Run in GUI (run-in-gui)

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This project contains two programs that assist you in executing programs in a separate desktop session (defined by the environment variables of any program executing in that session), and then switching to the session in real-time as the program executes. It's useful to start GUI programs from cron that need a graphical display and/or audio access.

Why is this necessary?

Lots of people ask me why this is useful, or some other variant of the same question, such as "Can't I just DISPLAY=:0 in my crontab?"

Well, because of the way that Linux has evolved, nowadays it's very hard to get certain computer programs to do things that were trivial in the past. Lots of GUI programs now depend on a wide array of session daemons and other services, such as:

• X11 authentication,
• D-Bus,
• KWallet,
• GnuPG agents,
• SSH agents,
• KIO services,
• PulseAudio.

These services are normally set up properly at the start of (and solely in the context of) your GUI session, but entirely unavailable for use in crontabs and other non-GUI shells, nominally disassociated with your desktop session.

For example: getting your music player to play a list of songs to wake you up -- unless you're running the program straight from a terminal in your desktop session's GUI, it won't actually work; either the program just won't run, or the audio will be corked.

How this works

So what we do in run-in-gui is simple: ''we cheat'' by stealing the necessary information from other programs running in your desktop session, and using it to recreate an environment in which we run your program.

Caveat: of course, this program ''still'' requires you to be logged in. If your session isn't active, run-in-gui will take the liberty to switch to your inactive session, activating -- but, if locked, not unlocking -- it, and then running your program.

Tools included in this set

This package contains several tools:

1. run-in-env-of: a tool that runs the command of your choice in the environment of the PID of your choice. If run as root, it can setuid() to the user and group of that PID.
2. run-in-gui: a tool that sorts out a desktop session you're running then uses run-in-env-of to execute the command on your choice under that desktop session. Prior to the execution of that program, it switches to the selected desktop session, to enable hardware access to devices that would otherwise be blocked (e.g. audio).

What you need to have before using this package

• Python 2.7 on your local machine
• loginctl fully operational
• /proc mounted

Installation

You will need to install this package on your local machine.

You can install this package directly from PyPI using pip::

pip install run-in-gui

If you are on an RPM-based distribution, build an RPM from the source package and install the resulting RPM::

python setup.py bdist_rpm

Otherwise, just use the standard Python installation system::

python setup.py install

You can also run it directly from the unpacked source directory::

export PYTHONPATH="$PWD"/src
./<program> <parameters>

Usage

Say, for example, you want to run Amarok from a crontab, but you want Amarok to start on your logged-in desktop session. No problem: you can stick this into your crontab:

20 4 * * * /usr/local/run-in-gui/bin/run-in-gui amarok -p Toke\ up.m3u

As you can see, at exactly 4:20 AM, Amarok will be executed in your desktop session, and will start playing the playlist Toke up.m3u in your home directory.

You can also do the exact same thing from an at job:

echo /path/to/run-in-gui amarok -p Matanga.m3u | at 5:45

If, for some reason, the program won't start, check your mail folder in /var/mail/$USERNAME, where cron traditionally deposits crontab output.