REISUB doesn't always work

Support
1

I am facing a weird issue. The REISUB works when my laptop is running fine. But when my laptop actually freezes, REISUB doesn’t work!!

2

If there’s a kernel panic and/or a hardware issue, it will not work.

3 Likes
3

As @Yochanan said. :wink:

The longer explanation is that the Magic SysRq keys are a set of direct one-key commands to the kernel, and they will continue to work for as long as the kernel itself is still alive, even when userspace has completely locked up. But of course, if the kernel itself has crashed, then pressing those keys won’t be doing anything anymore either.

Kernel crashes are rare ─ especially on long-term-support kernels ─ but they can happen, for instance due to faulty hardware, or when using a buggy proprietary driver that runs in the kernel’s address space.

The source code of proprietary software is kept as a trade secret by its authors , and as such, there’s no way of knowing what those drivers really do, while at the same time they are running with maximum privileges. This is why a kernel running a proprietary driver ─ e.g. Nvidia ─ is marked as “tainted” in the kernel logs, and consequently, why the upstream kernel developers will ignore bug and crash reports on such a kernel.

4 Likes
4
  1. The above explains clearly why it doesn’t work but it doesn’t help you further, so let the machine sit there for 1 minute when this happens and then please read this:
    How to provide good information
    and post some more information so we can see what’s really going on. Now we know the symptom of the disease, but we need some more probing to know where the origin lies…
  2. An inxi --admin --verbosity=7 --filter --no-host --width would be the minimum required information… (Personally Identifiable Information like serial numbers and MAC addresses will be filtered out by the above command)
    Also, please copy-paste that output in-between 3 backticks ``` at the beginning and end of the code/text.
  3. A journalctl --system --boot=-1 | tail --lines=50 might be helpful too, although that one might be corrupted by the kernel panic, so it’s a coin- toss whether that’ll give us the information we need.
  4. Have you tried REISUO too?

:+1:

2 Likes
5