working interactively on a remote computer

Thu 25 October 2012 | -- (permalink)

In my software/hardware setup post, I talked a little bit about working on a remote machine.  As promised, here are the details about how I make interactive coding easy for me.

Let's start from the very very beginning.  Our department has a pretty sweet set of really powerful computers ("the cluster") available for us to use.  Because the computers are so awesome, they have to be kept in a room that is specially cooled and maintained, and they don't have desktops that we can sit down and interact with.  As such, you need to use a different computer (i.e., a laptop) to remotely log in to the cluster and either (a) start an interactive session, in which you can type commands into the Linux shell, or open up an interactive version of (say) R or python and type commands there, or (b) submit a batch job or shell script to run without user interaction.

Batch jobs and scripts are pretty straightforward, so I'm not going to yammer on about that in this post.  But working interactively is a little trickier, mostly because it's good practice (in the name of reproducible research, scientific integrity, and organization) to keep a record of the commands you run to get your results.  If you get results interactively on the remote machine, there's not a built-in way to do this.  But never fear!  Software and shortcuts exist that allow you to save a script on your local computer, but run each line of that script interactively on the remote machine.  Since statisticians like me usually do most interactive work in R, I'll describe here how I run a local R script interactively on the cluster.

I'm currently a Mac user, so my main tool for this purpose is Aquamacs.  This is basically a version of an Emacs text editor.  My opinion on Emacs is that it's a really powerful tool, but requires a lot of customization to access all that power, and it has pretty funky keyboard shortcuts.  Aquamacs allows you to use either Emacs keyboard shortcuts OR common Mac keyboard shortcuts (e.g., command-Z for undo) in an Emacs session, which I find really useful.  Aquamacs makes use of ESS (Emacs Speaks Statistics) when interacting with R.

So let's get to the point: here are the steps!

​(1)  Install Aquamacs.

​(2)  Open your local R script inside Aquamacs.

​(3)  Type M-x shell (M means escape key), which will basically open up a Terminal window inside Aquamacs.  (Once you hit M-x, you won't be typing in the R script anymore, but will see your stuff appear at the bottom of the window).

​(4)  In the Terminal window that just opened up, log in to the remote machine. (I'm making the assumption here that the login process to the remote machine involves some variant of an "ssh" command in the terminal.)

​(5)  Click Window > Move tab to new frame.  The terminal window will slide over to the other side of your computer, so you're now seeing the R script and the prompt of the remote machine simultaneously.

​(6)  Start R on the remote machine.

​(7)  Staying in the remote-machine-R window, type M-x ess-remote.  You'll then be prompted for a dialect - type - the line "options(STERM='iESS')" will have been run inside your R session.

​(8)  Move back to the local R script.  You can now run line-by-line on the remote machine either using control-n to run just the current line, or using control-r to run a block of highlighted lines.

This has worked pretty well for me, but I am definitely interested in hearing others' ideas if someone knows of a more efficient way to do this from a Mac.  I use Aquamacs almost exclusively for this, which feels a little like using a sledgehammer for a tiny little nail, since I'm not really harnessing all the power of Aquamacs/Emacs or using it for any of its other intended purposes, and I haven't put a lot of time into customizing it.  But it does get the job done, and it's definitely better than the ol' copy-paste trick.

I'm incredibly happy with my Macbook (it's a delightfully fast, beautiful, efficient computer), but I really really miss Notepad++, the best text editor I've ever known - it's Windows-only.  Running interactively on a PC is smoother than the Mac workflow I described above: it basically involves (1) logging into the remote machine using something like PuTTY and opening R, (2) opening up your local R script in Notepad++, and (3) hitting F9 to run a line or highlighted set of lines.  So much more elegantly simple!  Something for Mac software developers to aspire to, I suppose...

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