Why is there only a period of time to upload after installing vsftpd in Ubuntu?

I used this tutorial: ide/ftp-server.html" rel=" nofollow noreferrer "> https://help.ubuntu.com/lts/s.. After finishing that tutorial, I can"t upload to VPS with FTP installed with my windows 10. Then do not know where to see it, execute sudo chmod-R 777 ftp (/ srv/files/ftp) to upload, and then can not upload after a while.

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