How do you refresh DNS cache on Mac? Understanding and Performing the Process

What is DNS and Why Refresh Its Cache?

When you type a website address, like www.google.com, into your web browser, your Mac doesn't instantly know where to find it on the internet. It needs to translate that human-readable name into a numerical IP address (like 172.217.160.142) that computers understand. This translation process is handled by the Domain Name System, or DNS.

Think of DNS like a giant phonebook for the internet. Your computer, to speed things up, keeps a local copy of recent DNS translations. This local copy is called the DNS cache. It's a temporary storage that allows your Mac to quickly access websites it has visited recently without having to ask a remote DNS server every single time. This significantly speeds up your browsing experience.

However, sometimes the information in your DNS cache can become outdated. This can happen if a website has moved to a new IP address, or if there are network issues. When this happens, your Mac might try to connect to the old, incorrect IP address, leading to:

Websites not loading
Slow website loading times
Errors like "Server not found"
Problems accessing network resources

Refreshing your DNS cache tells your Mac to clear out this outdated information and fetch the latest DNS records the next time it needs them. This is often a quick and effective fix for many internet connectivity issues.

How to Refresh DNS Cache on Mac: A Step-by-Step Guide

The process for refreshing your DNS cache on a Mac is straightforward and primarily involves using the Terminal application. The specific command can vary slightly depending on your version of macOS.

For macOS Monterey, Big Sur, Catalina, Mojave, High Sierra, Sierra, El Capitan, Yosemite, Mavericks, and Mountain Lion:

These operating systems use a consistent command for flushing the DNS cache.

Open the Terminal:
- You can find Terminal in your Applications folder, within the Utilities subfolder.
- Alternatively, you can use Spotlight search: Press Command + Space, type "Terminal", and press Enter.
Enter the command:
In the Terminal window, carefully type the following command and then press the Return key:
sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder
Enter your administrator password:
When prompted, you will need to enter your Mac's administrator password. As you type, you won't see any characters appear on the screen – this is a security feature. Just type your password correctly and press Return.

Once you've entered the command and your password, the DNS cache will be refreshed. There's usually no visual confirmation that the command has run successfully, but if you didn't see any error messages, it has likely worked.

For macOS Lion and Snow Leopard:

These older versions use a slightly different command.

Open the Terminal: (Same steps as above)
Enter the command:
Type the following command into the Terminal and press Return:
sudo killall -HUP mDNSResponder
Enter your administrator password: (Same as above)

For macOS Leopard:

This version uses a distinct command for DNS cache flushing.

Open the Terminal: (Same steps as above)
Enter the command:
Type the following command into the Terminal and press Return:
sudo lookupd -flushcache
Enter your administrator password: (Same as above)

Important Notes:

The sudo command allows you to run commands with administrator privileges. This is necessary for modifying system settings like the DNS cache.
dscacheutil -flushcache is the primary command to clear the directory service cache, which includes DNS information.
killall -HUP mDNSResponder sends a signal to the Multicast DNS Responder process (responsible for DNS resolution) to reload its configuration, effectively forcing it to re-read DNS records.

When to Refresh Your DNS Cache

While you don't need to refresh your DNS cache regularly, it's a good troubleshooting step to perform when you encounter specific issues. Here are some common scenarios where refreshing your DNS cache might help:

Website Not Loading: If a website that normally works suddenly won't load, and you've confirmed your internet connection is otherwise stable, an outdated DNS entry could be the culprit.
Slow Internet Speeds or Website Loading: If you're experiencing a general slowdown in web browsing or specific websites are taking a long time to load, a refreshed DNS cache might resolve it.
After Changing DNS Servers: If you've manually changed your DNS server settings (e.g., from your ISP's default to Google DNS or Cloudflare DNS), flushing the cache ensures your Mac starts using the new settings immediately.
After Website Migrations or Changes: If you know a website you frequently visit has recently changed its hosting or IP address, refreshing your DNS cache will help your Mac find the new location.
Network Connectivity Problems: If you're having trouble accessing certain network resources or experiencing intermittent connectivity issues, refreshing the DNS cache is a worthwhile first step.

It's important to remember that refreshing the DNS cache is a diagnostic tool. If it doesn't solve your problem, the issue might lie elsewhere, such as with your modem, router, internet service provider, or the website itself.

Frequently Asked Questions (FAQ)

How often should I refresh my DNS cache?

You generally don't need to refresh your DNS cache on a routine basis. Your Mac automatically updates its cache as needed. It's best to refresh it only when you're experiencing specific internet connectivity issues that might be related to DNS resolution, as outlined in the article.

Why is my computer not connecting to a specific website after it moved?

When a website moves to a new server with a new IP address, your computer might still be holding onto the old IP address in its DNS cache. Refreshing the DNS cache forces your computer to look up the website's current IP address, allowing you to connect to the new location.

What happens if I enter the wrong password when prompted?

If you enter the wrong administrator password in the Terminal, the command will not execute, and you will typically see an error message indicating that the password was incorrect. You will then have another chance to enter the correct password. If you continue to enter the wrong password repeatedly, the Terminal session might be terminated for security reasons.

Does refreshing the DNS cache affect my browsing history or cookies?

No, refreshing your DNS cache has absolutely no impact on your browsing history, cookies, saved passwords, or any other personal data stored by your web browser. It only clears the temporary DNS records stored by your operating system.