MacOS – How to keep an ssh tunnel alive using launchd

launchdmacossshtunnel

I would like to keep an ssh tunnel alive. Below is my launch agent plist file but it only keeps the tunnel up for a day or two at the most. I'm using OS X 10.10.3.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
        <dict>
                <key>Label</key>
                <string>com.my.ssh_tunnel</string>
                <key>ProgramArguments</key>
                <array>
                        <string>/usr/bin/ssh</string>
                        <string>-R 0.0.0.0:22221:localhost:22</string>
                        <string>-NTC</string>
                        <string>-f</string>
                        <string>-o ExitOnForwardFailure=yes</string>
                        <string>-o ServerAliveInterval=60</string>
                        <string>user@user.server.com</string>
                </array>
                <key>RunAtLoad</key>
                <true/>
                <key>KeepAlive</key>
                <true/>
        </dict>
</plist>

Best Answer

I think you need to add "ServerAliveCountMax". Since you don't have it set it defaults to 3. Try setting it to something higher than 3 and see if it relives some of your issues. In your case it would disconnect if the server is not responsive for 180 seconds.

From the ssh man page:

 ServerAliveCountMax:

     Sets the number of server alive messages (see below) which may be
     sent without ssh(1) receiving any messages back from the server.
     If this threshold is reached while server alive messages are
     being sent, ssh will disconnect from the server, terminating the
     session.  It is important to note that the use of server alive
     messages is very different from TCPKeepAlive (below).  The server
     alive messages are sent through the encrypted channel and there‐
     fore will not be spoofable.  The TCP keepalive option enabled by
     TCPKeepAlive is spoofable.  The server alive mechanism is valu‐
     able when the client or server depend on knowing when a connec‐
     tion has become inactive.

     The default value is 3.  If, for example, ServerAliveInterval
     (see below) is set to 15 and ServerAliveCountMax is left at the
     default, if the server becomes unresponsive, ssh will disconnect
     after approximately 45 seconds.  This option applies to protocol
     version 2 only.

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I think your basic strategy is correct, e.g.:

ssh -L 587:smtp.gmail.com:587 -L 993:imap.gmail.com:993 user@yourremotehost

should get you talking to Gmail via yourremote host. Potential problems are if you do not run this as root (with sudo), you are not allowed to specify local ports below 1024 - so you can't use 587 or 993 as your local ports. So, do something like this:

ssh -L 9587:smtp.gmail.com:587 -L 9993:imap.gmail.com:993 user@yourremotehost

...and configure Sparrow to talk to localhost on those high local port numbers instead of the defaults.

Again, you can debug by trying 'telnet localhost 9587' which should get you an SMTP prompt from Gmail. If that works, you should feel confident that the SSH part is working, and concentrate on Sparrow configuration.

If you get it all working, an alternative to the commandline switches is to make a file called 'config' in your local .ssh directory that looks like this:

Host yourremotehost    
        LocalForward    9587    smtp.gmail.com:587
        LocalForward    9993    imap.gmail.com:993

IOS – Reverse SSH tunnel on the iPad

So my idea is after I've connected to the network, ssh to my home server.

For SSH into a remote server you can use many apps available on the App Store. My favorite one is Prompt.

Then from my home server ssh back onto my iPad.

You can't SSH into an iOS device without jailbreaking (unless you are an Apple engineer). You would need to jailbreak first and then install the OpenSSH package from Cydia.

Or is there an even simpler solution that I'm missing?

Why do you need to SSH into your home server if you're just using it to get into the iPad? Seems like a lot of trouble, and you might need to mess around with port forwarding on the iPad's network.

SSHing into the iPad by connecting to localhost should do the trick. I assume you've jailbroken and installed all the utilities you need onto the iPad. Shouldn't be too bad as it looks like they're all open-source programs and you can recompile them if you really need to.

Best Answer

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IOS – Reverse SSH tunnel on the iPad

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