to release both what? a or b variant below?
a) 1st item: (Alt) and 2nd item: (Fn+S)
OR
b) 1st item (Fn) and 2nd item: (S)
?
The same in another words: Does Alt should be uninterruptedly pressed fro the very start of SysRq call and all the time 'till the end of REISUB phrase typing?
Remember, Fn+S = SysRq. Treat it as such. 
Thanks Yochanan for a great explanation.
Unfortunately Holding Alt then Fn + S, releasing Fn + S (whilst still holding Alt) and entering REISUB does not work for me.
Found the manual:
Fn+PrtSc Has the same function as the SysRq key.
That was a really cool thing to do, thank you.
Holding Fn+PrtScr whilst entering REISUB does not work for me. Is there a way REISUB could have been disabled?
This is a video of I am doing when I enter REISUB:
Why do you still hold your SysRq while typing REISUB??? As i undestand you need to call it and to release then.
Are you tried to type REISUB keys with 0.5-1 seconds delay or typed whole 6 chars during a single second?
It’s not enabled by default.
Or…
I managed to get a different distro on another machine to REISUB once by holding the SysRq key whilst typing out REISUB.
That being said:
if I press Fn + PrtSc, release both and type REISUB it does not work;
if I press Fn + PrtSc, release the PrtSc key and type REISUB it does not work.
Hold Alt the whole time while you…
I have entered the following terminal command:
~ echo kernel.sysrq=1 | sudo tee --append /etc/sysctl.d/99-sysctl.conf
Swipe your finger across the fingerprint reader
kernel.sysrq=1
I tried holding alt the whole time, pressing Fn + PrtSc, releasing Fn + PrtSc, then entering REISUB. I could not get this to work
That doesn’t take effect immediately, did you reboot after doing that?
I have rebooted but it is still the same as before.
Output of
cat /etc/sysctl.d/99-sysctl.conf
please?
Just FYI; you can test it by running journalctl -f and then do Alt+SysRq+h.
If it’s working you’ll get sysrq help output into journal:
kernel: sysrq: HELP : loglevel(0-9) reboot(b) crash(c) terminate-all-tasks(e) memory-full-oom-kill(f) kill-all-tasks(i) thaw-filesystems(j) sak(k) show-backtrace-all-active-cpus(l) show-memory-usage(m) nice-all-RT-tasks(n) poweroff(o) show-registers(p) show-all-timers(q) unraw(r) sync(s) show-task-states(t) unmount(u) force-fb(v) show-blocked-tasks(w) dump-ftrace-buffer(z)
Edit to expand on this:
If you can’t find SysRq key and still want to test if functionality is enabled, you can instead try:
echo h | sudo tee /proc/sysrq-trigger
~ cat /etc/sysctl.d/99-sysctl.conf
kernel.sysrq=1
This is the output of holding alt+Fn+PrtSc and typing REISUB looks most similar (pasted excluding a lot of Touchégg daemon errors):
Feb 02 14:52:52 Think kernel: sysrq: HELP : loglevel(0-9) reboot(b) crash(c) terminate-all-tasks(e) memory-full-oom-kill(f) kill-all-tasks(i) thaw-filesystems(j) sak(k) show-backtrace-all-active-cpus(l) show-memory-usage(m) nice-all-RT-tasks(n) poweroff(o) show-registers(p) show-all-timers(q) unraw(r) sync(s) show-task-states(t) unmount(u) force-fb(v) show-blocked-tasks(w) dump-ftrace-buffer(z)
Feb 02 14:52:52 Think kernel: sysrq: HELP : loglevel(0-9) reboot(b) crash(c) terminate-all-tasks(e) memory-full-oom-kill(f) kill-all-tasks(i) thaw-filesystems(j) sak(k) show-backtrace-all-active-cpus(l) show-memory-usage(m) nice-all-RT-tasks(n) poweroff(o) show-registers(p) show-all-timers(q) unraw(r) sync(s) show-task-states(t) unmount(u) force-fb(v) show-blocked-tasks(w) dump-ftrace-buffer(z)
The output whilst pressing and releasing Fn+PrtSc, then entering REISUB whilst still holding alt:
^[r^[e^[i^[s^[u^[b
So it is working then. HELP line gets printed only when you press a key that has no function. So you must be pressing something wrong. REISUB only works for QWERTY/AZERTY/etc, so if you are using some other layout, you need to press other keys.
echo h | sudo tee /proc/sysrq-trigger
This is the output :
~ echo h | sudo tee /proc/sysrq-trigger ✔
Swipe your finger across the fingerprint reader
h
Having re-read my last post I should clarify running Just FYI; you can test it by running journalctl -f and then doing Alt+SysRq+h gives no output.
It’s in the journal - same HELP line as with pressing actual keys.
I am using what look like a qwerty keyboard to me 