| # 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
 # |  |  |  |  |
 # *  *  *  *
 0 7 * * 2-7 root /xxx
 
 特别是周。周二到周末 7点执行XXX
 
 但是上面标注day of week (0 - 6)这里是0-6。后面又写到周末=0 or 7.......
 
 可不可以理解为周 可以写成 0-6 或者1-7 ????还是周只能写成0-6???????
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