[systemd-devel] [EXT] Re: Using timedatectl on a readonly rootfile system using mender

[Lennart Poettering]

On Mi, 09.09.20 09:23, Colin Guthrie (gmane at colin.guthr.ie) wrote:

> Alvin Šipraga wrote on 08/09/2020 22:54:
> > Hi,
> >
> > On 9/8/20 4:12 PM, Colin Guthrie wrote:
> >
> >> 2. Set your /etc/ master image to make /etc/localtime to be a symlink to
> >> /run/localtime and then ensure /run/localtime is a symlink to the
> >> appropriate file in /usr during early boot (e.g. in initramfs). Then
> >> when you want to to change the timezone, just update the /run/ symlink.
> > This might not work as expected - systemd sometimes assumes that
> > /etc/localtime is a symlink into /usr/share/zoneinfo and will not
> > understand double symlinks. See src/basic/time-util.c:get_timezone() for
> > at least one example.
>
> But that really depends on what you define as "not work". Sure
> timedatectl may not report correctly, but that shouldn't matter too much
> if you're not using to query or update (the latter obviously won't work
> anyway), but for the purposes of software *using* the timezone, I don't
> tihnk anything will actually break.

Actually, that's not quite true:

https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org/message/TVVXVO5HJGH5JOAWJJDJNA3BPBPPRS37/

(This is a current thread on the fedora ML)

glibc doesn't care what /etc/localtime is, but all code that wants to
know the timezone name, i.e. a string like "Europe/Berlin" generally
requires /etc/symlink to be a readable symlink.

https://www.freedesktop.org/software/systemd/man/localtime.html

Lennart

--
Lennart Poettering, Berlin