Cron> is a time-based scheduling service in a Linux or Unix-like computer operating systems. Cron job are used to schedule commands to be executed periodically. You can setup commands or scripts, which will repeatedly run at a set time. Cron is one of the most useful tool in Linux or UNIX like operating systems. The cron service (daemon) runs in the background and constantly checks the /etc/crontab file, /etc/cron.*/ directories. It also checks the /var/spool/cron/ directory.
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First, Login to UNIX/Linux system.
Type the following command to enter cronjob:
$ crontab -e
Each cronjob has the following syntax:
# +---------------- minute (0 - 59) # | +------------- hour (0 - 23) # | | +---------- day of month (1 - 31) # | | | +------- month (1 - 12) # | | | | +---- day of week (0 - 6) (Sunday=0 or 7) # | | | | | * * * * * command to be executed
To get crontab to run a task every 10 minutes you could type as follow:
*/10 * * * * /path/to/command
OR
*/10 * * * * /path/to/script
Save and close the file.
Where,
- The asterisk (*) operator specifies all possible values for a field. For example, an asterisk in the hour time field would be equivalent to every hour or an asterisk in the month field would be equivalent to every month.
- The */10 is used in conjunction with ranges. For example, 0-23/2 can be used in the hours field to specify command execution every other hour. Steps are also permitted after an asterisk, so if you want to say every two hours just use */2. In this example, */10 in the minutes field to specify command execution every 10 minute.
See also
- HowTo: Add Jobs To cron Under Linux or UNIX
- Man pages: cron(8)
This entry is 13 of 16 in the Linux Cron Jobs Howto & Tutorial series. Keep reading the rest of the series:
- What is cron on a Linux or Unix-like systems?
- How To Add Jobs To cron Under Linux or UNIX?
- Verify crond Daemon And Cronjobs Are Running
- Start Restart and Stop The Cron or Crond Service
- List / Display All Cron Jobs
- Linux / UNIX Crontab File Location
- Change Crontab Email Settings ( MAILTO )
- Disable The Mail Alert By Crontab Command On a Linux or Unix-like Systems
- At What Time Cron Entries In cron.daily, cron.weekly, cron.monthly Run?
- Execute Cron Job After System Reboot
- Setup and Run PHP Script As A Cron Job
- Run crontab job every minute on a Linux or Unix-like system
- Running crontab (cron jobs) Every 10 Minutes
- Cron Job Script Execution on the Last Day of a Month
- Execute / Run crontab (cron jobs) every 1 minute
- Ubuntu create cron.log file
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*/10 * * * * /home/test.sh > /dev/null 2>&1
crontab: error on previous line; unexpected character found in line.
crontab: errors detected in input, no crontab file generated.
Guess it does not work in Solaris 8
OR
sudo -i
cd /etc/cron.d
touch command
vi command
# in command file
MAILTO=rootmail@foo.bar
*/10 * * * * /path/to/command
# save command file and exit
if you do not want to receive a letter then
MAILTO=””
yeah, budacsik. why use one command when you can use 4 :)))
yes, just one line
sudo vi /etc/cron.d/command
what if I need to start the script at 3:00 AM exactly and consecutive executions should begin after every 10 mins.
eg: 3:00 3:10 3:20 etc… lifetime
But the clause is, it should start exactly at 3:00. I can play in scripts. But is there an option like this in crons?
*/10 3,4,5 * * *
It will be called
WHEN ( MINUITES DIVIDED BY 10 AND DIVISION REMAINDER EQUALS 0
AND
( HOUR EQUALS 3 ) OR ( HOUR EQUALS 4 ) OR ( HOUR EQUALS 5 ) )
So it will run at 3.00, 3.10, 3.20, 3.30, 3.40, 3.50, 4.00, 4.10….. 5.50
so can I go like this to start at 3AM and then by 10 mins invokes would this continue around the clock?
*/10 3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,1,2 * * *
*/10 3-24 * * *
you can define ranges within a cron job instead of separating everything with a comma
you can use range instead of separating everything with a comma
i.e */10 3-24 * * *
I think Mannoj wanted a cron job that runs 3:00 AM for the first time and every 10 minutes from 3:00 AM and goes on. But your cron job runs only at 3 to 24 every 10 minutes that is not the answer!
What this post doesn’t explain is why it works. In a crontab, the / symbol means that it will run if the current value can be divided by the following number without a remainder.
This isn’t important for simple timers like ‘every ten minutes’, but can be very useful when using more advanced calculations.
This is very helpful….thnx everyone. I got my queru answerd without any more search…u gyus rock…!!
hi, how to i create a cronjob for a folder with multiple subfolders and run them all at once?
don’t trust any crontab generator
You see the / option posted all over the net as a shortcut for “every” but I do not believe it is applicable to all systems, for instance I do not believe this will work on AIX.
Just sayin…
How would I output my file from a MySQL script to an FTP site?
It works and it is extremelly simple. Thank you man!
*/10 means every 10 min.It is understandable.But,when will the the scripts will run? I meant script run times…?
For eg. at 1am it will run at 1:00, 1:10, 1:30, 1:40, 1:50 times :)
thank you very much! working in my ubuntu
echo “Test of Mail body” | mail -s “Mail subject” to@somedomain.com
mysqldump -u root -p pss dbname /opt/backup/
/opt/script/mail.sh
every five minutes
*/5 * * * * /root/bin/showTime.sh
i want to run this script for 30 mins after every 15 mins how can i do that ??
the below one is doing for 5 min after 1 hour. i want 30 min after 15 mins break
0 * * * * nohup /home/pi/mmal/motion -n -c /home/pi/mmal/motion-mmalcam.conf 1>/dev/null 2>&1 </dev/null &
5 * * * * pkill -9 motion
how to set cron morning 8.30 AM to 11.30 PM every day.
hello,
we have a cron job that run every Saturday at 01:00 (0 1 * * 6) we want to modified to run every 2 weeks on Saturday at 01:00.
Thanks.