How to run a cronjob every X minutes?
Your CRON should look like this:
*/5 * * * *
CronWTF is really usefull when you need to test out your CRON settings.
Might be a good idea to pipe the output into a log file so you can see if your script is throwing any errors too - since you wont see them in your terminal.
Also try using a shebang at the top of your PHP file, so the system knows where to find PHP. Such as:
#!/usr/bin/php
that way you can call the whole thing like this
*/5 * * * * php /path/to/script.php > /path/to/logfile.log
If you want to run a cron every n
minutes, there are a few possible options depending on the value of n
.
n
divides 60 (1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30)
Here, the solution is straightforward by making use of the /
notation:
# 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)
# | | | | |
# * * * * * command to be executed
m-59/n * * * * command
In the above, n
represents the value n
and m
represents a value smaller than n
or *
. This will execute the command at the minutes m,m+n,m+2n,...
n
does NOT divide 60
If n
does not divide 60, you cannot do this cleanly with cron but it is possible. To do this you need to put a test in the cron where the test checks the time. This is best done when looking at the UNIX timestamp, the total seconds since 1970-01-01 00:00:00 UTC
. Let's say we want to start to run the command the first time when Marty McFly arrived in Riverdale and then repeat it every n
minutes later.
% date -d '2015-10-21 07:28:00' +%s
1445412480
For a cronjob to run every 42
nd minute after `2015-10-21 07:28:00', the crontab would look like this:
# 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)
# | | | | |
# * * * * * command to be executed
* * * * * minutetestcmd "2015-10-21 07:28:00" 42 && command
with minutetestcmd
defined as
#!/usr/bin/env bash
starttime=$(date -d "$1" "+%s")
# return UTC time
now=$(date "+%s")
# get the amount of minutes (using integer division to avoid lag)
minutes=$(( (now - starttime) / 60 ))
# set the modulo
modulo=$2
# do the test
(( now >= starttime )) && (( minutes % modulo == 0 ))
Remark: UNIX time is not influenced by leap seconds
Remark: cron
has no sub-second accuracy
In a crontab
file, the fields are:
- minute of the hour.
- hour of the day.
- day of the month.
- month of the year.
- day of the week.
So:
10 * * * * blah
means execute blah
at 10 minutes past every hour.
If you want every five minutes, use either:
*/5 * * * * blah
meaning every minute but only every fifth one, or:
0,5,10,15,20,25,30,35,40,45,50,55 * * * * blah
for older cron
executables that don't understand the */x
notation.
If it still seems to be not working after that, change the command to something like:
date >>/tmp/debug_cron_pax.txt
and monitor that file to ensure something's being written every five minutes. If so, there's something wrong with your PHP scripts. If not, there's something wrong with your cron
daemon.