HOWTO: Use Cron and OSCusage for Regular Emailed Reports

It is possible to utilize Cron and the OSCusage command to send regular usage reports via email

Cron

It is easy to create Cron jobs on the Owens and Pitzer clusters at OSC. Cron is a Linux utility which allows the user to schedule a command or script to run automatically at a specific date and time. A cron job is the task that is scheduled.

Shell scripts run as a cron job are usually used to update and modify files or databases; however, they can perform other tasks, for example a cron job can send an email notification.

Getting Help

In order to use what cron has to offer, here is a list of the command name and options that can be used

Usage: 
crontab [options] file 
crontab [options] 
crontab -n [hostname] 
Options: 
-u  define user 
-e edit user's crontab 
-l list user's crontab 
-r delete user's crontab 
-i prompt before deleting 
-n  set host in cluster to run users' crontabs 
-c get host in cluster to run users' crontabs 
-s selinux context 
-x  enable debugging 

Also, if this is your first time using cron, you will be asked to choose an editor for setting your cron job. Choose whatever you find to be easiest for you.

Running a Cron Job

To check for any running cron jobs on the server, use the command (As shown above)

crontab -l 

and to create and edit your cron job use the following command,

crontab -e 

Now, in order to write you first cron job, you need to be familiar with the formatting system that cron follows.

Linux Crontab Format

The formatting system has 6 fields, each field from 1-5 is used to define the date and time of the execution. The 6th field is used for the command or script to be executed. The format is the following,

MIN HOUR DOM MON DOW CMD 

where,

figure 1: Cron’s formatting syntax

Getting Notified by Email Using a Cron Job

You can get an email notification using a cron job as mentioned earlier. The following is an example of a cron job that runs every minute and sends an email notification every minute,

* * * * * {cmd} | mail -s "title of the email notification" {your email} 

A user can also set up email notifications regarding usage by using the OSCusage cmd,

12 15 * * * /opt/osc/bin/OSCusage | mail -s "OSC usage on $(date)" {your email} 2> /path/to/file/for/stdout/and/stderr 2>&1 

This cron job will run every day at (15:12 or 3:12 PM).

Using OSCusage

The OSCusage command offers many options, the following is a list that pertains to that,

$ /opt/osc/bin/OSCusage --help 
usage: OSCusage.py [-h] [-u USER] 
[-s {opt,pitzer,glenn,bale,oak,oakley,owens,ruby}] [-A] 
[-P PROJECT] [-q] [-H] [-r] [-n] [-v] 
[start_date] [end_date] 

positional arguments: 
start_date start date (default: 2020-04-23) 
end_date end date (default: 2020-04-24) 

optional arguments: 
-h, --help show this help message and exit 
-u USER, --user USER username to run as. Be sure to include -P or -A. (default: kalattar) 
-s {opt,pitzer,glenn,bale,oak,oakley,owens,ruby}, --system {opt,pitzer,glenn,bale,oak,oakle 
-A Show all 
-P PROJECT, --project PROJECT project to query (default: PZS0715) 
-q show user data 
-H show hours 
-r show raw 
-n show job ID 
-v do not summarize 

As it can be seen, one could for example use OSCusage to receive information regarding another user’s usage with the -u option and write a cron script that is set up with email notification.

Some other usage examples,

 OSCusage 2018-01-24 

where the command specifies the usage’s start time. The end time could also be specified with,

OSCusage 2018-01-24 2018-01-25 

Terminating a Cron Job

To terminate a cron job, you need to first determine the process id,

ps aux | grep crontab 

and then use,

kill {PID}

A user can also just clear out the cron script with,

crontab -e