A silly trick with X

Once upon a time, I was at home and really needed to see something that was displayed on my screen at work. This being Unix, there was no convenient remote desktop add-on that would have let me mirror my work display to home, but this being Unix, there are ways around that.

(Also, I was connecting over a slow dialup PPP connection, so a live remote desktop thing would have been difficult anyways.)

My first attempt was simple; ssh in to the work machine and do DISPLAY=:0 xwd -out /tmp/screen.xwd. This generated a large image that was unfortunately full of a lot of black, because I was running a screen locker, and the X screen locker actually puts a real window up on top of everything on the screen, instead of having a special side channel into X.

No problem; this is Unix and I had a hammer:

• ssh in to work
• export DISPLAY=:0
• kill the xlock process
• xwd the now revealed screen, complete with the window I needed to read
• run nohup xlock >/dev/null 2>&1 </dev/null & to re-lock my screen

(After all, xlock doesn't care exactly where it's being started from; all it needs is a $DISPLAY and enough privileges on the display.)

Technically I believe I didn't use xwd, but I've now forgotten whatever screen dump program it was. These days I would use import from ImageMagick; however much ImageMagick makes me wince vaguely with its swiss army chainsaw approach to life, it's convenient.