Timezone conversion on Ubuntu 20.04

Am Samstag, 25. April 2020, 01:02:38 CEST schrieb Jeroen Ooms:

Hi all,

I am testing R 4.0 and ran into an issue with timezones on Ubuntu
Focal: converting a timestamp to another timezone results in NA:

  as.POSIXct(as.POSIXlt(Sys.time(), tz = "CET"), tz = "EST")

This only happens on Ubuntu Focal, it seems to work fine on Ubuntu
Bionic. I am the standard ubuntu docker image icw/ r-base from Dirk's
ppa:edd/r-4.0 on both systems.

works fine using the backported R 4.0.0 on Debian buster:

R> as.POSIXct(as.POSIXlt(Sys.time(), tz = "CET"), tz = "EST")
[1] "2020-04-25 10:05:29 EST"

Perhaps the root cause of the change in behavior is that on the
focal/bullseye docker images, /usr/bin/timedatectl exists, but it does
not work:

   root at focal:/# timedatectl
   System has not been booted with systemd as init system (PID 1).
Can't operate.
   Failed to create bus connection: Host is down

R assumes that if it timedatectl exists, it can be used. On the docker
image of bionic and buster, timedatectl simply is not installed so R
does not call it.

The consequence though, is very subtle changes in behavior of time
conversion edge cases that I cannot explain. For example we get
differences between "UTC" and "Etc/UTC":

Sys.timezone()

[1] "Etc/UTC"
# System has not been booted with systemd as init system (PID 1). Can't operate.
# Failed to create bus connection: Host is down
Warning message:
In system("timedatectl", intern = TRUE) :
  running command 'timedatectl' had status 1

as.POSIXct(strptime("24.04.2020 01:00", format = "%d.%m.%Y %H:%M", tz
= "CET"), tz = "")
[1] NA

as.POSIXct(strptime("24.04.2020 01:00", format = "%d.%m.%Y %H:%M", tz
= "CEST"), tz = "")
[1] "2020-04-24 01:00:00 UTC"

as.POSIXct(strptime("24.04.2020 01:00", format = "%d.%m.%Y %H:%M", tz = "CET"), tz = "Etc/UTC")

[1] NA

as.POSIXct(strptime("24.04.2020 01:00", format = "%d.%m.%Y %H:%M", tz = "CET"), tz = "UTC")

[1] "2020-04-24 01:00:00 UTC"