Verify in ExecStartPre if bash binary exists

mosquetero

10/16/22, 11:50 AM

I want my service to start only if another service is not active. To do so, as explained in this other question, I am going to do:

ExecStartPre=/bin/bash -xc '/usr/bin/systemctl is-active --quiet other-unit.service && exit 1 || exit 0'

However, there is a small possibility that the OS does not include /bin/bash. In that case, I'd like the service to start anyway. I was trying to achieve this by using:

ExecStartPre=which bash 2>/dev/null && /usr/bin/bash -xc '/usr/bin/systemctl is-enabled --quiet nm-cloud-setup.service && exit 1 || exit 0' || exit 0

But systemd complains:

which[1122772]: /usr/bin/which: invalid option -- 'x'
which[1122772]: /usr/bin/which: invalid option -- 'c'
which[1122772]: /usr/bin/which: no && in (/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin)

I guess ExecStartPre= is quite limited. Is it possible to achieve what I want?

1 + 6

job-control

systemd

systemd-service

Michael Hampton

10/16/22, 1:09 PM

Why are you calling bash instead of /bin/sh?

mosquetero

10/16/22, 2:03 PM

I pasted what the other question answered. If I change to /usr/bin/sh, can I be sure that it will be part of all OS?

Michael Hampton

10/16/22, 2:07 PM

I said `/bin/sh`, not `/usr/bin/sh`. The former exists on literally everything vaguely Unix-like for the last 50 years. It's even on your phone. I said nothing about the latter and would not count on it.

mosquetero

10/16/22, 2:13 PM

ok. In that case, I don't need to check if `/bin/sh` is available, thanks. Could you write that as an answer so that I can mark the question as answered please?

Michael Hampton

10/16/22, 2:20 PM

OK. But just for curiosity I would like to know what system includes systemd but not bash.

mosquetero

10/16/22, 2:26 PM

I just wanted to cover all possible cases. I have seen one an Alpine OS using systemd because the user installed it somehow

Score:1

Server

Michael Hampton

10/16/22, 2:17 PM

Rather than calling bash, you should consider calling the Bourne shell /bin/sh which has been around pretty much since the beginning of Unix and exists on literally everything Unix-like, all the way down to your phone. (Though on modern systems it is generally substituted with a slightly more capable shell that runs in Bourne shell compatibility mode when called as /bin/sh.)

0 + 0

Elon Musk

I sit in a Tesla and translated this thread with Ai:

EN: Verify in ExecStartPre if bash binary exists

TH: ตรวจสอบใน ExecStartPre ว่ามี bash binary อยู่หรือไม่

RO: Verificați în ExecStartPre dacă există binarul bash

RU: Проверьте в ExecStartPre, существует ли двоичный файл bash.

VI: Xác minh trong ExecStartPre nếu nhị phân bash tồn tại

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