power management does not show in system preference

You can open Power Management by pressing Alt+F2 to open the "Run Application" window, then typing:
gnome-power-preferences

To put it in the menu, use the editor (System > Preferences > Main Menu; or right click the menu, and click Edit Menus)

It may just be a case of ticking the box next to Power Management, but, if not, click New Item and type gnome-power-preferences in the command box. The icon can be found somewhere (depending on theme) under /usr/share/icons and is called gnome-power-manager.svg

Hi Marc,

Thks for your reply.
After checking, found out that there is not a file call "gnome-power-manager.svg" under the folder /usr/share/icons.
Please adv how to add this file.
thks.

If you're using Ubuntu 9.10 or 10.04, the full path of the default icon is:
/usr/share/icons/Humanity/apps/48/gnome-power-manager.svg

I don't have any older versions available to check the location in them, but they'd probably store the icon _somewhere_ under /usr/share/icons too.

Or you could download the Humanity icon set from:
http://launchpad.net/humanity/0.4/0.4/+download/Humanity[0.4.6].tar.gz
and then extract the icon from Humanity/apps/48 within that archive.

That link isn't displaying properly. If you choose that route to an icon, go here:
https://launchpad.net/humanity
Then click the top big green rectangle, labelled Humanity[0.4.6].tar.gz, over on the right.

found the icon, with thanks.
but after adding it to the System > Preferences , and click the power manager, pop up an error massage box "Could not launch 'power manager', Failed to execute child process "/usr/share/icons/Humanity/apps/48/gnome-power-manager.svg" (Permission denied)"
what is that means?

I suspect that's because you typed the path to the icon in the "Command" box, which is for whatever you actually want to open, in this case gnome-power-preferences.

To recap more fully, in the "Launcher Properties" window you should have:
Type: Application
Name: Power Management
Command: gnome-power-preferences
Comment: Configure power management
Then click the icon on the left, and select the icon that is found at /usr/share/icons/Humanity/apps/48/gnome-power-manager.svg, which should give you a picture of a battery and plug when you return to the Launcher Properties window.
With all that set correctly, you can click Close, and then use the item in the System > Preferences menu.

If all else fails, so long as you have gnome-power-preferences in the "Command" box, the menu item should function correctly. The rest just makes the menu look a bit nicer.

Hi Marc, thanks for your prompt reply.
after setting accordingly, I click the power management again in the System > Preferences menu, but no reaction at all.
by the way, i am using ubuntu 9.10
thks

Can you open the preferences by opening a Terminal (Applications > Accessories > Terminal) and typing
gnome-power-preferences
or does it give you an error message? Copy and paste any error messages here.

If you can open the preferences window that way, you've probably made a mistake somewhere in the menu editing.
If, however, you get an error message, then there's a problem with gnome-power-preferences itself.

Hi Marc, I tried typing gnome-power-preferences in Terminal, after pressed ENTER, It returns a new line, but nothing happen, nor error message...

How very unhelpful of it. No "command not found" message implies that gnome-power-preferences does exist. No "permission denied" message suggests that it is set as executable. So it's trying to run but not actually being functional, assuming it isn't just opening on another workspace/monitor. I could suggest trying to run it in the terminal again with:
gnome-power-preferences --verbose
to see if that tells you anything, but I don't know anything about its inner workings so, beyond confirming that it's running at all (which you could do with the System Monitor), I'm afraid I wouldn't understand any of its debugging info anyway.

If another attempt at reinstallation with:
sudo apt-get install --reinstall gnome-power-manager
in the terminal doesn't fix it, then I really don't know, and all I can think then is that you've got one more reason to install Ubuntu 10.04 once it's released on Thursday.