In this article I am going to show you how to change the time on your Ubuntu machine using both the GUI and the command line. Hopefully, when you’re done with this, your computer clock will always be accurate.

Another option

Of course there is always another option. You can always set up NTP on your machine. I have already covered this in my article “Installing and configuring NTP on Linux“. That is, by far, the most reliable way to manage your clock. But when you don’t have constant access to the internet, or you simply don’t want to install a daemon on your machine – you have to resort to other methods. Let’s take a look at them here.

Command line

In order to set the date from the command line, you use the date command. The date command, however, is not the simplest command to figure out – at least not from the man page. If you look at the man page for date you see the time format uses a specific time string format like:

MMDDhhmmYYYY.ss

What the above string means is:

• MM is a two digit month, between 01 to 12.
• DD is a two digit day, between 01 and 31. NOTE: Regular rules for days, according to month and year, apply.
• hh is two digit hour, using the 24-hour period so it is between 00 and 23.
• mm is two digit minute, between 00 and 59.
• YYYY is the year; it can be two digit or four digit: your choice.
• ss is two digit seconds. The period (“.”) before the ss is necessary.

So, let’s say you want to set the correct date and time for this exact moment (the moment I am writing, not your reading). To do this I would enter the command:

sudo date 100507492010.00

at which point you would be returned:

Tue Oct 5 07:50:00 EDT 2010

GUI

Figure 1

Now, let’s take a look and see how this is done from the graphical front end. To do this click System > Administration > Time and Date. When you do this you will have to click the “lock” button to unlock this tool for changes. When you click this you will have to enter your sudo password. Upon proper authentication you will then be able to use the drop downs for hours, minutes, and seconds. When you change the time, you only need to close the tool, no saving required. NOTE: You can also change the date as well as the timezone with this same tool.

Final thoughts

Don’t be caught in the future or the past on Linux. Make sure your time is correct so you aren’t confusing those receiving your emails (unless you want them to think they are receiving emails from “future you”.)

Naturally the second reason is far more important than the first. But either way, you might very well be driven to keep your machine on the exact time. To that end you can either constantly monitor the time on your machine (manually changing it when necessary) or you can set up NTP to handle your time corrections for you.

Installing and configuring NTP is actually quite easy. It will, however, require the use of the command line. With that in mind, lets’ get busy.

Installing

You could open up your Add/Remove Software utility, do a search for “ntp” (no quotes) and install the matching results. Or you can open up a terminal window and install ntp with one of the following commands (remember, you will need either root access or sudo):

• apt-get install ntp
• yum install ntp
  
• urpmi ntp

One of the above commands will install the ntp daemon and the configuration file /etc/ntp.conf.

Before you fire up the daemon you will need to take a look at the /etc/ntp.conf to make sure you have the ntp servers you want to use configured.

Configuring

Most likely your NTP installation will already have a configuration file that is ready to go. My Debian-based NTP install had such a .conf file. All I had to do was start the daemon. But you might have special needs or your install might not have been as complete.

The section of the ntp.conf that you will want to take a look at is the server section. Each line in this section is set up like so:

server IP_ADDRESS OPTION(S)

Where IP_ADDRESS is the actual address of the server you want to use and OPTION(S) is/are the option(s) you want to use.

There are two options that you might want to use for every server. These are:

iburst: This option is used when the configured server is unreachable. When your machine can not contact its NTP server it will send out bursts of eight packets (instead of just one).

dynamic: This option allows a server to be configured even if the server is not reachable during configuration. This option assumes that at some point the server will be reachable.

If you look at my /etc/ntp.conf file you will see the following in the server section:

server 0.debian.pool.ntp.org iburst dynamic
server 1.debian.pool.ntp.org iburst dynamic
server 2.debian.pool.ntp.org iburst dynamic
server 3.debian.pool.ntp.org iburst dynamic

If you are not sure what servers to use visit the official NTP organization NTP.org to find a list of trusted servers.

Starting the Daemon

Once you have everything up and running go back to the root terminal and issue the command:

/etc/init.d/ntp start

or

/etc/rc.d/init.d/ntp start

which will start the ntp daemon. NTP will now slowly start to adjust the time on your server. But don’t worry, it makes the adjustment slowly. First the daemon waits for at least ten packets of information before trusting a source.

Now test to make sure your installation is working by issuing the following command:

ntpq -p

which should give you a listing like:
remote refid st t when poll reach delay offset jitter =========================================================
+point2.adamants 64.202.112.75 2 u 44 64 377 75.955 -7.045 2.992
*station.mars.or 209.81.9.7 2 u 10 64 377 75.477 -1.144 0.977
-www.broadbandja 64.34.180.101 3 u 56 64 377 72.764 3.766 0.977
+pxe.lax-noc.com 209.81.9.7 2 u 25 64 377 65.686 -7.753 2.539

If you see zeros for the values you know ntp is not connecting. As you can see above my setup is connecting.

Final thoughts

NTP is an easy way to ensure your servers or your desktop is always using the correct time. In mission-critical machines, this can be quite important. Employing NTP will give you the security of knowing your machine’s right “on time”.