我有一台 Debian 8 服务器，客户的 PCI 扫描失败，可能正在运行：
nmap -p 22 -sV customer.edu
返回
22/tcp open ssh OpenSSH 6.7p1 Debian 5+deb8u7
这应该很容易，因为我的 /etc/apt/sources.list 是这样的：
deb http://mirror.rackspace.com/debian jessie main
deb-src http://mirror.rackspace.com/debian jessie main
deb http://mirror.rackspace.com/debian-security/ jessie/updates main
deb-src http://mirror.rackspace.com/debian-security/ jessie/updates main
deb http://packages.dotdeb.org jessie all
deb-src http://packages.dotdeb.org jessie all
deb http://ftp.us.debian.org/debian/ jessie main contrib non-free
deb-src http://ftp.us.debian.org/debian/ jessie main contrib non-free
deb http://ftp.debian.org/debian jessie-backports main
deb http://security.debian.org/ jessie/updates main contrib non-free
sudo apt-get upgrade openssh-server返回：
Calculating upgrade... openssh-server is already the newest …