Systemd: how to get into rescue mode

[Tom H]

On Sat, Jan 11, 2020 at 6:22 AM Little Girl <littlergirl at gmail.com> wrote:
> Tom H wrote:
>> On Sat, Jan 11, 2020 at 1:52 AM Little Girl wrote:
>>>
>>> That command will work from an ordinary terminal (although I prefer
>>> the Alt + Shift + SysRq REISUO method so that everything is nice
>>> and neat and there are no loose ends).
>
>> In a default install, REISUB and REISUO will fail because, for
>> example, E and I aren't allowed.
>
> Interesting. They work for me right now in Ubuntu MATE and have been
> working for years. By that, I mean that they effectively shut down or
> reboot my system when I use them; I just tried them again to verify.
> Have you tried them?
>
> Also, where did you get that information? Do you have a link for
> further information on that? The E and the I are vital for
> safeguarding data. Without them, you may as well use any other
> shutdown or reboot method.
>
> Perhaps I'm not understanding you correctly. What, exactly, do you
> mean by a default install? I've never done the commands on an
> installation of an Ubuntu flavor without having done something to
> customize it. I have a whole bunch of things I do to my Ubuntu MATE
> or Kubuntu installations to "make them mine"  (tweaks and
> installations and start-up scripts) and any or all of them might
> qualify my set-up as non-default.
>
>>"systemctl poweroff" and all of its systemd-sysv equivalents are just
>> as "nice and neat" and have "no loose ends."
>
> I'll take your word for it since I haven't checked. I just know that
> REISUB and REISUO are presented as safe methods for rebooting or
> shutting down while making sure nothing is left unsaved, which is
> vital. I'm also pretty sure (but not positive) that shutdown -r now
> doesn't offer the same protection. I just checked the shutdown man
> page and didn't see a mention of that.

"procps" ships "/etc/sysctl.d/10-magic-sysrq.conf" which sets
"kernel.sysrq = 176" and this setting prevents using "e" and "i" among
others.

What's "cat /proc/sys/kernel/sysrq" on your system? If it's not "176"
either you or MATE (?) are overriding it.