一、问题背景
没事谁折腾这鬼玩意哦。。。还不是因为bug。
我们的应用，用户头像是存在ftp上的。之前的ftp服务器是一台windows，我们后台服务器程序收到用户上传头像的请求时，会用一个ROOT/ROOT的账户，连接ftp服务器。
获取到连接后，即进行上传。
上传：上传文件则存放在ROOT用户的home 目录（在windows上装的是server-U来充当ftp服务器，所以就是在Server-U里面配置了ROOT用户的home目录）。
上传完成后，会得到一个ftp协议类型的url。范例如：
ftp://10.10.20.2/userphoto/user7.png。
客户端拿到该url后，即用ftp客户端的库连接该url，获取到文件流，下载下来，进行展示。
这两天，ftp服务器从windows变到了redhat上。今天下午，测试突然报了个bug过来，说是用户头像不能正常展示了。what？于是开始查找问题。
梳理了半天，发现问题在于：linux上的ftp服务器，采用的是vsftpd软件。因为配置文件没配好的原因，利用前面的“ftp://10.10.20.2/userphoto/user7.png”就访问不到图片。
为什么说没配好呢，一开始报的错是：FTP 550 Failed to change directory
于是按照下面博文里的进行修改：https://blog.csdn.net/coreyC/article/details/80866533
没想到一波三折。
二、匿名访问
关于匿名访问，如果不成功的话，那么，请首先去下载一个工具，winscp。
按照下面的方式去进行匿名访问：
如果匿名登录失败的话，会提示具体的原因。
三、匿名上传
错误提示1：553 Could not create file
这个提示，有一个原因是，匿名用户的主目录，主目录的意思是，每个用户登录进去后所在的目录，后续的读取、上传都会在这个目录，相当于用户的base目录吧。
如果主目录的权限不够，就会提示这个问题，一般直接野蛮改为777权限。
至于主目录在哪？ 在配置文件中通过以下选项进行配置：
anon_root=/data/ftp
如下图所示，需要把主目录权限改为777，即可匿名上传：
修改权限的命令：
chmod /data/ftp
下述的报错也是同样的问题：
500 OOPS: vsftpd: refusing to run with writable anonymous root
二、支持匿名访问/上传的配置文件
正确的配置贴一份，这份配置再加上，对目录进行必要的权限设置，基本可以摆平大多数情况：
# Example config file /etc/vsftpd/vsftpd.conf
#
# The default compiled in settings are fairly paranoid. This sample file
# loosens things up a bit, to make the ftp daemon more usable.
# Please see vsftpd.conf. for all compiled in defaults.
#
# READ THIS: This example file is NOT an exhaustive list of vsftpd options.
# Please read the vsftpd.conf. manual page to get a full idea of vsftpd's
# capabilities.
#
# Allow anonymous FTP? (Beware - allowed by default if you comment this out).
# 这里需要打开，允许匿名访问
anonymous_enable=YES
#https://blog.csdn.net/bluishglc/article/details/42399439
allow_writeable_chroot=YES
#
# Uncomment this to allow local users to log in.
# 之前说到我们用ROOT/ROOT来访问ftp，我们这里，ROOT/ROOT是我们的linux可以登录的用户名密码。要允许这类用户访问ftp，需要开启下面的选项
local_enable=YES
#
# Uncomment this to enable any form of FTP write command.
# 要允许写入操作。否则应该不能上传文件
write_enable=YES
#
# Default umask for local users is . You may wish to change this to ,
# if your users expect that ( is used by most other ftpd's)
local_umask=
#
# Uncomment this to allow the anonymous FTP user to upload files. This only
# has an effect if the above global write enable is activated. Also, you will
# obviously need to create a directory writable by the FTP user.
# 匿名上传，需要配合write_enable=yes
anon_upload_enable=YES
#
# Uncomment this if you want the anonymous FTP user to be able to create
# new directories.
# 允许匿名用户创建目录;
anon_mkdir_write_enable=YES
#控制匿名用户对文件和文件夹的删除和重命名
anon_other_write_enable=YES
#
# Activate directory messages - messages given to remote users when they
# go into a certain directory.
dirmessage_enable=YES
#
# The target log file can be vsftpd_log_file or xferlog_file.
# This depends on setting xferlog_std_format parameter
xferlog_enable=YES
#
# Make sure PORT transfer connections originate from port (ftp-data).
connect_from_port_20=YES
#
# If you want, you can arrange for uploaded anonymous files to be owned by
# a different user. Note! Using "root" for uploaded files is not
# recommended!
#chown_uploads=YES
#chown_username=whoever
#
# The name of log file when xferlog_enable=YES and xferlog_std_format=YES
# WARNING - changing this filename affects /etc/logrotate.d/vsftpd.log
#xferlog_file=/var/log/xferlog
#
# Switches between logging into vsftpd_log_file and xferlog_file files.
# NO writes to vsftpd_log_file, YES to xferlog_file
xferlog_std_format=YES
#
# You may change the default value for timing out an idle session.
#idle_session_timeout=
#
# You may change the default value for timing out a data connection.
#data_connection_timeout=
#
# It is recommended that you define on your system a unique user which the
# ftp server can use as a totally isolated and unprivileged user.
#nopriv_user=ftpsecure
#
# Enable this and the server will recognise asynchronous ABOR requests. Not
# recommended for security (the code is non-trivial). Not enabling it,
# however, may confuse older FTP clients.
#async_abor_enable=YES
#
# By default the server will pretend to allow ASCII mode but in fact ignore
# the request. Turn on the below options to have the server actually do ASCII
# mangling on files when in ASCII mode.
# Beware that on some FTP servers, ASCII support allows a denial of service
# attack (DoS) via the command "SIZE /big/file" in ASCII mode. vsftpd
# predicted this attack and has always been safe, reporting the size of the
# raw file.
# ASCII mangling is a horrible feature of the protocol.
#ascii_upload_enable=YES
#ascii_download_enable=YES
#
# You may fully customise the login banner string:
#ftpd_banner=Welcome to blah FTP service.
#
# You may specify a file of disallowed anonymous e-mail addresses. Apparently
# useful for combatting certain DoS attacks.
#deny_email_enable=YES
# (default follows)
#banned_email_file=/etc/vsftpd/banned_emails
#
# You may specify an explicit list of local users to chroot() to their home
# directory. If chroot_local_user is YES, then this list becomes a list of
# users to NOT chroot().
#chroot_local_user=YES
#chroot_list_enable=YES
# (default follows)
#chroot_list_file=/etc/vsftpd/chroot_list
#
# You may activate the "-R" option to the builtin ls. This is disabled by
# default to avoid remote users being able to cause excessive I/O on large
# sites. However, some broken FTP clients such as "ncftp" and "mirror" assume
# the presence of the "-R" option, so there is a strong case for enabling it.
#ls_recurse_enable=YES
#
# When "listen" directive is enabled, vsftpd runs in standalone mode and
# listens on IPv4 sockets. This directive cannot be used in conjunction
# with the listen_ipv6 directive.
listen=YES
#
# This directive enables listening on IPv6 sockets. To listen on IPv4 and IPv6
# sockets, you must run two copies of vsftpd with two configuration files.
# Make sure, that one of the listen options is commented !!
#listen_ipv6=YES pam_service_name=vsftpd
userlist_enable=YES
tcp_wrappers=YES
#匿名用户的根目录。这个非常重要
anon_root=/home/ROOT
#匿名用户不要密码就靠这个
no_anon_password=YES
#本地用户，如我们上传用的用户（ROOT/ROOT）的根目录。当然，我们给匿名配了那么多，估计匿名也能上传了。
local_root=/home/ROOT
#该选项暂时不太清楚
ftp_username=ROOT
参考资料：