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On Thu, May 28, 2015 at 2:11 PM, Canek Peláez Valdés <caneko@×××××.com> wrote: |
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> |
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> Actually, it does work (see attached screenshot). I set my root= kernel |
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> command line parameter wrong on purpose, and systemd (inside dracut) dropped |
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> me inside a rescue shell. |
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Interesting. Perhaps it just enables shell access. |
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There is a separate option that configures whether dracut drops to a |
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shell at all, or if it just hangs on failure. The latter might be |
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desirable for security purposes in some cases. |
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Are you sure that you don't get a shell if you don't pass emergency on |
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the command line, but still have an invalid root=? |
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> |
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>> Usually when somebody |
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>> wants a rescue shell, they want it in their root filesystem, and not |
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>> in their initramfs before it has pivoted. That is why dracut has |
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>> options like rd.break. |
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> |
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> But that doesn't help you at all when the problem is exactly that you cannot |
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> mount your root filesystem. With the rescue shell of systemd (inside |
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> dracut), you can analyze the problem, or perhaps even mount your root |
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> filesystem and continue the boot process; the initramfs should have all the |
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> necessary tools to do that. |
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rd.break DOES give you a shell before root is mounted, if you tell it to. |
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rd.shell tells dracut to give you a shell if something fails |
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rd.break forces a shell at the specified point, whether something fails or not. |
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The official docs do not list emergency as a valid dracut option. |
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Obviously systemd uses it, but again the fact that you had to mangle |
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your root= option sugests that systemd within dracut ignores it if it |
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can mount your root. |
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> |
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>> If the problem were with systemd/services/etc in the actual root |
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>> filesystem (once the actual distro has started booting), then putting |
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>> emergency on the command line should get you a rescue shell. |
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> |
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> Again, what if the problem is before *that*? |
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Then you tell dracut to drop to a shell. I wasn't aware that the |
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emergency option actually made a difference, though I'm still not 100% |
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sure that was what did it. |
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> |
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>> The same generally applies to openrc - if the initramfs isn't mounting |
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>> your root filesystem, then passing instructions to openrc won't do |
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>> anything since in that case openrc isn't even running. |
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> |
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> But in this case, systemd *is* inside the initramfs: |
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> |
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> # ls usr/lib/systemd/ |
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> network systemd-cgroups-agent systemd-journald systemd-shutdown |
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> systemd-vconsole-setup |
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> system systemd-fsck systemd-modules-load systemd-sysctl |
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> system-generators |
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> systemd systemd-hibernate-resume systemd-reply-password systemd-udevd |
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> |
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> That's my initramfs. With dracut, systemd *is* the initramfs init system. |
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Sure, and that is how mine works as well. But, obviously systemd in |
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dracut is configured to ignore that parameter when root= is valid, |
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otherwise you'd get a shell every time. I'd have to check the docs, |
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but I suspect that the behavior is configurable, and systemd within |
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the initramfs is configured differently. If nothing else they could |
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just make the rescue target launch the default target/etc. |
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-- |
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Rich |
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