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This examples shows us how we can create a OpenSSH based SSH server with docker. After running our container, we will use phpseclib library to connect if within a PHP script. The library can be installed with composer require phpseclib/phpseclib command. This just gives you an idea so you should enhance it as per your needs.


Structure


.
├── docker
│   ├── Dockerfile
│   ├── entrypoint.sh
│   ├── ssh_config
│   ├── sshd_config
│   └── user.sh
├── .env
└── docker-compose.yml

Files


.env


SSH_MASTER_USER=master
SSH_MASTER_PASS=master

docker-compose.yml


version: '3'

services:
server:
build:
context: ./docker
args:
SSH_MASTER_USER: ${SSH_MASTER_USER}
SSH_MASTER_PASS: ${SSH_MASTER_PASS}
hostname: server
ports:
- "2222:22"

Dockerfile


FROM debian:9.5

ARG SSH_MASTER_USER
ARG SSH_MASTER_PASS

RUN apt-get update \
&& apt-get install -y --no-install-recommends \
nano \
sudo \
openssh-server

COPY ssh_config /etc/ssh/ssh_config
COPY sshd_config /etc/ssh/sshd_config

COPY user.sh /usr/local/bin/user.sh
RUN chmod +x /usr/local/bin/user.sh
RUN /usr/local/bin/user.sh

COPY entrypoint.sh /usr/local/bin/entrypoint.sh
RUN chmod +x /usr/local/bin/entrypoint.sh

ENTRYPOINT ["/usr/local/bin/entrypoint.sh"]

CMD tail -f /dev/null

user.sh


This file creates master user, assigns /home/master as home, ssh as user group and sets master as password. Apart from all that, it grants rm, mkdir, chown, useradd, deluser and chpasswd command usages with the help of sudo command. This user now can create a new SSH user and revert what he has done.


#!/bin/bash
set -e

printf "\n\033[0;44m---> Creating SSH master user.\033[0m\n"

useradd -m -d /home/${SSH_MASTER_USER} -G ssh ${SSH_MASTER_USER} -s /bin/bash
echo "${SSH_MASTER_USER}:${SSH_MASTER_PASS}" | chpasswd
echo 'PATH="/usr/local/bin:/usr/bin:/bin:/usr/sbin"' >> /home/${SSH_MASTER_USER}/.profile

echo "${SSH_MASTER_USER} ALL=NOPASSWD:/bin/rm" >> /etc/sudoers
echo "${SSH_MASTER_USER} ALL=NOPASSWD:/bin/mkdir" >> /etc/sudoers
echo "${SSH_MASTER_USER} ALL=NOPASSWD:/bin/chown" >> /etc/sudoers
echo "${SSH_MASTER_USER} ALL=NOPASSWD:/usr/sbin/useradd" >> /etc/sudoers
echo "${SSH_MASTER_USER} ALL=NOPASSWD:/usr/sbin/deluser" >> /etc/sudoers
echo "${SSH_MASTER_USER} ALL=NOPASSWD:/usr/sbin/chpasswd" >> /etc/sudoers

exec "$@"

entrypoint.sh


#!/bin/bash
set -e

printf "\n\033[0;44m---> Starting the SSH server.\033[0m\n"

service ssh start
service ssh status

exec "$@"

sshd_config


ChallengeResponseAuthentication no
# UsePAM yes # Prints login information
PrintMotd no
X11Forwarding no
AllowTcpForwarding no
AllowAgentForwarding no
PermitTunnel no
Subsystem sftp /usr/lib/openssh/sftp-server

ssh_config


# Prevents "Are you sure you want to continue connecting (yes/no)?" question while connecting to the server.
# The host IP below is the client machine where the ssh command is issued from.
# Host 192.168.99.*
# StrictHostKeyChecking no
# UserKnownHostsFile=/dev/null

Host *
HashKnownHosts yes
GSSAPIAuthentication yes

Test


Connection


$ ssh master@172.18.0.2 -p 22
master@server:~$

Create a new user


master@server:~$ sudo useradd -m -d /home/inanzzz inanzzz -s /bin/bash
master@server:~$ echo "inanzzz:inanzzz" | sudo chpasswd

Test new user login


$ ssh inanzzz@172.18.0.2 -p 22
inanzzz@server:~$

PHP


I assume that you have installed the phpseclib library with composer so use example below to test connection.


use phpseclib\Net\SSH2;

$ssh = new SSH2('172.18.0.2'); // My container IP
if (!$ssh->login('master', 'master')) {
exit('Login Failed');
}

echo $ssh->exec('pwd');
echo $ssh->exec('ls -la');

/home/master
total 20
drwxr-xr-x 2 master master 4096 Jul 31 10:21 .
drwxr-xr-x 3 root root 4096 Jul 31 10:21 ..
-rw-r--r-- 1 master master 220 May 15 2017 .bash_logout
-rw-r--r-- 1 master master 3526 May 15 2017 .bashrc
-rw-r--r-- 1 master master 721 Jul 31 10:21 .profile