Cron every 2 hours

1. Introduction

In this article, we are going to present cron expressions for executing tasks every 2 hours. Cron expression is a special format used for defining time for scheduled jobs.

2. Cron expression every 2 hours for crontab

In Linux there are a special crontab files used for cron jobs configuration. Each line in the crontab file contains six fields separated by a space followed by the command to be run. The cron expression for crontab daemons that execute task every 2 hours looks like the following:

The expression contains the following components:

1. 0 - at minute 0,
2. /2 - every 2 hours,
3. - every day of the month,
4. - every month,
5. - every day of the week.

Example crontabs:

Run PHP script every 2 hours:
0 /2 /usr/bin/php /home/username/public_html/cron.php >/dev/null 2>&1

Create MySQL dump every hour:
0 /2 mysqldump -u root -pPASSWORD database > /root/db.sql >/dev/null 2>&1

Run bash script every hour:
0 /2 /bin/bash /home/username/backup.sh >/dev/null 2>&1

3. Cron expression every 2 hours for Spring Scheduler

In Spring scheduler a cron expression consists of six sequential fields: second, minute, hour, day of the month, month, day(s) of the week. In Spring cron expression use to run tasks in 2-hour intervals looks like the following:

Let's break down the expression into separate components:

1. 0 - at second :00,
2. 0 - at minute :00,
3. 0/2 - starting at 0 every 2 hours,
4. 1/1 - starting at 1 every 1,
5. * - every month,
6. ? - any day of the week.

Example Spring scheduler configuration that executes task every hour:

import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;


@Component
public class MyScheduler {

    @Scheduled(cron = "0 0 0/2 1/1 * ?")
    public void doSomething() {
        // this code will be executed every hour
    }

}

4. Cron expression every 2 hours for Quartz

The Quartz is an open-source scheduling tasks library for Java application. Quartz expression has seven parameters: The last one stands for the year.

The following snippet creates a simple cron scheduler using Quartz library:

JobDetail job = newJob(SimpleJob.class)
    .withIdentity("job1", "group1")
    .build();

CronTrigger trigger = newTrigger()
    .withIdentity("trigger1", "group1")
    .withSchedule(cronSchedule("0 0 0/2 1/1  ? "))
    .build();

sched.scheduleJob(job, trigger);

5. Conclusion

In this article we presented several cron expression used for executing task every hour. Presented crons are ready to copy/paste.