xclipd - A Lightweight Clipboard Manager for X11

This is xclipd, a small X11 clipboard manager that I wrote for a very particular purpose: to support copy-and-paste on a Dockerized Linux laptop.

The Original Problem

tl;dr: X11 requires the application that copied to the clipboard to live for as long as you want the clipboard data to be paste-able. This daemon solves that for short-lived copiers.

ne;wm (not 't enough; want more): I wrote a whole blog post about this, over at jameshunt.us.

How It Works

xclipd sits in the background, with a single X11 window object, and waits for an appliation to assert ownership of the CLIPBOARD selection. At that point it:

1. Requests the selection from the current CLIPBOARD owner.
2. Converts that selection into UTF-8 (if possible).
3. Takes control of the CLIPBOARD selection.
4. Responds to any requests for copied data.

Repeat until process termination.

Any time an application copies data to the X11 clipboard, xclipd immediately pastes and re-copies that data, so that the original client can exit without loss of copied data.

Building It

Before you build it, you will need:

1. A C compiler. Tested with gcc and clang. (Don't forget to set the $CC environment variable)
2. libc + header files
3. libX11 + header files

This codebase has a Makefile that any compatible make variant should be able to use:

$ make
cc -Wall -Wextra -o xclipd src/xclipd.c -lX11

There is no make install - the easiest way to "install" this is to copy it to a directory in your $PATH:

$ sudo cp xclipd /usr/local/bin

It's probably easier to build the Docker image, assuming you're hooked up to a Docker daemon:

$ make docker
docker build -t docker/xclipd .
Sending build context to Docker daemon  100.9kB
Step 1/9 : FROM alpine:3 AS build
Step 2/9 : RUN apk update && apk add make gcc libc-dev libx11-dev
Step 4/9 : COPY . .
Step 5/9 : RUN make  && mv xclipd /usr/bin
Removing intermediate container 8e31eafad6d6
Step 6/9 : FROM alpine:3
Step 7/9 : RUN apk update && apk add libx11 && rm -f /var/cache/apk/*
Step 8/9 : COPY --from=build /usr/bin/xclipd /usr/bin/xclipd
Step 9/9 : ENTRYPOINT ["/usr/bin/xclipd"]
Successfully built 077d159902d5
Successfully tagged docker/xclipd:latest

Note that the image is tagged locally as docker/xclipd. If you're going to push this to an upstream registry (like quay.io or Docker Hub), don't forget to re-tag it.

Running It

There are no flags, no options, and $DISPLAY is the only environment variable honored:

$ xclipd

You'll need to arrange for your own process supervision, bootup, etc. Honestly, the Docker approach (shown next) is probably easier and more rock-solid if you've already committed to Docker.

Running It (in Docker)

$ docker run --rm -d -u $UID \
         -v /tmp/.X11-unix:/tmp/.X11-unix \
         -e "DISPLAY=unix$DISPLAY" \
         filefrog/xclipd

You're probably best off running this from something like your ~/.xinitrc.