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：elasticsearch单节点时集群健康值黄色

解决：

运行

curl -X PUT "hadoop03:9200/_settings" -H 'Content-Type: application/json' -d '{"number_of_replicas":0}'

问题：rpm如何指定安装路径？

方法：

sudo rpm -i elasticsearch-7.12.0-x86_64.rpm --prefix=/opt/module/
不过安装elasticsearch不建议指定目录

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问题：systemctl命令daemon-reload无法加载到服务

解决：

先使用 sudo systemctl --failed 查看错误服务

UNIT               LOAD      ACTIVE SUB    DESCRIPTION
prometheus.service not-found failed failed prometheus.service

可以看到未加载，那么就使用daemon-reload加载

sudo systemctl daemon-reload
# 结果是成功加载
prometheus.service loaded failed failed Prometheus Monitoring System
# 之后启动服务
sudo systemctl start prometheus.service
# 如果不行，就使用restart启动就好了
sudo systemctl restart prometheus.service