我有一个在 Vagrant 和 VirtualBox 下运行的 Ubuntu 14.04.4 LTS VM。将其时间与服务器的时间进行比较时，我看到如下内容：
$ ntpdate -q ntp.ubuntu.com
server 91.189.94.4, stratum 2, offset -0.527602, delay 0.11812
server 91.189.89.198, stratum 2, offset -0.415140, delay 0.12631
server 91.189.89.199, stratum 2, offset -0.666563, delay 0.12758
server 91.189.91.157, stratum 2, offset -0.561897, delay 0.04617
3 Aug 20:40:38 ntpdate[17776]: step time server 91.189.91.157 offset -0.561897 sec
$ ntpdate -q ntp.ubuntu.com
server 91.189.91.157, stratum 2, offset 0.005067, delay 0.04915
server 91.189.94.4, stratum 2, offset -0.969532, delay 0.11708
server 91.189.89.198, stratum 2, …