Bash script to generate custom bootable OS img files for Raspberry Pi
The script makes use of the following tools :
du
dd
losetup
fdisk
mkfs.vfat
Normally these are available in all distributions by default, but if anyone of them is missing please refer to the instruction manuals of your particular distribution.
Download the script (preferably in a empty folder) using the following commands : Using wget :
wget https://raw.githubusercontent.com/oddlyspaced/rpi-boot2img/main/generate-img.sh
Alternatively using cURL :
curl https://raw.githubusercontent.com/oddlyspaced/rpi-boot2img/main/generate-img.sh --output generate-img.sh
Once the script has been downloaded, make sure to set executable permissions on it by using the following command :
chmod +x generate-img.sh
Open the generate-img.sh file in a text editor and you'll notice a couple of different variables present in the top part of the script
The following variables are required to be edited by the user accordingly
# source files for boot partition (these files will be copied over to the image)
source_files=/home/hardik/Raspberry-Pi/mount-bkp/*
# final img file name
final_img=generated.img
The source_files variable points to a folder which contains the files you want to put in the boot partition.
The final_img variable will define the name of the generated custom img file.
Other global variables which the script uses exist in the section called Script variables and one can edit them accordingly if needed.
To generate the custom img file, just execute
./generate-img.sh
or
bash generate-img.sh
and it should generate the img file in the same directory successfully.
Do note that the script has several sudo commands in place and they would require user authentication, so make sure to enter the password when prompted.
I originally developed this script to generate custom OS images while learning bare metal development.
For Raspberry Pi 4B the source_files targets my folder which has the path /home/hardik/Raspberry-Pi/mount-bkp/* and contains the following files :
├── bcm2711-rpi-4-b.dtb
├── bootcode.bin
├── cmdline.txt
├── config.txt
├── kernel8-rpi4.img
├── overlays
│ ├── miniuart-bt.dtbo
│ └── overlay_map.dtb
└── start4.elf
1 directory, 8 files
Keep note of the * in the source_files path. This essentially tells the script to copy over the files inside the folder. Omitting the * can copy the whole folder as it is and can possibly result in a non functioning img file.
Other variables can be left as it is, and on executing ./generate-img.sh an img file is successfully created which is of 200 MB and has the following partition table :
Disk generated.img: 200 MiB, 209715200 bytes, 409600 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xc0844a25
Device Boot Start End Sectors Size Id Type
generated.img1 2048 409599 407552 199M c W95 FAT32 (LBA)
The generated image file can be flashed using the official Raspberry Pi Imager or via dd using the following command :
sudo dd if=generated.img of=<device path> bs=4M
where <device path> is the path of your SD card interface (Example: /dev/sdb)
Since the generated img contains only 1 partition, you can directly mount it using the following command :
sudo mount -v -o offset=1048576 -t vfat generated.img /path/to/mount/point
Where 1048576 is obtained by multiplying the start offset with 512. [512 * 2048]
Alternatively you can setup a loop device and mount the partition via that by running :
sudo losetup $(losetup -f) generated.img
sudo mount /dev/loop?p? /path/to/mount/point
Here ? in /dev/loop?p? would refer to the loop device on which the generated.img was mounted (Example /dev/loop0p1) and /path/to/mount/point is the mount point