我们在安装了iperf的客户端上安装了一个linux框（Raspberry Pi），我们将其作为客户端运行。
我们还在云端运行Ubuntu 16.04的xxxx虚拟机箱
当我们运行以下命令时：
iperf -c <xxxx> 我们得到以下内容：
------------------------------------------------------------ Client connecting to <xxxx>, TCP port 5001 TCP window size: 43.8 KByte (default) ------------------------------------------------------------ [ 3] local 192.168.30.11 port 34893 connected with <xxxx> port 5001 [ ID] Interval Transfer Bandwidth [ 3] 0.0-10.0 sec 63.9 MBytes 53.5 Mbits/sec
几乎每次我们手动运行50Mbits / sec的数量时，我们都能够获得类似的结果。 由于该网站运行在五千万线上，这是在期望之内。
但是，当我们运行以下命令时：
*/5 * * * * iperf -c <xxxx> | grep Mbits/sec >> speed.txt
我们已经插入到crontab中，我们实现了以下function：
sudo cat /root/speed.txt [ 3] 0.0-10.1 sec 22.4 MBytes 18.6 Mbits/sec [ 3] 0.0-10.1 sec 21.5 MBytes 17.8 Mbits/sec [ 3] 0.0-10.1 sec 22.5 MBytes 18.6 Mbits/sec [ 3] 0.0-10.1 sec 20.5 MBytes 17.0 Mbits/sec [ 3] 0.0-10.1 sec 21.4 MBytes 17.7 Mbits/sec [ 3] 0.0-10.1 sec 19.5 MBytes 16.1 Mbits/sec [ 3] 0.0-10.1 sec 19.8 MBytes 16.4 Mbits/sec [ 3] 0.0-10.1 sec 19.2 MBytes 15.9 Mbits/sec [ 3] 0.0-10.1 sec 20.9 MBytes 17.3 Mbits/sec [ 3] 0.0-10.1 sec 21.4 MBytes 17.7 Mbits/sec [ 3] 0.0-10.1 sec 19.6 MBytes 16.2 Mbits/sec [ 3] 0.0-10.1 sec 19.9 MBytes 16.4 Mbits/sec [ 3] 0.0-10.1 sec 21.4 MBytes 17.8 Mbits/sec [ 3] 0.0-10.2 sec 19.8 MBytes 16.3 Mbits/sec [ 3] 0.0-10.1 sec 20.9 MBytes 17.3 Mbits/sec [ 3] 0.0-10.2 sec 21.9 MBytes 18.1 Mbits/sec
我的问题是，为什么这些结果运行在crontab显然会显示一个不同的更慢的结果？