how to read time zone information

Question

I was looking at some book of system programming. It mentioned to use a variable TZ with a colon separated list which is used from /usr/share/zoneinfo. Probably the book is a bit outdated.

I checked on my Ubuntu system

/usr/share/zoneinfo/Asia$ file Oral

gives following output

Oral: timezone data, version 2, 14 gmt time flags, 14 std time flags, no leap seconds, 51 transition times, 14 abbreviation chars

I tried opening it in vi but the text could not be read. I also tried reading /etc/localtime but here also it could not be read.

1. How can I basically read above type of files?

2. Where is TZ environment variable defined in Ubuntu 10.04?

Solution

Well, it depends what you want to read it for?

Almost all programs just rely on $TZ being set in the environment or /etc/localtime being a link to a timezone file. The C library will then automatically arrange for eg localtime() to return the correct time.

1) How can I basically read above type of files

zdump -v /etc/localtime will show you what's inside the files.

These are compiled files not meant for humans to read. apt-get source tzdata will give you the source they come from.

2) Where is TZ environment variable defined in Ubuntu 10.04

It is not set by default. Instead, /etc/localtime is a copy of the relevant zoneinfo file, and /etc/timezone is the name of that zone.

You can change them with sudo tzconfig or through the GUI.

You could set it in for instance ~/.env if you want a different personal default for yourself.

Comments

[jiggunjer]

Nowadays it is tzselect

[poolie]

tzselect is not a replacement for tzconfig: it just chooses a timezone and prints it to stdout without changing any configuration. The actual modern replacement is dpkg-reconfigure tzdata.