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Accepted
orestis
Asked: 2016-04-16 10:14:19 +0800 CST

auto start a reverse ssh tunnel on system startup

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I am have a remote machine behind a firewall that I wish to connect to through SSH. As far as I understand this can be achieved by using a reverse ssh tunnel.

So the command I am using is 

ssh -N -f -R 0.0.0.0:1234:localhost:22  -i /home/username/.ssh/id_rsa.pub  [email protected]

My main problem is that I want to execute this command whenever the computer starts so that the computer is accessible after a reboot.

I tried to use cron by adding the command both my user's crontab and in /etc/cron. However the problem I have is that both commands are asked for a password. I have created the id_rsa.pub file and sent it to the remote-server but still it does not seem to work.

If I am logged in (e.g. through teamviewer) I can run the command and no password is asked. If I run the command as root (sudo) the (empty) password for the rsa file is asked. I suspect that my problem is here, i.e., when cron executes the command ssh asks for the password and the command hangs.

I have tried using both my user's rsa file and the root's rsa file and with none of them I manage to connect.

ssh

4 Answers

  1. Just add 'sleep 60;' before your ssh command:

    @reboot sleep 60;ssh -N -f -R 0.0.0.0:1234:localhost:22  -i /home/username/.ssh/id_rsa  [email protected]

    After reboot your network is still down.

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  2. A better solution may be autossh:

    "autossh is a program to start a copy of ssh and monitor it, restarting it as necessary should it die or stop passing traffic."

    As the quote says, this has the added benefit of providing 'always on' capabilities.

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  3. Best Answer

    After combining multiple sources, I created a service to auto start the reverse ssh channel. The configuration files and the necessary steps are found in this repository

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  4. Fixing SSH problem

    You can't authenticate remote machine with public key, you need to use private key to do that. Public key has to be at remote server. If you're not sure, then just copy public key to remote server like that:

    ssh-copy-id -i ~/.ssh/id_rsa.pub username@remoteserver

    and then run your command with private key:

    ssh -N -f -R 0.0.0.0:1234:localhost:22  -i /home/username/.ssh/id_rsa  [email protected]

    Running this command at boot-up

    As you went already with crontab then run crontab -e to edit your cron. Add following line to execute that command once your computer boots up.

    @reboot ssh -N -f -R 0.0.0.0:1234:localhost:22  -i /home/username/.ssh/id_rsa  [email protected]
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