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How does gentoo startup / init work?
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defer-
Tux's lil' helper
Tux's lil' helper


Joined: 11 Jun 2007
Posts: 140
Location: Finland

PostPosted: Fri Sep 19, 2014 12:18 pm    Post subject: How does gentoo startup / init work? Reply with quote

I would like to create custom init to get fast startup and shutdown times. I created sinit[1] ebuild and installed it. I chaged savedconfig and created /etc/rc script. My current setup boots fine to X but shutdown and module loading doesn't work.

How does Gentoo sysvinit/openrc startup work? What does init execute and how does openrc execute init scripts on startup or shutdown? What is needed for working system?

[1] http://git.suckless.org/sinit/
[2] /etc/rc
Code:

#!/usr/bin/env bash

if [[ "$1" = "start" ]]; then
        echo "Starting up Gentoo Linux"

        mkdir -p /proc
        mkdir -p /sys
        mount -n -t proc -o nosuid,noexec,nodev proc /proc
        mount -n -t sysfs -o nosuid,noexec,nodev sysfs /sys

        mount -n -t tmpfs -o nosuid,mode=0755 dev /dev
        mkdir -p /dev/pts
        mount -n -t devpts -o gid=5,mode=0620 devpts /dev/pts

        echo Running smdev
        smdev -s

        echo Setting smdev as the kernel hotplug
        echo /bin/smdev > /proc/sys/kernel/hotplug

        echo Loading kernel modules
        find /sys -name 'modalias' -type f -exec cat '{}' + | sort -u | xargs modprobe -b -a 2>/dev/null

        echo Remounting root as read-write
        mount -o remount,rw /

        echo Mounting filesystems
        mount -a

        hostname dfr-laptop

        /sbin/agetty --noclear 38400 tty1 linux &
        /sbin/agetty --noclear 38400 tty2 linux &
elif [[ "$1" = "reboot" ]]; then
        echo "Rebooting Gentoo Linux"

        killall5 -s KILL

        echo Remounting root as read-only
        mount -o remount,ro /

        echo Unmounting filesystems
        umount -a

        sync
        sleep 1
        wait

        reboot
elif [[ "$1" = "shutdown" ]]; then
        echo "Shutting down Gentoo Linux"

        killall5 -s KILL

        echo Remounting root as read-only
        mount -o remount,ro /

        echo Unmounting filesystems
        umount -a

        sync
        sleep 1
        wait
        halt
else
        echo "Unknown command"
fi

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steveL
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Joined: 13 Sep 2006
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PostPosted: Fri Sep 19, 2014 10:27 pm    Post subject: Reply with quote

First off, lose the awfully fscked-up shebang: #!/usr/bin/env bash is wrong on so many levels. Just use #!/bin/sh and learn to write portable sh.

Most of that looks ok, but I'd separate out into functions, and use a simple case.
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steveL
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PostPosted: Sun Oct 12, 2014 12:56 am    Post subject: Re: How does gentoo startup / init work? Reply with quote

defer- wrote:
How does Gentoo sysvinit/openrc startup work? What does init execute and how does openrc execute init scripts on startup or shutdown? What is needed for working system?

As with every Linux (and indeed Unix that I know of), "init" means pid1: it doesn't do very much, but it is configured via /etc/inittab -- the file is pretty well-commented. Though you really shouldn't edit it in general, in your case you likely need to.

pid1 must be robust, and simply-coded, since it must run for the entire uptime of the machine. It is the first process started by the kernel, and if it exits (or crashes), the kernel panics (ie: completely halts) and all your in-flight data is lost, FS may be corrupted, etc. ie: Game Over.

For this reason, it's not worth redoing pid1: complexity is much better handled elsewhere, in the default case by openrc (command: /sbin/rc) which you can see is run by init on entry to the various run-levels. So we still use sysvinit, since there's nothing more that would sanely be added to pid1. ie: sys-apps/sysvinit

Read man 8 init for more information; man runscript and man rc if you want to know more about openrc.
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