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The Installer can be opened from Extensions -> Install/Uninstall menu item.
You can extend your Joomla! based website functions by installing different types of extensions (components, modules, plugins, templates). All extension installations and uninstallations occur from the back-end administrator panel of your Joomla! install. Extensions can be installed from your local hard drive (installation package), from an install directory on your website, or from an URL.
Upload Package File
In the upload field named Package file you can specify the package of the extension to install. If GZip support is enabled with PHP on your server, the installer can extract the contents of a zipped or gzipped archive. You can browse your local hard drive and search for the package to upload with the Browse... button. After you find the package on your local drive, select it in the Upload File window and click on the Open button, so the specified package name with the path appears in the Package file field. Click on the Upload File & Install button. Joomla! uploads the package and automatically installs it. You can read a message about the success of the procedure. If you get an error message, read it thoughtfully and make any required correction.
Install from Directory
Create a temporary directory on your hard drive and decompress the compressed package into it, then with FTP you can upload the files and directories of the package into a directory on the server. Then in the Install Directory field specify the directory where you have uploaded the files and directories of the package. After that click on the Install button and Joomla! automatically installs the content of the given directory. You can read a message about the success of the procedure. If you get an error message, read it thoughtfully and make any required correction.
Install from URL
In the Install URL field specify the URL of the package to upload and click on the Install button and Joomla! automatically installs it. You can read a message about the success of the procedure. If you get an error message, read it thoughtfully and make any required correction.
Click on one of the tabs depending on which type of extension you want to uninstall. In the list select the extension and click on the Uninstall icon on the upper-right side of the screen. Joomla! automatically uninstalls the specified extension.
You can uninstall multiple modules, plugins, languages and templates in one step but you can uninstall only one component at a time.
Think twice if you want to uninstall a Joomla addon. For example sometimes it is a good idea to unpublish the modules you don't want to show on frontend. Generally the bundled Joomla modules cannot be reinstalled without a hitch.
Disable a component
If you do not want to use a component, then switch to the Components tab and click the green tick in the Enabled column. The green tick will be replaced with a red X. The disabled component will disappear in the Components menu.
Support old extensions in Legacy Mode
Some old 1.0.x extensions support Joomla! 1.5 in Legacy Mode. To be able to install such extensions please open the Plugin Manager screen from the Extensions menu and enable plugin System - Legacy as it is disabled by the default.
You can choose the mode of the installation. The mode used most frequently is the Upload Package File.
Some Core or System addons (Component, Module, Plugin) cannot be uninstalled so cannot be selected for uninstallation. Also the Default Template and Language are disabled for selection.
Important: Do not delete the Default Template and Languege files using FTP because it generates errors in error both front-end and back-end.
When you want to install a 3rd party developed module or plugin which belongs to a component, please keep in mind that you cannot use it unless you first install the related component.
When you uninstall a 3rd party developed component having its own module(s) or plugin(s), these modules cannot be used any more, so please uninstall them as well.
Some components coded by 3rd party developers may have their own modules and/or plugins included in the installer, so make sure the module/plugin directories are writable otherwise the extension will not work properly.
SECURITY WARNING: Please use only those 3rd party extensions on your site which you really need. Do not use your live site for testing purposes because it may compromise your site and server.
Please do not install Joomla! extensions downloaded from warez sites because they may be infected by a virus or malware that cause damage on the server and can contaminate the computer of your visitors! Installing from remote URL can be dangerous as well.
An installed component will be registered and listed in the Components menu.
You can assign a menu item to an installed component in the Menu Item Manager by clicking the New toolbar button. You can select it in the Internal Link branch.
An installed template will be added to the Site or Administrator list of the Template Manager where you can assign it to all of the pages or to the selected ones and customize its parameters, edit the HTML or CSS source or preview the available module positions.
An installed language will be added to the Site or Administrator list of the Language Manager depending on the client attribute where you can set it as the default language.
System - Legacy plugin should be enabled to be able to install the prepared Joomla! 1.0.x extensions.