Environment Variables in Cron — Complete Guide

# Cron provides minimal environment by default:
# HOME=/home/username
# LOGNAME=username
# PATH=/usr/bin:/bin
# SHELL=/bin/sh (not /bin/bash!)
# No interactive shell initialization files (.bashrc, .bash_profile)

# Check what environment cron provides:
* * * * * env > /tmp/cron-env.txt 2>&1
# Wait one minute, then:
cat /tmp/cron-env.txt

# Set PATH at the top of your crontab (before any job entries)
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

# Now cron jobs can use commands without full paths
0 3 * * * backup.sh    # Uses full PATH resolution

# You can also set PATH per job:
0 3 * * * PATH=/custom/bin:$PATH /custom/scripts/deploy.sh

# Common PATH settings for different environments:
# Python virtual environment
PATH=/var/www/venv/bin:/usr/local/bin:/usr/bin:/bin

# Node.js
PATH=/usr/local/node/bin:/usr/bin:/bin

# Docker
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

# Set common variables at the top of crontab
SHELL=/bin/bash
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
HOME=/home/deploy
MAILTO=admin@dodatech.com
LOGNAME=deploy

# Custom application variables
APP_ENV=production
APP_CONFIG=/etc/app/config.yml
DB_HOST=localhost
DB_PORT=5432
LOG_LEVEL=info

# Python-specific
PYTHONPATH=/var/www/app
PYTHONUNBUFFERED=1

# Node.js-specific
NODE_ENV=production
NODE_PATH=/usr/local/node/lib/node_modules

# Now use these in your commands
0 3 * * * /usr/bin/python3 /var/www/app/scripts/backup.py

# DEBUGGING TECHNIQUE 1: Dump environment to a file
# Add this temporary cron job:
* * * * * env > /tmp/cron-debug-env.txt 2>&1

# Compare with your terminal environment:
env > /tmp/terminal-env.txt
diff /tmp/terminal-env.txt /tmp/cron-debug-env.txt

# DEBUGGING TECHNIQUE 2: Wrap script with env capture
#!/bin/bash
# /usr/local/bin/cron-wrapper.sh
env > /tmp/cron-env-$(date +%Y%m%d-%H%M%S).txt 2>&1
exec /usr/local/bin/actual-script.sh "$@"

# DEBUGGING TECHNIQUE 3: Check PATH resolution
which python3            # Works in terminal
* * * * * which python3 > /tmp/cron-which.txt 2>&1  # Check in cron

#!/usr/bin/env python3
"""Cron-safe script that sets up its own environment."""
import os
import sys
import logging

def setup_environment():
    """Ensure critical environment variables are set."""
    env_vars = {
        'PATH': '/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin',
        'HOME': os.path.expanduser('~'),
        'LANG': 'en_US.UTF-8',
        'LC_ALL': 'en_US.UTF-8',
        'PYTHONUNBUFFERED': '1',
    }

    for key, default in env_vars.items():
        if key not in os.environ:
            os.environ[key] = default

    # Ensure we can find our own modules
    script_dir = os.path.dirname(os.path.abspath(__file__))
    if script_dir not in sys.path:
        sys.path.insert(0, script_dir)

def main():
    setup_environment()
    logging.basicConfig(level=logging.INFO)

    python_path = os.environ.get('PATH', 'not set').split(':')[0]
    home = os.environ.get('HOME', 'not set')
    logging.info(f"Running with PATH: {python_path}")
    logging.info(f"HOME: {home}")

    # Actual task logic here
    logging.info("Task completed successfully")

if __name__ == '__main__':
    main()

# Test script as cron would run it:
# Method 1: Use env -i to simulate cron's minimal environment
env -i HOME=/home/user PATH=/usr/bin:/bin SHELL=/bin/sh \
    /usr/local/bin/myscript.sh

# Method 2: Run via cron directly (temporary job for testing)
# Add to crontab for one-time test:
* * * * * /usr/local/bin/myscript.sh && crontab -r

# Method 3: Use crontest tool
# pip install crontest
crontest /usr/local/bin/myscript.sh

# Method 4: Shell wrapper that logs environment
#!/bin/bash
# /usr/local/bin/cron-debug.sh
exec >> /var/log/cron-debug.log 2>&1
echo "=== $(date) ==="
echo "PATH=$PATH"
echo "HOME=$HOME"
echo "PWD=$PWD"
echo "---"
exec "$@"

#!/usr/bin/env python3
import os
import sys
import platform
from datetime import datetime

def diagnose_environment():
    """Print diagnostic information about the cron environment."""
    print(f"Cron Environment Diagnostic")
    print(f"Time: {datetime.now().isoformat()}")
    print(f"Host: {platform.node()}")
    print()

    # Check critical variables
    critical_vars = ['PATH', 'HOME', 'SHELL', 'USER', 'LOGNAME', 'PWD', 'LANG']
    for var in critical_vars:
        value = os.environ.get(var, '*** NOT SET ***')
        print(f"  {var:10s} = {value}")

    print()

    # Check if common commands are available
    commands = ['python3', 'bash', 'git', 'mysql', 'docker', 'aws']
    print("  Command availability:")
    for cmd in commands:
        path = which(cmd)
        status = path if path else 'NOT FOUND'
        print(f"    {cmd:10s} -> {status}")

def which(cmd):
    for dir in os.environ.get('PATH', '').split(':'):
        path = os.path.join(dir, cmd)
        if os.path.isfile(path) and os.access(path, os.X_OK):
            return path
    return None

if __name__ == '__main__':
    diagnose_environment()