Essentially what I want to do is run a Bash script I created that switches WiFi SSIDs before starting the SSH connection, and after the SSH connection closes.
I have added this to ~/.ssh/config by setting ProxyCommand to ./run-script; ssh %h:%p but by doing this, I feel like it would ignore any parameters I passed when I run the ssh command. Also, I have no idea how to get the script to run again when the SSH connection closes.
For OpenSSH you can specify a LocalCommand in your ssh config (~/.ssh/config).
But for that to work you also need the system-wide option (in /etc/ssh/ssh_config) PermitLocalCommand to yes. (By default it is set to no.)
It gets executed on the local machine after authenticating but before the remote shell is started.
There appears to be no (easy) way of executing something after the connection has been closed, though.
Assuming that it is not possible to implement a wrapper to 'ssh' (using alias, or some other method), it is possible to implement the following in the proxyCommand.
Important to note that there is no protection against multiple invocation of 'ssh' - possible that during a specific invocation that WIFI is already connected. Also, it is possible that when a specific ssh is terminated, the WIFI has to stay active because of other pending conditions.
Possible implementation of the proxy script is
ProxyCommand /path/to/run-script %h %p
#! /bin/sh
pre-command # connect to WIFI
nc -N "$1" "$2" # Tunnel, '%h' and '%p' are passed in
post-command # Disconnect WIFI
You do not want to use simple ssh in the proxy script, as this will translate into another call to the 'run-script'. Also note that all options provided to the original ssh will be handled by the initial 'ssh' session that will be leveraging the proxy 'nc' tunnel.
I'm wondering if I already have an established SSH tunnel and I want to minimize re-authenticating with an ssh server for each task, is there a way to use an existing tunnel to pull a file from the SSH server using SCP on the local machine without re-authenticating?
I'm trying to avoid using ssh keys, I'd just like to minimize the amount of times a password needs to be entered for a bash script.
ssh -t user#build_server "*creates a build file...*"
Once that command is completed there is a file that exists on build_server. So if the above tunnel was still open, is there way to use that tunnel from my LOCAL machine to run SCP to and bring the file to the local machines desktop?
Yes, session sharing is possible: man ssh_config and search for ControlMaster and/or check here and here. Is this what you are looking for?
for a programming project I have to do some strange setup. Now, first of all, I have root rights on both servers, and I think an ssh tunnel is the best way (if you have a better idea, please feel free to tell me)
I have to write a piece of software running on an IRC server. That is not difficult, but the IRC server is only reachable on localhost. So I have to ssh to the box first and then use irssi or similar to connect to localhost:6667
Now I tried to do an ssh-tunnel from a second server (where I have irssi running all the time) and then tunnel to the server and use localhost through the tunnel, something like:
ssh -f user#server2 -L 2000:server2:6667 -N
Now this is not working as expected when I use irssi to connect to localhost:2000. I don't understand why, do you have any hint? I would be glad if you could help me.
Regards
Remember that that address you tunnel to (server2:6667 in your case) is from the point of view of the destination. For example: I have a VPS running with ssh installed. If I do ssh -f user#vps -L 2000:localhost:3306 I can connect to the MySql server running on it (which is only listening on the loopback interface).
So assuming the IRC server is running on server2 you should do:
you#server1:~$ ssh -f you#server2 -L 2000:localhost:6667 -N
You can then connect to localhost:2000 (on server1) with your IRC client and get a connection to the IRC-server running on server2.
I want to setup a simple ssh tunnel from a local machine to a machine on the internet.
I'm using
ssh -D 8080 -f -C -q -N -p 12122 <username>#<hostname>
Setup works fine (I think) cause ssh returs asking for the credentials, which I provide.
Then i do
export http_proxy=http://localhost:8080
and
wget http://www.google.com
Wget returns that the request has been sent to the proxy, but no data is received back.
What i need is a way to look at how ssh is processing the request....
To get more information out of your SSH connection for debugging, leave out the -q and -f options, and include -vvv:
ssh -D 8080 -vvv -N -p 12122 <username>#<hostname>
To address your actual problem, by using ssh -D you're essentially setting up a SOCKS proxy which I believe is not supported by default in wget.
You might have better luck with curl which provides SOCKS suport via the --socks option.
If you really really need to use wget, you'll have to recompile your own version to include socks support. There should be an option for ./configure somewhere along the lines of --with-socks.
Alternatively, look into tsock which can intercept outgoing network connections and redirecting them through a SOCKS server.
I have a small local network. Only one of the machines is available to the outside world (this is not easily changeable). I'd like to be able to set it up such that ssh requests that don't come in on the standard port go to another machine. Is this possible? If so, how?
Oh and all of these machines are running either Ubuntu or OS X.
Another way to go would be to use ssh tunneling (which happens on the client side).
You'd do an ssh command like this:
ssh -L 8022:myinsideserver:22 paul#myoutsideserver
That connects you to the machine that's accessible from the outside (myoutsideserver) and creates a tunnel through that ssh connection to port 22 (the standard ssh port) on the server that's only accessible from the inside.
Then you'd do another ssh command like this (leaving the first one still connected):
ssh -p 8022 paul#localhost
That connection to port 8022 on your localhost will then get tunneled through the first ssh connection taking you over myinsideserver.
There may be something you have to do on myoutsideserver to allow forwarding of the ssh port. I'm double-checking that now.
Edit
Hmmm. The ssh manpage says this: **Only the superuser can forward privileged ports. **
That sort of implies to me that the first ssh connection has to be as root. Maybe somebody else can clarify that.
It looks like superuser privileges aren't required as long as the forwarded port (in this case, 8022) isn't a privileged port (like 22). Thanks for the clarification Mike Stone.
#Mark Biek
I was going to say that, but you beat me to it! Anyways, I just wanted to add that there is also the -R option:
ssh -R 8022:myinsideserver:22 paul#myoutsideserver
The difference is what machine you are connecting to/from. My boss showed me this trick not too long ago, and it is definitely really nice to know... we were behind a firewall and needed to give external access to a machine... he got around it by ssh -R to another machine that was accessible... then connections to that machine were forwarded into the machine behind the firewall, so you need to use -R or -L based on which machine you are on and which you are ssh-ing to.
Also, I'm pretty sure you are fine to use a regular user as long as the port you are forwarding (in this case the 8022 port) is not below the restricted range (which I think is 1024, but I could be mistaken), because those are the "reserved" ports. It doesn't matter that you are forwarding it to a "restricted" port because that port is not being opened (the machine is just having traffic sent to it through the tunnel, it has no knowledge of the tunnel), the 8022 port IS being open and so is restricted as such.
EDIT: Just remember, the tunnel is only open so long as the initial ssh remains open, so if it times out or you exit it, the tunnel will be closed.
(In this example, I am assuming port 2222 will go to your internal host. $externalip and $internalip are the ip addresses or hostnames of the visible and internal machine, respectively.)
You have a couple of options, depending on how permanent you want the proxying to be:
Some sort of TCP proxy. On Linux, the basic idea is that before the incoming packet is processed, you want to change its destination—i.e. prerouting destination NAT:
iptables -t nat -A PREROUTING -p tcp -i eth0 -d $externalip --dport 2222 --sport
1024:65535 -j DNAT --to $internalip:22
Using SSH to establish temporary port forwarding. From here, you have two options again:
Transparent proxy, where the client thinks that your visible host (on port 2222) is just a normal SSH server and doesn't realize that it is passing through. While you lose some fine-grained control, you get convenience (especially if you want to use SSH to forward VNC or X11 all the way to the inner host).
From the internal machine: ssh -g -R 2222:localhost:22 $externalip
Then from the outside world: ssh -p 2222 $externalip
Notice that the "internal" and "external" machines do not have to be on the same LAN. You can port forward all the way around the world this way.
Forcing login to the external machine first. This is true "forwarding," not "proxying"; but the basic idea is this: You force people to log in to the external machine (so you control on who can log in and when, and you get logs of the activity), and from there they can SSH through to the inside. It sounds like a chore, but if you set up simple shell scripts on the external machine with the names of your internal hosts, coupled with password-less SSH keypairs then it is very straightforward for a user to log in. So:
On the external machine, you make a simple script, /usr/local/bin/internalhost which simply runs ssh $internalip
From the outside world, users do: ssh $externalip internalhost and once they log in to the first machine, they are immediately forwarded through to the internal one.
Another advantage to this approach is that people don't get key management problems, since running two SSH services on one IP address will make the SSH client angry.
FYI, if you want to SSH to a server and you do not want to worry about keys, do this
ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no
I have an alias in my shell called "nossh", so I can just do nossh somehost and it will ignore all key errors. Just understand that you are ignoring security information when you do this, so there is a theoretical risk.
Much of this information is from a talk I gave at Barcamp Bangkok all about fancy SSH tricks. You can see my slides, but I recommend the text version as the S5 slides are kind of buggy. Check out the section called "Forward Anything: Simple Port Forwarding" for info. There is also information on creating a SOCKS5 proxy with OpenSSH. Yes, you can do that. OpenSSH is awesome like that.
(Finally, if you are doing a lot of traversing into the internal network, consider setting up a VPN. It sounds scary, but OpenVPN is quite simple and runs on all OSes. I would say it's overkill just for SSH; but once you start port-forwarding through your port-forwards to get VNC, HTTP, or other stuff happening; or if you have lots of internal hosts to worry about, it can be simpler and more maintainable.)
You can use Port Fowarding to do this. Take a look here:
http://portforward.com/help/portforwarding.htm
There are instructions on how to set up your router to port forward request on this page:
http://www.portforward.com/english/routers/port_forwarding/routerindex.htm
In Ubuntu, you can install Firestarter and then use it's Forward Service feature to forward the SSH traffic from a non standard port on your machine with external access to port 22 on the machine inside your network.
On OS X you can edit the /etc/nat/natd.plist file to enable port fowarding.
Without messing around with firewall rules, you can set up a ~/.ssh/config file.
Assume 10.1.1.1 is the 'gateway' system and 10.1.1.2 is the 'client' system.
Host gateway
Hostname 10.1.1.1
LocalForward 8022 10.1.1.2:22
Host client
Hostname localhost
Port 8022
You can open an ssh connection to 'gateway' via:
ssh gateway
In another terminal, open a connection to the client.
ssh client