SFTP (SSH File Transfer Protocol) is a secure file protocol used to access, manage, and transfer files over an encrypted SSH transport session. Here SFTP only user means to create an account to access the server via SFTP only. That user doesn’t have SSH shell access. This allows you a secure channel to provide limited access to specific files and directories.
This blog post describes you create SFTP-only users without shell access on Ubuntu and Debian systems.
Step 1- Creating a New User
First of all, create a user account in your system to use as an SFTP user. The following command will create a new account named sftpuser with no shell access. You can change the username of your choice
sudo adduser --shell /bin/false sftpuser
The command will prompt for the password to be set for a new account.
Step 2 – Create Directory for SFTP
Now, create the directory structure to be accessible by the SFTP user.
sudo mkdir -p /var/sftp/files
Here we will allow users to access the “files” directory only.
Now, change the ownership of the
files directory to the
sftpuser. So that SFTP users can read and write on this directory only. No files outside of this directory will be accessible.
sudo chown sftpuser:sftpuser /var/sftp/files
And set the owner and group owner of the
/var/sftp to root. The root user has read/write access on this access. Group members and other accounts have only read and execute permissions.
sudo chown root:root /var/sftp
sudo chmod 755 /var/sftp
It will restrict SFTP users from writing files under
Step 3 – Configure sshd for SFTP Only
/etc/ssh/sshd_config is the main configuration file of the OpenSSH server. Be careful with changing this configuration file, because any mistake can lead to connection loss.
Edit the SSH configuration file in a text editor:
sudo vim /etc/ssh/sshd_config
then add the following settings at end of the file.
Match User sftpuser ForceCommand internal-sftp PasswordAuthentication yes ChrootDirectory /var/sftp PermitTunnel no AllowAgentForwarding no AllowTcpForwarding no X11Forwarding no
Save the file and close.
The directives are:
- Match User Defines the username, on which the SFTP only configurations applied. In our case it is: sftpuser
- ForceCommand internal-sftp enforce the SFTP only access to user and restrict for the shell access.
- PasswordAuthentication yes allows password authentication for the user.
- ChrootDirectory /var/sftp Restrict user to access directories under this directory only. Here /var/sftp is act as the root directory of the user.
- AllowAgentForwarding no Specifies whether ssh-agent forwarding is permitted. The default is yes.
- AllowTcpForwarding no Specifies whether TCP forwarding is permitted. The default is yes.
- X11Forwarding no Specified where the graphical application is permitted for not
Restart SSH service to apply new settings:
sudo systemctl restart ssh
That’s it. You have successfully completed the instructions to create an SFTP-only user on Debian-based systems.
Step 4 – Security Tips (Options)
Here are some basic but important security tips for SFTP accounts in a production environment.
- Run SSH server on a non-standard port
- Disallow the password authentication and configure key-based authentication
- Make sure the firewall is restricted to specific IP addresses only
- And keep the OpenSSH package up to date
This tutorial describes you create SFTP-only users in the Ubuntu system. It will disabled shell access for the same users to restrict to a specified directory only.