uEnv.txt boot file confusion with embedded Linux
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I am re-flashing the internal emmc on my BeagleBone Green board with a Debian image stored on the pluggable SD card.
The instructions I received are to modify the /boot/uEnv.txt file in the SD card image which must be flashed and un-comment the last line : cmdline=init=/opt/scripts/tools/eMMC/init-eMMC-flasher-v3.sh
This works and flashes the internal memory as expected. What I don't understand is when I then check the /boot/uEnv.txt file when the image is flashed, the line is then commented out again. What causes this?
Also, I thought the /boot/uEnv.txt file is part of the bootloader and not the kernel image. I have real confusion here.
Another thing, sorry if it's more than one question. If I wish to modify the uEnv.txt file on the SD card image and then send the modified image to someone else , how to do this?
embedded-linux beagleboneblack bootloader u-boot beagleboard
asked Nov 16 '18 at 10:19
Engineer999Engineer999
1,31821222
add a comment |
I am re-flashing the internal emmc on my BeagleBone Green board with a Debian image stored on the pluggable SD card.
The instructions I received are to modify the /boot/uEnv.txt file in the SD card image which must be flashed and un-comment the last line : cmdline=init=/opt/scripts/tools/eMMC/init-eMMC-flasher-v3.sh
This works and flashes the internal memory as expected. What I don't understand is when I then check the /boot/uEnv.txt file when the image is flashed, the line is then commented out again. What causes this?
Also, I thought the /boot/uEnv.txt file is part of the bootloader and not the kernel image. I have real confusion here.
Another thing, sorry if it's more than one question. If I wish to modify the uEnv.txt file on the SD card image and then send the modified image to someone else , how to do this?
embedded-linux beagleboneblack bootloader u-boot beagleboard
asked Nov 16 '18 at 10:19
Engineer999Engineer999
1,31821222
add a comment |
I am re-flashing the internal emmc on my BeagleBone Green board with a Debian image stored on the pluggable SD card.
The instructions I received are to modify the /boot/uEnv.txt file in the SD card image which must be flashed and un-comment the last line : cmdline=init=/opt/scripts/tools/eMMC/init-eMMC-flasher-v3.sh
This works and flashes the internal memory as expected. What I don't understand is when I then check the /boot/uEnv.txt file when the image is flashed, the line is then commented out again. What causes this?
Also, I thought the /boot/uEnv.txt file is part of the bootloader and not the kernel image. I have real confusion here.
Another thing, sorry if it's more than one question. If I wish to modify the uEnv.txt file on the SD card image and then send the modified image to someone else , how to do this?
embedded-linux beagleboneblack bootloader u-boot beagleboard
asked Nov 16 '18 at 10:19
Engineer999Engineer999
1,31821222
I am re-flashing the internal emmc on my BeagleBone Green board with a Debian image stored on the pluggable SD card.
The instructions I received are to modify the /boot/uEnv.txt file in the SD card image which must be flashed and un-comment the last line : cmdline=init=/opt/scripts/tools/eMMC/init-eMMC-flasher-v3.sh
This works and flashes the internal memory as expected. What I don't understand is when I then check the /boot/uEnv.txt file when the image is flashed, the line is then commented out again. What causes this?
Also, I thought the /boot/uEnv.txt file is part of the bootloader and not the kernel image. I have real confusion here.
Another thing, sorry if it's more than one question. If I wish to modify the uEnv.txt file on the SD card image and then send the modified image to someone else , how to do this?
embedded-linux beagleboneblack bootloader u-boot beagleboard
embedded-linux beagleboneblack bootloader u-boot beagleboard
asked Nov 16 '18 at 10:19
Engineer999Engineer999
1,31821222
asked Nov 16 '18 at 10:19
Engineer999Engineer999
1,31821222
edited Nov 16 '18 at 10:34
Engineer999
asked Nov 16 '18 at 10:19
Engineer999Engineer999
1,31821222
asked Nov 16 '18 at 10:19
Engineer999Engineer999
1,31821222
asked Nov 16 '18 at 10:19
Engineer999Engineer999
1,31821222
1,31821222
add a comment |
add a comment |
1 Answer
1
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The /boot/uEnv.txt file is being modified by the eMMC flasher script which executes when you boot the board with the uEnv.txt file containining the line cmdline=init=/opt/scripts/tools/eMMC/init-eMMC-flasher-v3.sh: the cmdline parameter in that file indicates the kernel command line, which U-Boot passes to the Linux kernel when booting.
So with that line in uEnv.txt you are basically telling U-Boot to tell the kernel to launch a "non-conventional" application instead of the default init program (which would boot the system "normally"). This application, which runs under Linux, can access the entire SD card and eMMC memories, including the partition containing the uEnv.txt file, and can change the file contents as it sees fit.
Regarding your last question, you can create a file containing your modified SD card image from a Linux shell, using the dd tool, e.g:
dd if=/dev/mmcblk0 of=mySDcard.img
In the above command, replace /dev/mmcblk0 with the block device file created in the system when you insert your SD card (whose partitions must NOT be mounted for this to work correctly); the image file will be created as mySDcard.img.
answered Nov 29 '18 at 20:32
Francesco LavraFrancesco Lavra
27318
add a comment |
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1 Answer
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votes
The /boot/uEnv.txt file is being modified by the eMMC flasher script which executes when you boot the board with the uEnv.txt file containining the line cmdline=init=/opt/scripts/tools/eMMC/init-eMMC-flasher-v3.sh: the cmdline parameter in that file indicates the kernel command line, which U-Boot passes to the Linux kernel when booting.
So with that line in uEnv.txt you are basically telling U-Boot to tell the kernel to launch a "non-conventional" application instead of the default init program (which would boot the system "normally"). This application, which runs under Linux, can access the entire SD card and eMMC memories, including the partition containing the uEnv.txt file, and can change the file contents as it sees fit.
Regarding your last question, you can create a file containing your modified SD card image from a Linux shell, using the dd tool, e.g:
dd if=/dev/mmcblk0 of=mySDcard.img
In the above command, replace /dev/mmcblk0 with the block device file created in the system when you insert your SD card (whose partitions must NOT be mounted for this to work correctly); the image file will be created as mySDcard.img.
answered Nov 29 '18 at 20:32
Francesco LavraFrancesco Lavra
27318
add a comment |
The /boot/uEnv.txt file is being modified by the eMMC flasher script which executes when you boot the board with the uEnv.txt file containining the line cmdline=init=/opt/scripts/tools/eMMC/init-eMMC-flasher-v3.sh: the cmdline parameter in that file indicates the kernel command line, which U-Boot passes to the Linux kernel when booting.
So with that line in uEnv.txt you are basically telling U-Boot to tell the kernel to launch a "non-conventional" application instead of the default init program (which would boot the system "normally"). This application, which runs under Linux, can access the entire SD card and eMMC memories, including the partition containing the uEnv.txt file, and can change the file contents as it sees fit.
Regarding your last question, you can create a file containing your modified SD card image from a Linux shell, using the dd tool, e.g:
dd if=/dev/mmcblk0 of=mySDcard.img
In the above command, replace /dev/mmcblk0 with the block device file created in the system when you insert your SD card (whose partitions must NOT be mounted for this to work correctly); the image file will be created as mySDcard.img.
answered Nov 29 '18 at 20:32
Francesco LavraFrancesco Lavra
27318
add a comment |
The /boot/uEnv.txt file is being modified by the eMMC flasher script which executes when you boot the board with the uEnv.txt file containining the line cmdline=init=/opt/scripts/tools/eMMC/init-eMMC-flasher-v3.sh: the cmdline parameter in that file indicates the kernel command line, which U-Boot passes to the Linux kernel when booting.
So with that line in uEnv.txt you are basically telling U-Boot to tell the kernel to launch a "non-conventional" application instead of the default init program (which would boot the system "normally"). This application, which runs under Linux, can access the entire SD card and eMMC memories, including the partition containing the uEnv.txt file, and can change the file contents as it sees fit.
Regarding your last question, you can create a file containing your modified SD card image from a Linux shell, using the dd tool, e.g:
dd if=/dev/mmcblk0 of=mySDcard.img
In the above command, replace /dev/mmcblk0 with the block device file created in the system when you insert your SD card (whose partitions must NOT be mounted for this to work correctly); the image file will be created as mySDcard.img.
answered Nov 29 '18 at 20:32
Francesco LavraFrancesco Lavra
27318
The /boot/uEnv.txt file is being modified by the eMMC flasher script which executes when you boot the board with the uEnv.txt file containining the line cmdline=init=/opt/scripts/tools/eMMC/init-eMMC-flasher-v3.sh: the cmdline parameter in that file indicates the kernel command line, which U-Boot passes to the Linux kernel when booting.
So with that line in uEnv.txt you are basically telling U-Boot to tell the kernel to launch a "non-conventional" application instead of the default init program (which would boot the system "normally"). This application, which runs under Linux, can access the entire SD card and eMMC memories, including the partition containing the uEnv.txt file, and can change the file contents as it sees fit.
Regarding your last question, you can create a file containing your modified SD card image from a Linux shell, using the dd tool, e.g:
dd if=/dev/mmcblk0 of=mySDcard.img
In the above command, replace /dev/mmcblk0 with the block device file created in the system when you insert your SD card (whose partitions must NOT be mounted for this to work correctly); the image file will be created as mySDcard.img.
answered Nov 29 '18 at 20:32
Francesco LavraFrancesco Lavra
27318
answered Nov 29 '18 at 20:32
Francesco LavraFrancesco Lavra
27318
answered Nov 29 '18 at 20:32
Francesco LavraFrancesco Lavra
27318
answered Nov 29 '18 at 20:32
Francesco LavraFrancesco Lavra
27318
27318
add a comment |
add a comment |
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