Voir : https://michauko.org/blog/sftp-chroot-et-pas-de-ssh-bloquer-un-utilisateur-dans-un-repertoire-1099/

Voir aussi : Monter un serveur SFTP avec ProFTPd

mkdir -p /chroot/shared/
chown root:nsc /chroot
chmod 750 /chroot
useradd sftpuser -M -d /dev/null -s /sbin/nologin
echo "/mnt/shared/ /chroot/shared/    none _netdev,bind 0 0" >> /etc/fstab

/etc/ssh/sshd_config

# Subsystem sftp /usr/lib/openssh/sftp-server
Subsystem     sftp   internal-sftp

Match User sftpuser
        ChrootDirectory /chroot
        ForceCommand internal-sftp
        AllowTcpForwarding no
        GatewayPorts no
        X11Forwarding no
        PermitTunnel no
        AllowAgentForwarding no
        PermitTTY no

mount /chroot/shared/
systemctl restart sshd
systemctl status sshd