我已經在裝有 Gentoo Linux 的電腦上安裝了 vsftpd。我從本地主機連接到它。網路或權限似乎沒有任何問題，因為我可以登入 ftp 伺服器並更改當前目錄。但是，當我嘗試使用“ls”、“get”或“put”時，ftp 客戶端聲稱錯誤 421 服務不可用。這是一個例子：
╭─ag@AprilGrimoire ~
╰─$ ftp 127.0.0.1
Connected to 127.0.0.1.
220 Welcome to blah FTP service.
Name (127.0.0.1:ag):
530 Please login with USER and PASS.
530 Please login with USER and PASS.
SSL not available
331 Please specify the password.
Password:
230 Login successful.
Remote system type is UNIX.
Using binary mode to transfer files.
ftp> cd OI
250 Directory successfully changed.
ftp> cd 2019
250 Directory successfully changed.
ftp> ls
200 PORT command successful. Consider using PASV.
150 Here comes the directory listing.
500 OOPS: 421 Service not available, remote server has closed connection
ftp> %