Home Backend Development PHP Tutorial crontab scheduled task configuration record

crontab scheduled task configuration record

Jul 30, 2016 pm 01:31 PM
amp cron crontab home test

1. Foreword

Today I will simply record the crontab configuration

2. crontab directory

/etc/crontab 文件
    这是系统运行的调度任务
 
/var/spool/cron 目录
    用户自定义的crontab任务放在此目录下
 
ls –lrt /etc/cron*
   /etc/cron.deny     表示不能使用crontab命令的用户
   /etc/cron.allow     表示能使用crontab命令的用户
   默认情况下,cron.allow不存在,如果都存在,cron.allow优先
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3. crontab command syntax

具体可 crontab --help 或者 man crontab|more

crontab –l   //查看当前用户的定时任务 
crontab –e  //编辑当前用户的定时任务
crontab –r  //删除当前用户的定时任务
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4. crontab task format

59 23 * * *  /home/xxx/crontab/test.sh > /dev/null  2>&1 &

前6列暂且用C1 - C6表示

C1 分    (1-59)
C2 时    (1-23,0表示子夜)
C3 日    (1-31)
C4 月    (1-12)
C5 星期   (0-6,0表示星期天,1表示星期一,以此类推)
C6 要运行的命令

前5列表示 命令执行的频率,最小频率是每分钟一次,其中Cn的值可用四种形式表示:
*  ,  */n  , T1-T2 , a,b,c  

当C1 为 * 时,表示每分钟都要执行命令
当C1 为 */n时,表示每隔n分钟执行一次命令
当C1 为 T1-T2时,表示从 T1分钟 到 T2分钟时间内都要执行命令
当C1 为 a,b,c 时,表示第 a,b,c 分钟都要执行命令


示例调用:

12  12 * * *  /home/xxx/crontab/test.sh >/dev/null 2>&1 
表示每天的12点12分 执行脚本

*/2 *  *  *  *  /home/xxx/crontab/test.sh >/dev/null 2>&1
表示每隔2分钟 执行一次脚本

0 23 * * 1-5  /home/xxx/crontab/test.sh >/dev/null 2>&1
表示每周一到周五的23点 执行一次脚本

0 19 * * 0  mail -s "xxx" xxx@mail.com < /tmp/maildata
表示每周日的19点 发送邮件到 xxx@mail.com
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5. Instructions on commands

关于命令中 /dev/null 2>&1 的解释

0  表示键盘输入
1  表示标准输出
2  表示错误输出

1.创建test.sh,内容如下

#! /bin/bash
echo "time is " `date`

2.添加定时任务

* * * * *    /home/xxx/crontab/test.sh > /home/xxx/crontab/test.log &    默认是1,和下面方法一致
* * * * *   /home/xxx/crontab/test.sh 1> /home/xxx/crontab/test.log &
* * * * *   /home/xxx/crontab/test.sh > /home/xxx/crontab/test.log  2>&1 &

3.说明

1代表,标准输出,所以上述命令会将脚本的输出结果,输出到后面指定的log文件中,而不是打印到屏幕;
2代表,错误输出,&1表示文件的描述,这里表示脚本执行的错误信息重定向到1(标准输出)
而1已经重定向到指定的log文件中,所以信息都会输出到log文件
不能写成 2>1 ,缺少&,会认为是错误信息输出到名称为 1 文件中
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6. Notes

1.shell中需设置必要的环境变量
  crontab的环境变量默认不包含系统当前用户的环境,所以需添加必要的环境变量

2.尽量采用完整路径方法,避免使用相对路径

3.避免脚本的重复执行
  if(exec("ps -ef |grep 'php'|grep 'updateScript'|grep -v 'grep' |wc -l ") > 2){
    die();  
  }

  grep -v 'grep'    表示结果去过滤掉 grep 那一行
  wc -l             表示统计满足条件的行数
  这样就可以判断 php进程中,名为 updateScript 的脚本 是否已经执行了
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7. References

http://www.cnblogs.com/kerrycode/p/3238346.html
http://www.cnblogs.com/hazir/p/sudo_command.html
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The above introduces the crontab scheduled task configuration record, including the relevant content. I hope it will be helpful to friends who are interested in PHP tutorials.

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