Beaglebone Black not booting due to modification of uEnv.txt

I accidently modified uEnv.txt file located in eMMC of my Beaglebone black. Now the board is not booting. I can not even see BBB for serial connection from terra term (Windows 7 after drivers are installed). How can I get access to the board? If I can just access to uboot I could reflash or run it using nfs. Any ideas?

Install one of the uSD card based distributions on a uSD card.
Boot from the uSD card, not the on-board eMMC.

cd /mnt

mkdir disk

mount /dev/mmcblk1p2 disk

cd disk

and you will see the root file system on the eMMC.
go find what you broke, and fix it.



remove the uSD and see if it boots from the eMMC.

— Graham

Thanks Graham, that helped me too. Somehow the uEnv.txt file seemed to have disappeared completely from the EMCC. I can still see other stuff I put there but not that file.

Well these instructions are for the later “single partition” Debian distributions.

The 7.5, distribution has the uEnv.txt file in a separate “FAT” partition, so

the mounting instructions are slightly different, if you need to get at the

file in a different partition.

— Graham

First of all apologies to the OP for crashing his thread :slight_smile: but it seems to be the same issue.

I have “initrd.img-3.8.13-bone47” (Debian) on the EMMC which becomes visible after the above instructions, the disk directory is still on the SD so I only need the “mount /dev/mmcblk1p2 disk” bit to access it and I can see other stuff I had put in my own directory for test purposes (bonescripts).

However I can’t see the original uEnv.txt file or the backup copy I had made before the fatal bricking, is it possible they are hiding elsewhere but boot or uboot directories of the EMCC? Copying the uEnv.txt from the SD to the boot directory of the EMCC doesn’t restore functionality but it is possible that that files needs to be different than what’s on the SD??

I have only started to mess around with the BBB and very lost!

Several Possibilities:

1.) When you write something to the file system, either a new file or modify a file, you need to

type ‘sync’ on the command line to flush the buffers to the file system, otherwise you can

loose the changes at unmount/shutdown.

2.) On the earlier Debian distributions, like 7.5, the uEnv.txt file is not in the ‘root’ partition, but is in

the ‘boot’ partition, which is what I suspect is going on.

“mount /dev/mmcblk1p2 disk” will mount the ‘root’ partition
“mount /dev/mmcblk1p1 disk” will mount the ‘boot’ partition (or something like that, I’m working from memory)

Since you can’t mount two different partitions with the same name, if you try to

mount them at the same time, you will need to call them something different, like disk1 and disk2 or

disk_root and disk_boot.

— Graham

Thank you very, very much. All good now, could not reply earlier because I have been “booting” myself after I figured out what I did wrong. :slight_smile:

Both the messed up uEnv.txt file and the copy were there so I just had to delete the bad uEnv.txt file and copy the back up I had made.

The file is now also copied to my PC…just in case…

I am still having issues with booting BBB with sd card. I have not even accessed eMMC.
These are the steps I did:

I downloaded bone-debian-7.5-2014-05-14-2gb.img.xz.
Extracted to bone-debian-7.5-2014-05-14-2gb.img
from Ubuntu Host machine executed: sudo dd if=bone-debian-7.5-2014-05-14-2gb.img of=/dev/sdc bs=1M
After some time about 681 MB image is written to Micro SD card. Now I am assuming this image has everything you need. kernel, filesystem and bootloader and I do not have to manually make partitions on the SD card.
Then I plug in the Micro SD card to the BBB and attached my USB cord from Host to target while pressing on S2 boot button.
All 4 LEDS flashed after a minute only fourth LED flashes interval of a second. LED next to 5V power supply is solid lit.
May be BBB booted with Linux but I have no way of knowing. I can not see it thru my COM port (like when it booted with eMMC).
I really wished BBB had serial port like most boards have.
Another question is I do not want Linux kernel loaded from either eMMC or MicroSD card I want to setup NFS and tftpboot for that I want to prompt on uboot. How can I do that?

It does, I use the console port with a RS232 converter at 115K. I have soldered a R/A connector at the back of the board so that I can use it even if a cape is plugged in. It’s designed to use a “standard” FTDI USB > TTL adapter.

The image I downloaded before was just a stripped down, console only, version which booted from SD. This allowed me to recover the EMCC version after fixing up the uEnv.txt file.

The serial port console starts spitting out stuff even before the USB COM port does.

Hello Graham!!!
I referred this link & deleted the MLO file so that the board will boot from SD card…From then the Board is booting from SD card… but if i remove the SD card & try to connect to the system using USB it is not connecting… I followed the above commands… but i am not getting how can i add that MLO file back to the eMMC & in which directory to add that MLO file…

Any help appreciated much…
Thanks & Regards

cd /mnt

mkdir disk

mount /dev/mmcblk0p1 disk

cd disk

and you will see the root file system on the eMMC.
go find what you broke, and fix it.


shutdown -h now

remove the uSD and see if it boots from the eMMC.

this is for Debian Image 2014-04-23

— Ajis

I have the same problem as OP, how do I do perform mount command if I can not ssh into bbb at all

On Tue, 12 Jan 2016 23:26:44 -0800 (PST), declaimed the

I have the same problem as OP, how do I do perform mount command if I can
not ssh into bbb at all

  Note the line near the bottom about removing uSD card?

  That implies (to me at least) that you first need to boot from an image
on an SD card... THEN mount the eMMC to fix the problem.