I am recording the steps I took here to enable hibernation on a default Pop!_OS installation with full-disk encryption. I have written my commands as a single executable script in order to better understand how they all relate, but they probably should not be executed this way. Use this guide with caution and only if you understand what each command does.
I did all of this on Pop!_OS version 21.04, but swapfile hibernation is still working for me as of 22.04. I expect that the following steps will work for that as well, but I haven't tested it.
This is the simplest method if you used the default Pop installation, since it does not involve resizing any encrypted partitions.
# Comment out the current swap from fstab
sudo sed -i 's!^/dev/mapper/cryptswap!# &!' /etc/fstab
# Optionally, comment out the current swap from crypttab
sudo sed -i 's!^cryptswap!# &!' /etc/crypttab
# Create a swapfile the same size as your RAM. You may want more space than that, however, and should probably assign $MEMSIZE manually
MEMSIZE="$(grep MemTotal /proc/meminfo | awk '{print $2}')KiB"
sudo fallocate -l $MEMSIZE /swapfile
sudo chmod 600 /swapfile
sudo mkswap /swapfile
SWAP_UUID=$(findmnt -no UUID -T /swapfile)
SWAP_OFFSET=$(sudo filefrag -v /swapfile | awk '{ if($1=="0:"){print $4} }')
KERNEL_OPTS="resume=UUID=$SWAP_UUID resume_offset=${SWAP_OFFSET/../}"
# Add the new swap to your fstab
echo '/swapfile none swap defaults 0 0' | sudo tee -a /etc/fstab
# Update the kernel options
sudo kernelstub -a "$KERNEL_OPTS"
echo "$KERNEL_OPTS" | sudo tee -a /etc/initramfs-tools/conf.d/resumeCheck that everything has been configured properly before running sudo update-initramfs -u -k all. Then reboot.
This method is a little more involved, but equally feasible. The only difficulty is allocating the appropriate space to the swap partition, as the swap partition created by a default Pop installation is probably too small to handle this. You may need to resize your existing swap, which is tricky if you added encryption during installation.
# Get device information
SWAP_DEVICE=$(sudo cryptsetup status cryptswap | grep 'device:' | awk '{print $2}')
CRYPT_DEVICE=/dev/mapper/cryptswap # default for new Pop install
SWAP_KEY=/root/.swap-key
# Close default cryptswap
sudo swapoff $CRYPT_DEVICE
sudo cryptsetup luksClose $CRYPT_DEVICE
sudo sed -i 's!^cryptswap!# &!' /etc/crypttab
# Create new cryptswap using a keyfile
sudo dd if=/dev/urandom of=$SWAP_KEY bs=1024 count=4
sudo chmod 400 $SWAP_KEY
sudo cryptsetup luksFormat -d $SWAP_KEY $SWAP_DEVICE
sudo cryptsetup open -d $SWAP_KEY $SWAP_DEVICE cryptswap
sudo mkswap $CRYPT_DEVICE
# Get UUIDs
SWAP_UUID=$(sudo blkid -s UUID -o value $SWAP_DEVICE)
CRYPT_UUID=$(sudo blkid -s UUID -o value $CRYPT_DEVICE)
ROOT_UUID=$(findmnt -no UUID -T $SWAP_KEY)
# Update configuration
echo "UUID=$CRYPT_UUID none swap defaults 0 0" | sudo tee -a /etc/fstab
echo "cryptswap UUID=$SWAP_UUID /dev/disk/by-uuid/$ROOT_UUID:$SWAP_KEY luks,discard,keyscript=/lib/cryptsetup/scripts/passdev,noauto" | sudo tee -a /etc/crypttab
echo "resume=UUID=$CRYPT_UUID" | sudo tee -a /etc/initramfs-tools/conf.d/resume
sudo kernelstub -a "resume=UUID=$CRYPT_UUID"Check that everything has been configured properly before running sudo update-initramfs -u -k all. Then reboot.
Guides I used to figure this out.