How To Set Environment Variables For Crontab Jobs?

Published July 13, 2024

Problem: Setting Environment Variables in Crontab Jobs

Crontab jobs often need access to environment variables, but these variables are not automatically available in the cron environment. This can cause unexpected behavior or errors when running scheduled tasks that depend on specific environment settings.

Solutions for Setting Environment Variables in Crontab

Method 1: Defining Variables Directly in Crontab

You can set environment variables in the crontab file. To do this:

Open the crontab file for editing:
```
crontab -e
```
Add your environment variables at the top of the file:
```
LANG=en_US.UTF-8
PATH=/usr/local/bin:/usr/bin:/bin
```
Add your cron job entries:
```
0 * * * * /path/to/your/script.sh
```

This method works for variables specific to your cron jobs.

Tip: Verify Environment Variables

After setting environment variables in crontab, you can verify them by adding a test job:

* * * * * env > /tmp/cron-env.txt

This will write all environment variables to a file, allowing you to check if they're set correctly.

Method 2: Sourcing Environment Files in Crontab Commands

You can source your environment files within crontab entries:

Edit your crontab file:
```
crontab -e
```
Add a command to source your environment file before running your script:
```
0 * * * * . $HOME/.bash_profile; /path/to/your/script.sh
```

This loads all variables from your .bash_profile (or .bashrc) for each cron job.

Method 3: Creating a Wrapper Script

A wrapper script can set up the environment before running your main script:

Create a wrapper script, e.g., 'wrapper.sh':

#!/bin/bash
source $HOME/.bash_profile
/path/to/your/main_script.sh

Make the wrapper script executable:
```
chmod +x wrapper.sh
```
In your crontab, call the wrapper script:
```
0 * * * * /path/to/wrapper.sh
```

This method is useful when you need to set up a complex environment for your cron jobs.

Example: Logging in Wrapper Script

You can add logging to your wrapper script to help with debugging:

#!/bin/bash
echo "Starting job at $(date)" >> /var/log/cron_jobs.log
source $HOME/.bash_profile
/path/to/your/main_script.sh
echo "Job finished at $(date)" >> /var/log/cron_jobs.log

This will log the start and end times of each job execution.

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