Systemd: how to get into rescue mode

[Volker Wysk]

Am Montag, den 06.01.2020, 21:14 -0500 schrieb Little Girl:
> Hey there,
> 
> Volker Wysk wrote:
> 
> > Thank you for your answer, but I think you've missed the point. I
> > can't type any command after doing "systemctl isolate
> > rescue.target". What I type isn't displayed. Nothing at all
> > happens.
> > It doesn't look like a rescue shell is running.
> 
> This page is for a different operating system, but the symptoms
> they're experiencing when going into single-user mode (which is what
> the rescue.target is) are just like yours:
> 
> https://bbs.archlinux.org/viewtopic.php?id=226555
> 
> Sadly, the final post in that thread suggests that the keyboard
> simply isn't available in that mode. I'm kind of boggled as to how
> they expect you to interact with it without a keyboard, but perhaps
> that's an actual oversight on the part of the devs.
> 
> > I've got the "systemctl isolate rescue.target" command from that
> > article in the LinxUser magazine. They advise to do it when making
> > a
> > backup, so there are no more files which are being used by running
> > services.
> 
> This video claims that the isolate command is only allowed on units
> where AllowIsolate is enabled:
> 
> https://www.youtube.com/watch?v=7P7ROr1-yjA
> 
> The systemd.unit(5) man page says that AllowIsolate defaults to
> false, which could explain the behavior you're seeing, but probably
> not. It looks like you found the /lib/systemd/system directory. Is
> AllowIsolate enabled in your rescue.target file? It is on my system,
> but I'm using an older Ubuntu MATE release, so yours may differ.

Yes, AllowIsolate is set to "yes" in my copy here:
/lib/systemd/system/rescue.target.


> This video gives a good run-down of the basics of systemctl:
> 
> https://www.youtube.com/watch?v=AtEqbYTLHfs

Ok, I've seen before, most of what is detailed in this video.

> The systemd.special(7) and systemd.target(5) and systemd.unit(5) man
> pages may be useful. They go into detail on what the different units
> and targets are and how to use systemd in general.

I'll read these.

> Last, but not least, this situation reminds me of our way of using
> non-graphical TTYs. We've never been able to interact with those TTYs
> without first using the cd command (cd plus the Enter key).

I have tried this, but still no reaction at all.

> We don't know why we have that issue on two different machines when
> the rest of the world just switches to a TTY and immediately types
> commands that work. We haven't seen this mentioned anywhere, but the
> cd command works for us every time and we'd be completely stuck and
> unable to interact with the TTY without it. We just happened to try
> it one day and it worked, so we remembered it. I have to wonder if
> your solution will be something you just happen to stumble into quite
> by accident as well.

Cheers
Volker