Initramfs development

This article explains how to modify the postmarketOS initramfs scripts, for which the source can be found in the postmarketos-mkinitfs pmaport. There's another page about adding a device specific initramfs hook.

We have two initramfs files
After the installation, you will have two initramfs files in your device's  folder.

% ls ~/.local/var/pmbootstrap/chroot_rootfs_samsung-i9100/boot initramfs initramfs-extra  vmlinuz Regular Linux distributions only have one initramfs file. We have split it into two to work around the size limitations that some devices have (see ). The regular initramfs is relatively small (~1.5 mb, and we could make it smaller if necessary!) and loads the contents of the initramfs-extra from the pmOS boot partition during the boot process.

The pmOS boot partition is a subpartition of the system partition (SD cards: simply a real partition on the SD card), so we can make it almost as big as we want.

Recommended development workflow

 * Only do one small change at a time
 * Rebuild and test on device
 * When it works, version your change with git
 * Repeat

When you change too much, it will simply not work and you most likely will have no idea why it does not work. Go back to the last working version and do smaller changes at a time.

Regenerating the two initramfs from the phone
You can regenerate both initramfs, even if the first is in a  by running as root

sudo mkinitfs

Tips and tricks

 * Familiarize with inspecting the initramfs
 * can do more than rebuilding the initramfs:

% pmbootstrap initfs --help usage: pmbootstrap initfs [-h] {hook_ls,hook_add,hook_del,ls,build,extract} ...

positional arguments: {hook_ls,hook_add,hook_del,ls,build,extract} hook_ls            list available and installed hook packages hook_add           add a hook package hook_del           uninstall a hook package ls                 list initramfs contents build              (re)build the initramfs extract            extract the initramfs to a temporary folder

optional arguments: -h, --help           show this help message and exit

Manual unpacking and repacking the initramfs file
Another way of unpacking

My device reboots with my customized init script
This is probably caused by a syntax error. Use  to check your scripts for syntax errors. You could also loop forever or spawn a shell (if you have a hardware keyboard or serial cable connected) at some point for debugging and use the telnet shell to test the commands, that are failing, interactively.

No log output on serial!
By default, all output from the initramfs get redirected to. If you want the output through the debug cable you need to add  to your  kernel command line.

How do i show logs on the screen at boot?
In order to disable the postmarketOS splash add  to your kernel command line,  in addition if you want the kernel logs to print to the screen make sure that   is set in the  kernel command line.