A Linux Cron Job

Introduction

In my recent consulting, I was asked to help to complete a task schedule in RedHat Linux environment. Here is the requirement:

1. The task should run every 5 minutes
2. If a task takes longer than 5 minutes, no new task should run while a live task is running
3. The task should not run between 5:30 am and 7:30 am

Solution

Apparently, this is a candidate for using Linux cron job based on the first statement. The requirement requires us to do a bit more than just cron job. I know that the second and third requirement can be done with the shell script. Thus, I decided to write a simple bash script. Of course, this can be done by using Perl as well. For now, I will provide the solution here.

The Cron Definition

The cron job definition is very simple as the following:

*/5     *       *       *       *       /opt/Apexus_DI/bin/ExecuteApexus_DI.sh

Linux/Unix cron job syntax can be in the following form. There are plenty references you can find in the internet. Here is the brief summary.

# * * * * *  command to execute
# ┬ ┬ ┬ ┬ ┬
# │ │ │ │ │
# │ │ │ │ │
# │ │ │ │ └───── day of week (0 - 7) (0 to 6 are Sunday to Saturday, or use names; 7 is Sunday, the same as 0)
# │ │ │ └────────── month (1 - 12)
# │ │ └─────────────── day of month (1 - 31)
# │ └──────────────────── hour (0 - 23)
# └───────────────────────── min (0 - 59)

Field name	Mandatory?	Allowed values	Allowed special characters Remarks
Minutes	Yes	0-59	* / , - -
Hours	Yes	0-23	* / , - -
Day of month	Yes	1-31	* / , - ? L W -
Month	Yes	1-12 or JAN-DEC	* / , - -
Day of week	Yes	0-6 or SUN-SAT	* / , - ? L # -
Year	No	1970–2099	* / , -	This field is not supported in standard/default implementations.

List Of The script

The complete list of the script is shown below. Line 5 - 9 is to check if a job is running. If yes, then just exit. Line 12 and 14 are to check if the time is between 5:30 am and 7:00 am.

1 #!/bin/bash 2 # check if Apexus DI job is runing or not 3 # 4 5 pInfo=$(ps -eaf | egrep java | egrep -v grep | egrep memberaccounts.apexus_diexecution) 6 if [[ -n "$pInfo" ]] ; then 7 echo "Process is running, stop now." 8 exit 101 9 fi 10 11 12 if [[ $(date "+%H%M") -ge "0530" ]] 13 then 14 if [[ $(date +%H) -lt "07" ]] 15 then 16 echo "$(date) : I don't run at this time " >> /opt/Apexus_DI/log/stdout.log 17 else 18 /opt/Apexus_DI/t_jobs/Apexus_DIExecution/Apexus_DIExecution_run.sh 2>&1 >> /opt/Apexus_DI/log/stdout.log 19 fi 20 else 21 /opt/Apexus_DI/t_jobs/Apexus_DIExecution/Apexus_DIExecution_run.sh 2>&1 >> /opt/Apexus_DI/log/stdout.log 22 fi 23

Cron Job Log

The cron job logs are located at /var/log/cron. You need to have admin permission to view the log.