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Old 11-04-2010, 02:23 PM
Rodolfo Medina
 
Default An experiment about file timestamp (was: Timestamps jump by one hour when switching timezone)

Chris Jackson <c.jackson@shadowcat.co.uk> writes:

> File timestamps are (or at least should be) stored in UTC. It's the
> display of them that's affected.



But I did the following experiment: on a computer with system time set to UTC,
I created a file at 14:43 UTC. Then I copied it via rsync and ethernet cross
cable to another PC with system time set to GMT, one hour late respect to UTC.
I expected that, on the 2nd PC, the timestamp was displayed in the local time,
i.e. 15:43; instead, it appears as 14:43 as well. (For the copy I used the -t
option.)

So, according with this experiment it is not true that the displayed time is in
local format.

I think this may cause serious errors: in fact, when someone read the timestamp
on the 2nd PC, he would believe that the file were created at 14:43 of the GMT
time, which is wrong: in fact, it was created at 15:43 GMT = 14:43 UTC.

What do you all think?

Rodolfo


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Old 11-04-2010, 02:57 PM
Camaleón
 
Default An experiment about file timestamp (was: Timestamps jump by one hour when switching timezone)

On Thu, 04 Nov 2010 15:23:13 +0000, Rodolfo Medina wrote:

> Chris Jackson writes:
>
>> File timestamps are (or at least should be) stored in UTC. It's the
>> display of them that's affected.
>
>
>
> But I did the following experiment: on a computer with system time set
> to UTC, I created a file at 14:43 UTC. Then I copied it via rsync and
> ethernet cross cable to another PC with system time set to GMT, one hour
> late respect to UTC. I expected that, on the 2nd PC, the timestamp was
> displayed in the local time, i.e. 15:43; instead, it appears as 14:43 as
> well. (For the copy I used the -t option.)
>
> So, according with this experiment it is not true that the displayed
> time is in local format.

(...)

Mmm, nope :-)

I think you didn't get the whole picture.

Look, it is very well explained in this Gentoo FAQ:

***
Consistent times on FAT filesystems over the whole year
https://forums.gentoo.org/viewtopic-t-579915-start-0.html
***

THT.

Greetings,

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Camaleón


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Old 12-02-2010, 08:39 AM
Lisi
 
Default An experiment about file timestamp (was: Timestamps jump by one hour when switching timezone)

On Thursday 04 November 2010 15:23:13 Rodolfo Medina wrote:


> Chris Jackson <c.jackson@shadowcat.co.uk> writes:


> > File timestamps are (or at least should be) stored in UTC. It's the


> > display of them that's affected.


>


> But I did the following experiment: on a computer with system time set to


> UTC, I created a file at 14:43 UTC. Then I copied it via rsync and


> ethernet cross cable to another PC with system time set to GMT, one hour


> late respect to UTC. I expected that, on the 2nd PC, the timestamp was


> displayed in the local time, i.e. 15:43; instead, it appears as 14:43 as


> well. (For the copy I used the -t option.)


>


> So, according with this experiment it is not true that the displayed time


> is in local format.


>


> I think this may cause serious errors: in fact, when someone read the


> timestamp on the 2nd PC, he would believe that the file were created at


> 14:43 of the GMT time, which is wrong: in fact, it was created at 15:43 GMT


> = 14:43 UTC.


>


> What do you all think?





That you have not fully understood what UTC is. UTC _is_ GMT. In winter, when we here are on GMT, my local time=UTC. So the statement 15:43 GMT


= 14:43 UTC is, I'm afraid, incorrect. 15:43 GMT = 15:43 UTC, not 14:43 UTC.


I have an idea that there may be some distinction at the atomic level between UTC and GMT. Can anyone enlighten me? Or was the decision to call it UTC in place of GMT purely political?





Lisi
 
Old 12-02-2010, 08:47 AM
Lisi
 
Default An experiment about file timestamp (was: Timestamps jump by one hour when switching timezone)

On Thursday 02 December 2010 09:39:46 Lisi wrote:
> I have an *idea that there may be some distinction at the atomic level
> between UTC and GMT. *Can anyone enlighten me?

Thanks, Chris - you foresaw my question and answered it before I asked it. ;-)

Lisi


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Old 12-02-2010, 10:06 AM
Jochen Schulz
 
Default An experiment about file timestamp (was: Timestamps jump by one hour when switching timezone)

Lisi:
>
> I have an idea that there may be some distinction at the atomic level
> between UTC and GMT. Can anyone enlighten me? Or was the decision to
> call it UTC in place of GMT purely political?

Ah, time for my favourite quote from the Java6 API documentation:

| Some computer standards are defined in terms of Greenwich mean time
| (GMT), which is equivalent to universal time (UT). GMT is the "civil"
| name for the standard; UT is the "scientific" name for the same
| standard. The distinction between UTC and UT is that UTC is based on an
| atomic clock and UT is based on astronomical observations, which for all
| practical purposes is an invisibly fine hair to split.
| -- http://download.oracle.com/javase/6/docs/api/java/util/Date.html

J.
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