How does journald know the PID of a process that produces log data?












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When I look at journalctl, it tells me the PID and the program name(or service name?) of a log entry.



Then I wondered, logs are created by other processes, how do systemd-journald know the PID of these processes when processes may only write raw strings to the unix domain socket which systemd-journald is listenning. Also, do sytemd-journald always use the same technique to detect the PID of a piece of log data even when processes are producing log using functions like sd_journal_sendv()?



Is there any documentation I should read about this?






systemd-journald ipc






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    0














    When I look at journalctl, it tells me the PID and the program name(or service name?) of a log entry.



    Then I wondered, logs are created by other processes, how do systemd-journald know the PID of these processes when processes may only write raw strings to the unix domain socket which systemd-journald is listenning. Also, do sytemd-journald always use the same technique to detect the PID of a piece of log data even when processes are producing log using functions like sd_journal_sendv()?



    Is there any documentation I should read about this?






    systemd-journald ipc






    share

























      0












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      0







      When I look at journalctl, it tells me the PID and the program name(or service name?) of a log entry.



      Then I wondered, logs are created by other processes, how do systemd-journald know the PID of these processes when processes may only write raw strings to the unix domain socket which systemd-journald is listenning. Also, do sytemd-journald always use the same technique to detect the PID of a piece of log data even when processes are producing log using functions like sd_journal_sendv()?



      Is there any documentation I should read about this?






      systemd-journald ipc






      share













      When I look at journalctl, it tells me the PID and the program name(or service name?) of a log entry.



      Then I wondered, logs are created by other processes, how do systemd-journald know the PID of these processes when processes may only write raw strings to the unix domain socket which systemd-journald is listenning. Also, do sytemd-journald always use the same technique to detect the PID of a piece of log data even when processes are producing log using functions like sd_journal_sendv()?



      Is there any documentation I should read about this?






      systemd-journald ipc




      systemd-journald ipc





      share












      share










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