In this post, I’ll show you how to set up secure ftp (SFTP) access to your Ubuntu server. (Instructions for Debian are very similar: leave out the sudo part and follow these steps as root:)

For this to work, you’ll need Ubuntu 8.10 “Intrepid”, Debian 5.0 “Lenny” or newer. In this example, mark is the user that can gain superuser rights through sudo. “peter” and a few other users are the ones I want to give sftp access to their personal folder, but not shell access or anything else.

Step 1: If it doesn’t exist yet, create a group for the users you want to have sftp access only:
mark@neuskeutel:~$ sudo groupadd sftponly

Step 2: Add user “peter” to this group:
mark@neuskeutel:~$ sudo adduser peter sftponly

Step 3: Install openssh-server if it’s not installed yet.
mark@neuskeutel:~$ sudo apt-get install openssh-server

Step 4: Open the default OpenSSH server configuration for editing:
mark@neuskeutel:~$ sudo nano /etc/ssh/sshd_config

Step 5: Change the default sftp server from:
Subsystem sftp /usr/lib/openssh/sftp-server

Subsystem sftp internal-sftp

Step 6: Some users can only use sftp, but not other OpenSSH features like remote login. Let’s create a rule for that group of users (we’ll create the group afterwards). Add the following section to the bottom of /etc/ssh/sshd_config:
Match group sftponly
ChrootDirectory /home/%u
X11Forwarding no
AllowTcpForwarding no
ForceCommand internal-sftp

Step 7: Pass ownership of peter’s directory you want to be sftp accessible to the superuser:
mark@neuskeutel:~$ sudo chown root.root /home/peter

Step 8: Now we change peter’s home directory (normally /home/peter) to /:
sudo usermod -d / peter

Step 9: Repeat steps 2, 7 and 8 for any other users that you want to give sftp access.