我在使用的时候报了这个错：421 Service not available, remote server has closed connection #4
Description
在stm32 的板子上使用
ftp连接的时候报错：421 Service not available, remote server has closed connection
log：
$ ftp loogg@192.168.1.30
Connected to 192.168.1.30.
220 -= welcome on RT-Thread FTP server =-
331 Password required.
Password:
421 Service not available, remote server has closed connection.
ftp: Login failedftp>
抓包：
16:12:30.570642 ARP, Request who-has 192.168.1.30 tell zhp-HP-Z240-SFF-Workstation, length 28
16:12:30.571059 ARP, Reply 192.168.1.30 is-at 00:80:e1:12:22:31 (oui Unknown), length 46
16:12:30.571078 IP zhp-HP-Z240-SFF-Workstation.41002 > 192.168.1.30.ftp: Flags [S], seq 4015184443, win 65535, options [mss 1460,sackOK,TS val 4201354021 ecr 0,nop,wscale 2], length 0
16:12:30.571698 IP 192.168.1.30.ftp > zhp-HP-Z240-SFF-Workstation.41002: Flags [S.], seq 6510, ack 4015184444, win 8196, options [mss 1460], length 0
16:12:30.571709 IP zhp-HP-Z240-SFF-Workstation.41002 > 192.168.1.30.ftp: Flags [.], ack 1, win 65535, length 0
16:12:30.573893 IP 192.168.1.30.ftp > zhp-HP-Z240-SFF-Workstation.41002: Flags [P.], seq 1:44, ack 1, win 8196, length 43: FTP: 220 -= welcome on RT-Thread FTP server =-
16:12:30.573918 IP zhp-HP-Z240-SFF-Workstation.41002 > 192.168.1.30.ftp: Flags [.], ack 44, win 65535, length 0
16:12:30.574102 IP zhp-HP-Z240-SFF-Workstation.41002 > 192.168.1.30.ftp: Flags [P.], seq 1:13, ack 44, win 65535, length 12: FTP: USER loogg
16:12:30.605804 IP 192.168.1.30.ftp > zhp-HP-Z240-SFF-Workstation.41002: Flags [P.], seq 44:68, ack 13, win 8184, length 24: FTP: 331 Password required.
16:12:30.646656 IP zhp-HP-Z240-SFF-Workstation.41002 > 192.168.1.30.ftp: Flags [.], ack 68, win 65535, length 0
16:12:33.605844 IP 192.168.1.30.ftp > zhp-HP-Z240-SFF-Workstation.41002: Flags [F.], seq 68, ack 13, win 8184, length 0
16:12:33.646825 IP zhp-HP-Z240-SFF-Workstation.41002 > 192.168.1.30.ftp: Flags [.], ack 69, win 65535, length 0
16:12:37.343771 IP zhp-HP-Z240-SFF-Workstation.41002 > 192.168.1.30.ftp: Flags [P.], seq 13:25, ack 69, win 65535, length 12: FTP: PASS loogg
16:12:37.343847 IP zhp-HP-Z240-SFF-Workstation.41002 > 192.168.1.30.ftp: Flags [F.], seq 25, ack 69, win 65535, length 0
16:12:37.344267 IP 192.168.1.30.ftp > zhp-HP-Z240-SFF-Workstation.41002: Flags [R.], seq 69, ack 25, win 8196, length 0
16:12:37.344751 IP 192.168.1.30.ftp > zhp-HP-Z240-SFF-Workstation.41002: Flags [R.], seq 69, ack 26, win 8196, length 0
在ubuntu环境下测的，没有开防火墙