Question about init conception

Fulgurance · Veteran Joined: 15 Feb 2017 Posts: 1239

Hi guys, I am actually doing test under virtualbox with an init system I am coding.

I just have one question.

Is it possible to compile an init system dynamically or not ?

Because if I compile my init dynamically, bascially it can't find the libraries. I have to compile it statically. Are there anyway to do ?
_________________
My actual project: https://github.com/Fulgurance/ISM

Ingenius Software Manager is a tool to build and manage a Linux system from scratch.
It will able to manage a linux installation just with a given path to the futur root path

pingtoo · Posted: Sun Jan 12, 2025 6:59 pm Post subject:

How you start your init?

Usually init start after rootfs already mounted so runtime libraries usually available.

But as you already experienced, init is better statically linked to support all kinds of condition.

Fulgurance · Veteran Joined: 15 Feb 2017 Posts: 1239

So by your explanation, I guess my init should first mount the root filesystem ? I thought will be already mounted.
_________________
My actual project: https://github.com/Fulgurance/ISM

Ingenius Software Manager is a tool to build and manage a Linux system from scratch.
It will able to manage a linux installation just with a given path to the futur root path

Hu · Administrator Joined: 06 Mar 2007 Posts: 22981

/sbin/init from sysvinit is dynamically linked, so yes, it is possible, and on a stock Gentoo system, it seems to work without user intervention.

Fulgurance · Veteran Joined: 15 Feb 2017 Posts: 1239

So how should I proceed ? Because there is not really documentation or anything about this.

So I just would like to make the rootfs available for my init system. How should I proceed exactly ?
_________________
My actual project: https://github.com/Fulgurance/ISM

Ingenius Software Manager is a tool to build and manage a Linux system from scratch.
It will able to manage a linux installation just with a given path to the futur root path

pingtoo · Posted: Sun Jan 12, 2025 7:40 pm Post subject:

GDH-gentoo · Last edited by GDH-gentoo on Sun Jan 12, 2025 8:20 pm; edited 1 time in total

Fulgurance · Veteran Joined: 15 Feb 2017 Posts: 1239

So to make sure it's clear.

When the kernel finish to initialize all it need, it give the hand to the program located (by default) at /sbin/init, with the PID 1 right ?
So normally at this stage, rootfs should be mounted yet isn't it ? ( and I think it make sens because to call /sbin/init, root should be mounted)

So my question now is, why I get this error (screenshot):

https://global.discourse-cdn.com/flex036/uploads/crystal_lang/original/2X/6/67f17012d1d552d6614cd31ee22798ccad4aedf2.png

Because the rootfs is mounted, and this file exist: /lib64/ld-linux-x86-64.so.2 (I checked by booting bash as init process)

And why /proc/stat isn't mounted ?
_________________
My actual project: https://github.com/Fulgurance/ISM

Ingenius Software Manager is a tool to build and manage a Linux system from scratch.
It will able to manage a linux installation just with a given path to the futur root path

zen_desu · Tux's lil' helper Joined: 25 Oct 2024 Posts: 101

If an initramfs is not being used, and the kernel is able to mount the root and run the init, you must be sure your init is doing things such as mounting a devtmpfs on /dev/, procfs on /proc, sysfs on /sys, etc. The devtmpfs can be avoided if you add static nodes for devices.
_________________
µgRD dev
Wiki writer

GDH-gentoo · Posted: Sun Jan 12, 2025 8:20 pm Post subject:

In other words, if no initramfs is used, the only things that the PID 1 program can assume are:

That the rootfs, and only the rootfs, is mounted. Nothing else, not even the proc or devtmpfs filesystems.
That standard input, output and error are already open and redirected to the console.

_________________

pingtoo · Posted: Sun Jan 12, 2025 8:26 pm Post subject:

GDH-gentoo · Posted: Sun Jan 12, 2025 8:41 pm Post subject:

pingtoo · Posted: Sun Jan 12, 2025 9:32 pm Post subject: