Vsftpd FTP Server With Virtual Users ( Berkeley DB + PAM )
Vsftpd supports virtual users with PAM (pluggable authentication modules). A virtual user is a user login which does not exist as a real login on the system in /etc/passwd and /etc/shadow file. Virtual users can therefore be more secure than real users, because a compromised account can only use the FTP server but cannot login to system to use other services such as ssh or smtp.
Required software
- Berkeley DB (version 4) databases
- pam_userdb.so
Install Berkeley DB And Utilities Under RHEL / CentOS
Type the following command:# yum install db4-utils db4
Create The Virtual Users Database
To create a "db4" format file, first create a plain text files with the usernames and password on alternating lines. For e.g. create user called "vivek" with password called "vivekpass" and sayali with password "sayalipass":# cd /etc/vsftpd
# cat > vusers.txt
Sample output:
vivek vivekpass sayali sayalipass
Next, create the actual database file like this:# db_load -T -t hash -f vusers.txt vsftpd-virtual-user.db
# chmod 600 vsftpd-virtual-user.db
# rm vusers.txt
Configure VSFTPD for virtual user
Edit the vsftpd configuration file. Add or correct the following configuration options:
anonymous_enable=NO local_enable=YES # Virtual users will use the same privileges as local users. # It will grant write access to virtual users. Virtual users will use the # same privileges as anonymous users, which tends to be more restrictive # (especially in terms of write access). virtual_use_local_privs=YES write_enable=YES # Set the name of the PAM service vsftpd will use # RHEL / centos user should use /etc/pam.d/vsftpd pam_service_name=vsftpd.virtual # Activates virtual users guest_enable=YES # Automatically generate a home directory for each virtual user, based on a template. # For example, if the home directory of the real user specified via guest_username is # /home/virtual/$USER, and user_sub_token is set to $USER, then when virtual user vivek # logs in, he will end up (usually chroot()'ed) in the directory /home/virtual/vivek. # This option also takes affect if local_root contains user_sub_token. user_sub_token=$USER # Usually this is mapped to Apache virtual hosting docroot, so that # Users can upload files local_root=/home/vftp/$USER # Chroot user and lock down to their home dirs chroot_local_user=YES # Hide ids from user hide_ids=YES
Save and close the file.
Create a PAM File Which Uses Your New Database
The following PAM is used to authenticate users using your new database. Create /etc/pam.d/vsftpd.virtual:# cat > /etc/pam.d/vsftpd.virtual
Append the following:
#%PAM-1.0 auth required pam_userdb.so db=/etc/vsftpd/vsftpd-virtual-user account required pam_userdb.so db=/etc/vsftpd/vsftpd-virtual-user session required pam_loginuid.so
Create The Location Of The Files
You need to set up the location of the files / dirs for the virtual users. Type the following command:# mkdir /home/vftp
# mkdir -p /home/vftp/{vivek,sayali}
# chown -R ftp:ftp /home/vftp
Restart The FTP Server
Type the following command:# service vsftpd restart
Test Your Setup
Open another shell session and type:$ ftp ftp.nixcraft.net
Sample output:
Connected to ftp.nixcraft.net.in. Name (localhost:root): vivek 331 Please specify the password. Password: 230 Login successful. Remote system type is UNIX. Using binary mode to transfer files. ftp>
Sample log from /var/log/secure:# tail -f /var/log/secure
Output
May 21 16:54:28 xentest vsftpd: pam_userdb(vsftpd.virtual:auth): user 'vivek' granted access