Attempt to mount a extX, vfat, CIFS, etc. filesystem to a mount point that is "busy" fails silently but appears to "work" in that "df" indicates the filesystem is mounted to that mount point (per /etc/fstab), and it appears to be normal in /etc/mtab, yet the partition files do not appear in the mount point directory and if were are any files in the (root FS) mount point directory, they are still accessible)! As illustrated in the example below, the failed mount can be remedied by umounting the partition, cd'ing to $HOME (to make the mount point not busy), then remounting the partition, the mount point then contains the files from the partition. Example: illustrates (under Raspbian, on a Raspbery Pi) how to reproduce a silent failure when vfat partition mounted to a busy mount point (made only busy because shell CWD is the mount point directory): Script started on Wed 03 Feb 2016 07:41:27 AM EST root@raspi2:/# df Filesystem 1K-blocks Used Available Use% Mounted on /dev/root 15186900 6421400 8098164 45% / devtmpfs 469752 0 469752 0% /dev tmpfs 94816 404 94412 1% /run tmpfs 5120 0 5120 0% /run/lock tmpfs 189620 0 189620 0% /run/shm //nas2/export.dmk 961301000 338699164 573747452 38% /media/nas1.dmk /dev/mmcblk0p1 57288 20304 36984 36% /boot root@raspi2:/# ls /boot bcm2708-rpi-b.dtb config.txt issue.txt overlays bcm2708-rpi-b-plus.dtb COPYING.linux kernel7.img start_cd.elf bcm2708-rpi-cm.dtb fixup_cd.dat kernel.img start_db.elf bcm2709-rpi-2-b.dtb fixup.dat LICENCE.broadcom start.elf bootcode.bin fixup_db.dat LICENSE.oracle start_x.elf cmdline.txt fixup_x.dat origCmdline.txt whereAmI root@raspi2:/# more /boot/whereAmI this is on the SD card. root@raspi2:/# root@raspi2:/# umount /boot root@raspi2:/# df Filesystem 1K-blocks Used Available Use% Mounted on /dev/root 15186900 6421400 8098164 45% / devtmpfs 469752 0 469752 0% /dev tmpfs 94816 404 94412 1% /run tmpfs 5120 0 5120 0% /run/lock tmpfs 189620 0 189620 0% /run/shm //nas2/export.dmk 961301000 338699164 573747452 38% /media/nas1.dmk root@raspi2:/# ls /boot whereAmI root@raspi2:/# more /boot/whereAmI this is in the root fs /boot directory root@raspi2:/# mount /boot root@raspi2:/# df Filesystem 1K-blocks Used Available Use% Mounted on /dev/root 15186900 6421400 8098164 45% / devtmpfs 469752 0 469752 0% /dev tmpfs 94816 404 94412 1% /run tmpfs 5120 0 5120 0% /run/lock tmpfs 189620 0 189620 0% /run/shm //nas2/export.dmk 961301000 338699164 573747452 38% /media/nas1.dmk /dev/mmcblk0p1 57288 20304 36984 36% /boot root@raspi2:/# ls /boot bcm2708-rpi-b.dtb config.txt issue.txt overlays bcm2708-rpi-b-plus.dtb COPYING.linux kernel7.img start_cd.elf bcm2708-rpi-cm.dtb fixup_cd.dat kernel.img start_db.elf bcm2709-rpi-2-b.dtb fixup.dat LICENCE.broadcom start.elf bootcode.bin fixup_db.dat LICENSE.oracle start_x.elf cmdline.txt fixup_x.dat origCmdline.txt whereAmI root@raspi2:/# more /boot/whereAmI this is on the SD card. root@raspi2:/# Script done on Wed 03 Feb 2016 07:42:34 AM EST
Actually, the mount succeeds, but the shell's CWD is not updated. A cd to somehwere else and back to /boot resolves this. Probably should withdraw this bug report. Sorry about that...