Linux FTP基础

Love The Way You Lie 2022-02-21 01:58 174阅读 0赞

Linux FTP

FTP（File Transfer Protocol, FTP）是TCP/IP网络上两台计算机传送文件的协议，FTP是在TCP/IP网络和INTERNET上最早使用的协议之一，它属于网络协议组的应用层。FTP客户机可以给服务器发出命令来下载文件，上载文件，创建或改变服务器上的目录。

FTP服务一般运行在20和21两个端口。端口20用于在客户端和服务器之间传输数据流，而端口21用于传输控制流，并且是命令通向ftp服务器的进口。

FTP有两种使用模式：主动和被动。主动模式要求客户端和服务器端同时打开并且监听一个端口以建立连接。在这种情况下，客户端由于安装了防火墙会产生一些问题。所以，创立了被动模式。被动模式只要求服务器端产生一个监听相应端口的进程，这样就可以绕过客户端安装了防火墙的问题。

一个主动模式的FTP连接建立要遵循以下步骤：

1.客户端打开一个随机的端口（端口号大于1024，在这里，我们称它为x），同时一个FTP进程连接至服务器的21号命令端口。此时，源端口为随机端口x，在客户端，远程端口为21，在服务器。

2.客户端开始监听端口（x+1），同时向服务器发送一个端口命令（通过服务器的21号命令端口），此命令告诉服务器客户端正在监听的端口号并且已准备好从此端口接收数据。这个端口就是我们所知的数据端口。

3.服务器打开20号源端口并且建立和客户端数据端口的连接。此时，源端口为20，远程数据端口为（x+1）。

4.客户端通过本地的数据端口建立一个和服务器20号端口的连接，然后向服务器发送一个应答，告诉服务器它已经建立好了一个连接。

常见的FTP服务器：

Windows：IIS、Serv-U

Linux：wu-ftpd，Proftpd，vsftpd（Very Secure FTP Daemon）

Linux vsftp配置详解

一.vsftpd说明:

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.

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.

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 format

xferlog\_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=YES

pam\_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 mode

listen=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