Nginx报错：FastCGI sent in stderr: “Primary script unknown“ while reading response header from upstream

1. 现象：

当nginx转发php文件到php-fpm服务时报错
[error] 101354#101354: *34 FastCGI sent in stderr: "Primary script unknown" while reading response header from upstream, client: 192.168.253.1, server: localhost, request: "GET /info.php HTTP/1.1", upstream: "fastcgi://127.0.0.1:9000", host: "192.168.253.131"
nginx显示：

nginx配置文件位置：/etc/nginx/conf.d
内容：

server {
    listen       80;
    server_name  localhost;

    location / {
        root   /usr/share/nginx/html;
        index  index.php index.html index.htm;
    }

    error_page   500 502 503 504  /50x.html;
    location = /50x.html {
        root   /usr/share/nginx/html;
    }
    location ~ \.php$ {
		    fastcgi_index index.php;
            fastcgi_pass 127.0.0.1:9000;
            include      fastcgi_params;
            fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
    }
}

2. 分析

$document_root是表示当前请求的资源所在的根目录，这个值由server块中的root指令定义，
但是server并未定义root根目录，location块也没有定义root根目录，导致请求不到指定的php文件。

3. 解决

以下三种方式皆可解决当前问题

3.1 第一种配置：location块添加root根目录配置

server {
    listen       80;
    server_name  localhost;

    location / {
        root   /usr/share/nginx/html;
        index  index.php index.html index.htm;
    }

    error_page   500 502 503 504  /50x.html;
    location = /50x.html {
        root   /usr/share/nginx/html;
    }
    location ~ \.php$ {
    		root   /usr/share/nginx/html;
		    fastcgi_index index.php;
            fastcgi_pass 127.0.0.1:9000;
            include      fastcgi_params;
            fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
    }
}

3.2 第二种配置：定义全局root根目录路径

server {
    listen       80;
    server_name  localhost;
	root   /usr/share/nginx/html;
	
    location / {
        index  index.php index.html index.htm;
    }

    error_page   500 502 503 504  /50x.html;
    location = /50x.html {
    }
    
    location ~ \.php$ {
		    fastcgi_index index.php;
            fastcgi_pass 127.0.0.1:9000;
            include      fastcgi_params;
            fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
    }
}

3.3第三种配置：替换内部变量为绝对路径

server {
    listen       80;
    server_name  localhost;

    location / {
        root   /usr/share/nginx/html;
        index  index.php index.html index.htm;
    }

    error_page   500 502 503 504  /50x.html;
    location = /50x.html {
        root   /usr/share/nginx/html;
    }
    location ~ \.php$ {
		    fastcgi_index index.php;
            fastcgi_pass 127.0.0.1:9000;
            include      fastcgi_params;
            fastcgi_param SCRIPT_FILENAME /usr/share/nginx/html/$fastcgi_script_name;
    }
}