As it is in the topic the problem is with vsftpd. For some time i used it normally and everything worked good. But once i started vsftpd and it gave out the message:
500 OOPS: config file not owned by correct user, or not a file
After some searching i tried:
to change the owner of the vsftpd.conf file by
sudo chown root vsftpd.conf;
to remove vsftpd and install again;
- to purge vsftpd and install again;
- to delete the content of the conf file and paste examples from internet.
Nothing helped, it did not work since. It is Ubuntu 16.04
Thank you in advance.