编辑（2015-03-08）：我认为这种行为是由 ubuntu-sdk 使用 schroot 和 overlayfs 安装其开发工具包引起的。请参阅https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/filesystems/overlayfs.txt和https://developer.ubuntu.com/en/apps/sdk /tutorials/building-cross-architecture-click-applications/
我有一台带有两个物理磁盘的笔记本电脑，每个大约 1TB。
franck@franck-ThinkPad-T430s:~$ blkid
/dev/sda3: UUID="waaa02-V9C4-YPqM-C6vu-wpAd-QwPe-6JDrCS" TYPE="LVM2_member" PARTUUID="e7e30cb9-1358-49b6-a991-9000fa32be70"
franck@franck-ThinkPad-T430s:~$ sudo blkid
Swipe your right index finger across the fingerprint reader
/dev/sda3: UUID="waaa02-V9C4-YPqM-C6vu-wpAd-QwPe-6JDrCS" TYPE="LVM2_member" PARTUUID="e7e30cb9-1358-49b6-a991-9000fa32be70"
/dev/sda1: UUID="B7ED-D7E9" TYPE="vfat" PARTLABEL="EFI System Partition" PARTUUID="5c17a74c-706e-4d2a-bb04-3157900ef3f6"
/dev/sda2: UUID="f4ce6839-ce59-4d7f-a106-e04c06bc0c03" TYPE="ext2" PARTUUID="610befd8-d98d-4306-acfe-d5aca7375a46"
/dev/sdb1: LABEL="data" UUID="82dc2f8e-91b9-4d96-8e80-01bb8139300c" TYPE="ext4" PARTUUID="d2bcce3b-0303-417b-b1a5-64054694f156"
/dev/mapper/ubuntu--vg-lv--root: UUID="76224107-a31a-4a71-b115-926e0eec320d" TYPE="ext4"
/dev/mapper/ubuntu--vg-lv--var: UUID="9ae852a7-68d6-45f0-acc5-ffb6eee62ccc" TYPE="ext4"
/dev/mapper/ubuntu--vg-lv--home: UUID="23b1c628-0b78-47bb-bba0-1cf694fcdb9d" TYPE="ext4"
（注意使用sudo时的区别...不知道有没有意义）
franck@franck-ThinkPad-T430s:~$ ll /dev/disk/by-id/
total 0
drwxr-xr-x 2 root root 400 Mar 6 09:01 ./
drwxr-xr-x 7 root root 140 Mar 6 09:01 ../
lrwxrwxrwx 1 root root 9 Mar 6 09:01 ata-Crucial_CT1024M550SSD1_14110C0AFD52 -> ../../sda
lrwxrwxrwx 1 root root 10 Mar 6 09:01 ata-Crucial_CT1024M550SSD1_14110C0AFD52-part1 -> ../../sda1
lrwxrwxrwx 1 root root 10 Mar 6 09:01 ata-Crucial_CT1024M550SSD1_14110C0AFD52-part2 -> ../../sda2
lrwxrwxrwx 1 root root 10 Mar 6 09:01 ata-Crucial_CT1024M550SSD1_14110C0AFD52-part3 -> ../../sda3
lrwxrwxrwx 1 root root 9 Mar 6 09:01 ata-Samsung_SSD_840_EVO_1TB_mSATA_S1KRNEAF300981W -> ../../sdb
lrwxrwxrwx 1 root root 10 Mar 6 09:01 ata-Samsung_SSD_840_EVO_1TB_mSATA_S1KRNEAF300981W-part1 -> ../../sdb1
lrwxrwxrwx 1 root root 10 Mar 6 09:01 dm-name-ubuntu--vg-lv--home -> ../../dm-2
lrwxrwxrwx 1 root root 10 Mar 6 09:01 dm-name-ubuntu--vg-lv--root -> ../../dm-0
lrwxrwxrwx 1 root root 10 Mar 6 09:01 dm-name-ubuntu--vg-lv--var -> ../../dm-1
lrwxrwxrwx 1 root root 10 Mar 6 09:01 dm-uuid-LVM-jBidHcOmS5PLgOnIfgfWxcu35IHAc3oA3XgOAXUIncgAvTG973Lh4L5Hp3RTv6WC -> ../../dm-0
lrwxrwxrwx 1 root root 10 Mar 6 09:01 dm-uuid-LVM-jBidHcOmS5PLgOnIfgfWxcu35IHAc3oADK8PIqDaAIz6E4rqHiPhf2Xjl0RxEfBO -> ../../dm-2
lrwxrwxrwx 1 root root 10 Mar 6 09:01 dm-uuid-LVM-jBidHcOmS5PLgOnIfgfWxcu35IHAc3oAKyrRw58kYqKSjMuTY0LJqVl6WHunWt0Y -> ../../dm-1
lrwxrwxrwx 1 root root 9 Mar 6 09:01 wwn-0x5002538844584d30 -> ../../sdb
lrwxrwxrwx 1 root root 10 Mar 6 09:01 wwn-0x5002538844584d30-part1 -> ../../sdb1
lrwxrwxrwx 1 root root 9 Mar 6 09:01 wwn-0x500a07510c0afd52 -> ../../sda
lrwxrwxrwx 1 root root 10 Mar 6 09:01 wwn-0x500a07510c0afd52-part1 -> ../../sda1
lrwxrwxrwx 1 root root 10 Mar 6 09:01 wwn-0x500a07510c0afd52-part2 -> ../../sda2
lrwxrwxrwx 1 root root 10 Mar 6 09:01 wwn-0x500a07510c0afd52-part3 -> ../../sda3
有这样安装的：
franck@franck-ThinkPad-T430s:~$ cat /etc/fstab
# /etc/fstab: static file system information.
# ...
# <file system> <mount point> <type> <options> <dump> <pass>
/dev/mapper/ubuntu--vg-lv--root / ext4 noatime,errors=remount-ro 0 1
# /boot was on /dev/sda2 during installation
UUID=f4ce6839-ce59-4d7f-a106-e04c06bc0c03 /boot ext2 defaults 0 2
# /boot/efi was on /dev/sda1 during installation
UUID=B7ED-D7E9 /boot/efi vfat defaults 0 1
/dev/mapper/ubuntu--vg-lv--home /home ext4 noatime,defaults 0 2
/dev/mapper/ubuntu--vg-lv--var /var ext4 noatime,defaults 0 2
#
UUID=82dc2f8e-91b9-4d96-8e80-01bb8139300c /srv/mm ext4 noatime,defaults 0 2
#
# /tmp in ram to preserve SSDs
tmpfs /tmp tmpfs defaults,mode=1777 0 0
但是我只有上面 df 命令的部分输出。请注意，/home 和 /var 挂载点没有出现在任何地方。事实上，此输出中几乎没有完整的磁盘。
franck@franck-ThinkPad-T430s:~$ df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/ubuntu--vg-lv--root 19G 7.9G 9.9G 45% /
none 4.0K 0 4.0K 0% /sys/fs/cgroup
/dev 7.8G 4.0K 7.8G 1% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-i386-2ce339c6-bce3-4a5e-8c60-06722a0f4bb1/dev
/tmp 7.8G 2.1M 7.8G 1% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-i386-2ce339c6-bce3-4a5e-8c60-06722a0f4bb1/tmp
tmpfs 1.6G 1.3M 1.6G 1% /run
none 5.0M 4.0K 5.0M 1% /run/lock
/run/shm 7.8G 496K 7.8G 1% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-i386-2ce339c6-bce3-4a5e-8c60-06722a0f4bb1/run/shm
none 100M 68K 100M 1% /run/user
/dev/sda2 985M 224M 712M 24% /boot
/var/lib/schroot/chroots/click-ubuntu-sdk-14.10-i386 28G 23G 4.0G 86% /var/lib/schroot/union/underlay/click-ubuntu-sdk-14.10-i386-2ce339c6-bce3-4a5e-8c60-06722a0f4bb1
/dev/sdb1 874G 570G 260G 69% /srv/mm
/dev/sda1 511M 3.4M 508M 1% /boot/efi
click-ubuntu-sdk-14.10-amd64 28G 23G 4.0G 86% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-amd64-2c10adb7-7c2d-44dd-b455-39e5b396dbb9
click-ubuntu-sdk-14.10-amd64 28G 23G 4.0G 86% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-amd64-6cdf130c-c5ed-4261-826f-0f1e8355b087
click-ubuntu-sdk-14.10-armhf 28G 23G 4.0G 86% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-armhf-396914cd-21f7-46ca-98ca-5c297c88be1a
click-ubuntu-sdk-14.10-armhf 28G 23G 4.0G 86% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-armhf-dca33aeb-316b-414b-ac88-7694565bfaac
click-ubuntu-sdk-14.10-i386 28G 23G 4.0G 86% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-i386-2ce339c6-bce3-4a5e-8c60-06722a0f4bb1
click-ubuntu-sdk-14.10-i386 28G 23G 4.0G 86% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-i386-5d7eb656-e0cf-4e22-a37e-a82d90152de9
但是 mount 命令给了我另一个故事：
franck@franck-ThinkPad-T430s:~$ mount | grep vg
/dev/mapper/ubuntu--vg-lv--root on / type ext4 (rw,noatime,errors=remount-ro)
/dev/mapper/ubuntu--vg-lv--home on /home type ext4 (rw,noatime)
/dev/mapper/ubuntu--vg-lv--var on /var type ext4 (rw,noatime)
（加上我为便于阅读而删除的一大堆东西）
为什么 df 如此困惑？我的 fs 有问题吗？这些 /var/lib/schroot/chroots/ 挂载点是如何工作的？
谢谢你的帮助。
EDIT1：发行 df -h -a 给了我一个更完整但奇怪的（对我来说）结果......
franck@franck-ThinkPad-T430s:~$ df -h -a
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/ubuntu--vg-lv--root 19G 7.9G 9.9G 45% /
proc - - - - /proc
sysfs - - - - /sys
none 4.0K 0 4.0K 0% /sys/fs/cgroup
none 0 0 0 - /sys/fs/fuse/connections
none 0 0 0 - /sys/kernel/debug
none 0 0 0 - /sys/kernel/security
none 0 0 0 - /sys/firmware/efi/efivars
udev - - - - /dev
devpts - - - - /dev/pts
tmpfs - - - - /tmp
tmpfs 1.6G 1.3M 1.6G 1% /run
none 5.0M 4.0K 5.0M 1% /run/lock
none - - - - /run/shm
none 100M 68K 100M 1% /run/user
none 0 0 0 - /sys/fs/pstore
/dev/sda2 985M 224M 712M 24% /boot
/dev/mapper/ubuntu--vg-lv--home - - - - /home
/dev/mapper/ubuntu--vg-lv--var - - - - /var
/dev/sdb1 874G 570G 260G 69% /srv/mm
/dev/sda1 511M 3.4M 508M 1% /boot/efi
binfmt_misc 0 0 0 - /proc/sys/fs/binfmt_misc
systemd 0 0 0 - /sys/fs/cgroup/systemd
/var/lib/schroot/chroots/click-ubuntu-sdk-14.10-amd64 - - - - /var/lib/schroot/union/underlay/click-ubuntu-sdk-14.10-amd64-2c10adb7-7c2d-44dd-b455-39e5b396dbb9
click-ubuntu-sdk-14.10-amd64 28G 23G 4.0G 86% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-amd64-2c10adb7-7c2d-44dd-b455-39e5b396dbb9
/proc 0 0 0 - /var/lib/schroot/mount/click-ubuntu-sdk-14.10-amd64-2c10adb7-7c2d-44dd-b455-39e5b396dbb9/proc
/sys 0 0 0 - /var/lib/schroot/mount/click-ubuntu-sdk-14.10-amd64-2c10adb7-7c2d-44dd-b455-39e5b396dbb9/sys
/dev 7.8G 4.0K 7.8G 1% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-amd64-2c10adb7-7c2d-44dd-b455-39e5b396dbb9/dev
/dev/pts 0 0 0 - /var/lib/schroot/mount/click-ubuntu-sdk-14.10-amd64-2c10adb7-7c2d-44dd-b455-39e5b396dbb9/dev/pts
/home 891G 218G 629G 26% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-amd64-2c10adb7-7c2d-44dd-b455-39e5b396dbb9/home
/tmp 7.8G 2.1M 7.8G 1% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-amd64-2c10adb7-7c2d-44dd-b455-39e5b396dbb9/tmp
/run/shm 7.8G 504K 7.8G 1% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-amd64-2c10adb7-7c2d-44dd-b455-39e5b396dbb9/run/shm
/var/lib/schroot/chroots/click-ubuntu-sdk-14.10-amd64 - - - - /var/lib/schroot/union/underlay/click-ubuntu-sdk-14.10-amd64-6cdf130c-c5ed-4261-826f-0f1e8355b087
click-ubuntu-sdk-14.10-amd64 28G 23G 4.0G 86% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-amd64-6cdf130c-c5ed-4261-826f-0f1e8355b087
/proc 0 0 0 - /var/lib/schroot/mount/click-ubuntu-sdk-14.10-amd64-6cdf130c-c5ed-4261-826f-0f1e8355b087/proc
/sys 0 0 0 - /var/lib/schroot/mount/click-ubuntu-sdk-14.10-amd64-6cdf130c-c5ed-4261-826f-0f1e8355b087/sys
/dev 7.8G 4.0K 7.8G 1% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-amd64-6cdf130c-c5ed-4261-826f-0f1e8355b087/dev
/dev/pts 0 0 0 - /var/lib/schroot/mount/click-ubuntu-sdk-14.10-amd64-6cdf130c-c5ed-4261-826f-0f1e8355b087/dev/pts
/home 891G 218G 629G 26% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-amd64-6cdf130c-c5ed-4261-826f-0f1e8355b087/home
/tmp 7.8G 2.1M 7.8G 1% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-amd64-6cdf130c-c5ed-4261-826f-0f1e8355b087/tmp
/run/shm 7.8G 504K 7.8G 1% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-amd64-6cdf130c-c5ed-4261-826f-0f1e8355b087/run/shm
/var/lib/schroot/chroots/click-ubuntu-sdk-14.10-armhf - - - - /var/lib/schroot/union/underlay/click-ubuntu-sdk-14.10-armhf-396914cd-21f7-46ca-98ca-5c297c88be1a
click-ubuntu-sdk-14.10-armhf 28G 23G 4.0G 86% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-armhf-396914cd-21f7-46ca-98ca-5c297c88be1a
/proc 0 0 0 - /var/lib/schroot/mount/click-ubuntu-sdk-14.10-armhf-396914cd-21f7-46ca-98ca-5c297c88be1a/proc
/sys 0 0 0 - /var/lib/schroot/mount/click-ubuntu-sdk-14.10-armhf-396914cd-21f7-46ca-98ca-5c297c88be1a/sys
/dev 7.8G 4.0K 7.8G 1% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-armhf-396914cd-21f7-46ca-98ca-5c297c88be1a/dev
/dev/pts 0 0 0 - /var/lib/schroot/mount/click-ubuntu-sdk-14.10-armhf-396914cd-21f7-46ca-98ca-5c297c88be1a/dev/pts
/home 891G 218G 629G 26% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-armhf-396914cd-21f7-46ca-98ca-5c297c88be1a/home
/tmp 7.8G 2.1M 7.8G 1% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-armhf-396914cd-21f7-46ca-98ca-5c297c88be1a/tmp
/run/shm 7.8G 504K 7.8G 1% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-armhf-396914cd-21f7-46ca-98ca-5c297c88be1a/run/shm
/var/lib/schroot/chroots/click-ubuntu-sdk-14.10-armhf - - - - /var/lib/schroot/mount/click-ubuntu-sdk-14.10-armhf-68af14d0-808d-4ef8-9f7b-5c8199937096
/proc 0 0 0 - /var/lib/schroot/mount/click-ubuntu-sdk-14.10-armhf-68af14d0-808d-4ef8-9f7b-5c8199937096/proc
/sys 0 0 0 - /var/lib/schroot/mount/click-ubuntu-sdk-14.10-armhf-68af14d0-808d-4ef8-9f7b-5c8199937096/sys
/dev 7.8G 4.0K 7.8G 1% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-armhf-68af14d0-808d-4ef8-9f7b-5c8199937096/dev
/dev/pts 0 0 0 - /var/lib/schroot/mount/click-ubuntu-sdk-14.10-armhf-68af14d0-808d-4ef8-9f7b-5c8199937096/dev/pts
/home 891G 218G 629G 26% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-armhf-68af14d0-808d-4ef8-9f7b-5c8199937096/home
/tmp 7.8G 2.1M 7.8G 1% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-armhf-68af14d0-808d-4ef8-9f7b-5c8199937096/tmp
/run/shm 7.8G 504K 7.8G 1% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-armhf-68af14d0-808d-4ef8-9f7b-5c8199937096/run/shm
/var/lib/schroot/chroots/click-ubuntu-sdk-14.10-armhf - - - - /var/lib/schroot/union/underlay/click-ubuntu-sdk-14.10-armhf-dca33aeb-316b-414b-ac88-7694565bfaac
click-ubuntu-sdk-14.10-armhf 28G 23G 4.0G 86% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-armhf-dca33aeb-316b-414b-ac88-7694565bfaac
/proc 0 0 0 - /var/lib/schroot/mount/click-ubuntu-sdk-14.10-armhf-dca33aeb-316b-414b-ac88-7694565bfaac/proc
/sys 0 0 0 - /var/lib/schroot/mount/click-ubuntu-sdk-14.10-armhf-dca33aeb-316b-414b-ac88-7694565bfaac/sys
/dev 7.8G 4.0K 7.8G 1% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-armhf-dca33aeb-316b-414b-ac88-7694565bfaac/dev
/dev/pts 0 0 0 - /var/lib/schroot/mount/click-ubuntu-sdk-14.10-armhf-dca33aeb-316b-414b-ac88-7694565bfaac/dev/pts
/home 891G 218G 629G 26% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-armhf-dca33aeb-316b-414b-ac88-7694565bfaac/home
/tmp 7.8G 2.1M 7.8G 1% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-armhf-dca33aeb-316b-414b-ac88-7694565bfaac/tmp
/run/shm 7.8G 504K 7.8G 1% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-armhf-dca33aeb-316b-414b-ac88-7694565bfaac/run/shm
/var/lib/schroot/chroots/click-ubuntu-sdk-14.10-i386 28G 23G 4.0G 86% /var/lib/schroot/union/underlay/click-ubuntu-sdk-14.10-i386-2ce339c6-bce3-4a5e-8c60-06722a0f4bb1
click-ubuntu-sdk-14.10-i386 28G 23G 4.0G 86% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-i386-2ce339c6-bce3-4a5e-8c60-06722a0f4bb1
/proc 0 0 0 - /var/lib/schroot/mount/click-ubuntu-sdk-14.10-i386-2ce339c6-bce3-4a5e-8c60-06722a0f4bb1/proc
/sys 0 0 0 - /var/lib/schroot/mount/click-ubuntu-sdk-14.10-i386-2ce339c6-bce3-4a5e-8c60-06722a0f4bb1/sys
/dev 7.8G 4.0K 7.8G 1% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-i386-2ce339c6-bce3-4a5e-8c60-06722a0f4bb1/dev
/dev/pts 0 0 0 - /var/lib/schroot/mount/click-ubuntu-sdk-14.10-i386-2ce339c6-bce3-4a5e-8c60-06722a0f4bb1/dev/pts
/home 891G 218G 629G 26% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-i386-2ce339c6-bce3-4a5e-8c60-06722a0f4bb1/home
/tmp 7.8G 2.1M 7.8G 1% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-i386-2ce339c6-bce3-4a5e-8c60-06722a0f4bb1/tmp
/run/shm 7.8G 504K 7.8G 1% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-i386-2ce339c6-bce3-4a5e-8c60-06722a0f4bb1/run/shm
/var/lib/schroot/chroots/click-ubuntu-sdk-14.10-i386 28G 23G 4.0G 86% /var/lib/schroot/union/underlay/click-ubuntu-sdk-14.10-i386-5d7eb656-e0cf-4e22-a37e-a82d90152de9
click-ubuntu-sdk-14.10-i386 28G 23G 4.0G 86% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-i386-5d7eb656-e0cf-4e22-a37e-a82d90152de9
/proc 0 0 0 - /var/lib/schroot/mount/click-ubuntu-sdk-14.10-i386-5d7eb656-e0cf-4e22-a37e-a82d90152de9/proc
/sys 0 0 0 - /var/lib/schroot/mount/click-ubuntu-sdk-14.10-i386-5d7eb656-e0cf-4e22-a37e-a82d90152de9/sys
/dev 7.8G 4.0K 7.8G 1% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-i386-5d7eb656-e0cf-4e22-a37e-a82d90152de9/dev
/dev/pts 0 0 0 - /var/lib/schroot/mount/click-ubuntu-sdk-14.10-i386-5d7eb656-e0cf-4e22-a37e-a82d90152de9/dev/pts
/home 891G 218G 629G 26% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-i386-5d7eb656-e0cf-4e22-a37e-a82d90152de9/home
/tmp 7.8G 2.1M 7.8G 1% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-i386-5d7eb656-e0cf-4e22-a37e-a82d90152de9/tmp
/run/shm 7.8G 504K 7.8G 1% /var/lib/schroot/mount/click-ubuntu-sdk-14.10-i386-5d7eb656-e0cf-4e22-a37e-a82d90152de9/run/shm
gvfsd-fuse 0 0 0 - /run/user/1000/gvfs
df --human结合的输出--all对于您所拥有的系统来说是绝对正常的，查看您安装的软件包。所以你可以不用担心了！;-)