When dealing with cron jobs and time discrepancies, it's crucial to recognize the multiple layers of timezone configuration:

1. System timezone (controlled by /etc/timezone or timedatectl)
2. PHP timezone (set in php.ini or via date_default_timezone_set())
3. User-specific timezone (for individual crontabs)

To verify your server's actual timezone setting:

# Method 1: Using timedatectl (modern systems)
timedatectl | grep "Time zone"

# Method 2: Checking symlink
ls -l /etc/localtime

# Method 3: Display current time with timezone
date +"%Z %z"

The common mismatch occurs because:

// PHP might be using:
date_default_timezone_set('America/Denver'); // MST

// While cron uses system timezone (often UTC by default)

Multiple approaches exist to align cron with your desired timezone:

Method 1: System-wide Configuration

# Set system timezone (requires root)
sudo timedatectl set-timezone America/Denver

Method 2: Per-user Cron Solution

Add this line to the user's crontab before any jobs:

CRON_TZ=America/Denver
0 8 * * * /path/to/your/script.php >/dev/null 2>&1

Method 3: PHP Script Adjustment

Make your script timezone-aware by adding this at the beginning:

<?php
if (!ini_get('date.timezone')) {
    date_default_timezone_set('America/Denver');
}
// Rest of your script

Create a test script to verify all time sources:

<?php
echo "System time: ".shell_exec('date')."<br>";
echo "PHP time: ".date('Y-m-d H:i:s')."<br>";
echo "PHP timezone: ".date_default_timezone_get();

• Always document timezone assumptions in cron job comments
• Consider using UTC for server time to avoid daylight saving issues
• For distributed systems, implement centralized timezone management

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Many developers encounter situations where their PHP scripts show one timezone (like MST), while cron jobs seem to execute at unexpected times. This discrepancy typically occurs because:

• Cron uses the system's timezone settings
• PHP applications might override this with date_default_timezone_set()
• Web servers and CLI might have different environment configurations

To identify the actual timezone your cron jobs are using, run these commands:

# Method 1: Check system timezone file
cat /etc/timezone

# Method 2: Alternative location on some systems
ls -l /etc/localtime

# Method 3: Comprehensive system time check
timedatectl status

PHP applications can override system timezone in several ways:

// php.ini setting
date.timezone = "America/Denver"

// Runtime setting
date_default_timezone_set('America/Denver');

// .htaccess setting (if using Apache)
php_value date.timezone "America/Denver"

For consistent behavior between cron and PHP:

# Option 1: Set system-wide timezone (Debian/Ubuntu)
sudo dpkg-reconfigure tzdata

# Option 2: Create symlink to desired timezone
sudo ln -sf /usr/share/zoneinfo/America/Denver /etc/localtime

# Option 3: Explicitly set timezone in cron jobs
0 * * * * TZ=America/Denver /usr/bin/php /path/to/script.php

Add this test script to verify timezones:

<?php
// cron_test.php
file_put_contents(
    '/tmp/cron_time_check.log',
    sprintf(
        "[%s] PHP timezone: %s, Current time: %s\n",
        date('c'),
        date_default_timezone_get(),
        date('Y-m-d H:i:s')
    ),
    FILE_APPEND
);

Then set up a temporary cron job:

* * * * * /usr/bin/php /path/to/cron_test.php

For systems running multiple timezones:

# Global crontab with TZ specification
echo "TZ=America/New_York" | sudo tee -a /etc/crontab

# Per-user crontab with environment variables
crontab -e
# Add this line at the top:
TZ=America/Los_Angeles

• Always use UTC for server-level operations
• Convert to local time only in presentation layers
• Document timezone assumptions in deployment guides
• Consider using NTP synchronization: sudo apt install ntp