Ubuntu 20.04
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OpenSSH : SFTP only + Chroot2020/04/27
 
Configure SFTP only + Chroot.
Some users who are applied this setting can access only with SFTP and also applied chroot directory.
[1] For example, Set [/home] as the Chroot directory.
# create a group for SFTP only

root@dlp:~#
groupadd sftp_users

# apply to a user [ubuntu] for SFTP only as an example

root@dlp:~#
usermod -aG sftp_users ubuntu

root@dlp:~#
vi /etc/ssh/sshd_config
# line 116: comment out and add a line like below

#
Subsystem sftp /usr/lib/openssh/sftp-server
Subsystem sftp internal-sftp
# add to the end

Match Group sftp_users
    X11Forwarding no
    AllowTcpForwarding no
    ChrootDirectory /home
    ForceCommand internal-sftp
root@dlp:~#
systemctl restart ssh

[2] Try to access with a user and verify the settings.
ubuntu@node01:~$
ssh ubuntu@dlp.srv.world 

Enter passphrase for key '/home/ubuntu/.ssh/id_rsa':
This service allows sftp connections only.
Connection to dlp.srv.world closed.   # denied as settings
ubuntu@node01:~$
sftp ubuntu@dlp.srv.world 

Enter passphrase for key '/home/ubuntu/.ssh/id_rsa':
Connected to dlp.srv.world.
sftp>
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