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I'm working on scripts to power the TV connected to my Mac (running Linux) on and off. These scripts make use of the cec-ctl util (part of video4l), which control the CEC pin of the HDMI output.

The main goal is to switch the TV off on shutdown (but not when rebooting).

So, how can I setup a systemd service/unit to execute a script as the last thing before powering off, but not when rebooting?

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    This question is similar to: How to run a script with systemd right before shutdown?. If you believe it’s different, please edit the question, make it clear how it’s different and/or how the answers on that question are not helpful for your problem. Refer to this answer: unix.stackexchange.com/a/39250/260833 Commented Jul 17, 2024 at 10:05
  • @ArtemS.Tashkinov, the question is clearly different as it specifies the script must be run when powering off and not when rebooting. The answers provided in the referred question you point to (which I have seen before asking here) doesn't differentiate the scenarios (and the proposed solutions there don't work as they execute the script in both scenarios). Thank you Commented Jul 17, 2024 at 15:10
  • The automatically-posted boilerplate text is sometimes oversimplified and misleading, by which I mean wrong.  We consider a question to be a duplicate if the other thread contains the answer to this one. … (Cont’d) Commented Jul 17, 2024 at 20:02
  • (Cont’d) …  Look at Piotr Jurkiewicz’s answer: “add [a] script executable to the /usr/lib/systemd/system-shutdown directory.”  The script will be run with one argument: “either "poweroff", "halt", "reboot" or "kexec", depending on the chosen action.”  So you should try writing a script that looks at its argument and switches the TV off if the argument is "poweroff" (or "halt"?), but not "reboot". Commented Jul 17, 2024 at 20:02
  • @G-ManSays'ReinstateMonica', although Piotr's answer doesn't really anser my original question, which is how to perform this using service/unit, his proposed solution using the/usr/lib/systemd/system-shutdown/ directory is a simpler to address the specified problem. Thank you. OBS: After some research on how to do this, I did found a way of doing this using a service (I'll answer my own question), but a simpler solution will be better. Commented Jul 18, 2024 at 23:34

3 Answers 3

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I tried to start a script, when powering off and it worked.
Made a service unit called myservice.service

[Unit]
Description=Run mycommand at shutdown
DefaultDependencies=no
Before=poweroff.target

[Service]
Type=oneshot
ExecStart=/usr/bin/bash -->absolute path to script<--

[Install]
WantedBy=poweroff.target

placed it in /usr/lib/systemd/system and enable it systemctl enable myservice.service

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  • did you test this to be sure it does not run the script when doing a reboot? Commented Jul 18, 2024 at 19:05
  • @ron yes i tested it, no action on reboot. Does it not work on your system? Commented Jul 19, 2024 at 16:24
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few notes on the service and the script:

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  • This doesn't really answer the question. Although useful, it should be added on comments instead. Commented Jul 18, 2024 at 20:20
  • i would have if the comments allowed that much detail Commented Jul 18, 2024 at 20:26
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After some deep research on how to execute a script using a service/unit but only when the system is being powered off, I managed to find a conditional execution that determines if this is a power down using the systemctl list-jobs command:

Determining within a script if the system is going to poweroff:

jobs=$(systemctl list-jobs)

if echo "$jobs" | grep -q "poweroff.target.*start"; then
  echo "System is going to poweroff"
  exit 0
fi

Anyway, as pointed out by @G-ManSays'ReinstateMonica ' in a comment, Piotr Jurkiewicz’s answer to a similar question proposes a simpler soluction that does address the specified objective. (Thank you @G-ManSays'ReinstateMonica for raising this to my attention. Really appreciated)

OBS: The only actual advantage this approach offers over Piotr's approach is that it allows the script to be run before filesystems get mounted readonly. But to achieve the goal I had when asking, it didn't make any difference anyway.

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