Suspend-to-RAM with systemd configuration

Question

I want to Suspend-to-RAM with systemd.

The Linux kernel user's and administrator's guide says:

[T]here is only one way to make the system go into the suspend-to-RAM state (write deep into /sys/power/mem_sleep and mem into /sys/power/state).

How do I "Suspend-to-RAM" (rather than plain "Suspend") using systemd?

Answer 1

mem_sleep modes are not supported via systemd

systemd-sleep.conf(5) only mentions /sys/power/disk and /sys/power/state but not /sys/power/mem_sleep.

Searching the code for mem_sleep returns nothing.

I raised the feature request: Support suspend modes "s2idle", "shallow", and "deep" #13451

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Workaround

Use the kernel command line mem_sleep_default=deep:

   mem_sleep_default=      [SUSPEND] Default system suspend mode:
                    s2idle  - Suspend-To-Idle
                    shallow - Power-On Suspend or equivalent (if supported)
                    deep    - Suspend-To-RAM or equivalent (if supported)
                    See Documentation/admin-guide/pm/sleep-states.rst.

HTML rendering of Documentation/admin-guide/pm/sleep-states.rst