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{{Warning| this article is outdated}}
 
== Overview ==
== Overview ==
Once you press the power button on your device with a postmarketOS installation, it goes through the following steps:
Once you press the power button on your device with a postmarketOS installation, it goes through the following steps:
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==  Early boot process ==
==  Early boot process ==


== UEFI ==
=== UEFI ===
On device that support UEFI , pmOS would boot via systemd-boot
On device that support UEFI , pmOS would boot via systemd-boot
== Andorid boot image ==
=== Andorid boot image ===
On most Andorid device  , the bootloader on that device would boot the android image that is in the partition that labeled at <code> boot </code>.that file contain initramfs and kerenl.pmOS would put its initramfs and kerenl into a Andorid boot image and flash it to the partition.However there are some android device that dont support  andorid boot image.
On most Andorid device  , the bootloader on that device would boot the android image that is in the partition that labeled at <code> boot </code>.that file contain initramfs and kerenl.pmOS would put its initramfs and kerenl into a Andorid boot image and flash it to the partition.However there are some android device that dont support  andorid boot image.
==== isorec ====
==== isorec ====
Very few Android devices don't expect a <code>boot.img</code> file written to the Android boot partition, but rather just the Linux kernel, with an embedded initramfs. But we want the initramfs packaging to be independent of the kernel (not require a kernel rebuild to change the initramfs!). Therefore we use the so-called "isorec" trick here: the initramfs script built into the kernel is just a very small stub, that loads the real initramfs from the postmarketOS boot partition ([https://gitlab.com/postmarketOS/pmaports/-/blob/1d2b62a1094e77e50e1a52c48b07eecb1fbfd26a/device/testing/linux-samsung-i9100/APKBUILD#L31-50 example]).
Very few Android devices don't expect a <code>boot.img</code> file written to the Android boot partition, but rather just the Linux kernel, with an embedded initramfs. But we want the initramfs packaging to be independent of the kernel (not require a kernel rebuild to change the initramfs!). Therefore we use the so-called "isorec" trick here: the initramfs script built into the kernel is just a very small stub, that loads the real initramfs from the postmarketOS boot partition ([https://gitlab.com/postmarketOS/pmaports/-/blob/1d2b62a1094e77e50e1a52c48b07eecb1fbfd26a/device/testing/linux-samsung-i9100/APKBUILD#L31-50 example]).


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== postmarketOS initramfs ==
== postmarketOS initramfs ==

Revision as of 11:11, 26 September 2024

Overview

Once you press the power button on your device with a postmarketOS installation, it goes through the following steps:

  1. Device specific bootloaders
  2. postmarketOS initramfs
  3. Init
  4. Display manager (if UI is not none, otherwise it stops at getty )
  5. User Interface of choice (Plasma Mobile, Phosh, ...)

Early boot process

UEFI

On device that support UEFI , pmOS would boot via systemd-boot

Andorid boot image

On most Andorid device , the bootloader on that device would boot the android image that is in the partition that labeled at boot .that file contain initramfs and kerenl.pmOS would put its initramfs and kerenl into a Andorid boot image and flash it to the partition.However there are some android device that dont support andorid boot image.

isorec

Very few Android devices don't expect a boot.img file written to the Android boot partition, but rather just the Linux kernel, with an embedded initramfs. But we want the initramfs packaging to be independent of the kernel (not require a kernel rebuild to change the initramfs!). Therefore we use the so-called "isorec" trick here: the initramfs script built into the kernel is just a very small stub, that loads the real initramfs from the postmarketOS boot partition (example).


postmarketOS initramfs

The postmarketOS initramfs consists of busybox, a shell script and very few other command-line programs. Find the source code in the postmarketos-mkinitfs pmaports. mkinitfs.sh generates the initramfs (and packages into a suitable format for the device specific bootloader if necessary, such as a boot.img file) and init.sh.in is what is actually running in the initramfs.

The initramfs takes care of many things during the early booting phase, such as setting up USB networking, resizing the root partition, displaying a charging UI. Some of the tasks are listed in detail here, for others refer to the source code for now and consider expanding this article. Furthermore, the initramfs supports hooks (which may be used to work around device specific quirks, for example).

Here is a list of the boot process related to initramfs:

  • Enable set -x if the verbose-initfs hook exists
  • Load deviceinfo data
  • Create busybox symlinks
  • Mount /dev, /proc and /sys
  • Redirect stdout to /pmOS_init.log and to the kernel log (dmesg)
  • Modprobe modules listed in deviceinfo
  • Enable mdev (busybox replacement for udev)
  • Make kernel detect subpartitions
  • Wait for /dev/fb0 to appear (if not disabled in deviceinfo) and set the framebuffer mode
  • Execute hooks
  • Show loading splash
  • Start networking
  • Find and mount the partition with the pmOS_boot label (or show "Boot partition not found" splash)
  • Unpack initramfs-extra from the boot partition (or show "Initramfs-extra not found" splash)
  • Start charging mode if one of the known charging kernel parameters was found in the cmdline (show battery icon for charging and waits for powerbutton press)
  • Search for a partition with the label pmOS_root or crypto_LUKS
  • Try to resize the partition containing the root filesystem to the maximum size
  • Start osk-sdl if the rootfs is a luks partition
  • Resize the root filesystem to match the partition it is in
  • Mount the root filesystem
  • Kill all processes running in the initramfs and pivot root to the real rootfs

Find the boot and root partitions

Due to the various possible partition layouts, the initramfs script has to look in various places for the postmarketOS boot and root partitions.

boot partition:

  • pmos_boot kernel parameter (from the device specific bootloader)
  • Any partition or subpartition with the pmOS_boot label

root partition:

  • pmos_root kernel parameter (from the device specific bootloader)
  • Any partition or subpartition with the pmOS_root label
  • Any partition or subpartition that is encrypted

Load initramfs-extra

Some Android devices require a very small initramfs, because otherwise the resulting boot.img file is too big for the Android boot partition. Therefore, we have split the initramfs into two parts, the tiny initramfs that is potentially placed in such a boot.img file (depending on the bootloader). And the initramfs-extra, which can hold bigger binaries, such as the UI to unlock an encrypted root partition (Unl0kr).

Switch root

Note It will look like this, once pmaports#664 is resolved.

At the end of the initramfs script, the root partition is mounted at /sysroot, and the boot partition is mounted at /sysroot/boot. The latter is done, so Init does not need to figure out the correct boot partition later on. Afterwards, the busybox command switch_root is called to switch over and pass control to Init.

See also