Getting ready

To complete this recipe, you will require a working installation of the CentOS 6 operating system with root privileges, a console-based text editor of your choice, and a connection to the Internet to facilitate the download of additional packages.

How to do it...

TZDATA is a compilation of the world's time zone information and we will start this recipe by showing you how to use the tzselect utility and applying the new time zone setting to a user of your choice.

How it works...

As we have seen, the tzselect utility can be used to tell you the time (anywhere in the world) by simply looking at your system clock and comparing it with Coordinated Universal Time (UTC). Its purpose is not to complete the task of updating your server's time zone, but it does provide the necessary information that will facilitate such changes for one or more users.

So what have we learned from this experience?

Having started by installing the relevant package, you were then guided to start the tzselect utility and use the supplied TZ value to update a user's profile.

Updating a user's profile was simply a matter of amending the appropriate file for each user. In most cases you would update the file found at /home/username/.profile. However, if this file was not available, then an alternative option located at /home/username/.bash_profile can be used.

For example, a revised bash profile will look like this:

# .bash_profile
# Get the aliases and functions
if [ -f ~/.bashrc ]; then
  . ~/.bashrc
fi
# User specific environment and startup programs
PATH=$PATH:$HOME/bin
export PATH
TZ='Europe/Moscow'; export TZ

You were also shown how to use the Posix Time Format, and if you did indeed decide to use this variation, then your revised bash profile will look like this:

# .bash_profile
# Get the aliases and functions
if [ -f ~/.bashrc ]; then
  . ~/.bashrc
fi
# User specific environment and startup programs
PATH=$PATH:$HOME/bin
export PATH
TZ='GMT-5'; export TZ

Remember, in the context of this recipe, the measurement of time is session based, so having made the preceding modifications, a user would then be required to re-login before they will notice any changes. They can do this by typing the following command:

date

Moreover, it is important to note that a change to a specific profile will not affect another user and none of these changes will affect the server as a whole. So with this in mind, this recipe can be used to enable multiple users to maintain different clocks.

So having completed this recipe, we can say that we now know how to obtain the required TZ value and provide a unique time zone setting for each user. As previously stated, it may not be a feature that you use on a regular basis, but it does provide a flexible solution in as much that you are now able you to configure a user account independently of the system as a whole and deliver a fully localized server environment regardless of how many users you serve or where they are located.

There's more...

Setting the time for your users is only one aspect of managing time on a server and it should not be forgotten that your server will run two clocks—a hardware-based clock that is supported by the battery on the motherboard and a secondary clock that is maintained by the operating system. Where the former is used to set the system clock during the boot process, the latter will be the clock that is used to keep a track of time.

Both of these time values can be run independently of each other (local time versus UTC) and on occasion this may even prove to be useful when considering a dual-boot situation. However, and in the case of most servers, it is common practice to ensure that both the hardware clock and system clock use the same reference in order to account for daylight.

As the root user you can use the following syntax to set a new date and time for your server's operating system by simply replacing MMDDhhmmYYYY.ss (Month, Day, Hour, Minute, Year, and seconds) with the correct values:

date MMDDhhmmYYYY.ss

For example, to change the time and date value to May 17, 13:21:22, 2012, you can use the following syntax:

date 051713212012.22

When ready, you should now synchronize the system with your hardware clock by typing:

hwclock–systohc

Finally, reboot your server to finalize the changes made:

reboot

On a successful reboot, you can confirm the status of your hardware clock with the following command:

hwclock–show

Similarly you can view the current operating system date and time by typing the following command:

date

rm /etc/localtime

ln -sf /usr/share/zoneinfo/XXX /etc/localtime

reboot