From Joomla! Documentation
There may be occasions when you will make your Joomla! website completely unavailable to visitors for a short time. There is a simple switch in the Administrator Backend that enables you to take your website offline quickly. It can be returned to service just as easily.
==讓網站暫時關站== 讓您的 Joomla! 網站暫時關站，讓訪問者看不到內容，您可以取代顯示的訊息:
- Log in to the Administrator Backend. To learn how to do this read: Logging in or out of the Administrator Backend.
- Click on the Global Configuration button in the main Control Panel or select the System → Global Configuration.
- There are so many configuration options that they have been divided into separate groups or tabs. The Site tab is the default first view displayed. If not, select that tab.
- Find where it says Site Offline and click the Yes button (see the screenshot below).
- Optional: Change the Offline Message to give your visitors some explanation about why your website is unavailable.
- Click the Save toolbar button to implement the new settings:
- The Save toolbar button will save your changes and but leave you in Global Configuration.
- The Save and Close button will save your changes and return you to the Administrator Control Panel.
- You should see a message confirming the settings have been changed.
- If you see an error message, refer to Cannot save Global Configuration changes.
To Put Your Joomla! Website Back Online
Repeat the steps above and making sure the site offline switch is set to off.
The site may be parsed by bots, search engines and other direct call methods.
Using the .htaccess Method (cPanel)
You can limit access to certain resources of your website by password protecting the directories they are in.
To password protect directory with cPanel Hosting Control Panel:
Login into your cPanel and click on Password Protect Directories.
Once you click on Password Protect Directories, you will see a list of directories.
Click on the directory that you wish to password protect.
Fill in a Username and Password at the bottom of the page, and click Add / modify authorized user.
Once the user is created successfully, just click Go Back.
Now, verify that the directory requires a password to access via the web.
Fill in Protected Resource Name. This is just the message that will show in the login window. Then highlight the user you just created from the Active Users list and click on Save button below the Protected Resource Name.
To ensure that your directory has been password protected, launch your browser and visit the folder. If the browser prompts you to login, your directory has been protected by password.