenance / upgrade mode)
Reboot into readonly or writable mode
sudo reboot-ro # Boot with overlay (rootfs effectively read-only) sudo reboot-rw # Boot with normal writable rootfs
Switch mode temporarily without full reboot (for testing)
mount-ro # Remount with overlay (read-only) mount-rw # Remount writable (with chroot)
The exact behavior of these commands depends on the root-ro tool’s implementation. The intended workflow is to perform development, debugging, and system updates in writable mode, then return to read-only mode for normal operation.
