PHP error and exception logging

When it comes to the error logs of the Nginx PHP service, we can usually think of Nginx access logs, error logs and PHP error logs. Although it seems to be a very simple question, it actually involves application configuration and log recording location. If you use apt-get to install it on a system such as ubuntu, it has its own set of more reasonable configuration files. Available. In addition, the configuration in the running application will also affect the method and content of logging.

The difference between errors and exceptions

Regarding errors and exceptions, we can use a simple example to understand:

<?php
try {
    1 / 0;
} catch (Exception $e) {
    echo "catched", PHP_EOL;
}

Executing this small example will Directly get a "PHP Warning: Division by zero..." error. The reason is simple: this is a logic error, not an exception, so it cannot be caught by try. Similarly, if a variable is not defined before use, a warning will be generated instead of being captured.

But this problem has some changes in PHP7. For example, in the above example, I changed / to %, and when executed in the PHP7 environment, I will get a different prompt:

PHP Fatal error: Uncaught DivisionByZeroError ...

According to this tip, if I modify the conditions in catch:

<?php
try {
    1 / 0;
} catch (DivisionByZeroError $e) {
    echo "catched", PHP_EOL;
}

In this way, the error can be captured normally and caught is output.

For the first example, if you change Excepiton to ErrorException, you can also catch it normally.

As for why the remainder and division are the same in PHP5 but division is not a DivisionByZeroError problem in PHP7 (my test environment is 7.0.4), this should be a BUG.

Log recording

PHP itself has the following configurable logs:

● php-fpm error log (php-fpm. conf, records the startup and termination information of the php-fpm process)

● php-fpm slow log (also configured in php-fpm.conf, records slow execution)

● php error log (configured in php.ini to record application error logs)

In addition, Nginx also has two configurable logs: access and error log. These log files have different functions and different recorded contents. But there is one point to note: if the error log location in php-fpm is configured, but the log location is not writable (the location must be correct during configuration, because php-fpm will check it when it starts), under the appropriate configuration conditions The error log will be returned to cgi and written to the error log of nginx.

So when we encounter problems, our general search ideas are:

1. Check the status code of the request in the Nginx access log

2. Check the php error log Error records and stack information

3. Check the php-fpm log for abnormal restart records (this will occur if there are core or extension problems)

But in the above situations You will also find that there is no log record of the exception thrown by the program mentioned above.

Exception record

Exception is different from error. Strictly speaking, it is an exception of application logic rather than an error. It can be manually triggered through reasonable program logic. . But in most cases exceptions also need to be recorded, such as exceptions triggered by the inability to connect to the database or improper use of the framework. We need to use logs to locate the problem and handle it in a timely manner.

PHP provides two functions for customizing error and exception handling methods:

● set_error_handler

● set_exception_handler

So you can use the set_exception_handler function The injected method catches all exceptions and logs them.

monolog is an excellent exception recording library and is also based on the implementation of the PSR-3 standard. It is also used by default in Laravel and Symfony to record exceptions. If necessary, you can also consider introducing it into your own projects.

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