Editor’s 2017 note: Lots of great alternatives are discussed in the Comments section.
Intro
I’ve done a couple things with my Raspberry Pi. There’s this post on setting it up without a monitor, keyboard or mouse, and this post on using it to monitor power and Internet connection at my home.
I eventually realized that the Pi could be accessed from anywhere, with one big assumption: that you have your own hosted server somewhere on the Internet that you can ssh to from anywhere. This is the same assumption I used in describing the power monitor application.
The details
I can’t really take any credit for originality here. I just copied what I saw in another post. My only contribution is in realizing that the Pi makes a good platform to do this sort of thing with if you are running it as a server like I am.
What you can do is to create a reverse ssh tunnel. I find this easier and probably more secure than opening up ssh (inbound) on your home router and mapping that to the Pi. So I’m not going to talk about that method.
First ssh log in to your Pi.
From that session ssh to your hosted server using syntax like this:
> ssh −f −N −R 10000:localhost:22 username@ip_address_of_your_hosted_sever
You can even log out of your Pi now – this reverse tunnel will stay*.
Now to access your Pi from “anywhere,” log into your server like usual, then from that session, login to your Pi thusly:
> ssh −p 10000 pi@localhost
That’s it! You should be logged on after supplying the password to the pi account.
*Except that in my experience the reverse tunnel does not stay! It’s staying up less than two hours.
But I think the approach is sound.
Feb 15th Update
This is a case of RTFM. That same web page I cited above has the necessary settings. I needed to have them on the Pi. It didn’t help when I put them on my Amazon server. Here they are repeated:
TCPKeepAlive yes ClientAliveInterval 30 #ClientAliveCountMax 30 ClientAliveCountMax 99999 GatewayPorts yes AllowTcpForwarding yes |
This goes into the /etc/ssh/sshd_config file. Make sure you don’t have these mentioned a second time in that file.
With these settings my reverse tunnel has been up all day. It’s a real permanent tunnel now!
Security note
Make sure you modify the default passwords to your Pi before attempting this. You’re potentially exposing your whole home network in creating a reverse tunnel like this so you really have to be careful.
Conclusion
You can use your Raspberry Pi to create a reverse tunnel tht allows you to access it from anywhere, assuming you have a cooperating hosted server on the Internet as a mutual meeting point for the ssh sessions. Exercise caution, though, as you are opening up your Home network as well.
Currently the tunnel doesn’t stay up for very long – perhaps an hour or so. If I find a way to extend that I’ll revise this post.
References
Having trouble ssh’ing to your Ras Pi under any conditions? This article explains how to get past one common cause of this problem.