什么可以导致连接拒绝unix套接字文件

Question

我安装了nginx服务器，并使用spawn-fcgi创建套接字但由于某种原因，套接字拒绝来自nginx的连接。

This is my config:
    location /sympa {
        gzip off;
        include       /etc/nginx/fastcgi_params;
        fastcgi_pass  unix:/var/run/sympa/wwsympa.socket;

        # If you changed wwsympa_url in sympa.conf, change this regex too!
        fastcgi_split_path_info ^(/sympa)(.*)$;
        fastcgi_param SCRIPT_FILENAME /usr/lib/cgi-bin/sympa/wwsympa.fcgi;
        fastcgi_param PATH_INFO $fastcgi_path_info;
    }

错误：

2018/02/10 15:21:37 [error] 4405#4405: *5 connect() to unix:/var/run/sympa/wwsympa.socket failed (111: Connection refused) while connecting to upstream, client: 127.0.0.1, server: 127.0.0.1, request: "GET /sympa HTTP/1.1", upstream: "fastcgi://unix:/var/run/sympa/wwsympa.socket:", host: "127.0.0.1"

有什么建议吗？