写在前面
现在WordPress安装、更新插件或主题时都需要通过FTP进行，由于之前并没有安装导致现在无法更新插件了。想着FTP这么常用的东西应该不难弄吧，就着手开始折腾了，没想到还是踩了坑，故在这里记录一下在Debian下的安装过程。
vsftpd
安装与配置
FTP本身的安装与配置确实并不复杂，都是常规操作，过程如下：
sudo apt update
sudo apt install vsftpd等待安装完成后需要进行一些简单的配置，vsftpd的配置文件路径默认为/etc/vsftpd.conf，修改配置如下：
# Example config file /etc/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.5 for all compiled in defaults.
#
# READ THIS: This example file is NOT an exhaustive list of vsftpd options.
# Please read the vsftpd.conf.5 manual page to get a full idea of vsftpd's
# capabilities.
#
#
# Run standalone? vsftpd can run either from an inetd or as a standalone
# daemon started from an initscript.
listen=NO
#
# This directive enables listening on IPv6 sockets. By default, listening
# on the IPv6 "any" address (::) will accept connections from both IPv6
# and IPv4 clients. It is not necessary to listen on *both* IPv4 and IPv6
# sockets. If you want that (perhaps because you want to listen on specific
# addresses) then you must run two copies of vsftpd with two configuration
# files.
listen_ipv6=YES
#
# Allow anonymous FTP? (Disabled by default).
anonymous_enable=NO
#
# Uncomment this to allow local users to log in.
local_enable=YES
#
# Uncomment this to enable any form of FTP write command.
write_enable=YES
#
# Default umask for local users is 077. You may wish to change this to 022,
# if your users expect that (022 is used by most other ftpd's)
local_umask=022
#
# 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.
#anon_upload_enable=YES
#
# Uncomment this if you want the anonymous FTP user to be able to create
# new directories.
#anon_mkdir_write_enable=YES
#
# Activate directory messages - messages given to remote users when they
# go into a certain directory.
dirmessage_enable=YES
#
# If enabled, vsftpd will display directory listings with the time
# in your local time zone. The default is to display GMT. The
# times returned by the MDTM FTP command are also affected by this
# option.
use_localtime=YES
#
# Activate logging of uploads/downloads.
xferlog_enable=YES
#
# Make sure PORT transfer connections originate from port 20 (ftp-data).
connect_from_port_20=NO
#
# 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
#
# You may override where the log file goes if you like. The default is shown
# below.
xferlog_file=/var/log/vsftpd.log
#
# If you want, you can have your log file in standard ftpd xferlog format.
# Note that the default log file location is /var/log/xferlog in this case.
#xferlog_std_format=YES
#
# You may change the default value for timing out an idle session.
#idle_session_timeout=600
#
# You may change the default value for timing out a data connection.
#data_connection_timeout=120
#
# 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 restrict local users to their home directories. See the FAQ for
# the possible risks in this before using chroot_local_user or
# chroot_list_enable below.
#chroot_local_user=YES
#
# 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().
# (Warning! chroot'ing can be very dangerous. If using chroot, make sure that
# the user does not have write access to the top level directory within the
# 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
#
# Customization
#
# Some of vsftpd's settings don't fit the filesystem layout by
# default.
#
# This option should be the name of a directory which is empty. Also, the
# directory should not be writable by the ftp user. This directory is used
# as a secure chroot() jail at times vsftpd does not require filesystem
# access.
secure_chroot_dir=/var/run/vsftpd/empty
#
# This string is the name of the PAM service vsftpd will use.
pam_service_name=vsftpd
#
# This option specifies the location of the RSA certificate to use for SSL
# encrypted connections.
rsa_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
rsa_private_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
ssl_enable=NO
#
# Uncomment this to indicate that vsftpd use a utf8 filesystem.
#utf8_filesystem=YES
# enable pasv mode
pasv_enable=YES
pasv_min_port=6000
pasv_max_port=7000
各个选项具体含义参见默认的vsftpd.conf文件里面注释，其中需要注意的是下面这两组参数。
chroot_local_user=YES
chroot_list_enable=YES
# (default follows)
chroot_list_file=/etc/vsftpd.chroot_list
与
pasv_enable=YES
pasv_min_port=6000
pasv_max_port=7000在chroot_local_user设为YES的情况下，如果chroot_list_enable设为YES， 那么chroot_list_file里面列出的用户有权限访问用户主目录之外的目录；一般情况下如不允许所有用户访问用户主目录之外的目录，直接设置chroot_local_user为NO即可。
而pasv_enable设置为YES代表FTP使用PASV（被动）模式，开启此模式是为了方便我的FTP客户端连接服务器。所谓被动模式，指的是FTP服务器“被动”等待客户端来连接自己的数据端口，其过程具体是：当开启一个FTP连接时，客户端打开两个任意的非特权本地端口（N >1024和N+1）。第一个端口连接服务器的21端口，但与主动方式的FTP不同，客户端不会提交PORT命令并允许服务器来回连它的数据端口，而是提交PASV命令。这样做的结果是服务器会开启一个任意的非特权端口（P > 1024），并发送PORT P命令给客户端。然后客户端发起从本地端口N+1到服务器的端口P的连接用来传送数据。pasv_min_port与pasv_max_port为端口号的最大最小范围。
添加用户
这里使用Linux系统本身存在的用户，作为FTP用户，具体哪些用户可以登录FTP，可以通过vsftpd.chroot_list指定，此文件中指定的本地用户被授予访问 FTP 服务器的权限。
sudo adduser ftpuser # 添加新用户
echo "ftpuser" | sudo tee -a /etc/vsftpd.userlist # 将FTP用户添加到vsftpd用户列表文件重启vsftpd，使配置生效。
sudo systemctl restart vsftpd.service修改防火墙设置
为了能够进行外部连接，需要修改防火墙设置开启对应端口，一般FTP默认为21端口。若开启了PASV模式，还需特别开启pasv_min_port与pasv_max_port范围内的端口。
iptables -I INPUT -p tcp --dport 6000:7000 -j ACCEPT配置用户权限
为了可以使用新添加的用户为WordPress对主题或插件进行操作，需要赋予ftpuser用户对Wordpress所在目录的读写权限。
首先检查哪个组拥有WordPress所在路径（一般为www-data），然后需确保该组递归拥有该目录。
sudo chown -R www-data.www-data /var/www/wordpressftpuser需要属于www-data组，可以使用下面的命令进行添加：
sudo usermod -a -G www-data ftpuser
groups ftpuser # 查看是否添加成功之后，将ftpuser的默认文件夹设置为WordPress目录。
usermod -d /var/www/wordpress ftpuser最后，需要赋予ftpuser用户对WordPress目录下文件的读写权限。
sudo chmod -R g+rw /var/www/wordpress至此便可以通过ftpuser用户与其对应的密码作为WordPress的FTP凭据，完成对主题或插件的操作。
参考链接：