Ftp services in linux

FTP Server

File Transfer Protocol (FTP) is a TCP protocol for downloading files between computers. In the past, it has also been used for uploading but, as that method does not use encryption, user credentials as well as data transferred in the clear and are easily intercepted. So if you are here looking for a way to upload and download files securely, see the OpenSSH documentation instead.

FTP works on a client/server model. The server component is called an FTP daemon. It continuously listens for FTP requests from remote clients. When a request is received, it manages the login and sets up the connection. For the duration of the session it executes any of commands sent by the FTP client.

Access to an FTP server can be managed in two ways:

In the Anonymous mode, remote clients can access the FTP server by using the default user account called “anonymous” or “ftp” and sending an email address as the password. In the Authenticated mode a user must have an account and a password. This latter choice is very insecure and should not be used except in special circumstances. If you are looking to transfer files securely see SFTP in the section on OpenSSH-Server. User access to the FTP server directories and files is dependent on the permissions defined for the account used at login. As a general rule, the FTP daemon will hide the root directory of the FTP server and change it to the FTP Home directory. This hides the rest of the file system from remote sessions.

vsftpd — FTP Server Installation

vsftpd is an FTP daemon available in Ubuntu. It is easy to install, set up, and maintain. To install vsftpd you can run the following command:

Anonymous FTP Configuration

By default vsftpd is not configured to allow anonymous download. If you wish to enable anonymous download edit /etc/vsftpd.conf by changing:

During installation a ftp user is created with a home directory of /srv/ftp . This is the default FTP directory.

If you wish to change this location, to /srv/files/ftp for example, simply create a directory in another location and change the ftp user’s home directory:

sudo mkdir -p /srv/files/ftp sudo usermod -d /srv/files/ftp ftp 

After making the change restart vsftpd:

sudo systemctl restart vsftpd.service 

Finally, copy any files and directories you would like to make available through anonymous FTP to /srv/files/ftp , or /srv/ftp if you wish to use the default.

User Authenticated FTP Configuration

By default vsftpd is configured to authenticate system users and allow them to download files. If you want users to be able to upload files, edit /etc/vsftpd.conf :

sudo systemctl restart vsftpd.service 

Now when system users login to FTP they will start in their home directories where they can download, upload, create directories, etc.

Similarly, by default, anonymous users are not allowed to upload files to FTP server. To change this setting, you should uncomment the following line, and restart vsftpd:

Warning

Enabling anonymous FTP upload can be an extreme security risk. It is best to not enable anonymous upload on servers accessed directly from the Internet.

The configuration file consists of many configuration parameters. The information about each parameter is available in the configuration file. Alternatively, you can refer to the man page, man 5 vsftpd.conf for details of each parameter.

Securing FTP

There are options in /etc/vsftpd.conf to help make vsftpd more secure. For example users can be limited to their home directories by uncommenting:

You can also limit a specific list of users to just their home directories:

chroot_list_enable=YES chroot_list_file=/etc/vsftpd.chroot_list 

After uncommenting the above options, create a /etc/vsftpd.chroot_list containing a list of users one per line. Then restart vsftpd:

sudo systemctl restart vsftpd.service 

Also, the /etc/ftpusers file is a list of users that are disallowed FTP access. The default list includes root, daemon, nobody, etc. To disable FTP access for additional users simply add them to the list.

FTP can also be encrypted using FTPS. Different from SFTP, FTPS is FTP over Secure Socket Layer (SSL). SFTP is a FTP like session over an encrypted SSH connection. A major difference is that users of SFTP need to have a shell account on the system, instead of a nologin shell. Providing all users with a shell may not be ideal for some environments, such as a shared web host. However, it is possible to restrict such accounts to only SFTP and disable shell interaction.

To configure FTPS, edit /etc/vsftpd.conf and at the bottom add:

Also, notice the certificate and key related options:

rsa_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem rsa_private_key_file=/etc/ssl/private/ssl-cert-snakeoil.key 

By default these options are set to the certificate and key provided by the ssl-cert package. In a production environment these should be replaced with a certificate and key generated for the specific host. For more information on certificates see Security — Certificates.

Now restart vsftpd, and non-anonymous users will be forced to use FTPS:

sudo systemctl restart vsftpd.service 

To allow users with a shell of /usr/sbin/nologin access to FTP, but have no shell access, edit /etc/shells adding the nologin shell:

# /etc/shells: valid login shells /bin/csh /bin/sh /usr/bin/es /usr/bin/ksh /bin/ksh /usr/bin/rc /usr/bin/tcsh /bin/tcsh /usr/bin/esh /bin/dash /bin/bash /bin/rbash /usr/bin/screen /usr/sbin/nologin 

This is necessary because, by default vsftpd uses PAM for authentication, and the /etc/pam.d/vsftpd configuration file contains:

auth required pam_shells.so 

The shells PAM module restricts access to shells listed in the /etc/shells file.

Most popular FTP clients can be configured to connect using FTPS. The lftp command line FTP client has the ability to use FTPS as well.

References

Источник

How To Set Up Your FTP Server In Linux

In this tutorial, I will explain to you how to set up your FTP server. But first, let me quickly tell you what is FTP.

What is FTP?

FTP is an acronym for File Transfer Protocol. As the name suggests, FTP is used to transfer files between computers on a network. You can use FTP to exchange files between computer accounts, transfer files between an account and a desktop computer, or access online software archives. Keep in mind, however, that many FTP sites are heavily used and require several attempts before connecting.

An FTP address looks a lot like an HTTP or website address except it uses the prefix ftp:// instead of http://.

What is FTP Server? How to set it up?

Typically, a computer with an FTP address is dedicated to receive an FTP connection. A computer dedicated to receiving an FTP connection is referred to as an FTP server or FTP site.
Now, let’s begin a special adventure. We will make FTP server to share files with friends and family. I will use vsftpd for this purpose.

VSFTPD is an FTP server software which claims to be the most secure FTP software. In fact, the first two letters in VSFTPD, stand for “very secure”. The software was built around the vulnerabilities of the FTP protocol.

Nevertheless, you should always remember that there are better solutions for secure transfer and management of files such as SFTP (uses OpenSSH). The FTP protocol is particularly useful for sharing non-sensitive data and is very reliable at that.

Step 1: Installing VSFTPD in Linux

You can quickly install VSFTPD on your Fedora/Red Hat/SUSE servers through the command line interface with:

If you are using Ubuntu/Debian-based distributions, you can install VSFTPD using this command:

sudo apt-get install vsftpd

If you are using Arch-based distributions, try this command for installing VSFTPD.

Step 2: Configuring FTP server

Most VSFTPD’s configuration takes place in /etc/vsftpd.conf. The file itself is well-documented, so this section only highlights some important changes you may want to make. For all available options and basic documentation see the man pages:

Files are served by default from /srv/ftp as per the Filesystem Hierarchy Standard.

Enable Uploading to the FTP server:

The “write_enable” flag must be set to YES in order to allow changes to the filesystem, such as uploading:

Allow Local Users to Login:

In order to allow users in /etc/passwd to login, the “local_enable” directive must look like this:

Anonymous Login

The following lines control whether anonymous users can login:

# Allow anonymous login
anonymous_enable=YES
# No password is required for an anonymous login (Optional)
no_anon_password=YES
# Maximum transfer rate for an anonymous client in Bytes/second (Optional)
anon_max_rate=30000
# Directory to be used for an anonymous login (Optional)
anon_root=/example/directory/

Chroot Jail

It is possible to set up a chroot environment, which prevents the user from leaving his home directory. To enable this, add/change the following lines in the configuration file:

chroot_list_enable=YES 
chroot_list_file=/etc/vsftpd.chroot_list

The “chroot_list_file” variable specifies the file in which the jailed users are contained to.

Step 4: Restart your FTP server

In the end you must restart your ftp server. Type in your command line

sudo systemctl restart vsftpd

That’s it. Your FTP server on Linux is up and running. FTP is increasingly being replaced by FTP over SSH protocol so you may want to setup SFTP server on Linux.

Any questions or suggestions is always welcomed.

Ali Miracle

Ali is a computer programmer and passionate about Linux. He uses Trisquel Linux and at times blogs about it. And he does all this using Orca screen reader program because he cannot see.

Источник