通过其他程序或脚本在非交互式模式下调用top命令，经常会出现:
top: failed tty get 错误
解决办法：加个-b 选项皆可
-b : Batch mode operation
Starts top in <A1><AF>Batch mode<A1><AF>, which could be useful for sending output from top to other programs or to a file. In this mode, top will not accept input and runs until the iterations limit you<A1><AF>ve set with the <A1><AF>-n<A1><AF> command-line option or until killed.
例如执行：top -bn 1
nohup top -b | grep init >> top.log & (top.log 内容显示的慢）
nohup /usr/bin/top -b | grep init >> top.log & (top.log内容显示的快）