(12) 关于Linux 定时任务crontab的一些存疑 解释

详细的crontab用法 百度可见，但是呢有些文章的描述是前后矛盾的，给读者的阅读造成误解。

诸如：http://www.cnblogs.com/God-froest/archive/2012/05/17/crontab_.html

在文中提到：

*  *  *  *  * commond

前面的五个星号分别表示 分 时 日 月 周，commond表示你要操作的命令

分（1-59）（*或*/1表示每分钟）     时（1-23）（0表示0点）    日（1-31）   月（1-12）    周（1-6）（0表示周日）

文中明确的说明了第一个  *   分（1-59）（*或*/1表示每分钟）

但是呢 又在  后文中说：

==========================================================================

在项目中有人写了个五小时定时执行的脚本 ，当时感觉有问题就提了出来。同事后来百度了下 说是没问题。看了下文章的描述--这与之前的理解有出入。

争执毫无意义，写个定时自己跑下即可。

==========================================================================

实践：

aa1.txt （有省略）

Thu Mar 12 10:07:01 UTC 2015Thu Mar 12 10:08:01 UTC 2015Thu Mar 12 10:09:01 UTC 2015Thu Mar 12 10:10:01 UTC 2015Thu Mar 12 10:11:01 UTC 2015Thu Mar 12 10:12:01 UTC 2015Thu Mar 12 10:13:01 UTC 2015Thu Mar 12 10:14:01 UTC 2015Thu Mar 12 10:15:01 UTC 2015Thu Mar 12 10:16:01 UTC 2015Thu Mar 12 10:17:01 UTC 2015Thu Mar 12 10:18:01 UTC 2015Thu Mar 12 10:19:01 UTC 2015Thu Mar 12 10:20:01 UTC 2015Thu Mar 12 10:21:01 UTC 2015Thu Mar 12 10:22:01 UTC 2015Thu Mar 12 10:23:01 UTC 2015Thu Mar 12 10:24:01 UTC 2015Thu Mar 12 10:25:01 UTC 2015Thu Mar 12 10:26:01 UTC 2015Thu Mar 12 10:27:01 UTC 2015Thu Mar 12 10:28:01 UTC 2015Thu Mar 12 10:29:01 UTC 2015Thu Mar 12 10:30:01 UTC 2015Thu Mar 12 10:31:01 UTC 2015Thu Mar 12 10:32:01 UTC 2015Thu Mar 12 10:33:01 UTC 2015Thu Mar 12 10:34:01 UTC 2015Thu Mar 12 10:35:01 UTC 2015Thu Mar 12 10:36:01 UTC 2015Thu Mar 12 10:37:01 UTC 2015Thu Mar 12 10:38:01 UTC 2015Thu Mar 12 10:39:01 UTC 2015Thu Mar 12 10:40:01 UTC 2015Thu Mar 12 10:41:01 UTC 2015Thu Mar 12 10:42:01 UTC 2015Thu Mar 12 10:43:01 UTC 2015Thu Mar 12 10:44:01 UTC 2015Thu Mar 12 10:45:01 UTC 2015Thu Mar 12 10:46:01 UTC 2015Thu Mar 12 10:47:01 UTC 2015Thu Mar 12 10:48:01 UTC 2015Thu Mar 12 10:49:01 UTC 2015Thu Mar 12 10:50:01 UTC 2015Thu Mar 12 10:51:01 UTC 2015Thu Mar 12 10:52:01 UTC 2015Thu Mar 12 10:53:01 UTC 2015Thu Mar 12 10:54:01 UTC 2015Thu Mar 12 10:55:01 UTC 2015Thu Mar 12 10:56:01 UTC 2015Thu Mar 12 10:57:01 UTC 2015Thu Mar 12 10:58:01 UTC 2015Thu Mar 12 10:59:01 UTC 2015Thu Mar 12 11:00:01 UTC 2015Thu Mar 12 11:01:01 UTC 2015Thu Mar 12 11:02:01 UTC 2015Thu Mar 12 11:03:01 UTC 2015Thu Mar 12 11:04:01 UTC 2015Thu Mar 12 11:05:01 UTC 2015Thu Mar 12 11:06:01 UTC 2015Thu Mar 12 11:07:01 UTC 2015Thu Mar 12 11:08:01 UTC 2015Thu Mar 12 11:09:01 UTC 2015Thu Mar 12 11:10:01 UTC 2015Thu Mar 12 11:11:01 UTC 2015Thu Mar 12 11:12:01 UTC 2015Thu Mar 12 11:13:01 UTC 2015Thu Mar 12 11:14:01 UTC 2015Thu Mar 12 11:15:01 UTC 2015

aa2.txt（有省略）

Thu Mar 12 10:07:01 UTC 2015Thu Mar 12 10:08:01 UTC 2015Thu Mar 12 10:09:01 UTC 2015Thu Mar 12 10:10:01 UTC 2015Thu Mar 12 10:11:01 UTC 2015Thu Mar 12 10:12:01 UTC 2015Thu Mar 12 10:13:01 UTC 2015Thu Mar 12 10:14:01 UTC 2015Thu Mar 12 10:15:01 UTC 2015Thu Mar 12 10:16:01 UTC 2015Thu Mar 12 10:17:01 UTC 2015Thu Mar 12 10:18:01 UTC 2015Thu Mar 12 10:19:01 UTC 2015Thu Mar 12 10:20:01 UTC 2015Thu Mar 12 10:21:01 UTC 2015Thu Mar 12 10:22:01 UTC 2015Thu Mar 12 10:23:01 UTC 2015Thu Mar 12 10:24:01 UTC 2015Thu Mar 12 10:25:01 UTC 2015Thu Mar 12 10:26:01 UTC 2015Thu Mar 12 10:27:01 UTC 2015Thu Mar 12 10:28:01 UTC 2015Thu Mar 12 10:29:01 UTC 2015Thu Mar 12 10:30:01 UTC 2015Thu Mar 12 10:31:01 UTC 2015Thu Mar 12 10:32:01 UTC 2015Thu Mar 12 10:33:01 UTC 2015Thu Mar 12 10:34:01 UTC 2015Thu Mar 12 10:35:01 UTC 2015Thu Mar 12 10:36:01 UTC 2015Thu Mar 12 10:37:01 UTC 2015Thu Mar 12 10:38:01 UTC 2015Thu Mar 12 10:39:01 UTC 2015Thu Mar 12 10:40:01 UTC 2015Thu Mar 12 10:41:01 UTC 2015Thu Mar 12 10:42:01 UTC 2015Thu Mar 12 10:43:01 UTC 2015Thu Mar 12 10:44:01 UTC 2015Thu Mar 12 10:45:01 UTC 2015Thu Mar 12 10:46:01 UTC 2015Thu Mar 12 10:47:01 UTC 2015Thu Mar 12 10:48:01 UTC 2015Thu Mar 12 10:49:01 UTC 2015Thu Mar 12 10:50:01 UTC 2015Thu Mar 12 10:51:01 UTC 2015Thu Mar 12 10:52:01 UTC 2015Thu Mar 12 10:53:01 UTC 2015Thu Mar 12 10:54:01 UTC 2015Thu Mar 12 10:55:01 UTC 2015Thu Mar 12 10:56:01 UTC 2015Thu Mar 12 10:57:01 UTC 2015Thu Mar 12 10:58:01 UTC 2015Thu Mar 12 10:59:01 UTC 2015Thu Mar 12 15:00:01 UTC 2015Thu Mar 12 15:01:02 UTC 2015Thu Mar 12 15:02:01 UTC 2015Thu Mar 12 15:03:01 UTC 2015Thu Mar 12 15:04:01 UTC 2015Thu Mar 12 15:05:01 UTC 2015Thu Mar 12 15:06:01 UTC 2015Thu Mar 12 15:07:01 UTC 2015Thu Mar 12 15:08:01 UTC 2015Thu Mar 12 15:09:01 UTC 2015Thu Mar 12 15:10:01 UTC 2015Thu Mar 12 15:11:01 UTC 2015Thu Mar 12 15:12:01 UTC 2015Thu Mar 12 15:13:01 UTC 2015Thu Mar 12 15:14:01 UTC 2015Thu Mar 12 15:15:01 UTC 2015Thu Mar 12 15:16:01 UTC 2015Thu Mar 12 15:17:01 UTC 2015Thu Mar 12 15:18:01 UTC 2015Thu Mar 12 15:19:01 UTC 2015Thu Mar 12 15:20:01 UTC 2015Thu Mar 12 15:21:01 UTC 2015Thu Mar 12 15:22:01 UTC 2015Thu Mar 12 15:23:01 UTC 2015Thu Mar 12 15:24:01 UTC 2015Thu Mar 12 15:25:01 UTC 2015Thu Mar 12 15:26:01 UTC 2015Thu Mar 12 15:27:02 UTC 2015Thu Mar 12 15:28:01 UTC 2015Thu Mar 12 15:29:01 UTC 2015Thu Mar 12 15:30:01 UTC 2015Thu Mar 12 15:31:01 UTC 2015Thu Mar 12 15:32:01 UTC 2015Thu Mar 12 15:33:01 UTC 2015Thu Mar 12 15:34:01 UTC 2015Thu Mar 12 15:35:01 UTC 2015Thu Mar 12 15:36:01 UTC 2015Thu Mar 12 15:37:01 UTC 2015

aa3.txt (全部)

Thu Mar 12 15:00:01 UTC 2015Thu Mar 12 20:00:01 UTC 2015Fri Mar 13 00:00:01 UTC 2015

结论

*  */1 * * * 的效果 是每个小时的 每一分钟都执行一次  ，也就是每一分钟都执行一次。

*  */5 * * * 的效果 是每5个小时的 每一分钟都执行一次  。

0  */5 * * * 的效果 是每5个小时的 仅仅第0分钟执行一次。

 《实践出真知 不能迷信书本》