Question About Linux Magic System Request Key

[Bugrahan İmal]

Hi!

    My name is Bugrahan, I hope you are doing well. I found this email 
in https://www.kernel.org/doc/html/v4.18/admin-guide/sysrq.html, and yes 
I have more question :).

    My case is about raspberry pi which run raspberry pi os based on 
debian. In my use case power may suddenly cuts off so I cannot schedule 
a shutdown perfectly so that leads sdcard corruption. But fortunately  I 
can have a clue that cuts off will be in next 5 minutes. So I was 
thinking remounting filesystem as read only for that 5 minutes. If power 
cuts off memory will be safe, else after that time I remount this rw 
again. I search and found I cannot remount / partition while working on 
it with "mount" command. After a search I found out magic sysrq-triggers 
that seems solve my problem. I run "echo u > sysrq-trigger" to make 
filesystem ro, and "mount -o remount, rw /" to return it rw. I want to 
be sure about this process has no side effect. I couldnt find any 
documentation especially related with "u" so I asked you.

Thank you for reading my problem, I would be glad if you guide me about 
this situation.

Sincerely

Bugrahan Imal