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Automatically setting $DISPLAY with NX

I do most of my research work on Linux, primarily with lots of X11 Emacs and OS X Terminal windows. I sit at my iBook, which doesn’t stay put network-wise or physically in any given day. Setting up my environment from scratch every time I need to start work in a new location is a huge time sink (in perception if not reality), so I’ve been doing some work to reduce this setup delay.

I can detach from my terminal sessions with screen as I’ve been doing for many years, but X11 is harder. In the past, I either used a local Emacs with TRAMP (for slow setup, slow synchronous file I/O, poor tolerance of network failure, and inability to do things like M-x compile), waited a long time for a remote Emacs to come up over SSH-forwarded X11 (for slow setup), or settled for Emacs running in a Terminal window (making, among other things, copy and pasting between OmniOutliner and Emacs very painful). VNC was out because it took over the entire screen, used lots of CPU, and was too slow over my home Internet connection; besides, I like being able to overlap X11 and Mac windows.

Thankfully, there is finally a good alternative: NX. It’s a primarily-GPL-but-with-commercial-pieces client/server X proxy system which massively speeds up X11, VNC and RDC traffic and reduces latency to the point that remote windowing is usable over a slow connection. As of version 1.5, it also provides detachable multiwindowed (rootless) sessions.

I’ve been using NX full-time for the past month or so, first with 1.4 which gave me “fast, detachable” (and windowed) or “slow, rootless” but not the best of both worlds, and finally this week with 1.5. The initial Mac 1.5 client was a bit broken, but the problems were in the open-source part of it, so Gian Filippo Pinzari from NoMachine was able to provide a patch in a mailing list post. I rebuilt the corresponding components, and everything works now! (Update, August 17: The official client as of version 1.5.0-106 now works without patching.) I even tried detaching my NX session from OS X, resuming on Windows, detaching from there, and resuming on Linux. Did I mention how fast everything is? I can hardly tell the difference between working at home and school now.

There’s also FreeNX, which is comprised primarily of shell scripts wrapping the GPL NX components. I used it before 1.5 came out. FreeNX has some advantages: more configurability, like being able to move my cache directory out of my home directory, since AFS tokens expiring can be a bit of a problem (I work around this with commercial NX using symlinks), and the ability to install as a non-root user. It also has some disadvantages: failures are difficult to troubleshoot, and I can’t get it to work with the NX 1.5 components. Commercial NX is downright cheap for a single user license, and the company is being incredibly generous with their support and code, so I plan to pay for it.

And finally, this brings us to some hopefully-unique information I have to add: a short zsh fragment I wrote so my display gets set automatically based on an already-open NX session. Since I don’t want any fancy desktop environments to start under NX—I already have OS X for that—the session is set to start a small terminal window which immediately goes into the Dock (rxvt -fn fixed -geometry 80x3 -iconic). After that’s set up, I head back to Terminal and ssh into the machine where my NX session runs, and this piece of my ~/.zshrc sets $DISPLAY for me:

  # use NX display if possible
  if [[ -z $DISPLAY ]] {
    case ${#nx_cache_dir} in
      0) ;;
      1) export DISPLAY=unix:${${(s:-:)nx_cache_dir[1]}[3]}.0
      *) echo '*** Potentially stale NX cache directories:'
         for i in ${(f)"$(cd ~/.nx; ls -ldt $nx_cache_dir)"}; do
           echo '***' ${${=i}[-4,-1]}

Then I start my screen session, and I’m ready to go.

In case you accidentally have some old session caches around, the script warns you it doesn’t know which one to pick; mostly, this was left over from when I was debugging NX problems (rant about GNU ls and cut‘s inflexibility deleted). Of course, you might have some legitimate reason for having multiple simultaneous sessions, too…

In other news, I’m using WordPress 1.5.2 now. The upgrade was pretty simple, though I had to be careful what I was doing (mv -i is your friend). I haven’t tested everything, so let me know if you have any difficulties with this site after the upgrade.

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