Access eMMC install from second storage medium

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This article explains step-by-step how you can get into a broken postmarketOS install from a second storage medium, and recover data from there or fix the installation. One use case is fixing postmarketOS on the eMMC of the PinePhone with an SD card.

Boot postmarketOS from second storage medium

Download a postmarketOS image and put it on the second storage medium. If there are no pre-built images for your device, build one yourself with pmbootstrap. Boot from the storage medium (in case of the PinePhone, it will automatically boot from the SD card once inserted.)

Get shell access

  • Attach a serial cable (remember to set killswitches accordingly), or
  • Attach an USB cable and use SSH, or
  • Connect to Wi-Fi and use SSH

Mount the eMMC's root partition

Use lsblk to figure out which storage device is eMMC (if there are only two, it's the one where nothing is mounted). In this example, it is /dev/mmcblk2.

$ lsblk
NAME         MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
mmcblk0      179:0    0 59.5G  0 disk 
├─mmcblk0p1  179:1    0  243M  0 part /boot
└─mmcblk0p2  179:2    0 59.2G  0 part /
mmcblk2      179:32   0 29.1G  0 disk 
├─mmcblk2p1  179:33   0  121M  0 part 
└─mmcblk2p2  179:34   0   29G  0 part 
mmcblk2boot0 179:64   0    4M  1 disk 
mmcblk2boot1 179:96   0    4M  1 disk

a) Encrypted

$ sudo cryptsetup luksOpen /dev/mmcblk2p2 emmc
Enter passphrase for /dev/mmcblk2p2:
$ sudo mount /dev/mapper/emmc /mnt

b) Not Encrypted

$ sudo mount /dev/mmcblk2p2 /mnt

Access your data

$ cd /mnt
$ ls
bin  boot  dev  etc  home  lib  lost+found  media  mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var

See also

  • Jumpdrive allows similar access by exposing storage devices over USB to your PC