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Fulgurance
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 Posted: Sun Jan 12, 2025 6:51 pm Post subject: Question about init conception |
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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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pingtoo
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| Posted: Sun Jan 12, 2025 6:59 pm Post subject: |
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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. |
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Fulgurance
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| Posted: Sun Jan 12, 2025 7:28 pm Post subject: |
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So by your explanation, I guess my init should first mount the root filesystem ? I thought will be already mounted.
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Hu
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| Posted: Sun Jan 12, 2025 7:29 pm Post subject: |
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| /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. |
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Fulgurance
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| Posted: Sun Jan 12, 2025 7:34 pm Post subject: |
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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 ?
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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 |
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pingtoo
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| Posted: Sun Jan 12, 2025 7:40 pm Post subject: |
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| Fulgurance wrote: | 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 ? |
This is why I ask you how you start init.
Normally init (the program) reside on rootfs, kernel usually got rootfs mounted then call /sbin/init by default. |
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GDH-gentoo
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| Posted: Sun Jan 12, 2025 7:41 pm Post subject: Re: Question about init conception |
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| Fulgurance wrote: | | Is it possible to compile an init system dynamically or not |
"Init system" means several components these days. In particular, yes, the PID 1 program can be (and, as Hu said, on Gentoo is) dynamically linked if:
- The filesystem that contains the expected location of the dynamic linker (/lib64/ld-linux-x86-64.so.2 for amd64 systems with GNU libc) is mounted by the time the kernel or initramfs' init file invokes the PID 1 program.
- The filesystem(s) that contain the locations where the dynamic linker searches for the PID 1 program's shared libraries are mounted by the time the kernel or initramfs' init file invokes the PID 1 program.
For the rest of the init system's components it depends.
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| Ionen wrote: | | As a packager I just don't want things to get messier with weird build systems and multiple toolchains requirements though |
Last edited by GDH-gentoo on Sun Jan 12, 2025 8:20 pm; edited 1 time in total |
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Fulgurance
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| Posted: Sun Jan 12, 2025 7:54 pm Post subject: |
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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 ?
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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 |
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zen_desu
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| Posted: Sun Jan 12, 2025 8:08 pm Post subject: |
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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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GDH-gentoo
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| Posted: Sun Jan 12, 2025 8:20 pm Post subject: |
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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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| NeddySeagoon wrote: | | I'm not a witch, I'm a retired electronics engineer |
| Ionen wrote: | | As a packager I just don't want things to get messier with weird build systems and multiple toolchains requirements though |
Last edited by GDH-gentoo on Sun Jan 12, 2025 8:39 pm; edited 1 time in total |
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pingtoo
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| Posted: Sun Jan 12, 2025 8:26 pm Post subject: |
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| Fulgurance wrote: | 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 ? |
How did you determine /lib64/ld-linux-x86-64.so.2 was missed in init start up? you screen shut does not show that.
rootfs (/) does not include /proc. /proc is just a mount point for pseudo file system proc. usually it is init job to invoke other program(s) to perform mounting of supporting pseudo file systems (for example sys, proc, devtmpfs, etc...
Not sure which "init" system you are using, but for example openrc on gentoo you can read /lib/rc/sh/init.sh for some idea. |
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GDH-gentoo
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| Posted: Sun Jan 12, 2025 8:41 pm Post subject: |
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| pingtoo wrote: | | Not sure which "init" system you are using, [...] |
The OP says Fulgurance is making one.
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| NeddySeagoon wrote: | | I'm not a witch, I'm a retired electronics engineer |
| Ionen wrote: | | As a packager I just don't want things to get messier with weird build systems and multiple toolchains requirements though |
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pingtoo
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| Posted: Sun Jan 12, 2025 9:32 pm Post subject: |
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| GDH-gentoo wrote: | | pingtoo wrote: | | Not sure which "init" system you are using, [...] |
The OP says Fulgurance is making one. |
Yes, I understand. however I believe he is refer to the binary program because OP is specific about run time linked library.
I think at this OP is yet to understand the "init" as whole is not just about binary program. It is entire system that describe a life cycle of OSE (Operating System Environment)
I am not saying init system cannot a single binary program, it just that if you programmed entire life cycle of OSE in single binary you lost many opportunity for later enhancement to OSE. because otherwise the init binary need to reprogrammed for new changes. it is just not very well engineering design. |
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Fulgurance
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| Posted: Mon Jan 13, 2025 12:54 pm Post subject: |
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| pingtoo wrote: |
How did you determine /lib64/ld-linux-x86-64.so.2 was missed in init start up? you screen shut does not show that. |
I never said it was missing, in my previous post I said:
| Fulgurance wrote: | | Because the rootfs is mounted, and this file exist: /lib64/ld-linux-x86-64.so.2 (I checked by booting bash as init process) |
That is my point, why my program get this error?
EDIT: So I think I understood the problem. Basically, the root filesystems when the kernel give the hand to the program PID 1 is in read only, so first it need to be remounted.
So basically I guess before I start any service, I need to make a small program that mount the necessary minimal things right ?
I know how to mount proc, but how do you mount /proc/stat ?
_________________
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 |
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GDH-gentoo
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| Posted: Mon Jan 13, 2025 1:58 pm Post subject: |
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| Fulgurance wrote: | EDIT: So I think I understood the problem. Basically, the root filesystems when the kernel give the hand to the program PID 1 is in read only, so first it need to be remounted.
So basically I guess before I start any service, I need to make a small program that mount the necessary minimal things right ? |
The PID 1 program receiving a rootfs mounted read-only, and the init system remounting it read-write at some point during the boot sequence is a common setup, yes, but has nothing to do with the /proc/stat thing if you are asking because you think that it is connected.
| Fulgurance wrote: | | I know how to mount proc, but how do you mount /proc/stat ? |
/proc/stat is a file, it will magically appear once the proc filesystem is mounted at /proc.
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| NeddySeagoon wrote: | | I'm not a witch, I'm a retired electronics engineer |
| Ionen wrote: | | As a packager I just don't want things to get messier with weird build systems and multiple toolchains requirements though |
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pingtoo
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| Posted: Mon Jan 13, 2025 2:18 pm Post subject: Re: Question about init conception |
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| Quote: | | but how do you mount /proc/stat ? |
Do you have running example of what is actually mounted on /proc/stat?
I am not aware /proc/stat is a mount point for anything.
Assume /proc/stat is NOT a mount point then when you successfully mount /proc than you should automatically got /proc/stat. |
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Fulgurance
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| Posted: Mon Jan 13, 2025 2:42 pm Post subject: |
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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
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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 |
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Hu
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| Posted: Mon Jan 13, 2025 3:16 pm Post subject: |
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| 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. |
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pingtoo
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| Posted: Mon Jan 13, 2025 3:31 pm Post subject: |
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| Fulgurance wrote: | 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 |
OK, Crystal could be problem. I am not sure if Crystal support static link concept. if it does then you can try that. other wise you may want to choose a programming language tool chain that support limited system library like C/C++ or Shell or Python/Perl etc...
I am not sure how a kernel NOT support Proc pseudo filesystem. So can you use the kernel that you plan for your init program but instead boot your init, just boot normally and share the "mount" command output. If the mount command output show /proc is mounted then please share the command (or script) you use that mount /proc.
if your command/script perform mount /proc and yet /proc is empty directory can you share "which mount" output. I am curous why the "mount" command can do such think without report error. |
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pingtoo
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| Posted: Mon Jan 13, 2025 3:48 pm Post subject: |
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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? |
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Zucca
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| Posted: Mon Jan 13, 2025 4:06 pm Post subject: |
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| Fulgurance wrote: | | when I mount /proc |
Please, post the exact command you used.
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Fulgurance
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| Posted: Mon Jan 13, 2025 4:17 pm Post subject: |
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So I find a way to do it with a crystal program !
Basically I made a minimal bash script as /sbin/init:
| Code: |
#!/bin/bash
mount -o remount rw /
mount --types proc /proc /proc
mount --rbind /sys /sys
mount --rbind /dev /dev
mount --bind /run /run
source /etc/profile
zeroinit
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And I compiled my custom small init with shared libraries in /sbin/zeroinit
I don't know if it's a proper way, but it's a beginning. And /proc/stat is here now
Any advices now maybe ? I mean like for security?
_________________
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 |
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Zucca
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| Posted: Mon Jan 13, 2025 5:02 pm Post subject: |
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| Fulgurance wrote: | And I compiled my custom small init with shared libraries in /sbin/zeroinit
:D
I don't know if it's a proper way |
Yup. There are /lib and /lib64 for such libs that need to be present on the system before kernel runs init.
Your mount command doesn't seem to have any errors.
| Fulgurance wrote: | | And /proc/stat is here now |
... so it started working?
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pingtoo
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| Posted: Mon Jan 13, 2025 5:10 pm Post subject: |
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| Fulgurance wrote: | So I find a way to do it with a crystal program !
Basically I made a minimal bash script as /sbin/init:
| Code: |
#!/bin/bash
mount -o remount rw /
mount --types proc /proc /proc
mount --rbind /sys /sys
mount --rbind /dev /dev
mount --bind /run /run
source /etc/profile
zeroinit
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And I compiled my custom small init with shared libraries in /sbin/zeroinit
I don't know if it's a proper way, but it's a beginning. And /proc/stat is here now
Any advices now maybe ? I mean like for security? |
One of "init" duty for linux is reap zombie process. Not sure if you program that into your init program. in order for init to reap zombie process it will need to run as PID 1 (or you did some rearrange as sub-init). so your bash script last line should be "exec zeroinit" |
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NeddySeagoon
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| Posted: Mon Jan 13, 2025 5:31 pm Post subject: |
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Fulgurance,
Lets back off a little.
You have a VM with a boot loader and a kernel and not much else.
What is in /dev is the VM root before anything is started.
You must have at least /dev/null and /dev/console or it all comes to a grinding halt.
The must be device special nodes too.
How does | Code: | | mount --bind /run /run |
work?
--bind makes an already mounted filesystem visible somewhere else ... but you have said nothing about mounting run anywhere.
The kernel has mounted root, then its all up to you.
/run is usually tmpfs, so that it can be rw, even an a read only root fs.
I don't know what the --rbind mounts do either, as those filesystems are not mounted anywhere yet.
needs shared libraries.
| Code: | $ lddtree /bin/bash
/bin/bash (interpreter => /lib64/ld-linux-x86-64.so.2)
libreadline.so.8 => /usr/lib64/libreadline.so.8
libtinfow.so.6 => /lib64/libtinfow.so.6
libtinfo.so.6 => /lib64/libtinfo.so.6
libc.so.6 => /lib64/libc.so.6 |
Start off with a statically linked busybox
Where do you set $PATH ?
mount is actually /bin/mount, so it won't be found with an empty $PATH.
Hint: look at some initrd init scrips.
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