multi-user.Rmd

---
author: Dirk Eddelbuettel, Vincent Arel-Bundock, Grant McDermott
title: Multi-user Concurrent Editing with Emacs
subtitle: "Part of the ESS-Intro (and t4) series"
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---


## Emacs: Multi-User Concurrent Editing

### Motivation

- A lot of love online for how _editor XYZ_ supports multi-user mode
- But ... we have been able to do that with standard Unix tools for two+ decades
- As in Dirk's [_t4_ series](http://dirk.eddelbuettel.com/blog/code/t4/) it
  is about _combining_ existing (shell) tools for better use
- Here: `tmux`, or its alternate frontend `byobu`, can shine

## Emacs: Multi-User Concurrent Editing

### Setup

- Requirement: We assume multiple accounts on the same machine
   - _e.g._ a departmental server, research group server, AWS/GCS/Azure/DO instance ...
- Each participant needs to
  - be able to access the box via `ssh` 
  - have access to a shared (_i.e._ "joint") "named" tmux socket
  - (and we do not cover account creation, `root` use, ...)
- We then merely invoke `tmux` (or `byobu`), once creating a named socket
   - *Everything* running inside the tmux/byobu session can then be shared
   - Including Emacs (in terminal mode) or anything else working in terminal
  mode 

## Emacs: Multi-User Concurrent Editing

### Simplest Demo: Launch It 

This runs starts the session, _i.e._ the one granting access to his session.

```sh
# start tmux: named socket (-S), group (-t) and session (-s) names
$ tmux -S /tmp/joint-session new-session -t joint -s joint
# we are now in a tmux session
> chmod o+rw /tmp/joint-session  # so that other user can access
```

\medskip

We created a _new session_ under the handle 'joint' and gave it `rw` (==
"read-write") rights. (In real settings you probably want both users under a
common 'group' for the joint project and make the socket group rw.)

## Emacs: Multi-User Concurrent Editing

### Simplest Demo: Joint It

This runs as one of the users accessing the session. The only requirements
are to be one the same machine, _and_ to be part of the group having access
to the shared socket.

```sh
$ tmux -S /tmp/joint-session attach-session -t joint     ## or also
$ byobu -S /tmp/joint-session attach-session -t joint 
```

That. Is. All. The two sessions mirror each other.

So do `emacs -nw` or `R` or ... whatever command session you want to share.

Best of all: _All_ the `byobu` (or `tmux`) goodness we talked about in t4
works the same way. Multiple concurrent sessions. Persistent sessions _i.e._
start this, leave it running, re-connect tomorrow. Or next month.


<!-- ## Emacs: Multi-User -->

<!-- ### Alternate Demo (as user `edd`) -->

<!-- - If you prefer `byobu` (as I do) and have it use `tmux` (instead of -->
<!--   `screen`) -->
<!-- - Just do `byobu -S /tmp/scratch/session new-session -t joint`  -->
<!-- - Followed by `chmod o+rw ....` or `chgrp` or ... -->

## Emacs: Multi-User Concurrent Editing

### Other Tricks

- Start `emacs --daemon` to have emacs sessions persist
- Log on and off, attach and detach `byobu` / `tmux` and resume
- Emacs sessions remain accessible
- Plotting on tty is an issue but _e.g._ `httpgd` may help 
  - but ideally we would be able to have it send traffic to mulitple devices
    / users


## Emacs: Multi-User Concurrent Editing

### Lastly ...

- This is not meant to be normative
- Other editors can do similar things just fine (`code` is popular)
- (Commercial) online solutions also available (\url{replit.io})

### But ... we really like Emacs as it 

- is 'always there' 
- has support for just about anything
- is extensible


## Emacs: Multi-User Concurrent Editing

### Security

- We do stress that letting other users access 
  - _your_ session via the shared socket 
  - gives them _your session_ with access to all _you_ can access
  - this may include mail, gpg or ssh keys and more
- That means _any_ files accessible to _you_ are now also accessible to them
- So use on personal servers containing personal data may not be the first choice
- However, on work or cloud settings with no personal files less of an issue

## Emacs: Multi-User Concurrent Editing

### Summary

- An _easy_ and _powerful_ and _generic_ way to share a session
- Works for Emacs, also works for other (console) editors, R, ...
- While keeping possible limitation in mind, it can facilitate collaboration


<!-- # Appendix -->

<!-- ## Open Questions -->

<!-- - Detach (normal) versus exit (once ?) -->