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Asked: 2024-09-24T19:50:53+05:30

How can I clear the DNS cache of dnsmasq without having to restart the entire service?

I’ve been diving into some troubleshooting with my home network setup, and I hit a bit of a snag with dnsmasq. I know it’s a great lightweight DNS and DHCP server for small networks, but I’m running into a problem that’s proving to be a little frustrating!

So, here’s the deal: I recently made some changes to the DNS records I’m using, but it seems like those changes are not reflecting. After doing some digging, I realized it’s likely because of the DNS cache that dnsmasq holds onto. I started searching for ways to clear that cache, but every solution I found either involves restarting the entire dnsmasq service or seems way too complicated for what I need.

I mean, I don’t want to disrupt everything just to flush the DNS cache, right? If I restart the service, that would mean I’d have to deal with downtime, and I really can’t afford to have my devices lose connectivity, especially when some of them are crucial for work-from-home operations and entertainment. It feels like there must be a simpler way to accomplish this without causing a major interruption!

I’ve seen some commands floating around, but I’m honestly not sure if they would do the trick or if they might mess something up. Plus, I wouldn’t want to accidentally flush something critical, you know? I’m kind of wary of getting my hands too dirty without having a solid understanding of what I’m doing first.

So, does anyone know if there’s a command or procedure that can let me clear the dnsmasq DNS cache without having to restart the whole service? Any insights or advice would be super helpful! I’d really appreciate hearing from anyone who’s dealt with this before or has some simple trick up their sleeve. Thanks!

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    2 Answers

    1. Looks like you’re in a bit of a bind with dnsmasq! I totally understand the frustration when things don’t work as expected. Clearing the DNS cache can definitely feel like a hassle, especially if you’re trying to avoid any downtime.

      So, here’s the scoop: while dnsmasq doesn’t have a built-in command to just flush the cache without a restart, there are a couple of things you could try that *might* help without causing a big disruption.

      • Temporary TTL Changes: If your changes aren’t taking effect because of a high TTL (Time To Live) value, you could reduce that value for future entries, but this won’t help with the current cache.
      • Send a SIGHUP Signal: This might be your best bet! You can send a SIGHUP signal to the dnsmasq process, which can make it re-read the configuration file and might clear the cache without a full restart. Here’s how you can do it: 
        sudo kill -SIGHUP $(pidof dnsmasq)

      Just be careful with the commands, especially if you’re not super familiar with the terminal! Always a good idea to make sure you have backups and notes on what you’ve changed before you dive in.

      By the way, if you do decide to try the SIGHUP method, keep an eye on your devices to see if they maintain their connections. Most should be okay, but better safe than sorry!

      Good luck! Hope this helps clear up that pesky cache without too much hassle!


    2. To clear the dnsmasq DNS cache without restarting the entire service, you can use a command that interacts directly with the process. The command sudo kill -SIGUSR1 $(pidof dnsmasq) sends a signal to the dnsmasq process to flush its cache. This approach allows you to refresh the DNS records without any significant disruption to your network, thereby retaining connections for your devices. Make sure to run this command in the terminal of your router or server where dnsmasq is running. Additionally, it’s important to verify that you are using the correct approach by checking the dnsmasq logs afterwards to ensure your changes have taken effect.

      It’s wise to take caution by backing up your dnsmasq configuration files before making any changes. This way, if something doesn’t go as planned, you can easily restore the previous settings. Familiarize yourself with the dnsmasq notes on common signals and their functions, as proper understanding can prevent unintended issues. If you’re unsure, consult the dnsmasq man page (man dnsmasq) for detailed documentation. This should help you navigate the nuances of any future troubleshooting with confidence.