解决：connect() to unix:/run/php/php8.1-fpm.sock failed (13: Permission denied)

装好了nginx与php8.1-fpm，两都能正常运行，但PHP文件不能正常显示，查看nginx的error.log，有这样的记录：

1	`connect() to unix:/run/php/php8.1-fpm.sock failed (13: Permission denied)` `while` `connecting to upstream, client: 192.168.0.114, server: localhost, request:` `"GET /test.php HTTP/1.1", upstream:` `"fastcgi://unix:/run/php/php8.1-fpm.sock:", host:` `"192.168.0.11"`

原因是　php8.1-fpm 的apt安装使用了缺省用户www-data，nginx的apt安装使用了缺省用户nginx，/run/php/php8.1-fpm.sock的所有者是www-data, nginx用户无权访问，导致以上报错。

查看nginx的缺省配置文件：

 1 user  nginx;
 2 worker_processes  auto;
 3 
 4 error_log  /var/log/nginx/error.log notice;
 5 pid        /var/run/nginx.pid;
 6 
 7 
 8 events {
 9     worker_connections  1024;
10 }
11 
12 
13 http {
14     include       /etc/nginx/mime.types;
15     default_type  application/octet-stream;
16 
17     log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
18                       '$status $body_bytes_sent "$http_referer" '
19                       '"$http_user_agent" "$http_x_forwarded_for"';
20 
21     access_log  /var/log/nginx/access.log  main;
22 
23     sendfile        on;
24     #tcp_nopush     on;
25 
26     keepalive_timeout  65;
27 
28     #gzip  on;
29 
30     include /etc/nginx/conf.d/*.conf;
31 }