wm-launch

wm-launch provides a shared library for use with LD_PRELOAD and a command-line tool to set IDs on newly created X11 windows. It is intended to be used by a window manager to uniquely identify clients it launches.

Packages

• Fedora (copr)

  dnf copr enable jcrd/wm-launch
  dnf install wm-launch

• Arch Linux (AUR)

  git clone https://aur.archlinux.org/wm-launch.git
  cd wm-launch
  makepkg -si

Usage

LD_PRELOAD can be specified along with WM_LAUNCH_ID in the environment of a command:

LD_PRELOAD=/usr/lib/wm-launch/wm-launch-preload.so WM_LAUNCH_ID=id1 xterm

The window created by xterm will have the property WM_LAUNCH_ID:

$ xprop WM_LAUNCH_ID
> WM_LAUNCH_ID(UTF8_STRING) = "id1"

A command-line tool is provided for convenience and for interacting with window factories:

usage: wm-launch [options] WM_LAUNCH_ID COMMAND...

options:
  -h          Show help message
  -s          Launch with systemd-run
  -j          Launch with firejail
  -f FACTORY  Launch via a window factory
  -w DIR      Launch workspace from DIR
  -v          Show version

Example use cases

wm-launch can be used to:

• reliably assign clients to window manager desktops/workspaces so that even slow-to-spawn windows appear where intended
• identify separate instances of the same application to be managed differently, focused via keybindings, etc.
• launch or focus a single instance of an application

Window factories

A window factory is an X11 client responsible for creating the windows of new clients. It can be either implicit or explicit, the key difference being that implicit factories create their own window.

Implicit factory

An implicit factory is an X11 client that reuses a single instance to create additional windows each time it's launched, e.g. qutebrowser, kitty -1.

To correctly set the WM_LAUNCH_ID of an implicit factory, always run it via wm-launch with the same argument to the -f flag:

wm-launch -f qute id2 qutebrowser

Explicit factory

An explicit window factory is a daemon that creates windows based on a client's request, e.g. emacsd and emacsclient, urxvtd and urxvtc.

To correctly set the WM_LAUNCH_ID of an explicit factory, run the daemon with LD_PRELOAD and WM_LAUNCH_FACTORY:

LD_PRELOAD=/usr/lib/wm-launch/wm-launch-preload.so WM_LAUNCH_FACTORY=emacs emacsd

Then launch with wm-launch -f emacs id3 emacsclient.

wm-launchd

wm-launchd must be running to handle window factories. Enable the systemd service to run when the graphical-session.target is reached:

systemctl --user enable wm-launchd

Workspaces

With the -w flag, wm-launch can initiate the startup of multiple clients based on a .workspace file. The programs therein are expected to be launched by the running window manager, which must implement the com.github.jcrd.wm_launch.WindowManager DBus interface.

.workspace files

A .workspace file contains one program per line to run. If preceded by a @, the program will be interpreted as one defined by the window manager, otherwise the window manager should execute it directly.

For example, given:

@terminal
xterm

@terminal should be defined by the window manager. This is useful when additional context is necessary, such as running with a factory, systemd-run, etc.

xterm should be executed directly by the window manager.

DBus interface

A window manager must implement the com.github.jcrd.wm_launch.WindowManager interface under the path /com/github/jcrd/wm_launch/WindowManager at the well-known name com.github.jcrd.wm_launch.

This interface must define the NewWorkspace method, which takes three arguments:

1. The workspace name as a string
2. The workspace working directory as a string
3. An array of strings representing clients to launch

It returns nothing.

systemd-run

A client can be launched with systemd-run by running it via wm-launch using the -s flag. This will run the command in a user scope with systemd-run --user --scope.

Firejail

A client can be launched with firejail by running it via wm-launch using the -j flag. This sets the required environment variables in the sandbox created by firejail.

Limitations

• Be aware of environment variable inheritance. This becomes a problem when launching a client from a terminal created by a factory, i.e. WM_LAUNCH_FACTORY is present in its environment. The new client will inherit this variable and expect the given factory to exist. This scenario can be avoided by launching the client with wm-launch -f "".

Window manager integration

• Integration with Awesome WM is provided by awesome-launch.

Building

Dependencies

• libxcb
• libx11
• perl
• go

Build with make.

Installing

Install with make install.

Testing

Tests have additional dependencies:

• xvfb

Run tests locally with make test or use make test-podman to run them in a supplantr/wm-launch container which includes all dependencies.

Note: firejail cannot run in containers. It must be tested locally.

License

wm-launch is licensed under the GNU General Public License v3.0 or later (see LICENSE).

Acknowledgements

wm-launch-preload.c is based on ld-preload-xcreatewindow-net-wm-pid.