How to enable hibernation in 16.04

I have lost the to me essential hibernate functionality after upgrading ubuntu. This is normal, but unfortunately I could not reenable it this time.

I tried these three previous solutions:

• setting 3 entries in /etc/polkit-1/localauthority/50-local.d/com.ubuntu.disable-suspend.pkla,
• setting two entries in /etc/pm/sleep.d/20_custom-ehci_hcd, and
• enabling two entries in /var/lib/polkit-1/localauthority/10-vendor.d/com.ubuntu.desktop.pkla plus restarting the menu/indicators and rebooting

but no hibernation option appears.

Some additional info:

• sudo pm-hibernate outputs nothing and appears to do nothing.

• sudo s2disk outputs:

  s2disk: Could not open the snapshot device. Reason: Operation not permitted

I guess this is my key clue, but I didn't find any obvious explanations/solutions when googling that - I'm afraid I'm ignorant of the meaning.

There is no change to dmesg output and /var/log/pm-suspend.log does not exist after running pm-hibernate.

The machine is capable of hibernating under ubuntu 15.04 and earlier - the above options worked previously.

(I am aware this is a potential duplicate of this question, but wanted to add more detail.)

You need to disable Secure Boot if you are using UEFI.

With Secure Boot enabled hibernation is disabled for security reasons.