Category: Tips

Disallow Directory Listing (in the terminal)

In today’s article, and for no apparent reason, we’re going to learn how to disallow directory listing in the terminal. This seems like a good article for beginners to learn, and it seems like something most folks might like to know. So, if you want to disallow directory listing read on!

You never know when you might want some additional privacy, though I’d definitely not confuse this for strong privacy measures like encryption, amongst your files. Perhaps you’re planning on releasing a memo and you don’t want anyone to read it until you’re done?

I dunno? It’s up to you as to why you’d want the potential privacy from making it so that the files in a directory can’t be listed. Your reasons are your own. I just share tidbits of knowledge.

We will be using ‘chmod’ in this exercise. The man page for ‘chmod’ describes itself like:

chmod – change file mode bits

But, for our purposes and generally speaking, it’s used to adjust the file permissions. As you should know, files have various permissions in Linux – and everything in Linux is a file. There are read, write, and executable bits that can be set (with said chmod, for example) and there’s also file ownership (for another day). We’ll be using those permissions to prevent listing the files in a directory.

Ready? It really won’t take long – and it should be easy enough for anyone…

Disallow Directory Listing:

As the title suggests, this is another ‘in the terminal’ application. So, of course, you’ll need an open terminal. You should open a terminal now. 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.

With your terminal now open, let’s first start by making a directory – just so that we can then use that to disallow directory listing. We’ll just do this in your /home directory. Start with:

Now, let’s move to the new ‘sample’ directory and make a couple of files.

Now, what we’re going to do is change the permissions of the ‘sample’ directory, like so:

You don’t need ‘sudo’ or anything, because these files belong to you. But, you can now test it. While still in the folder, try any of the following:

Or (from outside the directory, if you’d like):

In all cases, it should give you a ‘permission denied’ error, because you no longer have permission to list files from within that directory.

If you wish to reverse this, you can simply try changing the permissions again. You can just:

With that command, you can resume directory listing. So, it’s pretty easy to reverse the process. It’s also not the greatest security measure you can take, because of that. So, do what you will with it, as you now know how to disallow directory listing in the terminal.

Closure:

There you have it, it’s yet another article. This one seemed like an interesting one to write, so I figured I’d write it. You never know when you want to disallow directory listing, but now you know how to do so. If you have any questions, feel free to ask…

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How To: Find Files Over A Certain Size

Today’s article is going to be a quick article, one where we learn how to find files over a certain size. We’ll be using the ‘find’ command, which we’ve used previously, even though it can be fairly complicated to use. If you want to play around with the ‘find’ command, read on!

Also, and this wasn’t the first article I wrote tonight. I wrote another article. It was a good article. No, it was a great article! Then, as I’m wrapping that article up and hit the preview button, I scrolled down and saw the automatic article recommendation thing at the bottom…

Yup… It was such a good article, I wrote it twice! Well, I couldn’t let that pass – as I’d just done so recently, so I’m writing a new one and this one should be entirely new!

Making the find command approachable to new users means doing it in small bits. Fortunately, the command tells you what it does by its very name. It does exactly what you’d expect – it helps you find files. In fact, it defines itself as:

find – search for files in a directory hierarchy

So, it does what you’d expect it to do – though it can seem fairly complicated to a new user. Let’s do our best to make it approachable, shall we?

Lets Find Files Over A Certain Size:

If you’re a regular reader, you’ll know what’s coming next…

This article requires an open terminal, like many other articles on this site. 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.

So, if you just want to run this ‘find’ command in the directory (and recursive into sub-directories) you’re in, it’s nice and easy. Try this:

As you can guess, that finds files bigger than 100 MB in your current directory (and recursively). If you want to find files of a different size, you just change 100M to whatever you need – like 1000M (you can use G for gigabytes, for example).

If you want, you can specify a directory. Let’s say you want to do the entire system from the root directory (not to be confused with the root user). You just specify that – but you’ll want to use ‘sudo’ because you don’t have permission to read all those files.

Like this, you can specify the starting directory. If you want to find all files larger than 2 GB in your home directory (and sub-directories) then you just run this command:

There’s so much that you can do with the ‘find’ command. It’s really quite useful and I find myself using it with some regularity. Don’t forget to run the man find command to learn more about it. You can do a lot more than just find files over a certain size.

Closure:

So, I’ve tried to make the find command approachable by even novice users. It can be a bit complex looking, but it really is useful. If you think I’ve made it approachable, go ahead and comment. Of course, comment if you think the opposite is true. It’s all good, we’ve just tried to learn how to find files over a certain size.

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.

Show Disk Usage With ‘ncdu’

In today’s article, we’re going to learn how to show disk usage with ‘ncdu’. It’ll be a fun terminal exercise that lets you see your disk usage. I’d say this is on par with a beginner article, ’cause it’s just some simple terminal commands. So, do read on!

If you think ‘ncdu’ sounds familiar, it may be from a previous article. You should probably read the intro to that article, as it will save you some time and is reasonably informative.

How To: Find Large Files Using ‘ncdu’

We’ll be using that same tool, but we’ll be using it in a different manner. That article explains what ‘ncdu’ is. In short, it stands NCurses Disk Usage and it’s a handy enough tool. It describes itself as:

ncdu – NCurses Disk Usage

There are a few ways to use ‘ncdu’ and we’ll be using it to show disk usage in this article. Because you have that handy link up there, I’m going to skip some sections of this article.

Show Disk Usage With ‘ncdu’:

This article requires an open terminal, like many other articles on this site. 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.

First, you’re going to need to install ‘ncdu’. Rather than duplicate work, please visit this article. Scroll down and you’ll see how to install ‘ncdu’. 

See? All these previous articles sure make some future articles easier.

Anyhow, now that you have ‘ncdu’ installed, just navigate to the root directory run ‘ncdu’ from the there.

Depending on how much disk space you have attached to your system at the time, it could take a while to run. Let it run and eventually you’ll end up with a screen like this:

ncdu in action
Pretty basic looking, right? Well, look deeper.

As you can see, the first line is highlighted. Well, use the arrow keys to move up and down. Then, use the left and right arrow keys to move back and forth. To keep it simple, if you want to dig deeper, just navigate to the directory you’re curious about and run ‘ncdu’ in that directory.

Hmm… I probably should have timed it. I set ‘ncdu’ running on a desktop with a couple of internal disks and attached to an external disk with a whole lot of files on it. It’s like an 8 TB disk and the system is still trying to process that bad boy.

ncdu can take a long time to run...
It has been a while… It’s okay, I have faith, It’ll finish someday!

Anyhow, read the man page:

There’s more to be done with ‘ncdu’ when you want to explore disk usage. It can take a minute or ten to run, but the information is worth it.

Closure:

There you have it, a fairly short article that explains how to show disk usage with ‘ncdu’. It seemed like a good article to write and it was nice having already covered so much of it. That saves some time and I was a bit late in writing this one.

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.

A Little About The ‘echo’ Command

That’s right, in today’s article we’re going to learn a little about the ‘echo’ command. We’ll barely be scratching the surface of the ‘echo’ command. There are so many ways to use ‘echo’ that we simply can’t fit it all into an article. Do, read on!

So, what is ‘echo’? Well, basically, the ‘echo’ command is a command that tells the computer to output text – be it in the terminal or using standard output to add that text to a file. It’s useful for regular people, but you’ll find it’s most commonly used in things like bash scripting

That sort of thing, scripting, is outside the scope of this article – and probably beyond the scope of the entire site. Maybe I’ll get to it, but those would end up being long articles, or articles written in parts. Besides, I’m not really all that good with scripting. (If you are good with scripting and would like to write some articles, do let me know.)

This is how the man page describes the ‘echo’ command:

echo – display a line of text

That’s indeed what it does. When you combine it with things like variables, you open up a whole new world. I don’t actually have a very good article about variables, other than existing variables. I should probably have said article.

Anyhow, we’ll just be scratching the surface of the ‘echo’ command. There are all sorts of ways to use ‘echo’, but we’re just going to use it in ways that a new Linux user might use it. Some basic familiarity is probably a good thing.

The ‘echo’ Command:

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. Otherwise, just open your terminal like you normally would.

So, how you start with this ‘echo’ command:

You can also add quotes, and in some cases probably should:

You can also use the > operand and echo the text to a file. Like so:

Read: How To: Write Text To A File From The Terminal with “>” and “>>”

However, that’s not all you can do with the ‘echo’ command. You can also automatically fill in the information by way of environment variables. For example, try this:

Or you can try:

Read: How To: Show All Environment Variables

See? It’s good that I’ve written so many articles. I get to refer to ’em and save us all a bunch of time. So, be sure to visit those articles – especially if you’re a new user. If you’ve forgotten something, you can ‘echo’ the variable to be reminded.

Bonus:

This next bit is really just some information you’re gonna need down the road. I can sense it! This is a bit advanced for some of you, and you won’t need this until later in your Linux journey, but others will see this and suddenly understand the potential. If you’re new, you’ll get there.

The first thing we’re going to do is set a variable. It’s actually very easy to set your own variables in Linux. In this case, we’ll use:

Now, let’s just ‘echo’ the variable you just created:

Or, even better, you can then try:

See? It will output the variable when you echo it. You can create all the variables you’ll realistically ever need. 

You can actually format the output from the ‘echo’ command. For example, the -e flag with the \n separator. An example command looks like:

You can format the text in a variety of ways, just read the man page. You can do quite a lot with the ‘echo’ command and you should definitely check the man page if you’re interested in exploring all the possibilities:

There’s a ton of ways to use ‘echo’ (and with it variables) for those with a clever mind. When you do move on to learn about scripting, you’ll learn that it’s a basic tool used for all sorts of things, in all sorts of clever ways.

Closure:

And there you have it. You have a new article. This time, we’ve covered just the slightest bit of the ‘echo’ command. It’s enough to get your mind working, or so I hope. It’s enough to get a slight taste of the potential and to understand why you may want to be familiar with it.

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A Little About The ‘lspci’ Command

Today’s article is going to be another article where we get back to the basics, where we’ll learn a little about the ‘lspci’ command. As far as articles go, this one should be both fairly brief and easy to understand. To learn more about the ‘lspci’ command, read on! 

I am going to be writing some articles that cover the basics. I decided to not write them all at once, but to intersperse them with other articles. So far, we’ve had:

A Little About The ‘lsusb’ Command
A Little About The ‘lscpu’ Command

Well, this time around we’re going to cover ‘lspci’. 

So, what is ‘lspci’? We can find no better source than the man pages, which helpfully describe ‘lspci’ as:

lspci – list all PCI devices

Well, we see that it lists PCI devices, but what are those? PCI is another way hardware components talk with the CPU. If you have a fancy graphics card, it’s probably PCI-based (but likely PCI-X). If you’re really curious, PCI stands for “Peripheral Component Interconnect” but think of it as a way hardware can talk to the central processing unit.

So, the ‘lspci’ command will list things attached to the computer on the PCI bus. This is remarkably similar to the ‘lsusb’ command, though PCI can have a USB device attached to it through a hub.

Anyhow, that’s what PCI is and that’s what ‘lspci’ is meant to do. So, with that in mind, let’s just belly-flop into the article!

The ‘lspci’ Command:

You’ll find that ‘lspci’ is a terminal-based command. As such, you’ll have to have a terminal window open. If you don’t know how to open your default terminal emulator, just press CTRL + ALT + T and your default terminal should open.

We will not be covering everything that can be done with the ‘lspci’ command. We might have time and space (this time around), there’s really no reason to dive deeper into the ‘lspci’ command. We’re just going to cover the basics – because that’s all you’ll realistically have to worry about.

With your terminal now open, just run the command with no flags (but with sudo, ’cause ‘lspci’ wants elevated permissions to operate):

If you want a more verbose output, you can do that. Your choices are -v, -vv, and -vvv with ever-increasing amounts of verbosity. That can be pretty handy. Try this command to experience the most verbose output:

Where you might find the ‘lspci’ command most useful would be when you already know the class and category of information you want returned. When you use ‘lspci’ with ‘grep’, it gets more useful. For example, to learn about your memory:

See? It’s pretty straightforward. You’ll get this. I’m sure of it! (See 2nd edit below.)

As you can see, there’s quite a bit that you can do with the ‘lspci’ command. It’s a pretty handy command and we’ve just covered the ways you’re most likely to use ‘lspci’. 

EDIT: Fixed some information. I had somehow started to include lshw commands.
EDIT: So, this article was horribly written. Now it’s just short. I conflated ‘lspci’ with ‘lshw’ somehow – probably ’cause they’re next to each other in my notes. I’m just going to leave it as it is now.

Closure:

There it is, another new article! This time, we’re learning a little about the ‘lspci’ command. It’s a handy command to have learned, as you’ll eventually want to know about the hardware using the PCI bus. When that day does come, you’ll be able to use the command. Also, I’m ahead of schedule with pre-written articles.

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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