Question about init conception

[Fulgurance]

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 ?
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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]

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]

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]

/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]

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]

[GDH-gentoo]

[Fulgurance]

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]

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.
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µgRD dev
Wiki writer

[GDH-gentoo]

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.

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[pingtoo]

[GDH-gentoo]

[pingtoo]

[Fulgurance]

[GDH-gentoo]

[pingtoo]

[Fulgurance]

Basically it's simple, when I mount /proc, there is nothing. So how should I generate this file normally ?
So it's not a mount point, go it

So my guess now why I have this bug is, I think it's because of the language I am using. I started to code my program in Crystal (it's based on C). It look like the crystal language ask by default some libraries not available at boot time. A bit annoying
_________________
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]

How exactly are you mounting /proc such that afterwards "there is nothing" there? If you mount procfs there, then there should be useful pseudo-files there.

[pingtoo]

[pingtoo]

I just found CONFIG_PROC_FS is actually a thing. So proc (procfs) is actually configurable.

Fulgurance, is your kernel disable CONFIG_PROC_FS (CONFIG_PROC_FS=n)? that will explain why /proc is empty. But it does not explain why the "mount" command not report error. Or are you code you own mount command with system call mount(2) without checking return status?

[Zucca]

[Fulgurance]

So I find a way to do it with a crystal program !

Basically I made a minimal bash script as /sbin/init:

[Zucca]

[pingtoo]