Flashing or backing up your SD card¶

For both these tasks you will need the dd software. It comes with many Linux distributions and is available for MacOS and Windows, although I have not tried to use it on Windows myself.

Put your SD card in the SD card reader. We assume for the rest of this document that your SD card is /dev/mmcblk0

Always start by unmounting the SD card in case it is currently mounted. On linux you would do:

$ sudo umount /dev/mmcblk0

On MacOS you would do:

$ sudo diskutil unmountDisk /dev/mmcblk0

Flashing an SD card¶

Whether you got an image from somewhere else or you want to flash your own backup image after you bricked your Beaglebone, do as follows:
make sure that the SD card is inserted and that none of its partitions are mounted as explained above.
Then:

$ sudo dd if=~/bbb_images/your_own_your_precious_backup_image.img of=/dev/mmcblk0

As it happens, dd is a very simple program, so simple that it does not even display a progress bar.
If you are lucky enough to be on Linux, you can probably easily install pv which will display a progress bar for you:

pv ~/bbb_images/your_own_your_precious_backup_image.img | sudo dd of=/dev/mmcblk0

Backing up your SD card¶

If you are planning to compress your image file (e.g.: for sharing over the network, or for archiving), you may want to run this command, which fills the unused space with zeros, so that the compressed file will have a smaller size.
To do this, the lines below will create a file to fill the empty space in the partition and fill it with zeros. The second line will delete the file.

$ sudo dd if=/dev/zero of=/path/to/the/mounted/sdcard/bigfile bs=1M
$ sudo rm /path/to/the/mounted/sdcard/bigfile

Make sure that the SD card is inserted and unmount all of its partitions as explained above.

In case your partition is smaller than the size of the SD card, you do not need to backup the whole card, so if this is the case, run:

$ sudo fdisk -u -l /dev/mmcblk0

You might get something along the lines of

            Device Boot      Start         End      Blocks   Id  System
    /dev/mmcblk0p1   *          63      144584       72261    c  W95 FAT32 (LBA)
    /dev/mmcblk0p2          144585     3743144     1799280   83  Linux

You are interested in the higher value in the "End" column. Pass that value to dd as the count parameter:

$ sudo dd conv=sparse count=3743144 if=/dev/mmcblk0 of=~/bbb_images/your_own_your_precious_backup_image.img

If, instead, you want to backup the entire the SD card, simply use:

$ sudo dd conv=sparse if=/dev/mmcblk0 of=~/bbb_images/your_own_your_precious_backup_image.img