Debian not taking daylight saving time into account in R - r

Question

I use following code to find whether daylight saving is in use in Central Europe in day given by variables year, month and day.
timeString = paste(toString(year), formatC(month, width = 2, flag="0"), formatC(day, width = 2, flag="0"), "12", sep = "-")
time = strptime(timeString, format = "%Y-%m-%d-%H")
diff = as.numeric(as.POSIXct(time, tz="UTC") - as.POSIXct(time, tz="Europe/Prague"))
On my PC (Ubuntu 16.04), diff is 2 when daylight saving is active, 1 othervise, but on server with Debian 8.8 it is 1 in all cases. Do you know how to set-up the server to behave as Ubuntu? Thanks.
Update: The change of Debian time settings would also change time used for crontab, which is undesirable. Reinstaling R with new configuration seemed risky becase there runs a few R script operationally every few minutes. So i chose "ugly" solution in form of R function:
DaylightSaving = function(year, month, day) {
# years 2010-2030
if (year < 2010 || year > 2030) {
stop("The function is implemented now only for years 2010-2030")
}
dayStart = c(28, 27, 25, 31, 30, 29, 27, 26, 25, 31, 29, 28, 27, 26,
31, 30, 29, 28, 26, 25, 31)
dayEnd = c(31, 30, 28, 27, 26, 25, 30, 29, 28, 27, 25, 31, 30, 29,
27, 26, 25, 31, 29, 28, 27)
if (month < 3 || month > 10) {
return(FALSE)
} else if (month == 3 && day < dayStart[year - 2009]) {
return(FALSE)
} else if (month == 10 && day >= dayEnd[year - 2009]) {
return(FALSE)
}
return(TRUE)
}

Answer 1

First of all, if you want to check whether daylight saving is in use, you can simply do:
#Make a test date
atime <- as.POSIXct("2017-05-23 13:25",
tz = "Europe/Prague")
#test for DST
as.POSIXlt(atime)$isdst > 0
The POSIXlt class is internally a list with an element isdst that is 0 if daylight saving time is not active, positive when it is, and negative when that information is not available. (see ?DateTimeClasses).
I would also like to point out the following from the help pages on timezones :
Note that except where replaced, the operation of time zones is an OS
service, and even where replaced a third-party database is used and
can be updated (see the section on ‘Time zone names’). Incorrect
results will never be an R issue, so please ensure that you have the
courtesy not to blame R for them.
The problem isn't R, but your Debian installation disregarding daylight saving time. You can solve this by configuring R with the option --with-internal-tzcode, so it uses its own timezone database. But this is generally not necessary if your Debian's timezone system is set up correctly. More info on how to configure R can be found on the help page ?timezones and in the Installation and Administration manual - appendix B.
The best way to solve this, is to make sure that your Debian installation deals with daylight saving time correctly. You can start with checking whether you have a correct version of the tzdata package.
There's a similar question on unix.stackexchange.com :
https://unix.stackexchange.com/questions/274878/system-disregards-daylight-saving-time