How to Clone a Bootable SD Card on Linux & macOS for Backup 🖥️💾

Ever needed to back up a bootable SD card for your Raspberry Pi or embedded system? Whether you're safeguarding your work or preparing for disaster recovery, cloning your SD card is a smart move.

Here’s how to do it quickly and cleanly using just your terminal. 🚀

🔹 Step 1: Identify Your SD Card

Insert the SD card and find its disk identifier:

✅ For Linux:

lsblk

✅ For macOS:

diskutil list

Look for something like /dev/sdX (Linux) or /dev/disk2 (macOS).

🔹 Step 2: Create a Backup Image

Run this command to clone the SD card into an image file:

✅ For Linux:

sudo dd if=/dev/sdX of=~/sdcard_backup.img bs=4M status=progress

✅ For macOS:

sudo dd if=/dev/disk2 of=/Users/YOUR_USERNAME/sdcard_backup.img bs=4m status=progress

This creates sdcard_backup.img in your home directory. Replace YOUR_USERNAME with your actual home folder name.

🕒 Time Check:

This took about 50 minutes on a 2018 Mac mini i7 (32GB RAM) for a 32GB SD card running Raspberry Pi OS Lite with Pi-hole and Unbound.

🔹 Step 3: Verify the Backup Image

Check if the backup file exists and is the correct size:

ls -lh ~/sdcard_backup.img

(Optional) Mount the image to verify its contents:

✅ macOS:

hdiutil attach ~/sdcard_backup.img

🔹 Step 4: Restore the Image to a New SD Card

1️⃣ Insert the new SD card and identify it:

✅ For Linux:

lsblk

✅ For macOS:

diskutil list

2️⃣ Unmount the SD card(s) before writing:

✅ For Linux:

sudo umount /dev/sdX*

Use * if the disk has multiple partitions.

✅ For macOS:

diskutil unmountDisk /dev/disk2

3️⃣ Write the backup image to the new SD card:

✅ For Linux:

sudo dd if=~/sdcard_backup.img of=/dev/sdY bs=4M status=progress

Replace /dev/sdY with the correct device name of the new SD card.

✅ For macOS:

sudo dd if=/Users/YOUR_USERNAME/sdcard_backup.img of=/dev/disk2 bs=4M status=progress

🕒 Another 50 minutes later... and now you’ve got two identical bootable SD cards! ✅

💡 Why Should You Back Up Your SD Card?

✔️ Prevent data loss
✔️ Easily restore your system
✔️ Save time in case of failure

Backing up your bootable SD card gives you peace of mind when working with Raspberry Pi, embedded systems, or custom Linux builds. 🔥