watch - execute a program periodically [ˌpɪriˈɑːdɪkli] , showing output fullscreen
每隔10秒执行一次_Linux重复执行命令之watch命令10个案例
每隔1秒查看http连接数，怀疑受到CC攻击时非常实用
[root@zcwyou ~]# watch -n 1 -d 'pstree|grep http'
