I've just rebuilt a laptop with xubuntu 18.04. I'm having issues getting hibernation to work, swapfile has been increased to slightly more than the 6GB of memory installed, and seems to be available:
swapon -s
Filename Type Size Used Priority
/swapfile file 6655996 1992 -2
When I try and hibernate I see the following messages on screen:
PM: Cannot find swap device, try swapon -a
PM: Cannot get swap writer
The syslog entries before that seem to suggest hibernation was going going OK up to then.
etc/default/grub contains:
GRUB_DEFAULT=0
GRUB_HIDDEN_TIMEOUT=0
GRUB_HIDDEN_TIMEOUT_QUIET=true
GRUB_TIMEOUT=10
GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
GRUB_CMDLINE_LINUX=""
Any words of wisdom gratefully received...