Ubuntu 18.04 LTS 无法启动 vsftpd

Question

我vsftpd使用进行安装sudo apt install vsftpd。然后我/etc/vsftpd.conf按照本教程中的说明进行编辑： https://www.ubuntu18.com/setup-ftp-server-ubuntu-18/。我确定/etc/vsftpd.conf归root。文件内容如下：

listen=YES
listen_ipv6=YES
anonymous_enable=NO
local_enable=YES
write_enable=YES
local_umask=022
#anon_upload_enable=YES
#anon_mkdir_write_enable=YES
dirmessage_enable=YES
use_localtime=YES
xferlog_enable=YES
connect_from_port_20=YES
#xferlog_file=/var/log/vsftpd.log
#xferlog_std_format=YES
#idle_session_timeout=600
#data_connection_timeout=120
#nopriv_user=ftpsecure
#async_abor_enable=YES
#ascii_upload_enable=YES
#ascii_download_enable=YES
ftpd_banner=Welcome to WiseOldBird FTP Test service.
#deny_email_enable=YES
#banned_email_file=/etc/vsftpd.banned_emails
chroot_local_user=YES
#chroot_list_enable=YES
#chroot_list_file=/etc/vsftpd.chroot_list
#ls_recurse_enable=YES
secure_chroot_dir=/var/run/vsftpd/empty
pam_service_name=vsftpd
rsa_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
rsa_private_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
ssl_enable=NO
# utf8_filesystem=YES
allow_writable_chroot=YES

我使用以下命令禁用了 vsftpd 的自动启动：sudo systemctl disable vsftpd。我port 21使用以下命令启用了 vsftpd：sudo ufw allow 21/tcp。我使用以下命令启动了 vsftpd：sudo systemctl start vsftpd。

我在控制台上得到以下结果：

(venvs) jonathan@WiseOldBird:~$ sudo systemctl start vsftpd
(venvs) jonathan@WiseOldBird:~$ sudo systemctl status vsftpd
● vsftpd.service - vsftpd FTP server
   Loaded: loaded (/lib/systemd/system/vsftpd.service; disabled; vendor preset: enabled)
   Active: failed (Result: exit-code) since Thu 2018-11-08 18:57:52 CST; 13s ago
  Process: 20245 ExecStart=/usr/sbin/vsftpd /etc/vsftpd.conf (code=exited, status=2)
  Process: 20244 ExecStartPre=/bin/mkdir -p /var/run/vsftpd/empty (code=exited, status=0/SUCCESS)
 Main PID: 20245 (code=exited, status=2)

nov 08 18:57:52 WiseOldBird systemd[1]: Starting vsftpd FTP server...
nov 08 18:57:52 WiseOldBird systemd[1]: Started vsftpd FTP server.
nov 08 18:57:52 WiseOldBird systemd[1]: vsftpd.service: Main process exited, code=exited, status=2/INVALIDARGUMENT
nov 08 18:57:52 WiseOldBird systemd[1]: vsftpd.service: Failed with result 'exit-code'.

有人可以建议如何发现 INVALIDARGUMENT 是什么和/或如何纠正这种情况。