我想创建一个带有受限外壳的新用户，所以我：
ln -s bash rbash # create a symbolic link to bash with a name "rbash"
useradd -s /bin/rbash student # add a new user with a shell pointing to that symlink I've created
passwd student # create a password
su - student # Login as a user
但是之后我可以 cd 进入任何我想要的地方。看起来受限制的外壳不起作用。为什么 ？
每当我尝试更新时，它每次都会卡在 32% 并失败。
someone@somewhere:~/$ sudo apt update
Ign:1 http://linux.dropbox.com/ubuntu wily InRelease
Get:2 http://linux.dropbox.com/ubuntu wily Release [6,596 B]
Ign:3 http://developer.download.nvidia.com/compute/cuda/repos/ubuntu1604/x86_64 InRelease
Ign:4 http://dl.google.com/linux/chrome/deb stable InRelease
Get:5 http://linux.dropbox.com/ubuntu wily Release.gpg [473 B]
Hit:6 http://developer.download.nvidia.com/compute/cuda/repos/ubuntu1604/x86_64 Release
Hit:7 http://repo.steampowered.com/steam precise InRelease
Hit:8 http://ca.archive.ubuntu.com/ubuntu xenial InRelease
Get:10 http://security.ubuntu.com/ubuntu xenial-security InRelease [107 kB]
Hit:11 http://ppa.launchpad.net/freecad-maintainers/freecad-stable/ubuntu xenial InRelease
Hit:12 https://download.sublimetext.com apt/stable/ InRelease
Hit:13 http://dl.google.com/linux/chrome/deb stable Release
Hit:15 https://dl.winehq.org/wine-builds/ubuntu xenial InRelease
Get:16 http://ca.archive.ubuntu.com/ubuntu xenial-backports InRelease [107 kB]
Hit:18 http://ppa.launchpad.net/kubuntu-ppa/backports/ubuntu xenial InRelease
Hit:19 http://ppa.launchpad.net/webupd8team/java/ubuntu xenial InRelease
Get:14 http://ca.archive.ubuntu.com/ubuntu xenial-updates InRelease [109 kB]
Hit:20 http://ppa.launchpad.net/wireshark-dev/stable/ubuntu xenial InRelease
Ign:21 http://ca.archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages
Ign:22 http://ca.archive.ubuntu.com/ubuntu xenial-updates/main i386 Packages
Ign:23 http://ca.archive.ubuntu.com/ubuntu xenial-updates/main Translation-en
Get:24 http://ca.archive.ubuntu.com/ubuntu xenial-updates/main amd64 DEP-11 Metadata [320 kB]
Get:25 http://ca.archive.ubuntu.com/ubuntu xenial-updates/main DEP-11 64x64 Icons [227 kB]
Ign:26 http://ca.archive.ubuntu.com/ubuntu xenial-updates/restricted amd64 Packages
32% [Connecting to ca.archive.ubuntu.com (2001:67c:1560:8001::11)]
它阻止我升级包或更新包列表。