i.e.
http://g.unsa.edu.ar:6711/man?=crontab&=5. just googled for "man cron" or "man crontab"
Your settings will launch <command> once an hour, at 25 minutes after the full hour. Probably you want the script to be executed every 25 minutes.
I will try to explain the usage of crontab and also why 25 minutes of all step widths is -hmmm, let's say- tricky.
Let's start with the minute field of an crontab entry - all others stay *.
You entered 25. This causes cron to run the script every time the current time's minute-field equals 25 (as mentioned above: once an hour).
You may also enter a comma-separated list of 'matches', i.e. 0,10,20,30,40, 50 this will execute the script every 10 minutes (every time the current time's minute field is equal to one of the entries in the list).
You can enter a range using <start>-<stop>, i.e. 0-59 will run the script every minute. In conjunction with a step width parameter you can limit the execution, i.e. 0-59/10 will again execute the command every 10 minutes (matches start at 0 step width 10). Since the minute field can only contain values from 0 to 59 this is the same as */10.
All other fields in a crontab entry behave the same way.
The command is executed only if for all fields a match is found.
a single * means "doesn't matter"
i.e.
# minute, hour, day of month, month, day of week
*/10 */4 * 2-3 * doSomething
will launch doSomething every 10 minutes on every fourth hour in february and march.
ok, back to your 25 minutes.
60 (minutes of an hour) cannot be devided by 25 without remainder, so you can't find an expression that work on the minutes field alone.
You have to add several crontab entries (*), all execute the same script but on other conditions.
Your first entry will start at 0 minutes - next execution shall be 25 minutes later and so on. This leads to 0,25,50 for the first entry.
Next call must be on 15 (0:50 + 25 minutes) -> 15, 40 and so on.
Unfortunately the first number that can be devided by 25 AND 60 is 300.
300 minutes, that's 5 hours! Not until five different entries your 'minutes'-condition can start over again.
- minute field's conditions:
- 0, 25, 50
- 15, 40
- 5, 30, 55
- 20, 45
- 10, 35
But it's going on: you can't divide 24 (hours a day) by 5 without remainder.
Unfortunately again, 5 is prime so the least common multiple (is this the correct term?) must be 24*5
...and so on...
If you're lucky I missed something in the syntax of crontab or a way of simplifying the conditions
edit: (*) just as an example:
a script shall be executed every 40 minutes.
can't divide 60 by 40 without remainder, but 120 --> 2 entries.
On even hours excute the script at 0 and 40 minutes after the full hour.
On odd hours just at 20 minutes after the full hour -->
# minute, hour, day of month, month, day of week
0,40 0-23/2 * * * doSomething
20 1-23/2 * * * doSomething