A brief analysis of the reasons why Linux cannot query the php process

Linux server, as a commonly used server system, has led the development of Internet servers, and PHP, as one of the most widespread server-side development languages, has also become one of the necessary components on Linux servers. But sometimes we may encounter a problem: the running PHP process cannot be queried. Although this situation is rare, it can still cause great trouble to the normal operation of the server. This article will discuss several common possibilities to resolve this situation.

Stop or crash

One possibility is that the PHP process has stopped or crashed. If there is no appropriate script set up to regularly detect this situation, we can only obtain relevant information by viewing the log (usually located under /var/log/httpd/ or /var/log/nginx/). If no obvious error message is found, we can also try to check whether there is a PHP process running through the following command:

ps aux | grep php

This command will output all currently running PHP processes. If there is no output, it means that there is no running PHP process on the system.

Memory limit

If there is a large PHP application in our system, we may encounter the PHP process reaching the memory limit, causing the process to be killed. Condition. To solve this problem, we need to increase the memory limit by modifying the PHP configuration file:

memory_limit = 256M

This will set the memory limit to 256MB. Of course, if the server space is relatively rich, you can also modify this value to be higher.

PHP version issue

We also need to pay attention to the PHP version issue. Some servers may have multiple versions of PHP installed at the same time, but only one of them is running. Therefore, we must confirm the currently running PHP version, which can be viewed through the following command:

php -v

If the currently running PHP version does not match the version we expect, we can use the following command to change the current PHP version:

sudo a2dismod php7.1
sudo a2enmod php7.2
sudo service apache2 restart

The above command will uninstall version 7.1 of PHP, enable version 7.2 of PHP, and finally restart Apache.

PHP extension issues

Another common problem is that a PHP application requires certain PHP extensions but the system does not have them installed. In this case, we can install the missing extension through the following command:

sudo apt-get install php7.x-common php7.x-curl php7.x-gd php7.x-json php7.x-mbstring php7.x-mysql php7.x-xml php7.x-zip

You need to modify the x in the above command to the current PHP version. This command will install common PHP extensions required to run PHP applications. Remember to restart the web server after installation.

Summary

Possible situations when querying a Linux server for PHP processes that are not running include the process has stopped or crashed, memory limit issues, PHP version issues, and missing PHP extensions etc. Through the methods provided in this article, we can try to solve these problems and restore the server to normal operation. If the problem still exists, we can also try to consult the service provider or relevant technical forums to get more solutions.

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