A second environment.d file setting the same variable deletes the first one's value

scope: generic · severity: trap · confidence: proven · subsystem: media

Evidence

taimen 2026-08-30: device-google-taimen r36’s 60-taimen-av1.conf silently dropped soc-qcom-gstreamer’s v4l2 ranks

environment.d has no append. A later file assigning a variable REPLACES the earlier value outright, and nothing warns you – not the package build, not the boot, not the app that quietly loses the setting.

This bit a real device. soc-qcom-gstreamer-systemd ships /etc/environment.d/50-soc-qcom-gstreamer.conf, promoting the hardware decoders:

GST_PLUGIN_FEATURE_RANK=v4l2vp8dec:SECONDARY,v4l2vp9dec:SECONDARY,
v4l2h264dec:SECONDARY,v4l2h265dec:SECONDARY,v4l2mpeg2dec:SECONDARY,...

The device package then shipped 60-taimen-av1.conf to demote AV1, which the SoC cannot decode. 60 sorts after 50, so the running session had only:

$ systemctl --user show-environment | grep GST
GST_PLUGIN_FEATURE_RANK=dav1ddec:NONE,av1dec:NONE

Every v4l2 promotion was gone. The demotion existed because Venus decodes VP9 in hardware instead – and it deleted the ranks that said so. The package was working against itself, and the symptom is invisible: video still plays, just in software, hot and slow.

The fix is one line: reference the variable instead of replacing it.

GST_PLUGIN_FEATURE_RANK=${GST_PLUGIN_FEATURE_RANK},dav1ddec:NONE,av1dec:NONE

environment.d(5) expands ${VAR} against what earlier files already set, so this appends. If the other package is absent the reference expands to nothing and the value gains a leading comma, which GStreamer tolerates – checked with GST_PLUGIN_FEATURE_RANK=",dav1ddec:NONE" gst-inspect-1.0 dav1ddec, which reports rank none (0), identical to the value without it. No guard needed.

Check it without a session restart. The variable only reaches apps through the user manager, so a plain env in an ssh session tells you nothing. Run the generator directly:

/usr/lib/systemd/user-environment-generators/30-systemd-environment-d-generator

It prints the merged result exactly as the manager will compute it, which is also how you test a candidate fix before packaging it.

Generalise this. Before adding an environment.d drop-in, grep every environment.d directory for the variable you are about to set:

grep -rs '^YOUR_VAR=' /etc/environment.d /usr/lib/environment.d

If anything already sets it, reference it or you will delete it. The same holds for any last-writer-wins drop-in directory – this is not specific to GStreamer, and shipped-configuration-is-not-running-configuration is the law it belongs to: the file you shipped is not the value the process reads.