1 ============================ 2 SD and MMC Device Partitions 3 ============================ 4 5 Device partitions are additional logical block devices present on the 6 SD/MMC device. 7 8 As of this writing, MMC boot partitions as supported and exposed as 9 /dev/mmcblkXboot0 and /dev/mmcblkXboot1, where X is the index of the 10 parent /dev/mmcblkX. 11 12 MMC Boot Partitions 13 =================== 14 15 Read and write access is provided to the two MMC boot partitions. Due to 16 the sensitive nature of the boot partition contents, which often store 17 a bootloader or bootloader configuration tables crucial to booting the 18 platform, write access is disabled by default to reduce the chance of 19 accidental bricking. 20 21 To enable write access to /dev/mmcblkXbootY, disable the forced read-only 22 access with:: 23 24 echo 0 > /sys/block/mmcblkXbootY/force_ro 25 26 To re-enable read-only access:: 27 28 echo 1 > /sys/block/mmcblkXbootY/force_ro 29 30 The boot partitions can also be locked read only until the next power on, 31 with:: 32 33 echo 1 > /sys/block/mmcblkXbootY/ro_lock_until_next_power_on 34 35 This is a feature of the card and not of the kernel. If the card does 36 not support boot partition locking, the file will not exist. If the 37 feature has been disabled on the card, the file will be read-only. 38 39 The boot partitions can also be locked permanently, but this feature is 40 not accessible through sysfs in order to avoid accidental or malicious 41 bricking.
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