PHP openlog Function

last modified April 4, 2025

The PHP openlog function initializes a connection to the system logger. It's used with syslog and closelog for system logging.

Basic Definition

openlog prepares PHP to send messages to the system logger. It configures the logging identity and options before sending messages.

Syntax: openlog(string $prefix, int $options, int $facility): bool. Returns true on success, false on failure. Works with Unix-like systems.

Basic System Logging

This example demonstrates the most basic usage of openlog.

basic_logging.php

<?php

declare(strict_types=1);

openlog("MyPHPApp", LOG_PID | LOG_PERROR, LOG_USER);
syslog(LOG_INFO, "This is a test message");
closelog();

This opens a connection to the system logger with the identifier "MyPHPApp". The message will appear in system logs with the process ID (LOG_PID) and also print to stderr (LOG_PERROR).

Different Log Facilities

This shows how to use different logging facilities for various purposes.

facility_logging.php

<?php

declare(strict_types=1);

// Mail system logging
openlog("MailProcessor", LOG_PID, LOG_MAIL);
syslog(LOG_WARNING, "Failed to deliver email");
closelog();

// Security logging
openlog("AuthSystem", LOG_PID, LOG_AUTH);
syslog(LOG_ALERT, "Unauthorized access attempt");
closelog();

Different facilities categorize logs for different system components. LOG_MAIL is for mail system messages, while LOG_AUTH is for security/authorization.

Logging with Different Options

This example demonstrates various logging options available with openlog.

options_logging.php

<?php

declare(strict_types=1);

// Log to console immediately (LOG_CONS)
openlog("ConsoleApp", LOG_CONS, LOG_USER);
syslog(LOG_ERR, "Critical error occurred");
closelog();

// Delay opening until first message (LOG_NDELAY)
openlog("BackgroundApp", LOG_NDELAY, LOG_DAEMON);
syslog(LOG_INFO, "Background process started");
closelog();

LOG_CONS writes directly to system console if syslog fails. LOG_NDELAY opens the connection immediately rather than waiting for the first message.

Error Handling with Logging

This shows how to implement error handling with system logging.

error_logging.php

<?php

declare(strict_types=1);

function logError(string $message, int $severity = LOG_ERR): bool {
    if (!openlog("ErrorTracker", LOG_PID, LOG_LOCAL0)) {
        return false;
    }
    
    $result = syslog($severity, $message);
    closelog();
    return $result;
}

logError("Database connection failed", LOG_CRIT);

This wraps logging in a function with error checking. It returns false if openlog fails. The severity level can be customized when calling the function.

Custom Logging Class

This example demonstrates a simple logging class using openlog.

logger_class.php

<?php

declare(strict_types=1);

class SystemLogger {
    private string $ident;
    private int $options;
    private int $facility;
    
    public function __construct(string $ident, int $options, int $facility) {
        $this->ident = $ident;
        $this->options = $options;
        $this->facility = $facility;
    }
    
    public function log(string $message, int $priority): bool {
        if (!openlog($this->ident, $this->options, $this->facility)) {
            return false;
        }
        $result = syslog($priority, $message);
        closelog();
        return $result;
    }
}

$logger = new SystemLogger("MyApp", LOG_PID, LOG_USER);
$logger->log("Application initialized", LOG_INFO);

This class encapsulates the logging functionality for reuse. The constructor sets up the logging configuration, and the log method handles message sending.

Best Practices

Identifiers: Use meaningful identifiers for your application
Severity Levels: Choose appropriate severity levels
Error Handling: Always check if openlog succeeds
Cleanup: Close logging connection when done
Performance: Reuse connections for multiple messages

Source

PHP openlog Documentation

This tutorial covered the PHP openlog function with practical examples for system logging in various scenarios.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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