When placing scripts in system cron directories like /etc/cron.daily on CentOS/RHEL systems, execution context depends on several factors:

# Default behavior in most Linux distributions:
# Scripts in /etc/cron.* directories run as root
# This can be verified by adding whoami to a test script:
#!/bin/bash
whoami > /var/log/cron_user_test.log
date >> /var/log/cron_user_test.log

The execution context differs between these scenarios:

• System cron directories (/etc/cron.d, /etc/cron.hourly, etc.): Run as root by default
• User crontabs (crontab -e): Run as the creating user

To execute scripts as specific users from system cron directories:

# Method 1: Use runuser in the script
#!/bin/bash
runuser -l apache -c '/path/to/script.sh'

# Method 2: Create user-specific crontab
sudo crontab -u username -e

# Method 3: Use /etc/cron.d/ with user specification
# Format: minute hour day month day-of-week user command
* * * * * nginx /usr/bin/nginx_cron.sh

When dealing with cron execution context:

• Always audit scripts running as root
• Consider using chmod to restrict permissions
• Use sudo judiciously in cron scripts
• Log output to monitor execution

Common problems and solutions:

# Check cron logs (location varies by distro)
tail -f /var/log/cron

# Verify environment variables
env > /tmp/cron_env.log

# Test execution context
#!/bin/bash
{
  echo "User: $(whoami)"
  echo "PID: $$"
  env
} > /tmp/cron_debug.log 2>&1

When you place a script in /etc/cron.daily on CentOS (or most Linux distributions), it runs with root privileges by default. This is because the cron jobs in these system directories are executed by the system's crond service, which runs as root.

# Example script in /etc/cron.daily/my_script.sh
#!/bin/bash
# This will run as root
echo "Current user: $(whoami)"

The execution flow looks like this:

1. crond (running as root) checks the scheduled tasks
2. For system cron directories (/etc/cron.{hourly,daily,weekly,monthly}), it executes all scripts within
3. Each script inherits root's execution context unless modified

If you need to run scripts as a different user, you have several options:

# Method 1: Use su or sudo in the script
#!/bin/bash
sudo -u apache /path/to/script.sh

# Method 2: Create a user-specific crontab
crontab -e -u username

# Method 3: Use /etc/cron.d/ with user specification
# File: /etc/cron.d/custom_job
0 5 * * * username /path/to/script.sh

When dealing with cron jobs:

• Always validate scripts running as root
• Use appropriate file permissions (chmod/chown)
• Consider logging both output and errors
• For sensitive operations, implement proper user switching

# Recommended permission structure:
chmod 750 /etc/cron.daily/script.sh
chown root:root /etc/cron.daily/script.sh

To verify which user is executing your script:

#!/bin/bash
# Debug script
{
    echo "=== ENVIRONMENT ==="
    whoami
    id
    echo "=== ENV VARS ==="
    env
} >> /var/log/cron_debug.log 2>&1