Systemd user service that monitors the desktop screensaver over DBus and sends an HDMI-CEC Active Source command when the screen unlocks, waking an attached TV or display.

cec_wake_daemon subscribes to ActiveChanged signals from all common screensaver DBus interfaces (GNOME, KDE, Cinnamon, freedesktop). When the signal fires with is_active=False (unlock), it invokes cec-client with as\nquit\n (Active Source + exit). Active Source is preferred over on 0 because it does not assume the TV occupies logical address 0 in all HDMI topologies.

A udev rule (99-cec.rules) creates /dev/cec as a stable symlink for any USB CEC adapter whose product string contains "CEC" and grants seat-local write access via uaccess, so no supplemental groups are required.

The daemon is a systemd user unit, runs as the logged-in user, and integrates with sd_notify for Type=notify-style readiness signalling.

All packages are available in RHEL/AlmaLinux base repos or EPEL:

# Build from a source archive tagged v0.1.0
rpmbuild -ba cec-wake.spec

# Install
sudo dnf install ./cec-wake-0.1.0-1.<dist>.noarch.rpm

# Enable and start for your user session
systemctl --user daemon-reload
systemctl --user enable --now cec-wake.service

install -D -m 0755 cec_wake_daemon.py ~/.local/bin/cec_wake_daemon.py
install -D -m 0644 cec-wake.service \
    ~/.config/systemd/user/cec-wake.service

# Udev rule requires root
sudo install -D -m 0644 99-cec.rules \
    /usr/lib/udev/rules.d/99-cec.rules
sudo udevadm control --reload-rules
sudo udevadm trigger --subsystem-match=usb

systemctl --user daemon-reload
systemctl --user enable --now cec-wake.service

After installing the udev rule, replug the CEC adapter so the symlink and uaccess tag are applied.

The daemon accepts command-line arguments. Override them in the service unit via a drop-in:

systemctl --user edit cec-wake.service

[Service]
ExecStart=
ExecStart=/usr/libexec/cec_wake_daemon --adapter /dev/cec1 --wake-on-start

• org.freedesktop.ScreenSaver
• org.gnome.ScreenSaver
• org.kde.screensaver
• org.cinnamon.ScreenSaver

Interfaces not present on the running desktop are skipped silently. The daemon exits if none can be subscribed.

Check service status and logs:

systemctl --user status cec-wake.service
journalctl --user -u cec-wake.service -f

Verify the device symlink and permissions:

ls -l /dev/cec
# Confirm the adapter is accessible (exit 0 = writable)
test -w /dev/cec && echo ok

Test CEC manually:

echo -e "as\nquit" | cec-client -s /dev/cec

If /dev/cec does not appear after replugging, check that the product string contains "CEC":

udevadm info --query=all --name=<device> | grep PRODUCT

Why a user unit? The daemon subscribes to the session DBus, which is only reachable from within a user session. A system unit cannot subscribe to per-user session buses portably.

Why as instead of on 0? Active Source broadcasts to all CEC devices and does not require knowing the TV's logical address, which varies by topology.

Why synchronous subprocess.run? cec-client completes in under two seconds. GLib dispatches one signal callback at a time. A threading lock drops duplicate ActiveChanged(False) signals that arrive while a call is in flight. The added complexity of async dispatch is not justified.

Why uaccess instead of a supplemental group? uaccess is the systemd-recommended mechanism for seat-local device access. It requires no group membership changes and is revoked when the user's session ends.

GPL-3.0-or-later