1. Create the user that will run the agent service:

sudo useradd --system --create-home --user-group --shell "$(which nologin)" rssht-agent

2. Change to user rssht-agent and its HOME directory:

sudo -H -u rssht-agent bash
cd

3. Ensure .ssh directory exists and has correct permissions:

mkdir -p .ssh
chmod 700 .ssh

4. Generate the public/private rsa key pair the agent will use to connect to the intermediate SSH server, replace <AGENT-ID> accordingly:

ssh-keygen -C "<AGENT-ID>" -N "" -f ".ssh/id_rsa"

5. Copy the public key to the intermediate SSH server, replace <SSH-USER>, <SSH-SERVER> and <SSH-PORT> accordingly (see the configuration of the intermediate SSH server):

ssh-copy-id -i ".ssh/id_rsa.pub" <SSH-USER>@<SSH-SERVER> -p <SSH-PORT>

6. Download and change to the source code directory:

git clone https://github.com/guallo/remote-ssh-tunnel-agent.git
cd remote-ssh-tunnel-agent

7. Configure the agent with the corresponding <OPTION>'s (see the configuration of the intermediate SSH server):

sed -i 's/^\(SSH_USER=\).*$/\1<SSH-USER>/' rssht-agent.sh
sed -i 's/^\(SSH_SERVER=\).*$/\1<SSH-SERVER>/' rssht-agent.sh
sed -i 's/^\(SSH_PORT=\).*$/\1<SSH-PORT>/' rssht-agent.sh
sed -i 's!^\(SWAP_DIRECTORY=\).*$!\1"<SWAP-DIRECTORY>"!' rssht-agent.sh

8. Give execution permission to the agent's user:

chmod u+x rssht-agent.sh

9. Come back to original user and directory:

exit

10. Install, enable and start the systemd unit:

sudo cp /home/rssht-agent/remote-ssh-tunnel-agent/rssht-agent.service /lib/systemd/system/
sudo systemctl enable rssht-agent.service
sudo systemctl start rssht-agent.service

NOTICE: This method currently do not deploy (if upgraded) the systemd unit file rssht-agent.service.

1. Change to the agent's user and installation directory:

sudo -H -u rssht-agent bash
cd $HOME/remote-ssh-tunnel-agent

2. Configure temporary identification:

git config user.name temp
git config user.email temp

3. Temporarily save the local changes:

git add -A
git commit -m 'temp'

4. Apply last remote changes:

git pull --rebase

5. Resolve any conflicts (if any) that could arise from previous step.

6. Restore the local changes:

git reset HEAD~1
chmod u+x rssht-agent.sh

7. Discard temporary identification:

git config --unset user.name
git config --unset user.email

8. Come back to original user and directory:

exit

9. Restart the agent service:

sudo systemctl restart rssht-agent.service

1. Create the <SSH-USER> that the agents will use to fetch commands from and notify status to the <SSH-SERVER>:

sudo useradd --create-home --home-dir /home/rssht-server --shell /bin/bash rssht-server

2. Assign A VERY STRONG password to the <SSH-USER>:

sudo passwd rssht-server

3. It is convenient to set the <SSH-PORT> to 443 (commonly used for the https protocol) to avoid as much as possible the agents get blocked by their ISP's. To do that configure Port 443 into the /etc/ssh/sshd_config file.

4. Override the following settings for the <SSH-USER> and restart the ssh service:

sudo tee -a /etc/ssh/sshd_config >/dev/null <<EOF

Match User rssht-server
    PasswordAuthentication yes
    PubkeyAuthentication yes
    AllowTcpForwarding yes
    GatewayPorts yes
EOF

sudo systemctl restart sshd

5. Create the <SWAP-DIRECTORY> used by the agents to fetch commands from the <SWAP-DIRECTORY>/<AGENT-ID>.in file and notify status to the <SWAP-DIRECTORY>/<AGENT-ID>.out file:

sudo -H -u rssht-server bash -c 'mkdir /home/rssht-server/rssht-swap-dir'

6. Protect the <SWAP-DIRECTORY>:

sudo chmod 700 /home/rssht-server/rssht-swap-dir

To watch sshd's processes tree every second:

watch -n 1.0 "pstree -acglnp $(ps -C sshd -o pid,cmd --no-headers | grep /usr/sbin/sshd | grep -Po '\d+' | head -n 1)"