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I am playing around with journalctl and getting used to the whole systemd setup, but having a hard time defining what it is actually doing...

this site (https://www.loggly.com/ultimate-guide/using-journalctl/) says that journalctl is displaying messages from "the journal" but I can't search and find an answer to what "the journal" actually is.

what is "the journal?"

and...

  1. does journalctl eliminate the need to keep separate logs for everything?
  2. If I was to write a daemon, how can I make sure that it writes messages into "the journal" without then also writing them to a logfile for the daemon...is this possible? (I ask this because I seem to have an application statsd that does just this... there is no logfile but I can pull up its "journal" with journalctl -u statsd.service)
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The journal is the collection of messages collected and stored by systemd-journald, a component of the systemd suite. Systemd-journald collects messages from a variety of sources, including kernel messages, syslog messages and messages sent directly to it using its API; not all journaling channels are available on all systems -- see your system's documentation and man journald.conf. To get the manual pages for the systemd (including systemd-journald) API you need to install libsystemd-dev.

For more information on the journal facility, see man systemd-journald and man journald.conf. For general information about systemd system and service management suite, see systemd on freedesktop.org, and, of course, Lennart Poettering's blog Pid Eins.

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