Link With Server

Creates a link between the CLIENT and the LINK UP SERVER.

WARNING : StrictHostKeyChecking is disabled, you must get prepared for MITM attacks.

Setup SSH Server on Server Side (for the first time)

1. Install OpenSSH server if not installed.

2. You may use an existing user account on the server side. However, setting up a new account is recommended:

   1. Create a standard user account:

      adduser lws

   2. Add the following section to /etc/ssh/sshd_config:

      Match User lws
              AllowTcpForwarding yes
              PermitTunnel yes
              ForceCommand /home/lws/handler.sh  
              PasswordAuthentication no
              AuthorizedKeysFile /home/lws/your-authorized-keys-file

   3. Create your handler script: /home/lws/handler.sh (don't forget to make it executable):

      #!/bin/bash
      # This message will appear on the client side when the client 
      # tries to login to interactive shell:
      echo "ERROR: No shell access is allowed. Original command was: $SSH_ORIGINAL_COMMAND" 

   4. Restart sshd on server:

      sudo /etc/init.d/ssh restart

Setup per CLIENT on every deployment

sudo apt install netcat
git clone --recursive https://github.com/aktos-io/link-with-server
cd link-with-server
cp config.sh{.sample,} && nano config.sh  # edit accordingly
./gen-private-key-if-necessary.sh 
./send-public-key.sh  # and follow the instructions 
./link-with-server.sh --test && ./register-to-boot.sh # or run manually: ./link-with-server.sh
./watch-logs.sh

Usage

Assuming:

1. You have SSH access to the LINK_UP_SERVER
2. You want to connect to a client/node (AAA) that has put its SSHD port on LINK_UP_SERVER:1234 and the username is foo.

You can connect to foo@AAA from anywhere by:

• Either using https://github.com/aktos-io/dcs-tools (provides advanced backup and management tools)

• Or using link-with-server/ssh-jump.sh:

  ./ssh-jump.sh -t 1234 -u foo

• Or with the following one liner without any dependencies:

  assuming you would normally connect to LINK_UP_SERVER by ssh myuser@11.22.33.44 -p 2255

  ssh_jump(){ ssh -J myuser@11.22.33.44:2255 ${2}@localhost -p ${1}; }; ssh_jump 1234 foo

Hooks

Place any scripts on/connect and on/disconnect folders.

Recommended Tools

• aktos-io/service-runner: Run applications on boot and manage/debug them easily.