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On Thu, May 28, 2015 at 4:55 PM, <covici@××××××××××.com> wrote: |
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> Canek Peláez Valdés <caneko@×××××.com> wrote: |
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[...] |
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> > As I said, I did the following tests: |
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> > |
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> > 1. Adding "emergency" to the kernel command line, with a valid root=. |
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> > 2. Adding "rescue" to the kernel command line, with a valid root=. |
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> > 2. Leaving root= invalid without adding neither "emergency" nor |
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"rescue". |
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> > |
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> > If root= is valid, with emergency systemd drops you to a shell with your |
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> > root filesystem mounted read-only. With rescue, systemd drops you to a |
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> > shell with all your filesystems mounted read-write. |
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> > |
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> > If root= is invalid, it doesn't matter if you use emergency, rescue, or |
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> > neither, *dracut* drops you to a shell, still inside the initramfs |
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> > obviously. It takes a while; I didn't took the time, but I think it was |
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3 |
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> > minutes. Inside this shell, you can use systemd normally, and if you |
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manage |
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> > to mount the root filesystem, I'm sure you could continue the normal |
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boot |
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> > process. You'll have to pivot root manually, though. |
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> > |
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> > Hope that makes it clear. |
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> |
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> How do you pivot route manually? |
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|
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Basically, with pivot_root(8) [1]. Be aware that systemd does some things |
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before and after pivot_root'ing; in particular, it switches from the |
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instance running inside the initramfs to an instance running in the real |
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filesystem. I'm not sure how it does it, but the switching code is |
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relatively simple [2]. |
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|
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Regards. |
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|
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[1] http://linux.die.net/man/8/pivot_root |
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[2] |
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http://cgit.freedesktop.org/systemd/systemd/tree/src/shared/switch-root.c |
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-- |
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Canek Peláez Valdés |
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Profesor de asignatura, Facultad de Ciencias |
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Universidad Nacional Autónoma de México |
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