问题：php无法加载mysqli模块，已经安装了php7.4-mysql

解决：直接修改php.ini，将;extension=mysqli前分号去了是无用的，需要新建配置文件

方法：

cd /etc/php/7.4/fpm/conf.d
vim 20-mysqli.ini
添加下面代码
extension=mysqli.so
重启php-fpm
systemctl restart php7.4-fpm

问题：php7.4一直报错Uncaught Error: Undefined class constant 'MYSQL_ATTR_INIT_COMMAND'

方法：

vim /etc/php/7.4/fpm/php.ini
打开下面配置，没有添加
extension=mysqlnd
extension=pdo
extension=pdo_mysql
注：确保已经安装php7.4-mysql

修改完后重启php

sudo systemctl restart php7.4-fpm
sudo systemctl status php7.4-fpm

问题：重新安装php7.4-fpm时报错
Not replacing deleted config file /etc/php/7.4/fpm/php.ini
Failed to start The PHP 7.4 FastCGI Process Manager.
ERROR: failed to open configuration file '/etc/php/7.4/fpm/php-fpm.conf': No such file or directory

解决：这是因为卸载的不干净，所以无法安装

方法：

重新卸载
sudo apt remove php7.4-fpm
sudo dpkg -P php7.4-fpm
再次安装
sudo apt install php7.4-fpm

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问题：logstash如何配置系统服务？

方法：

在logstash项目下

bin/system-install

服务启动

sudo su
systemctl daemon-reload
systemctl start logstash.service

如果报错logstash.service: Failed with result 'exit-code'.
查看错误日志

vim /var/log/message
logstash.service: Failed at step USER spawning

说明是没有用户

vim /etc/systemd/system/logstash.service

将user,group改成当前logstash目录的用户和组，然后

systemctl daemon-reload
systemctl restart logstash.service

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