RogerBW's Blog

Upside Down and Inside Out 11 February 2023

Here's how I use graphical emacs as the working editor on a remote machine.

The basic setup: I have email, news, etc., on desktop machine D. I read it via ssh in a terminal window from laptop L. I want to edit posts using emacs session, ideally a graphical one rather than in that terminal.

There are some standard ways of doing this. Most obviously, you can run emacs(client) over X forwarding (ssh -X, or -Y), and this seems to be the usual approach. But I have some screens with quite different resolutions from others, and I want to use the emacs(client) that's tweaked for my local machine.

It's possible to tweak the emacs/emacsclient socket to allow remote access, but this is fiddly at best and going by others' accounts doesn't seem to be reliable.

I could use sshfs or TRAMP to tell the local machine to edit the remote temporary file. But that wouldn't be readily automatable.

So instead when the mail- or news-reader runs an editor, it hits this Perl program (using my standard principle of moving from shell to a better language whenever things look like getting complicated).

The various possiblities are:

  • I have an X display, or not. (If I'm away from home I generally turn off X forwarding because I'm on a mobile connection, or a bad hotel connection.)

  • I am coming in via ssh, or not (in which case I'm sitting directly at D).

    my $display = $ENV{DISPLAY} || '';
    (my $ssh = $ENV{SSH_CONNECTION} || '') =~ s/ .*//;
    if ($display) { # we have X
      if ($ssh) { # we're on remote X
  • I'm on L, but I'm allowing X-forwarding. ssh back to L, and tell it to edit the temp file, on the local display, via TRAMP. When that window is closed, the editing session ends.

        system('ssh','-tA',$ssh, "export DISPLAY=:0.0; emacsclient -c /ssh:heliophagous:'".$ARGV[0]."'")
      } else { # we're on local X
  • I'm on the local display. Just run local emacsclient.

        system(qw(emacsclient -c),@ARGV);
    } else { # we don't have X
  • I'm in some other situation, either being on a machine that doesn't have X (like Termux on the phone) or having deliberately turned it off (e.g. because ssh back to L won't be possible). Just run a simple console emacsclient.

      system(qw(emacsclient -nw),@ARGV);
Tags: computing

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