SFTP stands for Secure File Transfer Protocol, it is one of the most common method which is used to transfer files securely over ssh from our local system to remote server and vice-versa. The main advantage of sftp is that we don’t need to install any additional package except ‘openssh-server’, in most of the Linux distributions ‘openssh-server’ package is the part of default installation. Other benefit of sftp is that we can allow user to use sftp only not ssh.

Configure-sftp-debian10

Recently Debian 10, Code name ‘Buster’ has been released, in this article we will demonstrate how to configure sftp with Chroot ‘Jail’ like environment in Debian 10 System. Here Chroot Jail like environment means that User’s can go beyond from their respective home directories or users cannot change directories from their home directories.  Following are the lab details:

  • OS = Debian 10
  • IP Address = 192.168.56.151

Let’s jump into SFTP Configuration Steps,

Step:1) Create a Group for sftp using groupadd command

Open the terminal, create a group with a name “sftp_users” using below groupadd command,

[email protected]:~# groupadd sftp_users

Step:2) Add Users to Group ‘sftp_users’ and set permissions

In case you want to create new user and want to add that user to ‘sftp_users’ group, then run the following command,

Syntax: #  useradd -m -G sftp_users <user_name>

Let’s suppose user name is ’Jonathan’

[email protected]:~# useradd -m -G sftp_users jonathan

set the password using following chpasswd command,

[email protected]:~# echo "jonathan:<enter_password>" | chpasswd

In case you want to add existing users to ‘sftp_users’ group then run beneath usermod command, let’s suppose already existing user name is ‘chris’

[email protected]:~# usermod -G sftp_users chris

Now set the required permissions on Users,

[email protected]:~# chown root /home/jonathan /home/chris/

Create an upload folder in both the user’s home directory and set the correct ownership,

[email protected]:~# mkdir /home/jonathan/upload
[email protected]:~# mkdir /home/chris/upload
[email protected]:~# chown jonathan /home/jonathan/upload
[email protected]:~# chown chris /home/chris/upload

Note: In upload folder, user like Jonathan and Chris can upload files and directories from their local system .

Step:3) Edit sftp configuration file (/etc/ssh/sshd_config)

As we have already stated that sftp operations are done over the ssh, so it’s configuration file is “/etc/ssh/sshd_config“, Before making any changes I would suggest first take the backup and then edit this file and add the following content,

[email protected]:~# cp /etc/ssh/sshd_config /etc/ssh/sshd_config-org
[email protected]:~# vim /etc/ssh/sshd_config
………
#Subsystem      sftp    /usr/lib/openssh/sftp-server
Subsystem       sftp    internal-sftp

Match Group sftp_users
  X11Forwarding no
  AllowTcpForwarding no
  ChrootDirectory %h
  ForceCommand internal-sftp
…………

Save & exit the file.

To make above changes into the affect, restart ssh service using following systemctl command

[email protected]:~# systemctl restart sshd

In above ‘sshd_config’ file we have commented out the line which starts with “Subsystem” and added new entry “Subsystem       sftp    internal-sftp” and new lines like,

Match Group sftp_users”  –> It means if a user is a part of ‘sftp_users’ group then apply rules which are mentioned below to this entry.

ChrootDierctory %h” –> It means users can only change directories within their respective home directories, they cannot go beyond their home directories, or in other words we can users are not permitted to change directories, they will get jai like environment within their directories and can’t access any other user’s and system’s directories.

ForceCommand internal-sftp” –> It means users are limited to sftp command only.

Step:4) Test and Verify sftp

Login to any other linux system which is on the same network of your sftp server and then try to ssh sftp server via the users that we have mapped in ‘sftp_users’ group.

[[email protected] ~]# ssh [email protected]
[email protected]'s password:
Write failed: Broken pipe
[[email protected] ~]# ssh [email protected]
[email protected]'s password:
Write failed: Broken pipe
[[email protected] ~]#

Above confirms that users are not allowed to SSH , now try sftp using following commands,

[[email protected] ~]# sftp [email protected]
[email protected]'s password:
Connected to 192.168.56.151.
sftp> ls -l
drwxr-xr-x    2 root     1001         4096 Sep 14 07:52 debian10-pkgs
-rw-r--r--    1 root     1001          155 Sep 14 07:52 devops-actions.txt
drwxr-xr-x    2 1001     1002         4096 Sep 14 08:29 upload

Let’s try to download a file using sftp get command

sftp> get devops-actions.txt
Fetching /devops-actions.txt to devops-actions.txt
/devops-actions.txt                                                                               100%  155     0.2KB/s   00:00
sftp>
sftp> cd /etc
Couldn't stat remote file: No such file or directory
sftp> cd /root
Couldn't stat remote file: No such file or directory
sftp>

Above output confirms that we are able to download file from our sftp server to local machine and we cannot change directories too.

Let’s try to upload a file under “upload” folder,

sftp> cd upload/
sftp> put metricbeat-7.3.1-amd64.deb
Uploading metricbeat-7.3.1-amd64.deb to /upload/metricbeat-7.3.1-amd64.deb
metricbeat-7.3.1-amd64.deb                                                                        100%   38MB  38.4MB/s   00:01
sftp> ls -l
-rw-r--r--    1 1001     1002     40275654 Sep 14 09:18 metricbeat-7.3.1-amd64.deb
sftp>

This confirms that we have successfully uploaded a file from our local system to sftp server.

Now test the SFTP server with winscp tool, enter the sftp server ip address along user’s credentials,

Winscp-sftp-debian10

Click on Login and then try to download and upload files

Download-file-winscp-debian10-sftp

Now try to upload files in upload folder,

Upload-File-using-winscp-Debian10-sftp

Above window confirms that uploading is also working fine, that’s all from this article. If these steps help you to configure SFTP server with chroot environment in Debian 10 then please do share your feedback and comments.

from Linuxtechi https://www.linuxtechi.com/configure-sftp-chroot-debian10/