Cron job every three days

Question

Is it possible to run a cronjob every three days  Or maybe 10 times month

User · Answer

0 0 1-30 3       This would run every three days starting 1st  Here are the 20 scheduled runs -    2015-06-01 00 00 00 2015-06-04 00 00 00 2015-06-07 00 00 00 2015-06-10 00 00 00 2015-06-13 00 00 00 2015-06-16 00 00 00 2015-06-19 00 00 00 2015-06-22 00 00 00 2015-06-25 00 00 00 2015-06-28 00 00 00 2015-07-01 00 00 00 2015-07-04 00 00 00 2015-07-07 00 00 00 2015-07-10 00 00 00 2015-07-13 00 00 00 2015-07-16 00 00 00 2015-07-19 00 00 00 2015-07-22 00 00 00 2015-07-25 00 00 00 2015-07-28 00 00 00

User · Answer

You should learn the basics of crontab   Edit the cron by command crontab -e and then    CTRL    X then Y and finally press ENTER  return  on mac to save the file  You can check the new crons have been installed of not by crontab -l     A crontab file has five fields for specifying mins  hours  the day of   the month  month  and the day of the week followed by the command to   be run at that interval                             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      in the value field above means all legal values as in braces for that column   Here  I wrote a detailed post about it  Setup Cron in Unix

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It would be simpler if you configured it to just run e g  on monday and thursdays  which would give it a 3 and 4 day break   Otherwise configure it to run daily  but make your php cron script exit early with   if     date  z     3          exit

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How about   00 00           every 3 days  amp  amp  echo test   Where every is a script      bin sh  case  2 in     days          expr  date   j     1   0  gt   dev null                 weeks          expr  date   V     1   0  gt   dev null                 months          expr  date   m     1   0  gt   dev null            esac   So it runs every day   Using   3 runs on the 3rd  6th      27th  30th of the month  but is then wrong after a month has a 31st day   The every script is only wrong after the end of the year

User · Answer

If you want it to run on specific days of the month  like the 1st  4th  7th  etc    then you can just have a conditional in your script that checks for the current day of the month    I thought all you needed for this was instead of   3 which means every three days  use 1 3 which means every three days starting on the 1st of the month  so 7 3 would mean every three days starting on the 7th of the month  etc

User · Answer

Run it every three days     0 0   3       How about that   If you want it to run on specific days of the month  like the 1st  4th  7th  etc    then you can just have a conditional in your script that checks for the current day of the month   if    date  j   - 1    3      exit      or  as  mario points out  you can use date  k   to get the day of the year instead of doing it based on the day of the month

User · Answer

I don t think you have what you need with   0 0   3         lt  lt  lt  WARNING    CAUSES UNEVEN INTERVALS AT END OF MONTH     Unfortunately  the   3 is setting the interval on every n day of the month and not every n days  See  explanation here  At the end of the month there is recurring issue guaranteed    1st  at 2019-02-01 00 00 00 then at 2019-02-04 00 00 00  lt  lt  3 days  etc  OK then at 2019-02-07 00 00 00     then at 2019-02-25 00 00 00 then at 2019-01-28 00 00 00 then at 2019-03-01 00 00 00  lt  lt  1 day WRONG then at 2019-03-04 00 00 00       According to this article  you need to add some modulo math to the command being executed to get a TRUE  every N days   For example   0 0        bash -c       date    s    86400    3    0     amp  amp  runmyjob sh   In this example  the job will be checked daily at 12 00 AM  but will only execute when the number of days since 01-01-1970 modulo 3 is 0    If you want it to be every 3 days from a specific date  use the following format   0 0        bash -c       date    s -d  2019-01-01     86400    3    0     amp  amp  runmyjob sh

User · Answer

0 0               date   -j- 1     3      0    amp  amp  script  Get the day of the year from date  offset by 1 to start at 0  check if it is modulo three

User · Answer

Because cron is  stateless   it cannot accurately express  frequencies   only  patterns  which it  apparently  continuously matches against the current time   Rephrasing your question makes this more obvious     is it possible to run a cronjob at 00 01am every night except skip nights when it had run within 2 nights    When cron is comparing the current time to job request time patterns  there s no way cron can know if it ran your job in the past    it certainly is possible to write a stateful cron that records past jobs and thus includes patterns for matching against this state  but that s not the standard cron included in most operating systems   Such a system would get complicated by requiring the introduction of the concept of when such patterns  reset    For example  is the pattern reset when the time is changed  i e  the crontab entry is revised    Look to your favorite calendar app to see how complicated it can get to express Repeating patterns of scheduled events  and note that they don t have the reset problem because the starting calendar event has a natural  start  a k a  reset  date    Try rescheduling an every-other-week recurring calendar event to postpone by a week  over christmas for example   Usually you have to terminate that recurring event and restart a completely new one  this illustrates the limited expressivity of how even complicated calendar apps represent repeating patterns   And of course Calendars have a lot of state-- each individual event can be deleted or rescheduled independently  in most calendar apps     Further  you probably want to do your job every 3rd night if successful  but if the last one failed  to try again immediately  perhaps the next night  not wait 3 more days  or even sooner  like an hour later  but stop retrying upon morning s arrival    Clearly  cron couldn t possibly know if your job succeeded and the pattern can t also express an alternate more frequent  retry  schedule   ANYWAY-- You can do what you want yourself   Write a script  tell cron to run it nightly at 00 01am   This script could check the timestamp of something  which records the  last run   and if it was  3 days ago    perform the job and reset the  last run  timestamp     that timestamped indicator is a bit of persisted state which you can manipulate and examine  but which cron cannot     be careful with time arithmetic if you re using human-readable clock time-- twice a year  some days have 23 or 25 hours in their day  and 02 00-02 59 occurs twice in one day or not at all    Use UTC to avoid this

User · Answer

I am not a cron specialist  but how about   0   72         It will run every 72 hours non-interrupted    https   crontab guru  0  72

User · Answer

3      that says  every minute of every hour on every three days    0 0   3      says at 00 00  midnight  every three days

[cron] Cron job every three days

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