How to clone a bootable SD card to a USB flash drive without corrupting either device in Linux Ubuntu using dd command in terminal

Good question — this is a classic use for dd on Linux.
Here’s a safe, step-by-step method to clone a bootable SD card to a USB flash drive without corrupting either device.

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🧰 What you’ll need

• A Linux machine (with root privileges)
• A bootable SD card (source)
• A USB pendrive (target)
• Terminal access

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1. Identify the devices

Plug in both the SD card and the USB stick, then run:

lsblk

This will list all block devices.
Typical names:

• SD card: /dev/mmcblk0 or /dev/sdX
• USB pendrive: /dev/sdY

⚠️ Double-check which is which — overwriting the wrong device will destroy data.
Do not use the partition numbers like /dev/sdX1; use the whole device like /dev/sdX.

Example output:

NAME        MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT

sda           8:0    0 232G  0 disk

└─sda1        8:1    0 232G  0 part /

mmcblk0     179:0    0  32G  0 disk

└─mmcblk0p1 179:1    0  32G  0 part

sdb           8:16   1  32G  0 disk

Here:

• /dev/mmcblk0 = SD card
• /dev/sdb = USB pendrive

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2. Unmount partitions

Unmount any automatically mounted partitions from both devices:

sudo umount /dev/mmcblk0*

sudo umount /dev/sdb*

(Adjust device names if needed.)

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3. Copy the SD card to USB stick with dd

Basic syntax:

sudo dd if=/dev/mmcblk0 of=/dev/sdb bs=4M status=progress conv=fsync

• if= = input file (SD card)
• of= = output file (USB stick)
• bs=4M = copy in 4 MB blocks (faster than default)
• status=progress = show live progress
• conv=fsync = flush writes to disk properly

👉 If the USB stick is smaller than the SD, the copy will fail. The target must be the same size or larger.

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4. Sync and eject

After dd finishes, run:

sync

This ensures all writes are flushed to the USB.
Then remove the USB stick safely.

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5. (Optional) Expand filesystem on USB

If the USB drive is larger than the SD card, you may want to grow the root partition to fill the extra space.
For example:

sudo gparted /dev/sdb

or using growpart and resize2fs:

sudo growpart /dev/sdb 2

sudo resize2fs /dev/sdb2

(Replace 2 with the partition number containing the root filesystem.)

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6. Test the USB boot

You can now plug the USB into the target system and boot from it.

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✅ Summary:

• Identify devices with lsblk
• Unmount both
• Clone: dd if=/dev/source of=/dev/target bs=4M status=progress conv=fsync
• Sync and resize if needed

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