Re: [gentoo-user] systemd and initramfs

[Helmut Jarausch]

On 08/20/2013 08:54:26 AM, Canek Peláez Valdés wrote:
> On Tue, Aug 20, 2013 at 1:44 AM, Helmut Jarausch
> <jarausch@××××××××××××××××.de> wrote:
> > On 08/19/2013 04:55:29 PM, Mike Gilbert wrote:
> >>
> >> On Mon, Aug 19, 2013 at 5:58 AM, Helmut Jarausch
> >> <jarausch@××××××××××××××××.de> wrote:
> >> > Hi,
> >> >
> >> > what binaries and libraries have to be put into an initramfs for
> a
> >> > system
> >> > booting with init=/usr/lib/systemd/systemd ?
> >> > (I am building the initramsfs myself)
> >> >
> >>
> >> You need to get your root filesystem and /usr mounted. Just keep
> that
> >> goal in mind and start adding files to support it.
> >>
> >> There doesn't need to be anything systemd-specific.
> >>
> >
> > I am not sure about "timing".
> >
> > Initially the kernel has only the "mini" /usr partition contained
> within the
> > initramfs.
> > Then it switches to "real root" and only then it tries to mount the
> "real"
> > /usr partition.
> > Does this all happen before the kernel hands control over to the
> init
> > process (i.e. systemd) ?
>
> No, the kernel has a mini filesystem (doesn't matter which directory
> structure has inside), and it executes the init script (or binary
> program) in the root of the initramfs. This init program/script is the
> responsible for mounting the real root and other partitions, and
> handling control over to systemd (or OpenRC, or whatever).
>
> Dracut is able to create an initramfs (with the systemd Dracut module)
> that executes systemd inside the initramfs, which mounts /usr,
> switches to the real root, and gives control to the "real" systemd
> instance. At shutdown, the reverse happens: the "real" systemd
> surrenders control to the initramfs systemd, it umounts everything,
> and finish the shutdow process.
>
> If you generate an initramfs with Dracut using the systemd module, the
> init inside the initramfs is a link to /usr/lib/systemd/systemd.
>
> Unless you want to learn the ins and outs of using an initramfs (and
> having a lot of fun and failed boots in the process), I highly
> recommend using Dracut. It does everything for you.
>

Yes, I'd like to generate the initramfs myself and let the kernel store  
it within
its binary on /boot. This has been working just fine with openrc. Now I  
only need
to now the additional requirements when using systemd as init process.

I'll have a look at what Dracut is doing.

Thanks to you and Alan,
Helmut