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I wrote a program which automatically shuts down a Raspberry Pi 3b (Ubuntu Server 16.04) as soon as a button is pressed. It's nothing than a small bash script which reads a GPIO pin of the Pi every second and shuts down the device if the button is pressed.

However, I made a mistake and the condition is always true, meaning that the program shuts down the Pi as soon as it is started. Because of incredible stupidness, I already linked this program to systemd ('After=multi-user.target'). Meaning: as soon as the Pi finished booting, it shuts itself down again. I don't see any chance to interrupt this process. Is there a way to edit the '/boot/config.txt' in a way that certain 'systemd' processes are suppressed? Any other idea how I could fix this system? On my Mac I only see the boot partition and my Linux computer has no SD Card slot.

P.S.: I flashed one of these images to the SD card in the beginning https://ubuntu-pi-flavour-maker.org/download/ using 'dd'. P.S.2: Shutdown is initialized by 'poweroff'

Jeff Schaller
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h_uat
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    Common sense says it is time to buy an adapter. – Rui F Ribeiro Jun 23 '18 at 19:44
  • Have you tried forcing the system to boot into a different systemd target other than multi-user ? Check this answer which describes setting it up during boot. https://unix.stackexchange.com/a/252953/151609 – Jeff Jun 24 '18 at 01:36
  • The thing was that I somehow could not interrupt the boot process by key combinations. Not sure if this is a Pi specific thing. – h_uat Jun 24 '18 at 06:04
  • SD card adapter is ordered ;) – h_uat Jun 24 '18 at 06:05

2 Answers2

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With systemd for init, systemd's rescue target can be reached by appending systemd.unit=rescue.target (or emergency.target if that fails) to the boot command line in /boot/cmdline.txt.

If this doesn't work for some reason, or on a non-systemd system, instead add init=/bin/sh to the end of the line, which will cause the system to completely bypass anything to do with init.

You may need to mount the filesystem read-write in order to make any modifications. You may do this by appending rw to the boot command line, or issue mount -o remount,rw / upon boot.

multithr3at3d
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  • This is exactly what I was searching for! By adding init=/bin/sh to /boot/cmdline.txt I could edit my script after remounting the sd card by mount -o remount.rw /. Thanks a million, you saved my day / week! – h_uat Jun 24 '18 at 05:58
  • This answer is the wrong way around. Rescue and emergency modes, with -s and -b and their various synonyms, are the right first and second things to try, whereas init=/bin/sh is a poor idea for the reasons explained at https://unix.stackexchange.com/a/197472/5132 and https://unix.stackexchange.com/a/195978/5132 and should be a third choice, if used at all. The systemd doco also says this. – JdeBP Jun 24 '18 at 18:50
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systemd scan kernel argument . to disable for example cron.service add to your boot loader:

systemd.mask=cron.service

If you have access to config.txt , you must modify to cmdline.txt .

Source :

https://www.raspberrypi.org/documentation/configuration/config-txt/boot.md

Source : https://www.freedesktop.org/software/systemd/man/kernel-command-line.html

EchoMike444
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