Remote ssh copy paste buffers using fssh

3 minute read

Forward SSH

The goal of this project is to provide a wrapper around ssh to allow a user to execute commands on their local host from a remote host. This assumes that the user has ssh key forwarding via an ssh agent. Key forwarding is essential for the prompt-less login back to the local host machine.

This blog post is mostly the README from the repo. You can find the fssh repo on github.

Use Case

You connect to a remote server (referred to as remote host) and run tmux on it from Linux or OS X (referred to as local host). Occasionally you want to be able access the copy-paste buffer of your local host machine. How do you do that? Right now you probably rely on copy/pasting things from your terminal. This falls short when you want to copy/paste large amounts of data or have tmux panes side by side that get in the way.

There are tools like pbcopy/pbpaste for Mac OS X and xclip for Linux/X11 to modify the copy-paste buffer. However, the problem is that the remote host doesn’t know have any access to the local host.

Read on…

Goal of fssh

The goal of fssh is to leverage ssh port forwarding to setup a reverse ssh connection and passes the essential parameters though environmental variables. The environmental variables are critical to avoid port collisions with multiple sessions should the port numbers be hard coded.

---------------------                   ------------------
| local host        | -- ssh + fssh --> | remote host    |
|                   |                   |                |
| X11/Mac OS X GUI  | <-- ui_copy   --  | shell or tmux  |
|                   | --  ui_paste  --> |                |
---------------------                   ------------------

Example

No Documentation is complete without an example. Assume “laptop” is a machine running Mac OS X and “server” is running Ubuntu Linux.

user@laptop:~$ fssh server
>> Attempting reverse SSH forwarding via server:26336 to user@laptop
user@server:~$ md5sum /etc/services
22e9e61234a27da688971ba9377ec731  /etc/services
user@server:~$ cat /etc/services | ui_copy
user@server:~$ ui_paste | md5sum
22e9e61234a27da688971ba9377ec731  -
user@server:~$ exit
user@laptop:~$ ui_paste | md5sum
22e9e61234a27da688971ba9377ec731  -

The entire /etc/services file from the server is read in to the laptop’s copy-paste buffer by feeding it to ui_copy. The buffer is then read back from the laptop to the server and the hash is verified. The user then logs out and invokes ui_paste locally on the laptop to verify that the copy-paste buffer still works locally. The real use is that user running these terminal sessions can then just do Cmd+v on OS X or wheel click on Linux to paste the entire /etc/services file.

The opposite direction can be exercised as well

<User copies a long URL via <code>Cmd+v</code>
user@laptop:~$ fssh server
>> Attempting reverse SSH forwarding via server:16292 to user@laptop
user@server:~$ wget $(ui_paste)
<Download happens>

This is incredibly handy for things like: * Copying a semi-large text file (too big to fit on a terminal or broken up by tmux) from a remote machine or server so that it can be pasted in to a webpage (ie gist.github.com) or in to chat session for sharing. * The opposite direction like copying a large gist file or chat output on a workstation and fetching it from a server. * Copying text files from remotes to remotes by placing the text file in the workstation’s copy-paste buffer on one server (ie ui_copy) and then fetching it from the workstation’s copy-paste buffer on another connected server (ie ui_paste).

Utilities

  • fssh - create a forwarding ssh connection for use with ui_copy and ui_paste. In addition to creating the port forward, the ssh operation should operate transparently.
  • ui_copy - copy data from stdin to the local or remote GUI copy-paste buffer.
  • ui_paste - copy data from the local or remote GUI copy-paste buffer to stdout.

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