Chapter 5. File Transfer Protocol
File Transfer Protocol (FTP) is one of the oldest and most commonly used protocols found on the Internet today. Its purpose is to reliably transfer files between computer hosts on a network without requiring the user to log directly into the remote host or have knowledge of how to use the remote system. It allows users to access files on remote systems using a standard set of simple commands.
The Very Secure FTP Daemon (vsftpd) is designed from the ground up to be fast, stable, and, most importantly, secure. Its ability to handle large numbers of connections efficiently and securely is why vsftpd is the only stand-alone FTP distributed with Red Hat Enterprise Linux.
In Red Hat Enterprise Linux, the vsftpd package provides the Very Secure FTP daemon. Run rpm -q vsftpd to see if vsftpd is installed:
$ rpm -q vsftpd
If you want an FTP server and the vsftpd package is not installed, run the following command as the root user to install it:
yum install vsftpd
The vsftpd FTP daemon runs confined by default. SELinux policy defines how vsftpd interacts with files, processes, and with the system in general. For example, when an authenticated user logs in via FTP, they can not read from or write to files in their home directories: SELinux prevents vsftpd from accessing user home directories by default. Also, by default, vsftpd does not have access to NFS or CIFS file systems, and anonymous users do not have write access, even if such write access is configured in /etc/vsftpd/vsftpd.conf. Booleans can be turned on to allow the previously mentioned access.
The following example demonstrates an authenticated user logging in, and an SELinux denial when trying to view files in their home directory:
Run rpm -q ftp to see if the ftp package is installed. If it is not, run yum install ftp as the root user to install it.
Run rpm -q vsftpd to see if the vsftpd package is installed. If it is not, run yum install vsftpd as the root user to install it.
In Red Hat Enterprise Linux, vsftpd only allows anonymous users to log in by default. To allow authenticated users to log in, edit /etc/vsftpd/vsftpd.conf as the root user. Make sure the local_enable=YES option is uncommented:
# Uncomment this to allow local users to log in.
local_enable=YES
Run service vsftpd start as the root user to start vsftpd. If the service was running before editing vsftpd.conf, run service vsftpd restart as the root user to apply the configuration changes:
service vsftpd start
Starting vsftpd for vsftpd: [ OK ]
Run ftp localhost as the user you are currently logged in with. When prompted for your name, make sure your username is displayed. If the correct username is displayed, press Enter, otherwise, enter the correct username:
$ ftp localhost
Connected to localhost (127.0.0.1).
220 (vsFTPd 2.1.0)
Name (localhost:username):
331 Please specify the password.
Password: Enter your password
500 OOPS: cannot change directory:/home/username
Login failed.
ftp>
An SELinux denial similar to the following is logged:
setroubleshoot: SELinux is preventing the ftp daemon from reading users home directories (username). For complete SELinux messages. run sealert -l c366e889-2553-4c16-b73f-92f36a1730ce
Access to home directories has been denied by SELinux. This can be fixed by activating the ftp_home_dir Boolean. Enable this ftp_home_dir Boolean by running the following command as the root user:
# setsebool -P ftp_home_dir=1
Do not use the -P option if you do not want changes to persist across reboots.
Try to log in again. Now that SELinux is allowing access to home directories via the ftp_home_dir Boolean, logging in will succeed.
