Backing Up Docker Images to a USB Drive on Raspberry Pi / ARM Linux

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Overview

This is a battle-tested workflow for exporting Docker images from a Raspberry Pi (or any ARM-based Linux box) to an exFAT-formatted USB drive, then loading them back on a fresh install or different machine. It avoids network pulls, preserves exact image tags and IDs, and sidesteps common permission headaches when dealing with auto-mounted removable media.
Tested on Raspberry Pi 4B running Raspberry Pi OS / Debian-based distro, but the commands are generic to any modern Linux with Docker.

Why This Matters

Docker images on embedded devices eat up space fast. TF cards and small SSDs fill quickly, and rebuilding everything from scratch over slow or unreliable internet is painful. A reliable offline backup lets you:

  • Wipe/reinstall the OS without losing your container environment
  • Migrate to new hardware quickly
  • Keep a cold spare of critical images (e.g. transmission, cloudreve, custom builds)

Exporting Images to USB

Plug in the USB drive and identify it.

  • execute: lsblk

    Look for something like /dev/sda1 or /dev/sdb1 with exFAT filesystem. Never guess — double-check size and label.

Unmount any auto-mount (devmon/udisks2 usually mounts to /media//

  • execute: sudo umount /media/devmon/DockerIMGs
  • adjust path to match your system

Create a clean mount point

  • execute: sudo mkdir -p /mnt/docker-usb

Mount the drive manually with proper ownership and permissions

This is the most important step — auto-mounts almost always give root:root or 1000:1000 with restrictive umask, making it annoying to write from non-root.

  • execute:
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    sudo mount -t exfat \
    -o uid=1000,gid=1000,umask=022 \
    /dev/sdb1 /mnt/docker-usb
  • uid=1000,gid=1000 → files appear owned by your regular user
  • umask=022 → creates files as 644, directories as 755 (normal user-writable)

Create backup directory on the drive

  • execute 
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    cd /mnt/docker-usb
    sudo mkdir docker_images_backup
    sudo chown $USER:$USER docker_images_backup   # optional but cleaner

Export images

Use docker save to create a single .tar per image (or multi-image tar if you prefer).
Replace with your actual image:tag pairs.

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sudo docker save -o /mnt/docker-usb/docker_images_backup/transmission_latest.tar lscr.io/linuxserver/transmission:latest
sudo docker save -o /mnt/docker-usb/docker_images_backup/cloudreve_4.10.1-arm.tar cloudreve:4.10.1-arm

Run as your user if the mount is correctly owned; otherwise prefix with sudo.

Verify sizes and integrity

  • execute: 
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    ls -lh /mnt/docker-usb/docker_images_backup
    du -sh /mnt/docker-usb/docker_images_backup/*

Safely unmount

  • execute:
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    cd ~
    sudo umount /mnt/docker-usb

    Wait for the command to return, then physically remove the drive.

Restoring Images on a New / Reinstalled System

Plug in the USB drive.

It will probably auto-mount again (often to /media//

Locate the mount point and check contents

  • execute: 
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    lsblk -f
    ls -lh /mnt/docker-usb/docker_images_backup   # adjust path

Load the images

  • execute 
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    sudo docker load -i /media/devmon/ImgBackU/docker_images_backup/openwrt-aarch64.tar
  • You’ll see output like Loaded image: buddyfly/openwrt-aarch64:latest

Verify everything came back intact

  • execute: sudo docker images
  • Check that repository:tag and IMAGE ID match exactly what you had before. If IDs match, layers were preserved perfectly.

(Optional) Unmount when done

  • execute:
    • sudo umount /mnt/usb
  • or wherever it mounted

Quick Tips & Gotchas

  • Always use docker save / docker load — never copy /var/lib/docker directly. The latter is dangerous and usually breaks.
  • exFAT is ideal for cross-platform (Linux ↔ Windows/Mac) backups. If you only stay on Linux, ext4 works too but isn’t as portable.
  • If mount -t exfat fails → install exfatprogs or exfat-utils (sudo apt install exfatprogs).
  • Large images (>10–20 GB) take time to save/load — be patient and watch iotop or htop if curious.
  • For bulk export of all images: 
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    docker images --format '{{.Repository}}:{{.Tag}}' | xargs -n1 docker save -o backup.tar

    but single-file tar gets huge; per-image is usually better for manageability.

References

This workflow has survived multiple Pi reimages and migrations for me. Keep your USB drive in a safe place — it’s now your offline Docker lifeline.