Explain daemon log levels and journal filtering

The README gives the short log form and the meaning of each level. The
journal example selects warnings and errors without the normal events,
so a user can find the failures that need attention.

diff --git a/README.rst b/README.rst
index 16aabce997910ca3c9257a7e47e82d45f9d0617f..18af25626790ed7c2defd843f576c503b4fa3130 100644 (file)
--- a/README.rst
+++ b/README.rst
@@ -219,6 +219,34 @@ login. To stop it, or also remove its start at login:
    systemctl --user stop onechat.service
    systemctl --user disable onechat.service
 
    systemctl --user stop onechat.service
    systemctl --user disable onechat.service
 

+************
+ Daemon log
+************
+
+The daemon writes short events with the part prefix and ordered
+``key=value`` attributes. An error cause comes last. Normal events use
+info, failures that can be retried or lose nothing use warning, and
+failures that lose data or stop work use error.
+
+With ``JOURNAL_STREAM`` set, each line carries a syslog priority without
+a time stamp or level word. The user journal can show only warnings and
+errors:
+
+.. code:: console
+
+   journalctl --user -u onechat -p warning
+
+The summary warning names its node. A schedule run has ``late`` only
+when it ran late:
+
+.. code:: text
+
+   <4>onechat: summary failed level=0 index=0: fake failure
+   <6>onechat: schedule ran id=1
+   <6>onechat: schedule ran id=2 late=1m0s
+
+Outside the journal, each line starts with the time stamp and level.
+

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