Recovering the root password on a BeagleBone Black

I recently went to use a BeagleBone Black board on which I'd never booted from the eMMC before (that I could recall) and had been instead booting off of a microSD card. To the best of my knowledge, the root password on this board should never, ever have been changed from the default (blank password), but apparently it was. None of the passwords that I had ever used for any of my BeagleBone Blacks was working, which created a problem: I needed to recover the root password to this BeagleBone Black so that I could use it for my projects again. I was in luck. The BeagleBone Black has the tools that I needed to do it. I'm writing this blog post (like many other posts in the blog) so that I can have a reference to come back to if I ever need it in the future.

To recover the root password of a BeagleBone Black, you'll need the following items:

• A 5V, minimum 1 A dedicated power source (you shouldn't really be powering the board off of the micro USB port)
• An SD card (and reader, of course)
• An FTDI USB-to-serial cable for accessing the debug serial port of the BeagleBone Black.

Once you've acquired all of the required items above, perform the following steps:

1. Flash the SD card with an image that you can obtain from BeagleBone.org/GettingStarted.
2. Insert the SD card into the *unpowered* BeagleBone Black.
3. Apply power.
4. The BeagleBone Black should boot from the SD card (assuming that you've flashed the correct image)
5. Connect the FTDI serial cable to the board and your compter, and open your serial client of choice to connect to the board.
6. Hit enter once or twice, and a command prompt should come up, assuming you've used the correct settings:
1. 115200
2. 8N1
7. Log in using root and a blank password (should be the default on the SD card image that you downloaded from the BeagleBoard.org website.)

You're now logged into the image running on the SD card. However, we can't change the root password now because that will only change it for the root user on the SD card image. We need to change it for the permanent image stored on the BeagleBone Black's embedded eMMC flash. Being logged in as you are, perform the following steps to mount the eMMC image and change the password for that image's root user:

1. Mount the eMMC flash:  mount /dev/mmcblk1p2 /media/card
2. Change the root of the file system to be the partition on the eMMC flash which you just mounted: chroot /media/card
3. Change the password of the root user to something you know: passwd root
4. Exit out of the changed root: exit
5. Shutdown the BeagleBone Black : shutdown -h now
6. Disconnect the power from the board
7. Eject the microSD card.
8. Reconnect the power to the board
9. Watch the board boot up, and log in as root. You should be able to log in with the password that you just set.

Changing the password complexity requirements on Windows Server

To change the password complexity requirements on Windows Server (2008 at least) (for whatever reason), do the following :

Start -> Run -> gpedit.msc -> Computer Configuration -> Windows Settings -> Security Settings -> Account Policies -> Password Policy

Then in the right-hand policy pane, set 'Password must meet complexity requirements' to 'Disabled' (right-click -> Properties)

Two bash functions that will make your software development life 10% easier

... if you use SSH to move between machines a lot. Which I do. I have several machines that I work on regularly, and a centralized development machine shared with others that I frequently have to exchange files with. The following two functions are the most useful two bash functions that you can put in your .bashrc file if you use SSH as much as I do :

function ssh-create-keys {
ssh-keygen -t rsa
}

function ssh-setup-on {
cat ~/.ssh/id_rsa.pub | ssh $1 "cat - >>.ssh/authorized_keys"
}

The first sets up an SSH key file for you in your home directory, This key file will be used to identify you on other machines, and can be used for various purposes on your local machine as well. The second function logs you into the machine determined by the username@anothermachine given as the first argument to the function, and adds your public key to the list of authorized keys for that machine.

Once you've run the first function, and run the second function to setup your public key on an account on another machine, you'll now be able to use SSH to log in and copy files freely with the account on the other machine without having to enter a password. While this is incredibly convenience, it also comes with a caveat : it's dangerous. If somebody other than yourself gains physical access to your machine and can log on as you, (or use your already logged on account), they can move to those same machines freely and perform possibly malicious actions, as you. Keep that in mind.