SD/eMMC Setup Guide

This is a general guide for preparing SD/eMMC devices for use with Linux, including formatting, partitioning, mounting, and writing full disk images.

Manual Partitioning and Formatting

General guide for manually creating partitions and filesystems on SD/eMMC devices.

Identify the device
```
$ ls -l /dev/mmc*
$ dmesg | grep mmc
```
The device typically appears as /dev/mmcblk0.

Partition the device (using fdisk or parted)

$ fdisk /dev/mmcblk0

# Create a new partition table (type 'o' for DOS/MBR or 'g' for GPT)
# Create a new partition (type 'n')
# Set partition type if needed (type 't')
# Write changes (type 'w')

Format the partition

$ mkfs.ext4 /dev/mmcblk0p1    # For ext4 filesystem
$ mkfs.vfat /dev/mmcblk0p1    # For FAT32 filesystem

Mount the partition

$ mkdir -p /mnt/sdcard
$ mount /dev/mmcblk0p1 /mnt/sdcard

Verify mount

$ df -h | grep mmcblk
$ mount | grep mmcblk

Writing a Full Disk Image

General guide for writing a complete disk image to SD/eMMC devices.

If you have a complete disk image (with GPT partition table and all partitions), you can write it directly to the SD/eMMC device using dd:

Identify the target device
```
$ ls -l /dev/mmc*
```
Make sure you have identified the correct device. Writing to the wrong device will destroy its data.
Write the disk image
```
$ dd if=disk-image.img of=/dev/mmcblk0 bs=4M oflag=direct status=progress
$ sync
```
Where:
- if= specifies the input file (your disk image)
- of= specifies the output device (your SD/eMMC device)
- bs=4M sets the block size to 4MB for better performance
- oflag=direct bypasses the kernel buffer cache for direct writes
- status=progress shows transfer progress
- sync flushes device write caches (still recommended even with oflag=direct)

Verify the write

$ sync
$ blockdev --rereadpt /dev/mmcblk0
$ fdisk -l /dev/mmcblk0