How do I make Update Manager stop opening automatically?

This may work for you. I haven't verified if it works in GNOME.

• Open the Software Sources application.
• Select the "Updates" tab.
• For the "Automatically check for updates" option, select Never.

After this, you will have to open the Update Manager application manually.

I found this post with the following instruction:

open gconf-editor, browse down to Apps -> Update Notifier, and uncheck the auto_launch option

OK, try this one. It's similar to the other answer but disables it instead of deleting it entirely. It might be safer for you to open the file in an editor and change the line by hand instead of the sed command that post uses.

The procedure, using an editor:

1. Open a terminal
2. Move to the autostart directory (cd /etc/xdg/autostart) and list the files there (ls).
3. Find the startup program you want to run (in our case update-notifier.desktop) and open it in an editor (gksudo gedit update-notifier.desktop). Enter your password if necessary.
4. Be careful not to change anything except this line. Find this line:
   NoDisplay=true
   and change it to:
   NoDisplay=false
5. Save the file and exit.
6. Reboot to make sure it worked.

In Precise, it is done using dconf now rather than gconf.

1. Install dconf-tools

   $ sudo apt-get install dconf-tools

2. run dconf-editor and navigate to com > ubuntu > update-notifier.

3. Tick no-show-notifications

And here's how to do it from the command line:

dconf write /com/ubuntu/update-notifier/no-show-notifications true

Ubuntu 12.04 LTS

The Update Manager pops up when it detects a new update. This behaviour can be pretty annoying for many, especially when you are in the midst of your work. To make it worst, if you close it without updating, it will keep on popping up in regular intervals and each time after boot, until you have upgraded your system. To turn it off:

Method 1 - Disable Update Notifier from autostart

The Update Notifier autostarts on boot and triggers Update Manager. In this method, we prevent the Update Notifier itself from autostarting,so that Update Manager won't be triggered. Edit Update Notifier's entry in systemwide autostarts - /etc/xdg/autostart/update-notifier.desktop ( Note that you wont be able to use the Startup Applications app,as it only deals with per-user autostart entries ) and add the following line:

X-GNOME-Autostart-enabled=false

Reboot now, and you'll find that there's no Update Notification.

Disadvantage: This disables automatic Update Notifications altogether.You'll have to manually check for updates(which is fine by me,but may not be for some people)

Method 2 - Show Update Indicator

This option makes the Update Notifier show an Update Indicator in the panel, instead of popping up the Update Manager. I think this should be the default setting for Update Notifier in Ubuntu. To do it:

Graphical Way: Open dconf Editor. Navigate to com->ubuntu->update-notifier. Uncheck the entry auto-launch and close dconf Editor. To recover the Update Manager popup function, simply repeat the above step, but place a check in the auto-launch entry.

Command Way: For the terminal lovers out there, type in these commands to do the same.

gsettings set com.ubuntu.update-notifier auto-launch false

and to recover:

gsettings set com.ubuntu.update-notifier auto-launch true

These methods were tested and found to be working on Ubuntu 12.04 LTS with update-manager version 0.156.14.11. I got the idea from the post How to Remove The Annoying Update manager Pop-up in Ubuntu Jaunty and simply modified it to work on Ubuntu 12.04 LTS aka Precise Pangolin