我运行 Linux snore 3.16.0-4-amd64 #1 SMP Debian 3.16.39-1 (2016-12-30) x86_64 GNU/Linux，使用以下 fstab：
wr@snore:/etc$ cat /etc/fstab
# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point> <type> <options> <dump> <pass>
/dev/mapper/VG0-SLASH / ext4 errors=remount-ro 0 1
# /boot was on /dev/sdb1 during installation
UUID=9f0e490f-a55b-4335-8c6f-d7ef4d56a7d0 /boot ext4 defaults 0 2
/dev/mapper/VG0-HOME /home ext4 defaults 0 2
/dev/mapper/VG0-OPT /opt ext4 defaults 0 2
/dev/mapper/VG0-TMP /tmp ext4 defaults 0 2
/dev/mapper/VG0-USR /usr ext4 defaults 0 2
/dev/mapper/VG0-VAR /var ext4 defaults 0 2
/dev/mapper/VG0-SWAP none swap sw 0 0
/dev/sr0 /media/cdrom0 udf,iso9660 user,noauto 0 0
但是，df 命令显示：
wr@snore:/etc$ df
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/dm-0 1886280 314036 1458376 18% /
udev 10240 0 10240 0% /dev
tmpfs 3287660 9644 3278016 1% /run
/dev/dm-1 23897980 13848200 8812788 62% /usr
tmpfs 8219144 561516 7657628 7% /dev/shm
tmpfs 5120 4 5116 1% /run/lock
tmpfs 8219144 0 8219144 0% /sys/fs/cgroup
/dev/sdb1 944120 40576 838368 5% /boot
/dev/mapper/VG0-VAR 9480420 5436404 3539392 61% /var
/dev/mapper/VG0-OPT 14286320 1248128 12289444 10% /opt
/dev/mapper/VG0-TMP 9480420 22636 8953160 1% /tmp
/dev/mapper/VG0-HOME 480486104 249255728 206799992 55% /home
tmpfs 1643832 8 1643824 1% /run/user/120
tmpfs 1643832 20 1643812 1% /run/user/1000
其中 /usr 和 / 分别映射为 /dev/dm-1 和 /dev/dm-0。
有人知道为什么吗？到目前为止我没有遇到任何问题，但关机时出现警告。