Now that I fixed hibernation to resume at all, I found another thing I had added to my old install long ago.
The "problem" is, that resume from hibernation is very quiet. So all you see is the GRUB messages "loading kernel", "loading initrd", then nothing, just the disk light may be blinking for quite some time, and if resume is successful, you'll see the unlock prompt of your screenlock.
That's a bit too little "user interface" for my taste.
The reason it is like this is, that the kernel's progress messages (in 10% steps) are printed with level "pr_info":
if (!(nr_pages % m))
pr_info("Image loading progress: %3d%%\n",
nr_pages / m * 10);
But the default "quiet" boot suppresses KERN_INFO messages, which is good because without that, you cannot find the prompt for unlocking your crypted filesystems amongst all those KERN_INFO messages during boot... so how to fix it?
We can just adapt the systemd-hibernate-resume.service to increase the kernel log level just before starting to resume, via a dropin file in /etc/systemd/system/systemd-hibernate-resume.service.d/10-resume-verbose.conf:
[Service]
ExecStartPre=/bin/sh -c "echo 7 > /proc/sys/kernel/printk"
ExecStartPost=/bin/sh -c "echo 1 > /proc/sys/kernel/printk"
Also, add the file to your dracut config, so that it is actually included in the initrd:
install_items+=" /etc/systemd/system/systemd-hibernate-resume@.service.d/10-resume-verbose.conf "
now rebuild your initrd with "dracut -f" and enjoy :-)
Oh, and of course this only helps if you do not use things like plymouth which actually hide everything interesting during boot. Update 2022-02-12: it also works with plymouth, because image loading kicks in before plymouth can hide the interesting bits.
