This visual model follows a typical systemctl request from the command line through systemd and into a running service.
User Types Command
systemctl restart httpd
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systemctl
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D-Bus Request
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systemd
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Service Unit
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fork()
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exec()
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Running Process
httpd
The command typed at the shell is only the visible beginning of the operation. The request is sent to systemd using D-Bus, where the appropriate service unit is located and processed.
Systemd then creates or manages processes using mechanisms such as fork() and exec(). The final result is a running service that performs the requested work.
This diagram serves as a bridge between command-line actions and the deeper topics explored throughout HCAW.