How do I disable "suspend to RAM", and enable "suspend to idle"?

Question

I found some threads and articles with lots of info on this topic but I can't seem to make sense of it just yet. I'm running Fedora workstation with secure boot and full disk encryption on an Asus tuf gaming x570 board and AMD Ryzen 7 PRO 4750G

cat /sys/power/mem_sleep

s2idle [deep]

Here's the info I'm reading about this:

https://discussion.fedoraproject.org/t/laptop-appears-to-sleep-but-not-suspend/77193/3

https://www.kernel.org/doc/Documentation/power/states.txt

My device security report HSI-3 needs to show "suspend to RAM" disabled and "suspend to idle" enables, that is the goal of all other security checks passed.

I'm sure the answer is in the links I just shared, but I've never done this before and I could use some help figuring out what files to edit or what commands to use. Also, with security in mind do I want S0 S1 S4?

Answer 1

If you see s2idle in /sys/power, that means it is available, just not the default. There are two ways to alter that:

• You might find a firmware setting "Modern Standby" or "Connected Standby" – enabling it would make s2idle the default option.

• You can directly write the desired mode to /sys/power:

  echo s2idle > /sys/power/mem_sleep
  

  This can be done on boot via /etc/tmpfiles.d:

  w /sys/power/mem_sleep - - - - s2idle
  

Also, with security in mind do I want S0 S1 S4?

Yes; no; and probably no.

• S0 is the normal runtime state (so you probably do want it).

• S0ix is "suspend to idle" (aka 's2idle').

• S1 is an obsolete "standby" mode that disappeared from PCs in ~2000s.

• S3 is the regular "suspend to RAM" (aka 'deep').

• S4 is "suspend to disk" (aka hibernation).

If you're concerned about such unlikely physical attacks that would make S3 mode a risk, then you definitely don't want S4 (hibernation), and honestly it doesn't work well on Linux anyway.