How to find the cause of server unavailability via SFTP?

Question

ubuntu

The server has Ubuntu Server 16.04 + vesta panel installed. Recently, the server stopped letting me through SFTP through filezilla. Together, vesta installed vsftpd. I believe that access is through it. Connection in filezilla simply falls off on timeout.
filezilla connection log:

Соединяюсь с xxx.xxx.xxx.xxx...
Ответ:	fzSftp started, protocol_version=4
Команда:	open "[email protected]" 22
Ошибка:	Соединение прервано после 20 секунд неактивности
Ошибка:	Невозможно подключиться к серверу

The following is in the /var/log/auth.log log:

Feb 24 20:27:11 server sshd[7774]: Accepted publickey for user1 from 37.235.216.219 port 36621 ssh2: RSA SHA256:60oUUW3bHytzwcgeyRtU+Ow252596JXnFYSjw8dzfog
Feb 24 20:27:11 server sshd[7774]: pam_unix(sshd:session): session opened for user user1 by (uid=0)
Feb 24 20:27:11 server systemd-logind[841]: New session 5333 of user user1.
Feb 24 20:27:11 server systemd: pam_unix(systemd-user:session): session opened for user user1 by (uid=0)
Feb 24 20:27:31 server sshd[7774]: pam_unix(sshd:session): session closed for user user1
Feb 24 20:27:31 server systemd-logind[841]: Removed session 5333.
Feb 24 20:27:31 server systemd: pam_unix(systemd-user:session): session closed for user user1

Answer 1

What does tail -n 100 /var/log/vsftpd.log say?
login user1, but uid=0 is specified, that is, root. And the SSH settings allow root to log in to the server? Sometimes this is disabled by default.
as an option, generate a key and write it to .ssh/authorized_keys Try to access the server using the key.

Answer 2

SFTP is not FTP, it's SSH. Do you connect via sssh normally?

Answer 3

I do not want to necropost but you never know who will stumble upon a thread. Try to open port 22, usually I had a problem with this