Hybrid Sleep support - "hibernate" and suspend the system
Hybrid Sleep initially only writes hibernation image to SWAP space,
it does not power off the machine, as a whole Suspend To Disk (S4) does,
it rather Suspend To RAM (S3).
The benefit of this combination is pronto RESUME from S3,
whilst in case of battery drained or interruptions in power supply of any kind,
you ain't gonna lose your work.
Hybrid Sleep is the feature of the Linux kernel.
To test it directly via cli:
echo suspend > /sys/power/disk ; echo disk > /sys/power/state
However to make this feature work,
both Suspend To RAM (S3) and Suspend To Disk (S4)
must be provided by the hardware
ACPI: (supports ... S3 S4 ...)
in working order.
Furthermore Suspend To Disk (S4) requires a relatively simple configuration
an appendix to kernel command line:
resume=<path to resume partition>
i.e. directive to utilize particular SWAP space
man 7 dracut.cmdline