From: seismo!cuuxb!dlm (Dennis L. Mumaugh) Subject: Default timezone

Our reasoning is that in the majority of cases this is an error by the system administrator in setting or exporting the TZ variable and it is necessary for someone to notice the error. As it stands most developers/porters set the TZ to their local time zone (who is it that uses PST?!) and then never notice that their product has problems.

What "problems" does setting TZ to the local time zone (which *IS* PST here where we do *our* development) disguise, and why does defaulting to GMT if TZ is missing or empty reveal them?

Using wall clock as default merely propogates this development problem and results in products having problems when they are used in other environments.

So does setting TZ in "/etc/init". The only way to flush these problems out before the product is released is to *deliberately* run it with timezones other than the developers' zone.

From: seismo!cuuxb!dlm (Dennis L. Mumaugh) Subject: Re: Parsing /etc/TIMEZONE

I do like the idea of a single place for establishing the TZ for a system. It makes it very easy for new administrators.

Olson's scheme has this, as well; you just use the "-l" flag when running "tic". It causes a link name "localtime" to be made to the time zone specified as the argument to "-l".

Another problem with a routine to read and parse /etc/TIMEZONE is what does one do for non-ATT shells (c shell and others) the setting of TZ in the environment differs. That's why having /etc/init set things up is good. That guarentees a "standard environment". It is true someone could diddle with it, but I am more concerned with naive users than others.

You're going to need a routine to read and parse "/etc/TIMEZONE" anyway. "uucico" will have to use it; it does NOT want to use "TZ" to indicate what the local time zone is, precisely *because* somebody could diddle with it.

From: Robert Elz <seismo!munnari!kre> Subject: Re: Default timezone

Date: Wed, 17 Dec 86 11:09:09 cst From: cuuxb!dlm (Dennis L. Mumaugh) Message-ID: <8612171709.AA08584@cuuxb>

The issue here really, is how does a programmer exercise his "conscious choice" to get wall clock time?

If you wanted to define /etc/TIMEZONE or something as a file containing the right TZ string, so that programs that need wall clock time would be required to go read (and parse) that file, then that would be a solution. But you had better be prepared to define the format and name of that file, and stick to it forever more. You should also be prepared to go and find all the standard processes that need this (like uucico, and others) and insert the relevant code.

Actually, any scheme would require you to find all the processes that understand this, and insert some code to ensure that the machine's time zone is used.

Personally, I prefer a slightly simpler interface. That doesn't preclude putting the information in a file, of whatever format you prefer, but it should be the time functions that read the file, not the user's code.

Absolutely. This could be done in the S5R3.1 scheme, by providing a function to read "/etc/TIMEZONE". You could even call this function "settz()" (see below).

This also allows for more implementor flexibility, she has lots of choices she can make as to how to obtain the local wallclock time - from a simple ascii file, from a precompiled binary file, from a network information server, from the kernel via a system call, and I assume lots of others. I can even imagine processors where local time might be available as an instruction in the instruction set (I can imagine such processors because we have one...)

Do you mean "local wallclock time" or "local conversion rules"? With current UNIX interfaces, and with all the proposals that have popped up so far, all you could do is get the latter and use them to convert the result of "time()" to local wallclock time.

Certainly having local wall clock time be the default when TZ is not set is a very sensible way to do things, as it means that the system administrator doesn't need to set up TZ for every process in the system,

The S5R3.1 scheme does handle this, by having "init" put the time zone in its environment.

Most of the people on this list seem to feel that the right way for a program to choose wallclock time explicitly, is to putenv() TZ to a null value. Personally, I still think settz() is a cleaner interface.

Actually, "settz()" could be implemented in the S5R3.1 scheme. Assume that the time conversion code takes some string and uses it to set up the conversion rules (details deliberately left unspecified). "tzset" would use the value of 'getenv("TZ")' for this string. "settz" would do the following: if its argument is a null pointer, read "/etc/TIMEZONE" and use the string located therein; if its argument is a pointer to a null string, use GMT; otherwise, use its argument as the string in question. There is one issue here; should a process only be able to affect how its UNIX time <-> local time conversions are done, or should it also be able to affect any children it spawns? The former is effected by "settz"; as it stands, the later requires you to change TZ, either by eliminating it, nulling it out, or setting it from "/etc/TIMEZONE". "uucico" would probably want to affect its children; some other program might not. I do have another question; are we discussing UNIX or POSIX here? If the latter, should POSIX require that anything be supported other than local machine time? It may be convenient to permit users to specify other time zones, but user convenience is somewhat outside the scope of 1003.1, at least. POSIX should not *preclude* a user overriding the default time zone, and as such must provide a way for a process to override the user's override and get the default timezone; it probably must also provide a way to force its children to use the default time zone, as well. For this, all you need is a function that says "set time zone to the default"; the full generality of "settz" isn't necessary. You could have POSIX just define the behavior of "settz(char *)NULL)" and leave the rest up to the implementation. POSIX must also require that an application must, by default, get some "reasonable" time zone information, which would either be the system default time zone or, if supported, a user-specified time zone. It must do so in such a way that no application need explicitly set up anything (such as snarfing the right value of TZ from "/etc/TIMEZONE") in order to get this information, and in such a way that no application need be run in a special environment (i.e., saying "the way you set it is to put it in "/etc/profile" is out). Olson's scheme provides most of what is needed from the POSIX standpoint. "settz" could be added to the S5R3.1 scheme, and it would be equivalent (from the program's standpoint) to Olson's scheme. Both Olson's scheme, and the S5R3.1 scheme with "settz" added, would provide a way for a program to explicitly choose a particular time zone (and it would work in the same fashion in both schemes), and would use the value of TZ if one was provided. Both schemes make it simple for an administrator to set the default timezone; in Olson's scheme, you just run "zic" with the "-l" flag specifying the default zone, or make the link yourself, and in the S5R3.1 scheme you just set the "/etc/TIMEZONE" file. Neither scheme directly addresses the question of "how do you teach your children about the time zone you selected"? One way to do this would be to use "putenv"; however, that exposes various implementation details that really should not be exposed. Perhaps there should be a function like "settz" that propagates that change to children.