Ubuntu (and its derivatives – Xubuntu, Lubuntu, Kubuntu) normally come with hibernation disabled by default, mostly due to possible hardware compatibility issues.
Re-enabling it is not a simple thing to do, despite logic dictating the opposite.
Start by testing out whether or not your system is capable of hibernation. Save everything important and run pm-hibernate in a terminal. If it correctly hibernates and resumes, then it is safe to continue – otherwise, investigate what fails.
sudo nano /var/lib/polkit-1/localauthority/10-vendor.d/com.ubuntu.desktop.pkla and look for
[Disable hibernate by default in upower] [Disable hibernate by default in logind]
Change the ResultActive= from no to yes:
[Disable hibernate by default in upower] Identity=unix-user:* Action=org.freedesktop.upower.hibernate ResultActive=yes [Disable hibernate by default in logind] Identity=unix-user:* Action=org.freedesktop.login1.hibernate;org.freedesktop.login1.handle-hibernate-key; ResultActive=yes
Save changes. The hibernation option should instantly become available in Xubuntu’s power menu. If it does not, double-check that you’ve edited correctly.