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autossh

Due to network restrictions, you may be unable to connect via SSH to your computer. However, you can create a permanent, auto-reconnecting tunnel.

Autossh is available on Ubuntu with the Aptitude tool:

apt-get install autossh

Once this is installed, you can use the autossh.conf file from this repo in combination with an always-on Linux box you have access to (your home machine, or a VPS you own), to create a permanently available tunnel.

Create or edit the file: /etc/init/autossh.conf

  • 9999 Is the EXTERNAL port on your remote host (the always-on machine, e.g. VPS), so make sure there is no other service listening on that port and it's not blocked by a firewall. You may need to edit your Security Group if you're doing this on an Amazon EC2 instance, for example.

  • 22 is your SSH port on your computer

  • The last section of the autossh.conf file (just before -p) defines your SSH connection from your computer to the remote host. You should be able to run this independently, as a test, e.g. sudo ssh [email protected] -p22. You can, if you need to, append -i /home/user/.ssh/id_rsa or equivilant to this line to use key-based authentication with a different key. N.B. You should run the ssh connection test as sudo, as this is how it is run by the sudo start autossh command. It's also important that you do have key-based authentication setup, as you autossh is unable to prompt you for a password.

  • eth0 and eth1 are your possible ethernet network interfaces, confirm these by reviewing the output of ifconfig (equally wlan0 and iwconfig for WiFi connections - for these you may wish to add and net-device-up IFACE=wlan0 or and net-device-up IFACE=wlan1).

Now you've got the configuration setup, you can test it with:

sudo start autossh

and terminate it with:

sudo stop autossh

Run This Service Automatically

Add the following line to your /etc/rc.local:

sudo start autossh

To start tunel, go to root (or use sudo) and: start autossh.

From now on (if everything went ok), you can log-in to your external host and ssh to your machine behind the NAT using: ssh localhost -p 9999 -l username_on_your_computer

Troubleshooting

If you have problems, check out the logfiles under /var/log/upstart. There should be one logfile for each script/instance, so expect to find autossh.log as well as many autossh_host-N.log files.