Tag: cache

How To: Clear the DNS Cache

Today’s article will be a nice and easy article where we learn how to clear the DNS cache as a simple exercise. This isn’t very difficult and won’t take too much time, so this article should be relatively short.

If you don’t know what DNS cache is, that’s fine. I’ll do my best to explain.

Chances are good that you do not need to clear your DNS cache. This isn’t something you’ll need to do all that often, maybe not ever. I only clear the DNS cache when I need to.

What is DNS?

DNS stands for Domain Name Service. When you type a domain name into your browser’s address bar, it relies on an IP address behind the scenes. DNS is the interface between those two.

You can think of DNS like a phone book, translating names to numbers.

While not important, a single IP address can host many websites. So, think of DNS as the phone book and nameservers are like the names of people who live in the same apartment complex.

As you browse, your computer tries to save you some time. It saves a cache of DNS hits. It saves a cache of domain names and their IP addresses. With a speedy connection, you won’t notice this as much today. However, it’s meant to speed up browsing when you revisit a site you’ve already visited.

Make sense? 

Let’s say you’re like me and have a website. For reasons, you decide to change your hosting company. You do so and update the nameservers. You now have a new IP address for your domain name, at least you will when the changes propagate.

Suddenly, you have an old IP address cached for that domain name. Because it is in the cache, your system won’t look that address up again. What do you do to get access to the site again?

Clear DNS Cache:

We’ll learn to clear the DNS cache in the terminal. In fact, I don’t know of a GUI way to do this for the system. (It’s possible to clear the DNS cache in Chrome via a GUI.) So, open a terminal. Many of you can just press CTRL + ALT + T and your default terminal will pop open.

With your terminal now open, enter one of the following commands to see the state of affairs regarding your DNS cache:

Or:

One of those two commands should work for you.

Here’s an example output:

Now, let’s clear that cache.

One of the following commands should work for you:

Or:

There won’t be any output from that command to confirm that the cache has been cleared. If you run the first command all over again, you should see something like this after you’ve run the command:

See? It’s pretty easy to clear the DNS cache!

Closure:

This is only something a few people will need to do. If you’re having issues visiting a site you recently were able to access without issue then this might be something you try. You can try to clear the DNS cache to see if it helps but there are a million and ten reasons why a site may suddenly be down and DNS is unlikely to be the issue unless you have a specific reason to expect this particular problem and solution.

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How To: Clear The apt Cache

In today’s article, we’re going to learn how to clear the apt cache. This is only useful if your distro uses the apt package manager. If your distro doesn’t use apt, this article is of no use to you. This isn’t a complicated article, but it’s one that should probably be included on this site.

If you don’t know if your distro uses apt, you really need to pay more attention! However, run ‘which apt‘ in the terminal and it’ll let  you know if apt is present.

If you’re using Debian, Ubuntu, an official Ubuntu flavor, or any derivative thereof (such as Mint), you’re using ‘apt’ as your package manager. Of course, if you’re new and not all that familiar with apt, you’re able to use this site’s search feature and find out some more information. Feel free to do so, as I’ve written a few articles on various apt features.

If you want, you can read this article from FOSSLinux for a great rundown on APT vs aptitude, that’ll also answer some other questions along the way. It’s a great article to understand apt, not just the differences between apt and aptitude.

When you install applications and updates with apt, the .deb files are cached on your device. In time, this can build up and use more space than you really want to have spent on such a feature. So, let’s learn how to clean it.

Clear The apt Cache:

Obviously, this article requires an open terminal. If you don’t know how to open the terminal, you can do so with your keyboard – just press CTRL + ALT + T and your default terminal should open.

Now, you can see what is going to be deleted – which directories that is – by using the dry-run flag.

Those are the directories which will be cleaned. The first command you might already know is this one, which seems to be one of the favorites for new users:

However, that only removes cached packages if there’s a newer version in the repositories. I don’t really see much use for that, but it’s there, a feature, and often a command that newbies are told to run.

Instead, you can clear out all those directories of no-longer-needed .deb files. Just run the first command without actually doing a dry run. It is done like so:

That’s really all there is to it. I mostly wanted to ensure folks knew how to clear the cache – and that the difference between the commands was mentioned somewhere on the site. I don’t expect the site to be some giant repository that’s ‘complete’, but I do need to cover the basics now and again.

Closure:

Well, today you’ve learned to clear the apt cache. Again, this isn’t going to do you any good if you’re using RHEL, Fedora, or even Arch! But, if you use a distro that uses apt, you might as well know this information. And, well, now you do…

Also, I linked to another site with similar content! I don’t do that often! Their write-up was just too good to pass up, so I don’t mind sending them the traffic. It saved me like an hour’s worth of writing – while trying to fit it into a block of no more than 300 words. So, I’m very, very much okay with linking to content like that.

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Clear Cache, Buffer, And Swap Space

Many Windows users will want to clear cache, buffer, and swap space. It’s a holdover from their Windows days, and it’s possible to do those things with Linux. This article will explain how to clear your RAM cache, buffer, and swap space.

One of the first questions we should be asking is, “Will this help?” The answer is, like many things, “Well, it depends…” It depends on a number of variables, like how much RAM you have, and how aggressively the kernel is paging, or what your swap preferences are. For example, quite a few people have decided to forgo swap entirely. Cleaning swap space is not going to help them out one bit.

The second question should be, “What exactly are we cleaning, anyhow?” The answer to that is a bit clearer, thankfully. The things we’ll be dealing with are:

  1. PageCache/Page Cache; The Linux kernel stores data in unused sections of memory in case it needs it again. Since kernel 2.2, Buffer Cache and Page Cache have been combined and there’s just PageCache.
  2. Dentries; They’re “the in-memory representation of a directory entry” and include things like meta data.
  3. Inodes; Meta data about all the files on your mounted file systems.

Those things build up in RAM and they can be cleaned out. The Linux kernel is really good at managing these things and unused RAM is wasted RAM (within reasonable limitations), but they can be cleaned out and this article explains how.

Clear Cache, Buffer, And Swap Space:

This article requires an open terminal. To open one, you can just use your keyboard – press CTRL + ALT + T and your default terminal should open right up!

I took the time to explain what you’ll be cleaning in the article’s opening. That’ll make this section easier!

To clear PageCache by itself:

Or you can clear Dentries and Inodes:

Or even clear PageCache, Dentries, and Inodes at once:

NOTE: These work as advertised. Before you run one of these commands, run free -m before and after running the command. By doing that, you can see what the results are and what the results will probably look like in the future.

Frankly, I’d only see this as a very valuable tool if you have little RAM, or want to free up some resources before opening something that is resource-intensive. Other than that, just let Linux do its job – managing cache, memory, and other resources.

But, if you’re a Windows user and want the comfort of some familiarity, this won’t harm anything and could provide the very slightest of benefit. You could even alias it to an easier-to-type command and run it as often as you want. It’s your computer, you do what you want with it!

Closure:

There it is, another article! We’re rapidly approaching the 6 month mark and so far things have gone well. This time, you get an article letting you know how to clear cache, buffer, and swap. Who knows what the next article will be?

Thanks for reading! If you want to help, or if the site has helped you, you can donate, register to help, write an article, or buy inexpensive hosting to start your own site. If you scroll down, you can sign up for the newsletter, vote for the article, and comment.

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