为什么不能 apt-get 安装 i386 版本的 libpcap-dev？
$ sudo apt-get install libpcap-dev:i386
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package libpcap-dev:i386 is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package 'libpcap-dev:i386' has no installation candidate
但是，该包显然存在：https://launchpad.net/ubuntu/trusty/i386/libpcap-dev. 我在 Ubuntu 14.04 x64 上。
我为每个用户设置了 SSH 密钥，他们通过 SSH 连接到正确的机器。问题是很多FTP程序不支持SSH登录。因此，仅对于 FTP，我希望允许用户使用密码登录。我如何实现这一目标？