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At one of the production servers, some processes are using crontab to start periodically.

When I inspect the crontab entries, I see:

* * * * * some job

I cannot find out what this actually does. The only example I find, which relates to this is from wikipedia, which runs some job every minute.

* * * * ? some job

Are the two crons above identical?

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up vote 1 down vote accepted

Source: http://adminschoice.com/crontab-quick-reference

*     *     *   *    *        command to be executed
-     -     -   -    -
|     |     |   |    |
|     |     |   |    +----- day of week (0 - 6) (Sunday=0)
|     |     |   +------- month (1 - 12)
|     |     +--------- day of month (1 - 31)
|     +----------- hour (0 - 23)
+------------- min (0 - 59)

So yes, it runs every minute.


Regarding your question mark, this is the reason:

Both in classic and extended modes, nnCron users can use a "nonstandard" character "?" in the first four fields of cron format. It stands for time of nnCron startup, i. e. when a field is processed, startup time will be substituted for the question mark: minutes for Minute field, hour for Hour field, day of the month for Day of month field and month for Month field.

Source: http://www.nncron.ru/help/EN/working/cron-format.htm#STARTTIME

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if * * * * ? is every minute, what is * * * * * –  Dog eat cat world Aug 24 '11 at 20:01
    
No, look again. * * * * * is every minute. Your Wikipedia example is misleading. –  user3463 Aug 24 '11 at 20:02
    
Good, it seems you are right. –  Dog eat cat world Aug 24 '11 at 21:04
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