Resume from hibernate failed silently on Debian

After I changed my swap partition, my computer hibernated fine but would not resume, i.e. it booted normally, as if I had done a hard power-off beforehand.

This happened because hibernating saves the contents of RAM etc. into your swap partition.  Therefore, <initramfs>/conf/conf.d/resume now contained an incorrect UUID (of the old, no-longer-existing partition).  See Debian linux mint, resume after hibernation fails for how to fix this.  Don't forget to modify your /etc/fstab and also regenerate the blkid cache by running "sudo blkid -p".

(See Wikipedia.org's Initrd article for background and the initramfs-tools package for how initramfs is managed under Debian.)

You have to shut down after changing your swap partition.  For some reason the kernel's power management subsystem won't hibernate to the new swap partition until after the next boot.  If you try, you'll get the error "Cannot find swap device, try swapon -a" on the console.

PS -- Don't be fooled by "PM: Resume from disk failed." in /var/log/kern.log (this is a normal error that you get when you boot after shutting down).  Debian's initramfs will check for the presence of /dev/disk/by-uuid/$resume and /sys/power/resume and only run <initramfs>/bin/resume if they both exist.  If they don't, it doesn't do anything and just continues to boot.