Why doesn't CHROOT work with php-fpm?

Question

PHP

I have to chroot my ftp directory on the site. My config php-fpm.conf:

[mysite.com]
listen = /var/run/php7-fpm-chroot-filemanager.sock
chroot = /var/www/mysite.com/fileman
chdir = /
user = filemanuser
group = filemangroup
pm = dynamic
pm.max_children = 5
pm.start_servers = 2
pm.min_spare_servers = 1
pm.max_spare_servers = 3

Part of the config in the virtual host, which is responsible for the ftp directory:

location ~* /fileman/(.+\.php)$
    {

            root /var/www/mysite.com/;
            include /etc/nginx/fastcgi_params;
            if (!-f /var/www/mysite.com$fastcgi_script_name) {
                    return 405;
            }
            fastcgi_index index.php;
            fastcgi_pass unix:/var/run/php7-fpm-chroot-filemanager.sock
            fastcgi_param SCRIPT_FILENAME /var/www/mysite.com$fastcgi_script_name;
    }

After restarting the php-fpm service, on the page, I see:
File not found.
In the nginx logs:

2017/02/24 20:12:22 [error] 18390#18390: *108 FastCGI sent in stderr: "Primary script unknown" while reading response header from upstream, client: 192.168.110.25, server: www.mysite.com, request: "GET /fileman/index.php HTTP/1.1", upstream: "fastcgi://unix:/var/run/php7-fpm-chroot-filemanager.sock:", host: "www.mysite.com"

The very fact that everything works without CHROOT. Tell me what I'm doing wrong and where I have an error? For the second day I've been fighting and changing ways, I've tried different things.

Answer 1

chroot is a change of the root ("/") of the file system. PHP having switched to the new root knows nothing about the levels above, for it the root is now /var/www/mysite.com/fileman. Those. when you say - execute script fastcgi_param SCRIPT_FILENAME /var/www/mysite.com$fastcgi_script_name; - it searches from its new root, which means that it actually searches the file system for the file /var/www/mysite.com/fileman/var/www/mysite.com$fastcgi_script_name
If you don't understand why you are cheating, it's better not to use it. There may be many nuances.