```sh
if [ ! -f /etc/fstab.old ]; then sudo cp /etc/fstab /etc/fstab.old; fi
sudo cp /etc/fstab.old /etc/fstab
sudo tee -a /etc/fstab <<'EOF'
tmpfs   /mnt/ramdisk   tmpfs   rw,size=120G,uid=1000,gid=1000   0 0
EOF
cat /etc/fstab

sudo mkdir -p /mnt/ramdisk
sudo umount /mnt/ramdisk
sudo systemctl daemon-reload
sudo mount -a
ls -l /mnt/ramdisk
```