SELinux will cause this error on CentOS/RHEL 7+ by default :(
CentOS/RHEL 7+ 系统默认会因为SELinux出现这个报错
To test if SELinux is the source of your woes, do
你可以通过下面这个命令关闭SELinux，进行测试
setenforce
... and see if everything works. If that fixed it, you can leave SELinux off (weak, you're better than that), or you can turn it back on with
看看是否运行正常，如果成功修复了，你可以修改配置文件永久保留关闭，或者再打开SELinux
setenforce
... and then properly fix the issue.
然后妥善解决这个问题。
If you do
如果你执行
tail -f /var/log/audit/audit.log
... you'll see the SELinux issue. In my case, it was denying PHP-FPM access to web files. You can run the following directives to fix it:
你将会看到是SELinux的问题。在我看来，这是因为SELinux拒绝了PHP-FPM访问Web文件。您可以运行以下指令来修复它：
setsebool -P httpd_can_network_connect_db
setsebool -P httpd_can_network_connect
This actually didn't fix it for me at first, but then restoring SELinux context did it
这一步还没有完全修复好，继续执行下面命令修复上下文
restorecon -R -v /var/www（你的web目录）
Hope that helps.
希望能帮到你