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--- hibernate_from_a_non_activate_swapfile_from_btrfs [2020/12/16 06:47] – created memeruiz
+++ hibernate_from_a_non_activate_swapfile_from_btrfs [2021/02/01 05:55] (current) – external edit 127.0.0.1
@@ Line 1: / Line 1: @@
 ====== Hibernate from a non activate swapfile from btrfs ======
+*** 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 swapfile =====
@@ Line 11: / Line 15: @@
-  UUID=8f9ede3a-912f-40d6-9335-90ed3186e3e4   		      	    /swap	      	     btrfs defaults,noatime,subvol=swap	0 0
+  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
@@ Line 23: / Line 27: @@
   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 and offset =====
@@ Line 30: / Line 35: @@
   sudo findmnt -no UUID -T /swap/swapfile
-  * swap_offset doesn't work correctly with btrfs. Download this https://github.com/osandov/osandov-linux/blob/master/scripts/btrfs_map_physical.c and compile it:
+  * swap_offset 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 btrfs_map_physical btrfs_map_physical.c
@@ Line 38: / Line 43: @@
   sudo btrfs_map_physical /swap/swapfile | head -n 2
+  * Result:
+  FILE OFFSET	FILE SIZE	EXTENT OFFSET	EXTENT TYPE	LOGICAL SIZE	LOGICAL OFFSET	PHYSICAL SIZE	DEVID	PHYSICAL OFFSET
+	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
+===== Configure system for hibernation =====
+  * 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:
+  GRUB_CMDLINE_LINUX_DEFAULT="resume=UUID=8f9ede3a-912f-40d6-9335-90ed3186e3e4 resume_offset=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: my_server_hibernate.sh:
+#!/bin/bash
+  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"
+===== References =====
+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