Sites are not operational after migration from CentOS 7 and Ubuntu 20

Symptoms

After migrating from CentOS 7 or Ubuntu 20, sites running in FastCGI and CGI modes display the following errors:

• ERR_TOO_MANY_REDIRECTS for CGI;
• Internal Server Error for FastCGI.

The web server log contains errors of the following format:

cgid: error reading data from FastCGI server, referer: https://domain.con 
End of script output before headers: index.php, referer:https://domain.con 

Causes

The suexec utility in modern distributions (AlmaLinux 8, Ubuntu 22 and above) allows running PHP in FastCGI and CGI modes only for users with a GID and UID greater than 1000.

Solution

There are two solutions:

• Create new users and transfer data using the Change website owner tool (recommended).
• Create backups of all users and their data, delete users, then restore from a previously created backup.