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https://github.com/JamiKettunen/initramfs-tools

Create small and adaptable Linux initramfs' mainly intended for embedded (e.g. Android) devices.
https://github.com/JamiKettunen/initramfs-tools

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Create small and adaptable Linux initramfs' mainly intended for embedded (e.g. Android) devices.

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# initramfs-tools

Create small and adaptable Linux initramfs' mainly intended for embedded (e.g. Android) devices.



## Building

Create a `config.custom.sh`, tweak options defined in [`config.sh`](config.sh) as you please & simply run the [`build.sh`](build.sh) script:

```

$ ./build.sh

```

For e.g. scripting you can additionally add the `-N` flag to avoid interactive actions (or `-c alternate_config.sh` to override [`config.sh`](config.sh) defaults).



## Features

* An easily configurable environment based around [Buildroot](https://buildroot.org) & [BusyBox](https://busybox.net)

* Kernel module support

* Shell script hook system with ordering and early/late triggers

  * Execution order is decided by the numbering of the hook filenames

  * Early triggers run as soon as the initramfs is reached

  * Late triggers run **after** a rootfs is mounted and **right before** `switch_root`

  * Optionally extra hooks can be added and triggered manually via kernel cmdline

* Produced `cpio` archives can be compressed with either `gzip` or `lz4`

* Optional PPM image splash screens ([or even boot animations with some limitations](https://github.com/JamiKettunen/initramfs-tools/blob/0e66266/config.sh#L87-L107))

* Ideally boots any OS (distro) using the Linux kernel



## Runtime configuration

A bunch of the initramfs features can be configured via kernel cmdline using the following options:

|Option|Example values|Comment|

|------|--------------|-------|

|`rd.rootfs`|`/dev/sde21`, `nbd:rootfs:512`|Rootfs location (mandatory!)|

|`rd.extra_hooks`|`late/extra-hook`, `a,b,c`|Additional hooks to run in initramfs|

|`rd.mass_storage_rw`|`0` (default) or `1`|Mount all mass storage devices as read-write|

|`rd.silent_boot`|`0` (default) or `1`|Silence logs from kernel and initramfs, implied on when splash image set|

|`rd.no_clear`|`0` (default) or `1`|Don't clear console on initramfs enter|

|`rd.no_fwdcon`|`0` (default) or `1`|Don't forward kernel messages to `tty8` while starting|



## Booting

* Block device: `rd.rootfs=/dev/sde21`

* Block device by UUID: e.g. `rd.rootfs=uuid:abcd-1234` or `rd.rootfs=uuid:abcd-1234/rootfs.img`

* Block device by label: e.g. `rd.rootfs=label:system` or `rd.rootfs=label:system/rootfs.img` 1

* Image on a block device: `rd.rootfs=/dev/sda13/rootfs.img`

* Directory on a block device: `rd.rootfs=/dev/sda13/rootfs_dir`

* Network Block Device (NBD): `rd.rootfs=nbd` or e.g. `rd.rootfs=nbd:rootfs:512` 2

  * A default export name of `rootfs` is assumed unless specified otherwise after the first colon (`:`)

  * A default block-size of `512` is assumed (choices: `512`, `1024`, `2048` or `4096`) unless specified otherwise after the second colon (`:`)

* Dynpart under Android super partition: `rd.rootfs=super:system_a` 3



1 **NOTE:** Filesystem labels containing `/` aren't supported!

2 **WARNING:** Make sure you don't (re)configure USB ConfigFS from userspace, or the network connection will cut out!


3 **NOTE:** Remember to add `BR2_CONFIGS+=",super_par_mount"` to your config to build the required extra utilities!



### NBD server example

Here is an example tree of a NBD server setup I've used successfully:

```

├── allowed_clients

├── nbd_config

└── rootfs.img

```

`allowed_clients`:

```sh

# subnet of initramfs RNDIS connection

172.16.42.0/24

```

`nbd_config`:

```ini

[generic]

authfile = allowed_clients

copyonwrite = false

allowlist = true

max_threads = 16

maxconnections = 1

timeout = 5



[rootfs]

exportname = 

```

With those files in place you can start a server with `nbd-server -C nbd_config`, confirm output of `nbd-client -l 127.0.0.1` and test network-booting a target device!



## Kernel requirements

Core

* `CONFIG_RD_GZIP=y` (if using `gzip` compression)

* `CONFIG_RD_LZ4=y` (if using `lz4` compression)

* `CONFIG_DEVTMPFS=y` (populate `/dev` automatically when `devtmpfs` is mounted)



Booting

* `CONFIG_BLK_DEV_LOOP=m` (booting from loopback images)

* `CONFIG_BLK_DEV_NBD=m` (NBD rootfs booting)



USB

* `CONFIG_USB_GADGET=y` (UDC core driver)

* `CONFIG_USB_CONFIGFS=m` (configure USB via ConfigFS)

* `CONFIG_USB_CONFIGFS_RNDIS=y` (enable RNDIS access)

* `CONFIG_USB_CONFIGFS_MASS_STORAGE=y` (enable Mass Storage access)



## Debugging

If you have a working virtual console, you should have logs visible on the display itself.



Otherwise assuming the `configfs`, `rndis` and `telnet` hooks are on the initramfs, you should be able to use `telnet 172.16.42.1` to gain an ash shell on the target device.



To view the boot console (display) from telnet, you can use `conspy`.



## Silent boot

Adding `console=tty2 vt.global_cursor_default=0` to kernel cmdline appears to have helped with Void & Arch Linux at least and allowed the boot splash to show up without issues.



Keep in mind if disabling global VT cursor you should re-enable it on a per-rootfs basis with the following:

```

# setterm -cursor on >> /etc/issue

```



Adding `audit=0` might also help especially on distros using systemd init.



## License

All code in this repository is licensed under a [`GPL-3.0-only`](LICENSE) license.



## To-Do

* Fix [`list_pars()`](functions/blk.sh) to work with eMMC partitions

* Minimal BusyBox config

* Recursive hook depdendencies

* Booting from a block devices based on UUID?

* Booting from subpartitions (e.g. stock postmarketOS setup) via e.g. `rd.rootfs.subpars`

* Booting LVM/LUKS2 encrypted root?

* Mount options for root via e.g. `rd.mount_opts`

* x86 support?