swapon

NAME      TYPE       SIZE USED PRIO
/dev/sda2 partition 15.6G   0B   -2

cat /etc/initramfs-tools/conf.d/resume
RESUME=UUID=857ff79e-586a-4364-9ee7-47c77f6debd1

update-initramfs -u -k all
apt-get install --reinstall initramfs-tools

cat /etc/default/grub | grep RESUME
GRUB_CMDLINE_LINUX="RESUME=UUID=857ff79e-586a-4364-9ee7-47c77f6debd1"

blkid | grep swap
/dev/sda2: LABEL="swap" UUID="857ff79e-586a-4364-9ee7-47c77f6debd1" TYPE="swap" PARTUUID="e0c5913d-02"