Connecting to Ubuntu server via SSH externally

First of all, the correct command is: ssh [email protected]

And the router should be configured to forward the SSH port 22 to your server's local IP address.

For further debugging:

1) Check that port 22 (SSH) is open on your server and on the router (port forwarding).

2) Check that the SSH server is running on your server

3) Use ping, ssh -v while connecting and look at /var/log/auth.log to debug any further connection problems.

1) On your router: follow router specific instructions

On your server: sudo ufw status (unless you use another firewall configuration utility) or sudo iptables -L (general method, but complex output)

To open port 22: sudo ufw allow 22

cf https://help.ubuntu.com/12.04/serverguide/firewall.html

2) Check it is installed: dpkg -l openssh-server

Check it is running: service ssh status or ps aux | grep sshd

3) On the connecting client:

On the server:

  • sudo less /var/log/auth.log

You can check the router logs as well if necessary.

Here's an online port scanner: https://www.grc.com/x/ne.dll?bh0bkyd2

I think you can use tools like nmap or other as well, but I'm not that familiar with them yet.

Dealing with a changing external IP address:

1) Get a dynDNS or similar account: http://dyn.com/dns/

Lists of dynamic DNS providers:

  • http://dnslookup.me/dynamic-dns/
  • http://www.dmoz.org/Computers/Internet/Protocols/DNS/DNS_Providers/Dynamic_DNS/

2) Another solution, is to set up a crontab job, which regularly mails you your external IP address or puts in into an online storage service like dropbox.

Here's a script a friend of mine uses:

    #!/bin/bash
    # Bash script to get the external IP address
    MYWANIP=$(curl http://mire.ipadsl.net | sed -nr -e 's|^.*<span class="ip">([0-9.]+)</span>.*$|\1| p')
    echo "My IP address is: $MYWANIP"

    IPold=$(cat /home/USER/Dropbox/test.txt)
    echo "Previous IP Address: $IPold"

    if [[ $IPold != $MYWANIP ]] ;
    then
      echo "New IP"
      rm /home/USER/Dropbox/test.txt
      echo $MYWANIP >> /home/USER/Dropbox/test.txt;
      echo $MYWANIP;
    else
      echo "Same IP";
    fi

    # example crontab entry:
    ## m h  dom mon dow   command
    ## */10 * * * * /home/USER/Dropbox/test_ip.sh

Router port forwarding:

1) First, figure out your router's local IP address by running:

ip route | grep default

It is usually something like 192.168.x.x.

Alternative ways and other OS solutions:

  • https://www.cyberciti.biz/faq/how-to-find-gateway-ip-address/
  • http://www.howtogeek.com/233952/how-to-find-your-routers-ip-address-on-any-computer-smartphone-or-tablet/
  • https://wiki.amahi.org/index.php/Find_Your_Gateway_IP
  • https://portforward.com/networking/routers_ip_address.htm

2) Using any computer connected locally to the router, access the IP found previously, i.e. via http://192.168.1.1 for example. This should bring up the router configuration interface.

3) The next steps vary depending on your router. Here is how it is done on a router with OpenWRT for example:

https://newspaint.wordpress.com/2012/08/26/how-to-add-a-port-forward-using-the-web-interface-on-openwrt-10-03-1/


By default in Ubuntu (Desktop) SSH is not installed.

You can install it by the following command in Terminal:

sudo apt-get install openssh-server

It should install and start the service right away.

Tags:

Ssh

Openssh

Server

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