LutzCle / autossh-daemon

Setup an SSH reverse tunnel on FreeBSD

autossh on FreeBSD

This is a guide to setup autossh-daemon, a small script to automatically run autossh as a reverse SSH tunnel on FreeBSD.

We assume three hosts: a user device (e.g., a laptop), $proxy_host, and $remote_host. After following the guide, it will be possible to ssh from user device to $remotehost via $proxy_host. Substitute the variables with actual hostnames as required.

Setup guide on proxy host

Create a new user account called autossh, and make it accessible via SSH.

Setup guide on remote host

# Install autossh
pkg install autossh

# Edit autossh-daemon file to configure $proxy_host
vim autossh

# Install autossh-daemon file
install -o root -g wheel -m 755 autossh $proxy_host:/usr/local/etc/rc.d/autossh

# Create user
pw useradd -n autossh -g autossh -u 2223 -c 'The autossh daemon' -s /usr/bin/nologin -w no

# Generate ssh key
su -m autossh -c '/usr/bin/ssh-keygen -t ecdsa'

# Copy public key to remote host
cat ~autossh/.ssh/id_ecdsa.pub | ssh $proxy_host tee --append ~autossh/.ssh/authorized_keys

# Login manually to create ~autossh/.ssh/known_hosts
su -m autossh -c '/usr/bin/ssh autossh@$proxy_host'

/usr/local/etc/rc.d/autossh enable
/usr/local/etc/rc.d/autossh start

Setup guide on user device

cat >> ~/.ssh/config <<EOF
Host $remote_host
    Hostname $proxy_host
    Port 7000
    ProxyJump $proxy_host
EOF

SSH into remote host from user device

ssh $remote_host