[systemd-devel] emergency mode vs rescue mode

[Michael Biebl]

Thanks for the response Lennart.
I think something like this should be added to the man page. I opened
a bug report for this.


Michael

2016-02-03 22:58 GMT+01:00 Lennart Poettering <lennart at poettering.net>:
> On Wed, 03.02.16 22:03, Michael Biebl (mbiebl at gmail.com) wrote:
>
>> Hi everyone
>>
>> I wonder that emergency.target/emergency.service/emergency mode is good for.
>>
>> Afaics, it doesn't offer anything that rescue mode doesn't also offer.
>> I find this situation a bit confusing.
>>
>> Can anyone enlighten me why we need two different modes which are
>> basically the same?
>
> Emergency mode means the only running process is a shell, besides
> systemd itself.
>
> rescue mode means all early-boot services have been started, all
> mounts have been established, and then gives you a shell.
>
> emergency mode is a bit like booting with init=/bin/sh except that you
> actually have systemd up properly, and can start services bit-by-bit
> if you like. emergency mode is also entered if fsck fails, as in that
> case rescue mode is unachievable, as we cannot mount the failed
> disks...
>
> rescue mode is usually what admins want to boot into for single-user
> maintainance tasks. The only reason when you want to boot into
> emergency mode instead if you have some fuckup with your disks.
>
> Note that sysvinit had the very same distinction, though the feature
> is little-known. Booting sysvinit with "emergency" on the kernel
> cmdline would give you just sysvinit as PID1 plus /bin/sh forked
> off. Booting sysvinit with "1" on the kernel cmdline would give you
> runlevel 1 services including mounts, and then a shell. In fact,
> systemd understand the same kernel cmdline keywords and does the right
> thing...
>
> Lennart
>
> --
> Lennart Poettering, Red Hat



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