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Message-ID: <20230211144220.GG4163@brightrain.aerifal.cx>
Date: Sat, 11 Feb 2023 09:42:21 -0500
From: Rich Felker <dalias@...c.org>
To: alice <alice@...ya.dev>
Cc: musl@...ts.openwall.com, "yubing (C)" <yubing12@...wei.com>,
liudongxu <liudongxu3@...wei.com>,
"wangyunhe (A)" <wangyunhe@...wei.com>,
qiuguorui <qiuguorui1@...wei.com>,
"Wanglieming (VRP SSP)" <wanglieming@...wei.com>
Subject: Re: Time zone has not updated after call tzset()
On Sat, Feb 11, 2023 at 03:30:58PM +0100, alice wrote:
> On Sat Feb 11, 2023 at 3:20 PM CET, Rich Felker wrote:
> > On Sat, Feb 11, 2023 at 03:10:40PM +0100, alice wrote:
> > > On Sat Feb 11, 2023 at 7:53 AM CET, zhoujingqiang (A) wrote:
> > > > Hello,
> > > >
> > > > Normally, /etc/localtime is a soft link to a file that stores time zone
> > > > information.
> > > >
> > > > Without setting the TZ environment variable, I change the time zone by
> > > > changing the file linked to /etc/localtime. After calling tzset(), I find that
> > > > the time zone does not change. The test code is as follows:
> > >
> > > musl does not support changing the timezone while running.
> > > see https://www.openwall.com/lists/musl/2017/06/09/9 ,
> > > for a response to an identical bug report
> > >
> > > tl;dr without semantics: you have to restart a running process to get a new
> > > timezone.
> >
> > This is not quite accurate. It does, but only via application intent,
> > in the form of changing its value of TZ. It does not re-scan files if
> > the application doesn't do that, for two important reasons:
>
> yes, with the semantics, something like:
>
> setenv("TZ", "something", 0);
> tzset();
> unsetenv("TZ");
>
> will update to a new /etc/localtime symlink. it's mentioned in
> https://marc.info/?l=musl&m=141374003126007&w=2
> from the above thread.
>
> (apologies, i worded that poorly; what i mean is you cannot rely on /
> etc/localtime being read on update (without the hack above), which was the
> question. setenv("TZ") is also supported, of course.)
One small note: if you unsetenv afterwards like that, you'll never get
to use the newly selected zone since the next tz-using operation will
implicitly perform another tzset (as required by POSIX).
Rich
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