Category: Command Line

Short: Show The Groups You Belong To

Today’s article, as was indicated in the title, is a short article where we learn how to show the groups you belong to. It’s just a simple command, so we’ll toss in some extra knowledge. But, this is just a short article. You won’t have much to do in this article.

The latest article explained groups and can be read by clicking this link:

List All The Groups In Linux

The last article explained how to list all the available groups in Linux. This one will explain all the groups your user account belongs to. If you want to know the groups you belong to, it’s simple enough.

If you didn’t read the article, Linux is a multi-user operating system. There are also groups. A user can belong to multiple groups and have permissions matching those groups. The example I gave in the previous article was the sudoers group. You (probably) belong to that group, giving you access to the sudo command. That is how you have elevated permissions for your account, which is quite different than using the root account.

Even if you don’t know this, you’re almost certainly a member of multiple groups. In the previous article, we learned how to show those groups and today we’ll learn how to show the groups you belong to.

Show The Groups You Belong To:

If you want to show the groups you belong to, you’ll need to have an open terminal. Just press CTRL + ALT + T and your default terminal should open. Otherwise, open a terminal from your application menu.

With your terminal open, you can show the groups you belong to with this command:

Your output will be different but here’s an example:

This also works with other users. Here’s the syntax:

That will show the groups that the user belongs to. It’s a pretty simple thing to learn and a pretty handy thing to learn. It’s so simple and easy that this is an intentionally short article.

Closure:

There you have it… It’s a short article but showing the groups you belong to isn’t a complicated affair. This is something anyone can do and there’s no reason to make the article longer than it already is. While I could make it longer, it’d be wasting my time and your time. It’s just that easy.

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List All The Groups In Linux

This is going to be a simple enough article where we list all the groups in Linux – specifically your Linux. (Your list of groups may not be the same as my list of groups, of course.) This isn’t complicated but might be important to some of you, so we might as well write about it.

I’ve often mentioned that Linux is a true multi-user operating system. That is, you have many users, each with assigned tasks and permissions. You have users for everything from root to printing.

Well, along those same lines, Linux also uses groups. You can not only set permissions on a per-user basis, you can set permissions on a per-group basis. Any member belonging to that group will have the same permissions as that group.

A good example is ‘sudo‘. That’s a group you likely belong to. Because you belong to the sudo group you have access to the sudo command. This lets you have elevated permissions to perform various operations on your system. Make sense?

We’ll be using a new tool for this…

getent:

The getent command is used to read various databases. This is fine because ‘groups’ is one of the databases that getent can read. You won’t need to install anything to run this command.

You can check the man page with this command:

From there, you’ll see that getent is described like so:

getent – get entries from Name Service Switch libraries

So, it’s a database reading tool more than anything else.

If you’d like an easier way, we’ll do the same with the cat command.

cat:

I really shouldn’t have to describe the cat command. We’ve used it plenty of times. It takes the contents of a file and spits them out to your terminal (standard output). It’s an oft-used tool in the Linux world. Once again, you won’t have to install anything.

You can check the man page with this command:

At that point, you’ll see that the cat command is described like this:

cat – concatenate files and print on the standard output

See? It’s the correct tool for the job. We want to take the contents of a file and read it in the terminal. The cat command is perfect for that.

I’ll show you how to list all the groups in Linux with both commands. You can pick your favorite and just use that command. Either command will work just fine for this job.

List All The Groups In Linux:

If it wasn’t obvious from the above, this is yet another task for the terminal. If you don’t have an open terminal, you can probably open one by pressing CTRL + ALT + T. If that doesn’t work, find the terminal in your application menu and click it.

With your terminal open, run the following command:

While not of much use, here’s an example output:

You can get the same output with the cat command. That might be easier to remember for newer users. After all, you should be familiar with the cat command. That command is simple enough.

That will give you the same results as the ‘getent’ command above. Obviously, the group name is the first column.

I’m not sure where I learned this, but you can just list the first field and get a list of groups without any additional information. Just use this command:

That’s not nearly as useful as it could be, but I figured I’d share.

Closure:

Well, if you wanted to list all the groups in Linux, you now know how to do so. If you didn’t know about groups, you now know that you have groups and how to list them. So, you might as well add that to your notes and keep it in mind. (The groups subject may appear in a future article!)

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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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Is Your Storage Drive An SSD Or An HDD?

Today’s article aims to answer a simple question, simply is your storage drive an SSD or an HDD? This is not something most folks will have trouble knowing, but it’s still something worth knowing how to do. After all, you never know when you’ll be attached to a remote computer with disks of different types.

And, yes, due to expense and sizes, HDDs still exist and are still in use all over the place. Not everything has been converted to an SSD.

We’ve relied on spinning media for quite some time. We used this in hard disk drives. They were the norm for many years. SSDs (solid-state drives) are more common in end-user computers these days. If you can, you might even have an NVME SSD which is exceptionally fast.

We’re only going to use one command in this article, so it will be quite short. That’s not a bad thing. Not every article needs to be all that long.

We’ll simply be using the cat command. We’ve used this command many times in the past because it’s a handy command to use!

cat:

The cat command is a command used in the terminal. We want to read a file and cat is the correct tool for the job. The cat command reads a file and sends the output to the terminal. You won’t need to install anything.

Let’s check the man page (with man cat) to see:

cat – concatenate files and print on the standard output

See? If we want to read a file to the terminal, this is the correct tool for the job. Again, you won’t need to install anything.

An SSD Or An HDD:

Like oh so many articles, you will need an open terminal. Just press CTRL + ALT + T and your default terminal should open.

With your terminal open, let’s see if you’ve got an SSD or an HDD.

First, identify your drives with this command:

Now, ignoring the partitions, you can run the following command:

So, for example, you’d run this command:

And here’s an example output:

The zero means that it’s an SSD. 

If we run this command against a drive that I know is an HDD (a plugged-in external HDD that’s used for backups and storage):

The 1 means that it is a spinning HDD.

So, if you have both you can now distinguish between an SSD and an HDD.

Closure:

So, now you know how to tell if your device is an SSD or an HDD. This is something easily determined. If you have questions about your storage, this will help answer those questions. I’m not sure that I’d memorize this command, but it’s worth adding to your notes.

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Short: The Halt Command

Today’s article is intentionally short because we’re simply going to learn about the basics of the halt command. There won’t be much to this article, because there doesn’t need to be.

If you have a Linux system, you can access the halt command. The halt command is one of the commands used for power management but not one you’re likely to use. You’re more likely to run reboot or shutdown command.

Why the halt command? Well, it’s archaic these days. I really can’t think of all that many, or any really, reasons to use it. I’m told you can use this command for low-level maintenance but I’ve never been able to use that for anything.

The Halt Command:

Under the hood, when you issue the halt command, the operating system goes through a series of steps to ensure a clean shutdown. It stops all running processes, unmounts filesystems, and sends signals to devices and services to shut down gracefully. Once everything is properly shut down, it halts the CPU and powers off the system hardware.

If you check the man page (with man halt) you’ll see that it agrees with the above statement and is a tool for managing your power state.

halt, poweroff, reboot – Halt, power-off or reboot the machine

While there’s more to the command, we’ll just cover the basics. So, press CTRL + ALT + T and open your default terminal emulator.

Or not… You only want to run the halt command when you need the command. It will shut everything down and that’s not something you necessarily want to do while reading this article.

The syntax is quite simple:

This will halt all the processes and leave the computer running. To completely turn it off, you’ll need to use the power button.

You can also try this command:

Now the -p is handy. After halting the computer, it will initiate a shutdown.

Then, you might find this a bit handier…

If it’s not obvious, the --reboot flag will reboot the computer. This means you needn’t use the power button for anything. It should just halt the system and then initiate a reboot sequence.

Closure:

That’s all there is today. I told you, it’s a short article. We just covered the halt command and nothing more. This isn’t complicated enough for a full-length article but is still a command that deserves to be mentioned. So, it has been mentioned. The good news is that there might be a future article that refers to this article, so my time might not be wasted.

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