Use FTP server user liwu to try to log in. 8. Troubleshooting ideas

Table of contents

1. FTP service 1. FTP contract introduction

FTP is a file transfer contract. It is a TCP-based contract and adopts the customer/server model. Through the FTP contract, users can upload or download files on the FTP server.

Use ports TCP 20 and 21:

Port 20: used to build data connections and transfer file data.

21 port: used to build control connections.

Disadvantages: Data cannot be automatically synchronized and needs to be automatically synchronized.

2. FTP service principle

FTP services are divided into 2 typeslinux adds ftp servicelinux operating system version, active connection and passive connection.

Active connection principle:

Passive connection principle:

3. Configuration file path

Service configuration file:/etc/vsftpd/vsftpd.conf

Blacklist configuration file:/etc/vsftpd/user_list

Default root directory of anonymous user FTP service: /var/ftp

Default root directory of local user FTP service: /home/Account file with the same name

Error log path:/var/log/messages

2. FTP server setup 1. Build environment

centos7.4 system virtual machine onelinux add ftp service, configure to turn off the firewall and selinux.

systemctlstopfirewalld #关闭防火墙
setenforce0#关闭selinux

2. Detect the environment and install the ftp service

rpa -q vsftpd#检查是否安装ftp服务
yum-y installvsftpd#安装ftp服务

3. Back up the configuration file and add users

useraddlisi #添加lisi用户
useraddliwu #添加liwu用户
echo '123456' |passwd --stdinlisi #设置账户lisi的密码为123456
echo '123456' |passwd --stdinliwu #设置账户lisi的密码为123456
cd/etc/vsftpd/ #进入ftp配置文件目录
cp vsftpd.conf vsftpd.conf.bak#备份配置文件 

4. FTP configuration file analysis

anonymous_enable=YES 
#允许匿名用户访问(账户名为ftp，不需要密码)，默认允许建议关闭
local_enable=YES
#允许本地用户访问（本地可登录账户）
write_enable=YES
#开放服务器的写权限，上传文件到服务器必须开启，默认开启
local_umask=022
#本地用户文件权限反掩码，文件权限777-umask，文件权限666-umask
dirmessage_enable=YES
#开启日志消息，默认开启
xferlog_enable=YES
#开启上传现在日志，默认开启
connect_from_port_20=YES
#确保端口数据传输来自20端口，默认开启
xferlog_std_format=YES
#日志文件设置为标准ftpd xferlog格式，默认开启，日志位置/var/log/xferlog
chroot_local_user=YES
#将用户访问权限限制在用户自己的根目录下，默认关闭。
allow_writeable_chroot=YES
#允许被限制用户对自己根目录进行写操作
anon_root=/var
#设置本地用户的默认根目录为/var，注意需要此目录给其他用户读写权限才可上传下载
userlist_enable=YES
#开启user_list用户列表，文件位置/etc/vsftpd/user_list,默认关闭
userlist_deny=YES
#若user_list是开启状态userlist_deny=YES是黑名单文件中的用户不能登录，默认关闭
#若user_list是开启状态，userlist_deny=NO则只允许user_list中的用户登录

5. Configure local users to access ftp

6. Enable ftp service

systemctlstartvsftpd #开启vsftpd服务
systemctlstatus vsftpd #查看vsftpd服务状态

7. Verification service

①Configure read and write permissions for other users in the /mnt directory

chmod766 -R /mnt #修改/mnt目录用户其他权限具有读写权限

② Configure the liwu user into the user_list file in the blacklist, the file location is /etc/vsftpd/user_list

③Create an a.txt file under /mnt with the content of 123

④Open your own windows computer cmd window and enter the ftp server IP to log in with the account password

⑤The file path downloaded to the local area is under C:Users

⑥Delete the a.txt under /mnt and upload the local a.txt.

⑦. Use blacklist user liwu to try to log in

8. Troubleshooting ideas

①First check whether the local firewall, ftp firewall and selinux are turned off

②Check the configuration file content for errors

③ Check whether the service status is normal. Linux restart command. If it is not normal, check the /var/log/messages log for troubleshooting.

④The default root directory of anonymous users cannot have read permissions, otherwise they will not be able to connect to the ftp server

⑤You can get but cannot put to view the permissions and ownership of the root directory

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