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A general description is here.
‘Sys.timezone(location = FALSE)’ is defunct, and is ignored (with a warning).
‘Sys.timezone()’ tries even more heuristics on Unix-alikes. As some of these ways are slow, the value is cached at first use in a session. For the slowest method, a warning is given recommending that ‘TZ’ is set to avoid the search.
The same ways are now used to find the system timezone to pass the code used when R is configured with ‘--with-internal-tzcode’.
‘Sys.timezone()’ tries more heuristics on Unix-alikes and so is more likely to succeed (especially on Linux).
‘Sys.timezone(location = FALSE)’ (which was a stop-gap measure for Windows long ago) is deprecated. It no longer returns the value of environment variable ‘TZ’ (a location).