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nickjacob/systemd-prblm.service

Last active March 17, 2023 16:11
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execute arbitrary bash code/variable substitution in systemd units
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systemd-prblm.service
[Unit]
Description=Demonstrate Bash
[Service]
ExecStartPre=/usr/bin/bash -c "/usr/bin/systemctl set-environment MYVAR=$(( 2 + 2 ))"
ExecStart=/usr/bin/echo "2 + 2 = ${MYVAR}"
@KalanaDananjaya
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KalanaDananjaya commented Mar 17, 2023 •
edited

Beware that there's a pitfall if you have to use %s with your command.
echo (date +%s)
SystemD sees this as user shell and resolve to /bin/sh instead. You need to use %%s to avoid that.

EnvironmentFile=/tmp/timestamp.txt
ExecStartPre=/bin/bash -c "echo TIMESTAMP=$(date +%%s) > /tmp/timestamp.txt;"

Although this seems simple, it was quite hard to find this info. ChatGPT was not yielding a correct result either.

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