Joubu: I did it. It shows:  An ExecStart= process belonging to unit mariadb.service has exited.
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░░ The process' exit code is 'exited' and its exit status is 1.
Aug 04 09:27:13 library systemd[1]: mariadb.service: Failed with result 'exit-c>
░░ Subject: Unit failed
░░ Defined-By: systemd
░░ Support: https://www.debian.org/support
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░░ The unit mariadb.service has entered the 'failed' state with result 'exit-co>
Aug 04 09:27:13 library systemd[1]: Failed to start mariadb.service - MariaDB 1>
░░ Subject: A start job for unit mariadb.service has failed
░░ Defined-By: systemd
░░ Support: https://www.debian.org/support
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░░ A start job for unit mariadb.service has finished with a failure.
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░░ The job identifier is 291585 and the job result is failed.
Aug 04 09:27:13 library systemd[1]: mariadb.service: Consumed 1.693s CPU time.
░░ Subject: Resources consumed by unit runtime
░░ Defined-By: systemd
░░ Support: https://www.debian.org/support
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░░ The unit mariadb.service completed and consumed the indicated resources.