Question
How can one change the dateformat of syslog entries?
Answer
This is done via setting the UCR var syslog/template/default according to https://www.rsyslog.com/doc/v5-stable/configuration/templates.html#string-based-templates:
ucr set syslog/template/default=RSYSLOG_FileFormat
afterwards the service needs to be restarted to reload the config:
service rsyslog restart
Now you should see something like
2021-01-14T13:58:41.520135+01:00 ucs-6956 systemd[1]: Started System Logging Service.
instead of
Jan 14 13:58:34 ucs-6956 nagios: Auto-save of retention data completed successfully.