sftpでchrootの設定をする。 ref: https://qiita.com/kooohei/items/5cf0bb6e5c1e372fc55b

file1.txt

$ sudo mkdir /opt/chroot
$ sudo chown root.root /opt/chroot
$ sudo mkdir /opt/sftpuser
$ sudo chown sftpuser /opt/sftpuser/data
$ sudo chmod 755 /opt/sftpuser/data

file2.txt

$ sudo cp -pi /etc/ssh/sshd_confg /etc/ssh/sshd_config.bk
$ sudo vim /etc/ssh/sshd_config

file4.txt

$ sudo systemctl restart sshd.service
$ sudo systemctl status sshd.service

file5.txt

$ touch test
$ sftp sftpuser@localhost
sftp> cd data
sftp> put test
sftp> ls
sftp> rm test
sftp> ls
sftp> quit

ユーザー作成

$ sudo useradd sftpuser
$ sudo passwd sftpuser

追加

Subsystem sftp  internal-sftp
Match User sftpuser
    ChrootDirectory /opt/sftpuser
    X11Forwarding no
    AllowTcpForwarding no
    PasswordAuthentication yes
    ForceCommand internal-sftp