# Remote emacs+Julia workflow

In my role at Beacon, I spend most of my working day interacting with Julia on a remote machine, and I wanted to document the workflow that I’ve settled on. The very short version is that emacs/TRAMP, emacs-jupyter, and IJulia together provide a pretty smooth—but not perfect—experience.

My main criteria are

1. Support interactive workflows in Julia
2. Can display rich output inline (super important for exploratory plotting)
3. Operates over an SSH connection
4. Persistent sessions that survive network hiccups
5. Emacs-based, because my brain was ruined in my first CS classes and I can’t use anything else at this point

## Emacs/TRAMP mode

TRAMP mode is wonderful in that it mostly Just Works™ and allows you to pretend you’re interacting with the remote host as if it’s local. To activate TRAMP mode you type C-x C-f to open a file (like usual), and then type /ssh:<hostname>: and hit Enter. Assuming you’ve set up SSH keys for the remote host, this should open an SSH connection behind the scenes and then show the remote filesystem in the normal file picker interface.

Any files you open can be edited exactly as if they’re on the local host, and any changes are sent (in a compressed form) over SSH when you save as usual with C-x C-s.

One nice thing is that TRAMP mode is sticky, in the sense that if you’re in a buffer visiting a remote file, when you hit C-x C-f to open another file it starts you in the directory on remote host. So once I’ve opened one file it’s pretty seamless.

### Tips for working with TRAMP mode

Sometimes things go sideways for reasons that are completely mysterious to me, and when that happens I do a “superstitious reset” with M-x tramp-cleanup-all-connections which clears the connections cache.

To break out of the sticky find-file mode, type /~ <Enter> to reset to the local host home directory, or / <Enter> for root. However, with swiper/counsel, I found that didn’t work, and you need to use / C-j (which in normal circumstances is equivalent to <Enter>, but I guess counsel hijacks that somehow)

Most of the emacs packages you use Just Work™ under TRAMP mode, including magit (my absolute favorite git interface). However, beware of magit operations that assume you can roundtrip many small files without significant latency (e.g., when rebasing a large number of commits).

## emacs-jupyter and IJulia

Interacting with Julia is a bit trickier. I’ve been using emacs-jupyter with pretty good results for a while now, and like many things it does Just Work™ with tramp (if you M-x run-jupyter-repl in a remote buffer, it’ll launch a kernel on that remote machine). However, if you do that then when the connection drops, the kernel dies, which is not ideal.

Instead, I’ve settled on using the “server” mode, where you run a jupyter server on the remote host and connect to it over a forwarded port. Here are the steps for that:

1. On the remote host, install jupyter and run jupyter notebook. If you’re only going to interact with Julia, I prefer to do this directly in Julia via something like

using Pkg
using IJulia
IJulia.notebook()


Make sure you run this in a way that can survive a dropped connection (so in screen, tmux, etc.), otherwise you’ll defeat the whole point of this exercise :)

2. Forward a port on your localhost to the remote host over SSH (assuming you don’t want to or can’t expose the jupyter port on your remote host):

\$ ssh -L 8888:localhost:8888 <hostname>

3. In emacs, start a new kernel with M-x jupyter-run-server-repl. This will start the kernel on the remote server and create an emacs-jupyter REPL buffer, and associate it with the current buffer if you’re visiting a buffer in julia-mode. Now C-c C-z will switch point to the associated REPL buffer (raising it if it’s not currently displayed), and C-c C-c will send code in the current region for eval (defaults to the current line if no region is active).

4. To connect a buffer visiting a .jl file to a running kernel (say, in a new emacs session), then you can M-x jupyter-connect-server-repl.

5. To associate a buffer with a REPL buffer that’s already connected to a kernel, use M-x jupyter-repl-associate-buffer.

I prefer using emacs-jupyter over a direct REPL connection especially for interacting with a remote host because it displays (some) rich output directly in the REPL buffer (PNG and SVG images chief among them). It’s also nice to have workspace-aware tab-completion like you get in an actual jupyter notebook (with M-TAB).

### Tips

There was for some time a pretty nasty font-locking bug in emacs-jupyter triggered by sending long-ish chunks of text to the REPL. It’s been fixed at least on trunk but it doesn’t look like it’s made it into a release yet, so make sure you’re getting a version since that PR landed.

You can have multiple REPL buffers in a single emacs session

There isn’t necessarily a 1-1 relationship between REPL buffers and running kernels on the remote server: there may be kernels with no REPL buffer connected to them, and there can be multiple buffers connected to the same kernel.

There’s a difference between connecting to a kernel and associating a buffer with a REPL. If you already have a REPL buffer connected to a kernel and you just want to interact with it from another .jl buffer, you want to M-x jupyter-repl-associate-buffer. If you have a running kernel on the remote host but not REPL buffer locally, you want to M-x jupyter-connect-server-repl. If you do this and already have a local REPL buffer, than I think that it’ll (confusingly) create a new buffer connected to the same kernel.

I prefer to keep the associated REPL buffer open because if it’s not, emacs-jupyter will open a million new buffers to display STDOUT, STDERR, and anything that’s displayed, in seemingly random locations. There’s probably a way to turn this off but I’m too lazy to dig into it.

Sometimes things interrupt the connection in a way that emacs-jupyter has a hard time recovering from. When this happens, I find that it’s best to kill the port-forwarding connection to the server, which causes emacs-jupyter to detect that the websocket connection is closed and clean up after itself. Then, you can re-connect the port forwarding SSH connection and everything should pick up where it left off.