While Ubuntu comes with a number of icon packs you can select from, online a small number is installed by default. The first place to look for more icons is on the default repositories.
Icon packs in repository
- Open Synaptic - Press "Alt+F2" and enter "gksu synaptic", you will be asked for your password.
- Type "icons theme" in the search box. There will be several themes listed.
- Right-click and mark the ones you like for installation.
- Click "Apply" and wait for them to install.
Go to System->Preferences->Appearance->Customize->Icons and select the one you like.
Icon packs from theme websites
Some websites provide a list of themes including icons, which can be downloaded. A good place is GnomeLook.
- Go to the website and download the icon file.
- Extract the archive in ~/.icons directory.
- The new icons will appear in the appearance preferences.
Use another icon set while keeping the Ubuntu Mono panel icons
- Press ALT+F2 and type "gksu nautilus /usr/share/icons".
- Make a copy of the "ubuntu-mono-dark" or "ubuntu-mono-light" folder.
- Rename the folder to a new name.
- Open the index.theme file
- Change the "Name" field to a new name ("Name=Ubuntu-Mono-Dark" to "Name=My-New-Icons")
- Change "Inherits" field to the name of the icon theme you want to use ‘Inherits=Humanity-Dark,gnome,hicolor’ to the name of the folder of the icons you want to use.(This folder may be in ~/.icons or in /usr/share/icons)
- Save the file and go to appearance preferences to set the new icon theme.
Creating your own Icon Theme
Using Tango Generator
This is an application that lets you create a simple theme by selecting your own icons. TangoGenerator
Creating a Theme Manually
To create themes from scratch follow the tutorial on the Gnome Wiki: IconThemesTutorial(copy from archive.org)