PHP closelog() Function: What it is and How to Use it

The closelog() function closes the connection PHP keeps open to the system logger (syslog). You open that connection with openlog(), write to it with syslog(), and closelog() is the matching call that tears it down. This page covers what it does, its signature and return value, when you actually need it, and how it fits into a typical logging flow.

Syntax

closelog(): true

The function takes no arguments. As of PHP 8.0 it always returns true; in PHP 7 and earlier the declared return type was bool. You almost never need to check the result.

What closelog() does

closelog() closes the descriptor PHP opened to the system logger and releases the resources tied to that connection. A few details worth knowing:

• Calling closelog() is optional. PHP automatically closes the syslog connection when the script ends, so for a short-lived web request you rarely need to call it explicitly.
• It is only meaningful after a connection exists. Calling it when no openlog()/syslog() connection is open is harmless and simply does nothing useful.
• After closelog(), the next call to syslog() reopens the connection automatically, optionally re-reading the ident and options you passed to a fresh openlog().

When you actually need it

Because PHP cleans up at the end of the request, the cases where calling closelog() matters are long-running or multi-context scripts:

• Long-running CLI workers and daemons. A process that stays alive for hours should release file descriptors it no longer needs instead of holding them open.
• Switching log identity. If you want later messages to use a different ident or facility, call closelog() and then openlog() again with the new settings.
• Cleanliness in shared code. In a library that opens its own syslog connection, closing it avoids leaking that connection into the caller's code.

How to use closelog()

Using it is just a single call with no arguments. The realistic pattern is open → write → close:

<?php

// Open a connection, tagging each line with "myapp" and the process ID
openlog("myapp", LOG_PID | LOG_PERROR, LOG_LOCAL0);

// Write a message at the INFO priority level
syslog(LOG_INFO, "User login succeeded");

// Release the connection
closelog();

LOG_PID adds the process ID to each entry, LOG_PERROR also echoes the message to standard error, and LOG_LOCAL0 selects a logging facility. See openlog() for the full list of options and facilities.

Reusing the connection with a new identity

closelog() is the clean way to switch the tag (ident) used for subsequent messages:

<?php

openlog("auth-service", LOG_PID, LOG_LOCAL0);
syslog(LOG_NOTICE, "Authentication attempt");
closelog();

// Later messages are tagged "billing-service" instead
openlog("billing-service", LOG_PID, LOG_LOCAL0);
syslog(LOG_NOTICE, "Invoice generated");
closelog();

Common mistakes

• Expecting closelog() to flush a buffer or "save" logs. Each syslog() call already hands the message to the system logger; closelog() only closes the connection.
• Calling it after every single message. Opening and closing repeatedly adds overhead. In a simple request, open once, write as many lines as you like, and close at the end (or just let PHP close it for you).
• Assuming it stops further logging. A later syslog() call transparently reopens the connection — closelog() does not lock logging out.

Related functions

• openlog() — open the connection to the system logger.
• syslog() — generate a system log message.

Conclusion

closelog() closes the syslog connection opened by openlog(), releasing its resources. It takes no arguments and returns true. For ordinary web requests PHP closes the connection for you, so reach for closelog() mainly in long-running processes or when you need to switch logging identity mid-script.

Practice