* Important! * This didn't work! It is not secure! When wiping happens, the file gets moved to another place by btrfs, then, this doesn't work for two reasons: 1) Wiping happens in other parts of the disk, and the offset changes and has to be updated in all configurations files after wiping everytime.

• This was just a stupid experiment.

• Create a separate swap volume (not necessary)

  sudo btrfs subvolume create /mnt/btrfsbase/swap

  • Add it to /etc/fstab

  UUID=8f9ede3a-912f-40d6-9335-90ed3186e3e4 /swap btrfs defaults,noautodefrag,nodatacow,nodiscard,noatime,subvol=swap 0 0

• Be sure there is no discard nor autodefrag options activated for this subvolume
• Create a swapfile

  cd /swap sudo truncate -s 0 swapfile sudo chattr +C swapfile btrfs property set swapfile compression none sudo chmod 600 swapfile sudo dd if=/dev/zero of=swapfile bs=1M count=24576 #reserve 24GB sudo mkswap /swap/swapfile

• Find out resume device:

  sudo findmnt -no UUID -T /swap/swapfile

• swapoffset command doesn't work correctly with btrfs. Download this https://github.com/osandov/osandov-linux/blob/master/scripts/btrfs_map_physical.c and compile it: gcc -O2 -o btrfsmapphysical btrfsmap_physical.c
• Calculate offset
• Write down the last number from the output of the following command:

  sudo btrfsmapphysical /swap/swapfile | head -n 2

• Result:

  FILE OFFSET FILE SIZE EXTENT OFFSET EXTENT TYPE LOGICAL SIZE LOGICAL OFFSET PHYSICAL SIZE DEVID PHYSICAL OFFSET 0 134217728 0 regular 134217728 4594864128 134217728 1 4594864128

• Write down the output of the following command:

  sudo getconf PAGESIZE

  Result: 4096

• Calculate offset: Divide the first number under the PAGESIZE: offset = PHYSICAL_OFFSET/PAGESIZE

4594864128/4096=1121793

• Create /etc/initramfs-tools/conf.d/resume and put the resume and offset data on it:

  RESUME=UUID=8f9ede3a-912f-40d6-9335-90ed3186e3e4 resume_offset=1121793

• Modify /etc/default/grub with the corresponding resume and offset values:

  GRUBCMDLINELINUXDEFAULT=“resume=UUID=8f9ede3a-912f-40d6-9335-90ed3186e3e4 resumeoffset=1121793 quiet btusb.enable_autosuspend=n”

• Activate the swap file

  sudo swapon /swap/swapfile

• Install uswsusp package
• Edit /etc/uswsusp.conf:

  resume device = /dev/disk/by-uuid/8f9ede3a-912f-40d6-9335-90ed3186e3e4 early writeout = y image size = 0 RSA key file = /etc/uswsusp.key shutdown method = platform resume offset = 1121793

• Activate a systemd service:

  sudo systemctl edit systemd-hibernate.service

• With:

  [Service] ExecStart= ExecStartPre=-/bin/run-parts -v -a pre /lib/systemd/system-sleep ExecStart=/usr/sbin/s2disk ExecStartPost=-/bin/run-parts -v –reverse -a post /lib/systemd/system-sleep

• Update initramfs and grub

  sudo update-grub sudo update-initramfs -k all -u sudo update-grub

• Test the hibernation:

  sudo s2disk

I have a system with encrypted swap, but I don't want to have encryption on the hibernation swap file. My idea is to use hibernation only when strictly necessary, because I don't want to need to put a password during booting. Then, this swap file should actually be always deactivated except before hibernation. When resuming, this swap space should be deactivated and then securely wiped! The script to do this would be this: myserverhibernate.sh:

echo "Activating swap from swapfile"
sudo swapon /swap/swapfile
sleep 1
echo "Hibernating"
sleep 0.2
xtrlock -b &
sudo s2disk
echo "Returning from Hibernate"
sleep 10
echo "Deactivating swapfile"
sudo swapoff /swap/swapfile
sleep 5
echo "Wiping swapfile"
#sudo wipe -k -f -q -Q 1 /swap/swapfile
sudo dd if=/dev/zero of=/swap/swapfile bs=1M count=24576 status=progress #reserve 24GB
sync
sleep 1
echo "Making swapfs again"
sudo mkswap /swap/swapfile
echo "All done, ready to hiberante again"

https://wiki.archlinux.org/index.php/Power_management/Suspend_and_hibernate#Hibernation_into_swap_file_on_Btrfs

https://wiki.archlinux.org/index.php/Power_management/Suspend_and_hibernate#Hibernation_into_swap_file

https://wiki.archlinux.org/index.php/Swap#Swap_file_creationhttps://wiki.archlinux.org/index.php/Swap#Swap_file_creation

https://askubuntu.com/questions/6769/hibernate-and-resume-from-a-swap-file

https://wiki.debian.org/Hibernation/Hibernate_Without_Swap_Partition

https://wiki.debian.org/Hibernation

https://unix.stackexchange.com/questions/521686/using-swapfile-for-hibernation-with-btrfs-and-kernel-5-0-16-gentoohttps://unix.stackexchange.com/questions/521686/using-swapfile-for-hibernation-with-btrfs-and-kernel-5-0-16-gentoo