How to Set Up Unix Domain Sockets with Nginx and PHP‑FPM on Linux

What is a Unix Domain Socket

Unix domain socket (also called IPC socket ) is an endpoint that allows two or more processes on the same operating system to exchange data. Unlike pipes, Unix domain sockets can use both byte streams and datagram queues. Their API resembles Internet sockets, but they do not rely on network protocols; instead they use a file system path as their address, enabling kernel‑level communication without network traffic.

— Wikipedia

Create the Socket File

In /dev/shm run the following commands:

touch php-fcgi.sock
chown admin:admin php-fcgi.sock
chmod 777 php-fcgi.sock

Nginx Configuration

server {
    listen       80;
    server_name  cdai.net;
    autoindex    off;
    error_page 403 /index.php;
    error_page 404 /index.php;

    if ($fastcgi_script_name ~ \..*\/.*php) {
        return 403;
    }

    location / {
        index  index.php;
        root   /home/cdai;
    }

    location ~ \.php$ {
        root               /home/cdai;
        include            fastcgi_params;
        fastcgi_pass       unix:/tmp/php-fcgi.sock;
        fastcgi_index      index.php;
        fastcgi_param      SCRIPT_FILENAME /cdai.net$fastcgi_script_name;
    }
}

PHP‑FPM Configuration

Edit /etc/php-fpm.d/www.conf with the following changes:

listen = /tmp/php-fcgi.sock
listen.owner = admin
listen.group = admin

Restart Services

Reload Nginx and restart PHP‑FPM. Use a full stop‑and‑start sequence rather than a USR2 graceful reload.

nginx -s reload
# then restart PHP‑FPM (service php-fpm restart)

After restarting, the socket file type changes to s, indicating that the communication channel has been successfully established.