After some experiments i have this situation: i have sda1,sda2,sda3 in /mnt directory, but in fact, /dev/sda1,sda2,sda3 not mounted. But if i use sudo mount /dev/sda2, for example, create a file at here, then reboot, then file will remains. Very strange things. Why i have something in /mnt directory when devices are not mounted?