When Nginx is using socket to communicate with PHP-FPM, in the PHP-FPM configuration file, the section below must be configured. Assuming that Nginx is running with user nginx, the socket file must be configured with the appropriate permission, as in the configuration file. So Nginx has the right permission to communicate with PHP-FPM through socket file.
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; Set permissions for unix socket, if one is used. In Linux, read/write
; permissions must be set in order to allow connections from a web server. Many
; BSD-derived systems allow connections regardless of permissions.
; Default Values: user and group are set as the running user
; mode is set to 0666
listen.owner = nginx
listen.group = nginx
;listen.mode = 0666
Since all the php file requests are redirected to PHP-FPM, so the file system must be set with a permission where PHP-FPM has the privileges to access them, specially write permission. The section below sets the user identity to PHP-FPM to use when accessing the system files. In this case, PHP-FPM is using nginx to access system files, so nginx should be set to the file permissions.
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; Unix user/group of processes
; Note: The user is mandatory. If the group is not set, the default user's group
; will be used.
; RPM: apache Choosed to be able to access some dir as httpd
user = nginx
; RPM: Keep a group allowed to write in log dir.
group = nginx
The default setting for user and group above is apache. In some cases, the file system would set to nginx, but since PHP-FPM is configured by default to access file system with identity apahce, so permission denied issue would occur. The problem can be solved by changing user and group from apache to nginx and restart PHP-FPM service OR add user apache into nginx group and change the permission to 775.
Command to add apache into nginx’s group
- -a = append
- -G = supplementary group
- nginx = add to this group
- apache = user to add
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usermod -a -G nginx apache
chmod 775 /your/system/file/location
PHP-FPM must be restarted so the change of permission would take effect.