Once when running proftpd with configured users in a file, I noticed the following error:
mod_auth_file/1.0: unable to use world-readable AuthUserFile ‘/etc/proftpd/ftpd.passwd’: Operation not permitted
Fatal: AuthUserFile: unable to use /etc/proftpd/ftpd.passwd: Operation not permitted on line 39 of ‘/etc/proftpd/proftpd.conf’
The error occurs because the mod_auth_file module requires read and write access to the /etc/proftpd/ftpd.passwd file to be denied for all users and only allowed to one user (from which proftpd is running), so I changed the file permissions:
chmod 640 /etc/proftpd/ftpd.passwd
chown proftpd:root /etc/proftpd/ftpd.passwd
If you specify a user not from which proftpd is running (it is specified in the /etc/proftpd/proftpd.conf file), then proftpd will start, but an error may occur when connecting:
530 Login incorrect.
Then I started proftpd, it started successfully, you could connect to it and no more errors occurred:
service proftpd restart
See also my articles:
Configuring ProFTPd with virtual users in a file
The solution to the error in ProFTPd “unable to open passwd file”
Installing and Configuring ProFTPd in Ubuntu