Ssh – ‘Reversed shell’ – pull shell commands from remote host with human-controlled input

.ncssh

I would like to connect to a remote machine, ideally over SSH, and then pull the commands from there.

To be precise, I would like make a remote machine connect to my local machine, where I would have an interactive console, send commands and see the output.
Functionally it would be similar to Windows Remote Assistant or what's the name.

I can imagine I would implement a HTTP server that would have a GUI, and on request, it would keep the connection forever and send any line that I type to the GUI; and receive everything the other side sends as its output. I would only have to take care of the HTTP headers. However, that's not too elegant.

Is there some such ready-made solution? Or perhaps using nc or some tool that would connect the TTY with a listening port?

Best Answer

If you run:

socat "unix-listen:$HOME/.shell-access,mode=600,fork" \
      "exec:$SHELL,pty,stderr,setsid,ctty"

That allows you to do for instance:

socat -,raw,echo=0 "unix:$HOME/.shell-access"

locally, to connect and interact with that shell.

Then you can remote-port-forward it over ssh with:

ssh -R "/path/to/socket/on/host:$HOME/.shell-access" user@host

(assumes a relatively recent version of openssh (both client and server)).

And then user on host can interact with that shell by doing that

socat -,raw,echo=0 "unix:/path/to/socket/on/host"

Instead of running $SHELL, you could run screen -xRS some-screen-session to attach a given screen session so several people can see the same screen session.

Related Solutions

Ssh – Linux ssh launching GUI application and leaving it running

Yes, you can do this with xpra. From their homepage:

"To start an application (a simple xterm in this example) on a remote system and display it your local machine, simply run:
xpra start ssh:SERVERHOSTNAME:100 --start-child=xterm
This is similar to ssh -X, except it is faster and you can disconnect and re-connect to the session as many times as you like. (obviously xpra must be installed on your server host) To re-connect or to connect to this session from another machine, use the attach command (you can also use the xpra_launcher GUI):
xpra attach ssh:serverhostname:100

SSH – How to Send a HEREDOC Over SSH to a Remote Host from a Local Script?

If you wrap the entire command that you want executed inside backticks it's likely you'll get the correct solution. There are issues regarding the evaluation of variables and other interpolated elements, but I'll put those to one side for a moment.

However, I'm not entirely sure why you want anything in backticks. Your Question says you want to run a local script remotely. Your first example does this.

ssh -q user@host << ENDSSH
hostname
ls -l
id
ENDSSH

Perhaps you want to get the output of the remote execution into a variable? It doesn't say that anywhere in the Question, but you'd do it like this (bash)

RESULT=$(ssh user@host <<ENDSSH
hostname
id
ENDSSH
)
...
echo "$RESULT"

Or, since you mentioned csh, like this

set result = `ssh -q user@host` <<ENDSSH
hostname
id
ENDSSH
...
echo "$result"

Note that for the csh variant all output lines are concatenated together.

I see that you have reported an error, stty: standard input: Invalid argument. This is probably occurring because you have an stty command in your login script on the remote server. This should be wrapped in a test for an interactive shell. In bash you would do something like this:

if test -n "$PS1"
then
    # Interactive setup here
    stty ...
fi

Best Answer

Related Solutions

Ssh – Linux ssh launching GUI application and leaving it running

SSH – How to Send a HEREDOC Over SSH to a Remote Host from a Local Script?

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