Hibernate not working 15.04

To know your swap partition, run swapon -s. Let's say it reports /dev/sda5.

Open /etc/default/grub and find the line with GRUB_CMDLINE_LINUX_DEFAULT=. This is the list of kernel command line options GRUB will pass to Linux. Add resume=/dev/sda5, so the line

GRUB_CMDLINE_LINUX_DEFAULT="nosplash enable_mtrr_cleanup=1"
will now look like this

GRUB_CMDLINE_LINUX_DEFAULT="nosplash enable_mtrr_cleanup=1 resume=/dev/sda6"

Save the file and run this to enable the new configuration:

sudo update-grub2

And that's it..!!