마운트 지점에 chdir을 연결할 수 없는 이유는 무엇입니까?

내 운영체제는 debian8입니다.

cat /etc/group |grep 'debian8'
root:x:0:debian8
debian8:x:1000:

debian8은 루트 그룹의 구성원입니다.

cat /etc/sudoers
root    ALL=(ALL:ALL) ALL
%sudo   ALL=(ALL:ALL) ALL
debian8  ALL=(ALL:ALL)ALL

debian8은 루트로 어떤 명령이라도 실행할 수 있습니다.

root@hwy:/home/debian8# find / -name 'vimrc'
/home/debian8/openwrt/feeds/packages/utils/vim/files/vimrc
/root/openwrt/feeds/packages/utils/vim/files/vimrc
/usr/share/vim/vimrc
/etc/vim/bundle/Vundle.vim/test/vimrc
/etc/vim/bundle/vundle/test/vimrc
/etc/vim/vimrc

출력이 없습니다 Cannot chdir into mountpoint .

root@hwy:/home/debian8# sudo find / -name 'vimrc'
Cannot chdir into mountpoint.
/home/debian8/openwrt/feeds/packages/utils/vim/files/vimrc
/root/openwrt/feeds/packages/utils/vim/files/vimrc
/usr/share/vim/vimrc
/etc/vim/bundle/Vundle.vim/test/vimrc
/etc/vim/bundle/vundle/test/vimrc
/etc/vim/vimrc
Cannot chdir into mountpoint.
root@hwy:/home/debian8# su debian8
debian8@hwy:~$ sudo find / -name 'vimrc'
[sudo] password for debian8:
Cannot chdir into mountpoint.
/home/debian8/openwrt/feeds/packages/utils/vim/files/vimrc
/root/openwrt/feeds/packages/utils/vim/files/vimrc
/usr/share/vim/vimrc
/etc/vim/bundle/Vundle.vim/test/vimrc
/etc/vim/bundle/vundle/test/vimrc
/etc/vim/vimrc
Cannot chdir into mountpoint.

Cannot chdir into mountpoint 마지막 두 사례에 대한 출력입니다.
왜 두 줄의 출력이 있습니까 Cannot chdir into mountpoint.?
@Julie, 그게 제가 얻은 것입니다.

debian8@hwy:~$ cd  /tmp
debian8@hwy:/tmp$ cd

출력이 없습니다.

debian8@hwy:~$ cd /tmp
debian8@hwy:/tmp$ sudo bash -c "cd /"
Cannot chdir into mountpoint.
Cannot chdir into mountpoint.    

이제 두 줄의 출력이 있습니다. Cannot chdir into mountpoint.

root@hwy:~# cd /tmp
root@hwy:/tmp# sudo su -;
Signature not found in user keyring
Perhaps try the interactive 'ecryptfs-mount-private'
Signature not found in user keyring
Perhaps try the interactive 'ecryptfs-mount-private'