FTP的全称是File Transfer Protocol(文件传输协议),就是专门用来传输文件的协议.它工作在OSI模型的第七层,即是应用层,使用TCP传输而不是UDP.这样FTP客户端和服务器建立连接前就要经过一个"三次握手"的过程.FTP服务还有一个非常重要的特点是它可以独立于平台.

     LINUX下实现FTP服务的软件很多,最常见的有vsftpd,Wu-ftpd和Proftp等.Red Hat Enterprise Linux中默认安装的是vsftpd.

     通常,访问FTP服务器时需要经过验证,只有经过了FTP服务器的相关验证,用户才能访问和传输文件.vsftpd提供了3种ftp登录形式:

(1)anonymous(匿名帐号)

     使用anonymous是应用广泛的一种FTP服务器.如果用户在FTP服务器上没有帐号,那么用户可以以anonymous为用户名,以自己的电子邮件地址为密码进行登录.当匿名用户登录FTP服务器后,其登录目录为匿名FTP服务器的根目录/var/ftp.为了减轻FTP服务器的负载,一般情况下,应关闭匿名帐号的上传功能.

(2)real(真实帐号)

     real也称为本地帐号,就是以真实的用户名和密码进行登录,但前提条件是用户在FTP服务器上拥有自己的帐号.用真实帐号登录后,其登录的目录为用户自己的目录,该目录在系统建立帐号时系统就自动创建.

(3)guest(虚拟帐号)

     如果用户在FTP服务器上拥有帐号,但此帐号只能用于文件传输服务,那么该帐号就是guest,guest是真实帐号的一种形式,它们的不同之处在于,geust登录FTP服务器后,不能访问除宿主目录以外的内容.

下面就对其详细介绍

一、安装与启动vsftpd

     先使用命令查看是否安装.

     可看到安装了版本为2.2.2.如果没有安装可在桌面上选择"应用程序"/"系统设置"添加/删除应用程序"命令.来安装FTP软件包或者在命令行界面进行安装都可.；

     安装和配置好vsftpd软件包后,需要启动FTP服务器才能使用.启动方法有以下两种：

     ①使用图形化方式启动,选择"应用程序"/系统设置/服务器设置/服务.可看到vsftpd,打上勾,开始启动；

     ②使用命令行界面用命令启动。

二、FTP相关配置文件说明

     其相关配置文件有/etc/vsftpd/vsftpd.conf, /etc/vsftpd.ftpusers, /etc/vsftpd.user_list,在配置FTP服务器时,主要是修改这些文件中的相关语句。

1.vsftpd.conf文件说明

     # 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.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.## Allow anonymous FTP? (Beware - allowed by default if you comment this out).anonymous_enable=YES //是否允许anonymous登录FTP服务器,默认是允许的.## Uncomment this to allow local users to log in.local_enable=YES //是否允许本地用户登录FTP服务器,默认是允许## Uncomment this to enable any form of FTP write command.write_enable=YES //是否允许用户具有在FTP服务器文件中执行写的权限,默认是允许## 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//设置本地用户的文件生成掩码为022,默认是077## 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 //是否允许匿名账户在FTP服务器中创建目录## Activate directory messages - messages given to remote users when they# go into a certain directory.dirmessage_enable=YES //激活目录信息,当远程用户更改目录时,将出现提示信息## Activate logging of uploads/downloads.xferlog_enable=YES //启用上传和下载日志功能## Make sure PORT transfer connections originate from port 20 (ftp-data).connect_from_port_20=YES //启用FTP数据端口的连接请求## 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 //设置日志文件的文件名和存储路径,这是默认的## If you want, you can have your log file in standard ftpd xferlog formatxferlog_std_format=YES//是否使用标准的ftpd xferlog日志文件格式## You may change the default value for timing out an idle session.#idle_session_timeout=600 //设置空闲的用户会话中断时间,默认是10分钟## You may change the default value for timing out a data connection.#data_connection_timeout=120//设置数据连接超时时间,默认是120秒.## 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 turning on ascii_download_enable enables malicious remote parties# to consume your I/O resources, by issuing the command "SIZE /big/file" in# ASCII mode.# These ASCII options are split into upload and download because you may wish# to enable ASCII uploads (to prevent uploaded scripts etc. from breaking),# without the DoS risk of SIZE and ASCII downloads. ASCII mangling should be# on the client anyway..#ascii_upload_enable=YES#ascii_download_enable=YES //是否允许使用ASCII格式来上传和下载文件## You may fully customise the login banner string:#ftpd_banner=Welcome to blah FTP service.//在FTP服务器中设置欢迎登录的信息.## 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_list_enable=YES //如果希望用户登录后不能切换到自己目录以外的其它目录,需要设置该项,如果设置chroot_list_enable=YES,那么只允许/etc/vsftpd.chroot_list中列出的用户具有该功能.如果希望所有的本地用户都执行者chroot,可以增加一行:chroot_local_user=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=YESpam_service_name=vsftpd //设置PAM认证服务的配置文件名称,该文件存放在/etc/pam.d/目录下.userlist_enable=YES //用户列表中的用户是否允许登录FTP服务器,默认是不允许#enable for standalone modelisten=YES //使vsftpd 处于独立启动模式tcp_wrappers=YES //使用tcp_wrqppers作为主机访问控制方式

2.vsftpd.ftpusers文件说明

     这个文件是用来记录"不允许"登录到FTP服务器的用户,通常是一些系统默认的用户。

     下面是该文件中默认的不允许登录的名单：

     # Users that are not allowed to login via ftp

     root //默认情况下,root和它以下的用户是不允许登录FTP服务器的.可以将不允许登录的用户添加到这里来.但切记每个用户都要单独占用一行。

     bindaemonadmlpsyncshutdownhaltmailnewsuucpoperatorgamesnobody

3.vsftpd.user_list文件说明

     其实它的内容跟上面那个文件内容一样,只是在系统对文件vsftpd.conf 进行检测时,会检测到"userlist_deny=YES",因此这个文件必须存在.下面是这个文件的内容。

     # vsftpd userlist# If userlist_deny=NO, only allow users in this file# If userlist_deny=YES (default), never allow users in this file, and# do not even prompt for a password.# Note that the default vsftpd pam config also checks /etc/vsftpd.ftpusers# for users that are denied.rootbindaemonadmlpsyncshutdownhaltmailnewsuucpoperatorgamesno