linux下设置定时执行脚本

yum install vixie-cron
yum install crontabs
service crond start
service crond stop
service crond status

出现以下信息则表示crond启动成功

● crond.service - Command Scheduler
   Loaded: loaded (/usr/lib/systemd/system/crond.service; enabled; vendor preset: enabled)
   Active: active (running) since Fri 2019-02-15 02:13:57 EST; 1 weeks 0 days ago
 Main PID: 94183 (crond)
    Tasks: 1
   Memory: 344.0K
   CGroup: /system.slice/crond.service
           └─94183 /usr/sbin/crond -n

2.将crond加入开机启动
就是把service crond start加入开机启动脚本
开机启动脚本可以参考我的另一篇博客：https://blog.csdn.net/qq_41969358/article/details/87798908

3.添加定时任务
vi /etc/crontab，例如设置每天晚上12点重启服务器
tip:定时任务失败很多时候都是crontab时间格式错误

SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root

# For details see man 4 crontabs

# Example of job definition:
# .---------------- minute (0 - 59)
# |  .------------- hour (0 - 23)
# |  |  .---------- day of month (1 - 31)
# |  |  |  .------- month (1 - 12) OR jan,feb,mar,apr ...
# |  |  |  |  .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat
# |  |  |  |  |
# *  *  *  *  * user-name  command to be executed
  0 0  *  *  * root reboot

4.添加完定时任务后，重启crond，使改动生效

service crond restart

5.查看是否生效
实时查看crontab执行内容

tail -f /var/log/cron

通过系统日志来查看Cron任务是否有执行过

grep "reboot" /var/log/cron