The traditional cron's manpage crontab(5) discusses the issue that one can specify the day of a calendar event with two different fields: day of month and day of week. The same is true for systemd.time, where one could write Mon,Fri *-*-3,1,2 *:30:45 Following cron's interpretation, this would mean the calendar event is trigger on the first three days of a month *and* on every Monday or Friday. Does the same hold for systemd.time? The documentation (man page) should specify this explicitly.
I do not believe that is how systemd.time works. As is noted in the man page: "Calendar events may be used to refer to one or more points in time in a single expression. They form a superset of the absolute timestamps explained above: Thu,Fri 2012-*-1,5 11:12:13 The above refers to 11:12:13 of the first or fifth day of any month of the year 2012, given that it is a Thursday or Friday." I read this as saying that only days which are both Thurs/Fri AND 1/5 would be included. I tested this by creating a timer which included "OnCalendar=Thu,Fri 2015-*-5 11:12:13". I then started it on Thur 2014-12-31 and ran "systemctl list-timers", which showed the service would run on Thur 2015-02-05, the next day which is the fifth calendar day of a month and a Thursday.
Documentation updated in http://cgit.freedesktop.org/systemd/systemd/commit/?id=a780d4cb1c. This should clear up the issue.
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