siva, change test to brightness so that the source file looks like this:

#include <stdio.h>
#include <fcntl.h>	// Use "open"
#include <unistd.h>	// For "close"

int main() {
	// Open the brightness file.
	FILE *fp = fopen("/sys/class/backlight/acpi_video0/brightness", "w+");
	// Adjust brightness value.
	fprintf(fp, "5");
	// End.
	fclose(fp);
	return 0;
}

Then compile the file, change ownership to root, and set SUID:

$ gcc -o testing testing.c
$ sudo chown root:root testing
$ sudo chmod u+s testing

Now run the executable as regular user and it will change the brightness:

$ ./testing # boom! brightness changes

It was segfaulting because the binary did not have enough permissions to open the file.

Just one note about iridium: The control file inside the .deb package provided by the developers specifies a version of libfontconfig1 that's higher than what's available in the Devuan ASCII repositories. However, the browser does work just fine with the older version of libfontconfig1 that Devuan ASCII uses. The workaround is to unpack the .deb, delete the specified libfontconfig1 version number, and repack the .deb before installing it. Then it works like a charm.

Thank you very much for that, ToxicExMachina. Great find!!! My laptop does happen to run Libreboot. I had not heard of nvramcui (or its cousin, nvramtool) before. Very interesting.

According to this, Libreboot locks the CMOS table, so the only way to modify BIOS settings is to download the Libreboot rom, modify it with nvramtool, then flash the modified rom.

Alas, touchpad does not seem to be an option in my CMOS table:

$ sudo nvramtool -a
boot_option = Fallback
baud_rate = 115200
debug_level = Spew
sata_mode = AHCI
power_on_after_fail = Disable
first_battery = Primary
bluetooth = Enable
wwan = Enable
wlan = Enable
trackpoint = Enable
fn_ctrl_swap = Disable
sticky_fn = Disable
boot_devices = 
boot_default = 0x0
power_management_beeps = Enable
low_battery_beep = Enable
uwb = Disable
hybrid_graphics_mode = Integrated Only
gfx_uma_size = 256M
volume = 0x3

This is the closest I've come to a software solution.

Cool! I love distros like this. Thanks for pointing it out.

Tiny Core Linux, which I have grown to really appreciate, has some similarities: Busybox init, Busybox userland, minimalistic package manager. Differences are that it uses glibc (instead of musl) and--the biggest difference--that it's designed in such a way that, at every boot, the system is rebuilt from a "fresh install" based on the instructions you provide.

There are four places where the user provides instructions:
1. Boot loader "boot codes"
2. List of packages to load
3. A special tarball that holds your configuration files
4. Startup jobs in /opt/bootlocal.sh (root jobs) and in ~/.X.d/ (normal user jobs)

At most, only /opt and home directories are persistent. It's an ingenious design that gives you quite the clean feeling because all changes to the base system are in only one of these four places and can be reverted by simply editing a file or tarball then rebooting.

You can read all about it here: http://distro.ibiblio.org/tinycorelinux/corebook.pdf

Thank you for that, fsmithred.

I can confirm that if I remove the executable bit from dbus-launch and dbus-daemon, yad is still able to create the notification icon. However, if dbus-launch and dbus-daemon are executable, dbus is consistently launched each time yad creates an icon. This is very strange.

I'll ask yad's developer and will keep exploring. I'll take a look at some PPIDs to exclude the possibility that some other utility/daemon is starting dbus when yad is detected.

@fsmithred - On your no-dbus system, are you able to create a system tray icon using yad? What happens when you run $ yad --notification --image=dialog-ok --text="testing" &?

I redirected the script's stderr to a log to investigate what's going on when pgrep -f 'regex' && foo fails to work as expected.

Lo and behold, a bunch of "pgrep: write error" entries show up in the log.

So it seems the issue here is that when a shell script runs in the background, pgrep gets grumpy unless its stdout is redirected somewhere (even if only to /dev/null).

HevyDevy, wifi-monitor is a barebones shell script that assumes the user only uses wifi, never ethernet.

What you are suggesting would certainly be possible, but the more complex logic would require an overhaul of the script.

Feel free to adapt the script to suit your needs. If you run into issues, email me on here and I'll try to help.

@HevyDevy - I looked around and the only utility I could find to easily put an icon and tooltip in the system tray is yad. It's either yad or roll your own...

...so I did roll my own tiny alternative to yad using python:

#!/usr/bin/python3

import sys
from PyQt4 import QtGui, QtCore

def show_icon(icon, tooltip):
	class SystemTrayIcon(QtGui.QSystemTrayIcon):
		def __init__(self, icon, parent=None):
		   QtGui.QSystemTrayIcon.__init__(self, icon, parent)
		   self.setToolTip(tooltip)
		def exit(self):
		  QtCore.QCoreApplication.exit()

	app = QtGui.QApplication(sys.argv)
	w = QtGui.QWidget()
	trayIcon = SystemTrayIcon(QtGui.QIcon(icon), w)
	trayIcon.show()
	sys.exit(app.exec_())

icon=sys.argv[1]
tooltip=sys.argv[2]
show_icon(icon, tooltip)

If you'd like to try it:
1. Paste this code into a blank text file, name it show-icon, put it somewhere in your PATH, make it executable
2. Install the script's two dependencies: $ sudo apt install python3 python3-pyqt4
3. Test it: $ show-icon /path/to/icon.png "hello world" &

If the yad test I suggested in post #5 doesn't work, try this python script. If the python script ("show-icon") works, let me know and I can customize wifi-monitor for you (to use show-icon instead of yad).

Thanks, fsmithred. Good to know it works in Beowulf with lxpanel

It should work in Xfce as well. Note that, in the interest of simplicity, the icon only shows up when internet is connected. If there is no internet connectivity, then no icon is the expected behavior.