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On Tue, Aug 20, 2013 at 7:32 PM, Walter Dnes <waltdnes@××××××××.org> wrote: |
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> On Tue, Aug 20, 2013 at 01:54:26AM -0500, Canek Peláez Valdés wrote |
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>> |
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>> No, the kernel has a mini filesystem (doesn't matter which directory |
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>> structure has inside), and it executes the init script (or binary |
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>> program) in the root of the initramfs. This init program/script is the |
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>> responsible for mounting the real root and other partitions, and |
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>> handling control over to systemd (or OpenRC, or whatever). |
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>> |
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>> Dracut is able to create an initramfs (with the systemd Dracut module) |
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>> that executes systemd inside the initramfs, which mounts /usr, |
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>> switches to the real root, and gives control to the "real" systemd |
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>> instance. At shutdown, the reverse happens: the "real" systemd |
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>> surrenders control to the initramfs systemd, it umounts everything, |
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>> and finish the shutdow process. |
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> |
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> A possibly stupid question from a non-user of initramfs... why not |
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> simply treat the initramfs as "the real system"? This would avoid the |
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> hand-off to a second fs at start-up, and the reverse process at |
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> shutdown. |
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If I understand correctly, because it's a ramfs, as its name implies |
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(it lives on your RAM). You don't want it to hold all your system, |
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only the necessary parts to mount the filesystems necessary to boot. |
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|
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> There would be no need to worry about keeping files synced in |
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> 2 different locations, because there would only be one location. |
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The worry about falling out of sync, although justified, I think it's |
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a little overreacted; even for things like LVM2 and NFS, how many |
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times changes the metadata or format used by different versions? |
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Normal filesystems present no problems: almost all of them are |
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future-proof. |
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And (as Allan suggested) you can (easily and automagically) regenerate |
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the initramfs everytime sometimes inside it changes. |
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|
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> If |
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> necessary, one could use UnionFS http://en.wikipedia.org/wiki/Unionfs to |
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> make the hard drive and userspace stuff all look like part of the |
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> initramfs. |
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|
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No unionfs has been accepted in the mainline kernel, although several |
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have been proposed. It's a hard problem, and nothing has satisfied the |
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kernel devs until now. |
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The initramfs has several advantages: it's supported directly by the |
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kernel, it works the same from embedded systems to big iron servers, |
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and it just works. |
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I just installed two systems (a server and a desktop) to systemd |
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directly, and Dracut just worked. And I like that now my kernels have |
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*EVERYTHING* as a module (that can be compiled as module). Even the |
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filesystems! |
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|
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Regards. |
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-- |
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Canek Peláez Valdés |
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Posgrado en Ciencia e Ingeniería de la Computación |
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Universidad Nacional Autónoma de México |
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