我使用Apache FtpServer并构建了自己的ftp服务器。我在VM（VPS）上使用此服务器。我能够登录并列出文件，但我无法下载或上传文件。我每次尝试都会收到错误
220 Service ready for new user.
USER testuser
331 User name okay, need password for testuser.
PASS ********
230 User logged in, proceed.
FEAT
211-Extensions supported
SIZE
MDTM
REST STREAM
LANG en;zh-tw;ja;is
MLST Size;Modify;Type;Perm
AUTH SSL
AUTH TLS
MODE Z
UTF8
TVFS
MD5
MMD5
MFMT
211 End
OPTS UTF8 ON
200 Command OPTS okay.
SYST
215 UNIX Type: Apache FtpServer
STAT /
212-
drwx------ 3 user group 0 Oct 25 02:46 lost+found
drwx------ 3 user group 0 Oct 25 06:27 v
-rw------- 1 user group 4496 Oct 25 06:30 working.txt
212 End of status.
TYPE I
200 Command TYPE okay.
PORT 10,9,226,222,220,45
200 Command PORT okay.
STOR /Records.xls
150 File status okay; about to open data connection.
220 Service ready for new user.
当我在localhost上运行代码时，我可以下载，修改和上传文件。为什么这不适用于虚拟机？