Various major changes
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murdrum
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README.md
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README.md
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# secure-reverse-ssh-tunnel
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This project provides ready-to-use tools to configure a remote host via an ssh tunnel and a jump host.
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## Example
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Consider this situation:
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- a) Your personal computer (behind NAT)
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- b) A remote machine, like an internal server (behind NAT)
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### Premise:
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- HTE) Host you wish to expose. Currently network restricted (behind a FW or a NAT)
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- EUD) End user device such as a laptop or mobile device provided with an ssh client.
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- JH) A host publicly accessible over the internet (or a network accessible to voth HTE and EUD) running Openssh server.
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To connect to your "b" machine you should configure the remote router to expose something and this should be avoided when unnecessary.
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So using "c" (jump server) we can create a tunnel from "b" to "c" and connect "a" to "c" and jump to "b" securely, using SSH and our private keys.
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### Scenario:
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- EUD wants to access a service running on HTE, but HTE can be accessed only from within its own network.
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- EUD can generate outgoing traffic to the internet or external networks.
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- HTE can't accept incoming connections from the internet or other networks.
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- HTE can generate outoing traffic to the internet or external networks.
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- JH is accessible to both HTE and EUD and runs an Openssh server.
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Normally, to allow communication between EUD and HTE, you would need to setup a portforward for HTE on its network's edge router. Then have EUD connect to the edge router's Public IP at the forwarded port.
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This might not be feasible or out of HTE's control, thus an ssh reverse tunnel can be used.
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By using a jump server we can establish a tunnel from HTE to JH and respectively a communication from EUD to JH securely, using SSH and our private keys.
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At this point EUD can access HTE's service just like any other service running on JH.
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The Reverse tunnel binds HTE's port to JH's network-interface:port (JumHost's localhost by default, see **GatewayPorts yes**)
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Every request sent to JH binded port is going to be forarded to HTE's port.
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**In ssh cli terms:**
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```bash
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ssh -R ${JH_PORT}:localhost:${HTE_PORT} ${USER}@${TARGET}
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```
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---
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## Support us
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@ -23,20 +43,20 @@ Whether you use this project, have learned something from it, or just like it, p
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## Components
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- setup-remote-host.sh: This script must be run as root after setup step
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- authorized_keys: should contains the signatures you want to use for remotehost
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- config: example host configuration for "a" computer
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- secure-tunnel@.service: SystemD example but ready to use service
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- authorized_keys: should contains the ssh pubkey for HTE
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- config: example host configuration for "EUD" computer
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- secure-tunnel@.service: SystemD ready to use example service
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- targets/* : contains multiple targets that need to be used as jump servers
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___
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## Setup
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Before run the script as root user, you should:
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1) append signature of your ssh keys into authorized_keys
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2) adjust various targets using the example provided and remove the example
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3) adjust your ~/.ssh/config like the provided one
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4) now you are able to run the script as root on the remote machine "b".
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Before you run the script as root user, you should:
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1) append your keypair's pubkey into JH authorized_keys
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2) edit targets based on the example provided
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3) adjust your EUD's ~/.ssh/config like the one provided.
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4) now you are able to run the script as root on HTE.
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___
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@ -69,15 +89,43 @@ netstat -tupln | grep 20001
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You should see your port associated to autossh process :)
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### Remote port forwarding
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By default **sshd** will bind forwarded ports only to the server's loopback interface (localhost, 127.0.0.0/8)
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For instance the following reverse tunnel :
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```bash
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ssh -R ${JH_PORT}:localhost:${HTE_PORT} ${USER}@${TARGET}
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```
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would result in a bind like this:
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```bash
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127.0.0.1:${JH_PORT} LISTEN pid/sshd
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```
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To expose forwarded ports over every jumphost's IP add the following to `/etc/ssh/sshd_config`
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```bash
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GatewayPorts yes
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```
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###### Note:
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Every forwarded port will now be publicly exposed (unless FW rules are in place.)
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A better aproach would be:
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```bash
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GatewayPorts userspecified
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```
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The reverse tunnel above becomes;
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```bash
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ssh -R ${JH_ADDR}:${JH_PORT}:localhost:${HTE_PORT} ${USER}@${TARGET}
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```
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### Local port forward
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You can use your jump server "c" even to expose locally a web interface of your remote host "b" or something else with:
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You could use your Jump Host even to bind to a local port a web interface of a remote host or something else with:
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```bash
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ssh -N -L <LOCALPORT>:127.0.0.1:<REMOTEPORT> <TARGET>
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ssh -N -L ${LOCALPORT}:127.0.0.1:${JH_PORT} ${USER}${TARGET}
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```
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For example to access the pihole web interface :)
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For example to access a remote pihole web interface locally :)
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___
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@ -5,8 +5,10 @@ After=network.target
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[Service]
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Environment="AUTOSSH_GATETIME=0"
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EnvironmentFile=/etc/default/secure-tunnel@%i
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ExecStart=/usr/bin/autossh -M 0 -o "ServerAliveInterval 30" -o "ServerAliveCountMax 3" -NR ${REMOTE_PORT}:localhost:22 ${USER}@${TARGET}
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ExecStart=/usr/bin/autossh -M 0 -o "ServerAliveInterval 30" -o "ServerAliveCountMax 3" -o "ExitOnForwardFailure" -NR ${JH_PORT}:localhost:22 ${USER}@${TARGET}
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User=autossh
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Restart=on-failure
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RestartSec=5s
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[Install]
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WantedBy=multi-user.target
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@ -0,0 +1,132 @@
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#!/bin/bash
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REMOTE_USER="root"
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function check_if_running_as_root {
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if [[ $EUID -ne 0 ]]; then
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echo "This script must be run as root."
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exit 1
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fi
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echo "OK: Root user detected."
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}
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check_if_running_as_root
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read -p "Did you run this script on the remote host? " -n 1 -r
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echo
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if [[ ! $REPLY =~ ^[Yy]$ ]]
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then
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echo "Please rerun this script on HTE as root user."
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[[ "$0" = "$BASH_SOURCE" ]] && exit 1 || return 1
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fi
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read -p "Did you setup various targets and adjusted configurations as described in README?" -n 1 -r
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echo
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if [[ ! $REPLY =~ ^[Yy]$ ]]
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then
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echo "Please read README and rerun this script."
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[[ "$0" = "$BASH_SOURCE" ]] && exit 1 || return 1
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fi
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function check_necessary_packages {
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echo "NEXT: Checking for valid package manager."
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APT_GET_CMD=$(which apt-get)
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YUM_CMD=$(which yum)
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DNF_CMD=$(which dnf)
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if [[ ! -z $APT_GET_CMD ]]; then
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echo "OK: apt-get found."
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apt-get --yes install autossh
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elif [[ ! -z $YUM_CMD ]]; then
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echo "OK: yum found."
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yum install autossh
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elif [[ -z $DNF_CMD ]]; then
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echo "OK: yum found."
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dnf install autossh
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else
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echo "No valid package manager found. Exiting."
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exit 1;
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fi
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echo "OK: Autossh installed"
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}
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function check_for_autossh_user {
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echo "NEXT: Check for existence of autossh dedicated user."
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if [ ! id -u autossh >/dev/null 2>&1 ]; then
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echo "The user is missing so we will create for you."
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useradd -m -s /bin/false autossh
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fi
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if [ ! id -u autossh >/dev/null 2>&1 ]; then
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echo "There are some problems with user creation. Exiting."
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exit 1;
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fi
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}
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function adjust_ssh_folder_for {
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homedir=$( getent passwd $REMOTE_USER | cut -d: -f6 )
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echo "NEXT: Setup ${1} home: ${homedir}."
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mkdir -p "${homedir}/.ssh"
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touch -a "${homedir}/.ssh/authorized_keys"
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if [ ! -s authorized_keys ]; then
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echo "WARNING: authorized_keys in setup folder seems empty so you should manually setup host authorized_keys or rerun this script."
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fi
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cat authorized_keys >> "${homedir}/.ssh/authorized_keys"
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echo "OK: Files and content ready."
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echo "NEXT: Setup file and folder permissions."
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chown -R "$1":"$1" "${homedir}/.ssh"
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chmod 700 "${homedir}/.ssh"
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chmod 600 "${homedir}/.ssh/authorized_keys"
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echo "OK: File and folder permissions setup."
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}
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function setup_systemd_service_if_available {
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echo "NEXT: Checking for systemd."
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SYSTEMCTL_CMD=$(which systemctl)
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if [[ ! -z $SYSTEMCTL_CMD ]]; then
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echo "NEXT: Copy targets into /etc/default."
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cp -n targets/* /etc/default/
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echo "OK: Targets copied."
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echo "NEXT: Setup systemd service."
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cp secure-tunnel@.service /etc/systemd/system/
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systemctl daemon-reload
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echo "OK: Systemd service created."
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else
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echo "WARNING: No systemd installation found. You should manually setup an autossh service to keep tunnel alive."
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fi
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}
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check_necessary_packages
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check_for_autossh_user
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adjust_ssh_folder_for "${REMOTE_USER}"
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setup_systemd_service_if_available
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echo -e "All done. Remaining steps:\n
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- generate an ssh keypair with ssh-keygen for user autossh and push pubkey to the jump server
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i.e. ssh-keygen -f autossh@"$jumpserver-ip" -c "$USER@$HOSTNAME" && ssh-copy-id -i autossh@"$jumpserver-ip" user@"$jumpserverip"
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- Edit JumpHost's /etc/ssh/sshd_config with
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Match User autossh
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AllowTcpForwarding yes
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X11Forwarding no
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PermitTunnel yes
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GatewayPorts no
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AllowAgentForwarding no
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- configure your client's (EUD) ~/.ssh/config like the provided one with this repo \n"
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USER=autossh
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TARGET=example
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REMOTE_PORT=20001
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TARGET=jumphost
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JH_PORT=20001
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