How to use hibernation without a swap partition.
First, create a swap file:
fallocate -l 256m /swap mkswap /swap chmod 600 /swap
"256" refers to the size in MBs ('m' after it). Set this for at least half the size of your RAM. "/swap" is a location of your swap file. It can be located on any partition (root or home, for example).
Add this to /etc/fstab:
/swap swap swap defaults 0 0
Now stop the kernel from using the swap file for swapping:
sysctl -w vm.swappiness=1
Create a file called local.conf in /etc/sysctl.d and add the kernel variable there so it sticks:
vm.swappiness=1
(but see https://www.howtogeek.com/449691/what-is-swapiness-on-linux-and-how-to-change-it/ for a thorough explanation of swappiness)
Activate the swap file:
swapon /swap
You now need to update grub and initramfs to let the kernel know where to find the swapfile during resume from hibernation. First of all, get the UUID of the root partition and the physical offset of the swapfile in it:
findmnt / -o UUID -n
gives the correct label, and
filefrag -v /swap|awk 'NR==4{gsub(/\./,"");print $4;}'the offset required.
Put both in /etc/default/grub, like this (retain existing parameters as needed, of course):
GRUB_CMDLINE_LINUX_DEFAULT="resume=UUID=xxxx resume_offset=yyyyy"
Put both also in /etc/initramfs-tools/conf.d/resume (create the file if it is missing):
RESUME=UUID=xxxx resume_offset=yyyyy
With these changes in place, regenerate both grub config and initramfs with
update-grub update-initramfs -k all -u
To test it straight away, use
systemctl hibernate
Older method (pre-systemd)
You can use uswsusp which is an alternate suspend method for the linux kernel that can use a swap file instead of a swap partition and also supports features like compression and encryption.
Install it:
aptitude install uswsusp
Configure uswsusp:
dpkg-reconfigure -pmedium uswsusp
At the "Continue without a valid swap space?" question, answer Yes.
At the "Swap space to resume from:" prompt, select the partition where the file above was created.
Answer the "Encrypt snapshot?" and "Show splash screen?" questions as you please.
You might have to add yourself to the powerdev group.
Typically a uswsusp.conf file looks like this:
# /etc/uswsusp.conf(8) -- Configuration file for s2disk/s2both resume device = /dev/sda1 compress = y early writeout = y image size = 238941634 RSA key file = /etc/uswsusp.key shutdown method = platform resume offset = 8288
The "resume offset = 8288" is where the swapfile actually is. You may obtain this value by running:
swap-offset /swap
The "resume device" must be the partition and not the swap file.
Note that after editing the /etc/uswsusp.conf file, you may need to run:
update-initramfs -u
To test hibernation:
s2disk
This will write the content of the RAM to the swap file and shut down. Press the power button to wake up. To enable this method as the default system for hibernation, edit /usr/lib/hal/scripts/linux/hal-system-power-hibernate . There is a bug in this script and it will look for s2disk in the wrong place, you will have to edit it so it looks like this:
/sbin/s2disk
This script is in the HAL package, which means it will break if HAL is updated. If hibernate doesn't work after an update, you will have to re-edit /usr/lib/hal/scripts/linux/hal-system-power-hibernate . A good idea would be to make a backup of the file for quick re-insertion after an update breakage.
If s2disk hibernates, but initramfs fails to see your swap file on startup and system continues to boot up normally like the swap file is not there, you'll need to add the "resume" hook to your /etc/default/grub:
GRUB_CMDLINE_LINUX_DEFAULT="resume=/dev/sda1 quiet"
where "/dev/sda1" is a partition where your swap file is located.
After that, issue "update-grub" to recreate initramfs.
If you want to lock the screen, save the swap to disk (in case your system runs out of power) and suspend to ram (to resume quickly if it still has power), create a script called /usr/local/bin/gotosleep containing:
/usr/bin/xscreensaver-command -lock sleep 2 sudo /usr/sbin/s2both
Make sure sudo does not prompt you for a password:
sudo visudo -f /etc/sudoers.d/local %powerdev ALL=NOPASSWD: /usr/sbin/s2both, /usr/sbin/s2ram
Caveats. -- The console is apparently broken. More on this later.
Tricks when the system is fully encrypted
This works even with Debian Jessie and systemd: the steps are the same, but once configured uswsusp with dpkg, edit /etc/uswsusp.conf and change the resume device:
resume device = /dev/mapper/sda2_crypt
Being sda2_crypt the name of your encripted partition, you can list the ones available in "/dev/mapper".
Then, re-execute the configuration, but this time select the new detected partition. This is necessary to reconfigure initramfs:
dpkg-reconfigure -pmedium uswsusp
You should also make the proper modifications in "/etc/default/grub", and re-execute "update-grub":
GRUB_CMDLINE_LINUX_DEFAULT="resume=/dev/mapper/sda2_crypt quiet"
Debian Jessie requirement: make it work with systemd
Systemd does not use this kind of hibernation to a file by default. That means that if you try to hibenate using Gnome, KDE or similar, it may not work. To make it compatible with systemd:
cp /lib/systemd/system/systemd-hibernate.service /etc/systemd/system/
Now edit "/etc/systemd/system/systemd-hibernate.service" and change the last line:
ExecStart=/bin/sh -c 's2disk && run-parts --regex .\* -a post /lib/systemd/system-sleep'
Finally restart systemd:
systemctl daemon-reload
To-Do
-- Create the swapfile at the moment of hibernation - and delete (optionally) after resuming.
For more on Partitioning, Swap and Hibernation - see -