Dual-boot PostmarketOS

By Fenguoerbian

March 16, 2025

PostmarketOS (Dualboot with android)

To dual boot postmarketos with android, it’s recommended to have android on slot A and postmarketos on slot B. Also TWRP recovery is used here for sgdisk (parted, or other partitioning tools).

Boot into TWRP recovery and in Advanced->Terminal you can use sgdisk to check the status of your internal drive
```
#Get userdata number and info on the disk
sgdisk /dev/block/sda --print
```

Prepare partition for postmarket os. I’m using Slot B only and shrink down the userdata partition for installing postmarket os

Note: This is a change to your partition table and you will loss ALL data and systems installed on your device! I’m re-flash Android rom to slot A after this work!

sgdisk /dev/block/sda --delete=17    # 17 (sda17) is `userdata` in my sda, originally it's 229.2 GiB


#Make userdata 200 gigabytes, minimum size unknown (postmarket website uses 2G, which is still not the minimum)
sgdisk /dev/block/sda --new=0:0:+200G --change-name=0:userdata

# !!! Here you need to format the new `userdata` as well
# maybe `ext4` is suited?

Stay in TWRP recovery for the next step.

Next, the choice is either to use a subpartition to store postmarketos, or the WHOLE DISK.

Subpartition

WHOLE DISK

#Make pmOS boot partition 256 megabytes (default size)
sgdisk /dev/block/sda --new=0:0:+256M --change-name=0:pmOS_boot

#Make pmOS system partition uses the rest of the disk
# __NOTE:__ This is a DANGER step! It will take all the remaining sectors 
#   and make `sgdisk` not able to modify partitions any more!
# You better keep at least 10 sectors for the end!
# That's because GPT parition table will be saved on both ends of the disk!
sgdisk /dev/block/sda --new=0:0:0 --change-name=0:pmOS_root

(Optional) use parted to save the wrong sgdisk partition table.

Currently my sgdisk /dev/block/sda --print shows the following:

OnePlus6:/ # sgdisk /dev/block/sda --print

Warning! Main partition table overlaps the first partition by 6 blocks!
You will need to delete this partition or resize it in another utility.
Disk /dev/block/sda: 61677568 sectors, 235.3 GiB
Sector size (logical/physical): 4096/4096 bytes
Disk identifier (GUID): 714F415D-AEF4-7531-A367-496564A0F5EE
Partition table holds up to 32 entries
Main partition table begins at sector 2 and ends at sector 2
First usable sector is 6, last usable sector is 61677562
Partitions will be aligned on 2-sector boundaries
Total free space is 0 sectors (0 bytes)

Number  Start (sector)    End (sector)  Size       Code  Name
   1               6               7   8.0 KiB     A02C  ssd
   2               8            8199   32.0 MiB    A026  persist
   3            8200            8455   1024.0 KiB  A01F  misc
   4            8456            8711   1024.0 KiB  FFFF  param
   5            8712            8839   512.0 KiB   A02D  keystore
   6            8840            8967   512.0 KiB   FFFF  frp
   7            8968           74503   256.0 MiB   A039  op2
   8           74504           77063   10.0 MiB    FFFF  oem_dycnvbk
   9           77064           79623   10.0 MiB    FFFF  oem_stanvbk
  10           79624           81647   7.9 MiB     FFFF  reserve1
  11           81648           85695   15.8 MiB    FFFF  reserve2
  12           85696           85823   512.0 KiB   FFFF  config
  13           85824          817983   2.8 GiB     A038  system_a
  14          817984         1550143   2.8 GiB     FFFF  system_b
  15         1550144         1575743   100.0 MiB   FFFF  odm_a
  16         1575744         1601343   100.0 MiB   FFFF  odm_b
  17         1601344        54030143   200.0 GiB   8300  userdata
  18        54030144        54095679   256.0 MiB   8300  pmOS_boot
  19        54095680        61677562   28.9 GiB    8300  pmOS_root

And from parted’s print free command, it shows:

(parted) print free                                                       
Model: SAMSUNG KLUEG8U1EA-B0C1 (scsi)
Disk /dev/block/sda: 253GB
Sector size (logical/physical): 4096B/4096B
Partition Table: gpt
Disk Flags: 

Number  Start   End     Size    File system  Name         Flags
20      0.00B   4095B   4096B                             boot, esp
21      0.00B   4095B   4096B
        12.3kB  24.6kB  12.3kB  Free Space
 1      24.6kB  32.8kB  8192B                ssd
 2      32.8kB  33.6MB  33.6MB  ext4         persist
 3      33.6MB  34.6MB  1049kB               misc
 4      34.6MB  35.7MB  1049kB               param
 5      35.7MB  36.2MB  524kB                keystore
 6      36.2MB  36.7MB  524kB                frp
 7      36.7MB  305MB   268MB   ext4         op2
 8      305MB   316MB   10.5MB               oem_dycnvbk
 9      316MB   326MB   10.5MB               oem_stanvbk
10      326MB   334MB   8290kB               reserve1
11      334MB   351MB   16.6MB               reserve2
12      351MB   352MB   524kB                config
13      352MB   3350MB  2999MB  ext2         system_a
14      3350MB  6349MB  2999MB  ext2         system_b
15      6349MB  6454MB  105MB   ext4         odm_a
16      6454MB  6559MB  105MB   ext4         odm_b
17      6559MB  221GB   215GB   ext4         userdata
18      221GB   222GB   268MB                pmOS_boot
19      222GB   253GB   31.1GB               pmOS_root
        253GB   253GB   12.3kB  Free Space

And I use parted to remove partitions with number 18 and 19 (since I want to use subpartition for postmarketos, not the entire space.) and Remove partition with number 20 and 21 (this seems to be created by postmarket OS when I previously install to use the whole space? I’m not sure about this, but maybe this is causing the overlapping in partition table problem.)

After that, sgdisk seems to work fine and I just reboot to recovery again to test if this really works.

Turns out we indeed need to reboot to recovery! Then sgdisk will complain about partition tables differ! And you will need gdisk to fix this problem.

gdisk /dev/block/sda

Then use ? command to show detail help page, find the “recovery/…..(expert only)” mode, and regenerate backup partition table at then end of storage (because for me it’s the end-device version that’s being corrupted.)

The sgdisk, gdisk, parted tools can be push to your recovery with adb enabled. (TWRP comes with some of these commands available, but for Lineage recovery you can just adb push these commands.)

adb push path/to/local/parted /sbin/parted    # push local `parted` to oneplus's /sbin folder
adb shell    # access phone device shell with adb
chmod 777 /sbin/parted    # give `parted` exceutable attribute
parted    # then you can use it!

For my device, it’s arm64, but seems like the 32bit and 64bit version both work for my.

Flash postmarket os to your slot B and the newly created partitions

fastboot erase dtbo_b    # erase the device tree on slot B

option 1: If you use subpartition

sudo fastboot flash systempmos 20250219-1313-postmarketOS-v24.12-phosh-22.5-oneplus-enchilada.img 
sudo fastboot flash boot_b 20250219-1313-postmarketOS-v24.12-phosh-22.5-oneplus-enchilada-boot.img

option 2: If you want to use ALL disk space (including android userdata)

fastboot flash pmOS_boot /tmp/postmarketOS-export/oneplus-enchilada-boot.img
fastboot flash pmOS_root /tmp/postmarketOS-export/oneplus-enchilada-root.img
fastboot flash boot_b /tmp/postmarketOS-export/oneplus-enchilada-boot.img

fastboot set_active b
ls fastboot getvar current-slot
fastboot reboot

After works

Dual boot status

The Oneplus 6 uses A/B slots, so it has dtbo, boot, system both with A and B, i.e. dtbo_a and dtbo_b, boot_a and boot_b, and system_a and system_b. The android system is flashed to system partitions and recovery flashed to boot partitions. The postmarket os data is flashed to systempmos partition (I’m using the subpartition method) and boot image is flashed to boot_b.

Therefore, for a working dual boot device, I have:

dtbo_a: the android device tree.
boot_a and system_a: the android recovery and system, currently I’m using LineageOS recovery and LineageOS.
dtbo_b: erased for booting postmarket OS.
boot_b: the postmarketOS boot image.
system_b: the backup android system image.
systempmos: the system data of postmarket os.

Switch slots:

- postmarketos(slot B) to android (slot A): use the `qbootctl` in postmarketos

- android (slot A) to postmarket os (slot B): boot to fastboot mode and `fastboot set_active b`

Upgrade LineageOS:

1. flash back android images to `dtbo_b` and `boot_b`

    ```
    fastboot flash dtbo_b dtbo.img    # not sure if this is necessary. It works out for me without this dtbo flash
    fastboot flash boot_b boot.img    
    ```
    
    After this, the android in Slot B should be accessible, then you have android just like before.
    
    __Note:__ You might also need to fix the overlapping partition problem mentioned before for the update to work.
    
1. Upgrade LineageOS version according to their manual. Just remember to make sure you got slot A the latest version of LineageOS.

1. Check the Lineage OS in slot A is updated and works fine, then go to fastboot/flash mode

1. Flash the boot image for postmarketos

    ```
    fastboot erase dtbo_b
    fastboot flash boot_b postmarketos-boot.img
    fastboot set_active b    # activate postmarket os to check its status
    fastboot reboot
    ```

Upgrade postmarketos:

To be added.

Configure postmarketos (phosh UI)

1. Update and reboot the system

1. Enable SSH

1. Manual scale factor to 2.5

1. Install (Re-install flathub remote repo) according to Alpine linux's flathub guidance (https://flatpak.org/setup/Alpine/)

1. Chinese input method?

Reference

A post about unlock and installing TWRP recovery on OnePlus 6

A post offering attachment of parted

A post about change the size of system partition, offering links to gdisk attachment

A post about gdisk, sgdisk download