Category: Tips

How To: Protect a file or directory from being deleted or changed by root

The following article is a guest article that will teach you how to protect a file or directory from being deleted or changed – even by root. This is a handy skill to have as you may have files you want to ensure are never changed.

This time, I’m going to do very little editing – but not out of laziness, but because I really don’t seem to need to do much. I really only need to do some formatting changes and we’ll be good.

Note: I forgot to ask the author if they want me to disclose their name. It’s a little late in the day now, as they’re in another time zone entirely, so when they see this they can let me know if they want their name credited/anything linked from it.

Without further ado…

Protect A File Or Directory:

Sometimes we come across files/directories in Linux that we don’t want to be changed. It won’t be long before we realize making a file “read only” through the GUI of our desktop environment doesn’t work the way we want to because the root user is still able to alter that file.

In this article I’m going to show you how to protect ANY file or directory from being deleted or changed even by the root user. For this example I’ll use xorg.conf which is nvidia’s config file.

Files:

In order to make xorg.conf immortal, as I like to call this process, open terminal and type:

and press enter. To make sure the file has become immutable, which is what the +i stands for, open it as root in your favorite text editor (sudo gedit /etc/X11/xorg.conf). Some text editors will allow you to write new content to the file but they won’t allow you to save the changes because the file is already immutable. Other text editors won’t react to pressing keys and there will be a “read only” string in the title bar next to the file name.

Undoing a file immutable is pretty much the same, with the only difference being that instead of a + you must use a minus symbol:

Directories:

You can also make a directory immutable or even a set of subdirectories. For this example open your home directory in your favorite file manager, then open terminal and type:

Now, here comes a little tricky part that you need to remember for the immutabling of the directories to work: placing a slash after the names tells the shell that dir2 is a directory and not a file. If you type /testdir/dir2, the shell will think dir2 is a file and will return an error.

If you have entered the command correctly, you will see this output:

If you have closed terminal, open it again in your home directory where you just created these two directories and type (exactly the way you see it, with the capital R and V):

-R stands for “recursive”, meaning it will do the same operation to all subdirectories, including dir2.
-V stands for “verbose” which will display what has been done.

In order to test this, simply select test dir and press Delete to try and delete it. You’ll see an error message which means testdir and the dir2 inside it have both become “immortal” and now nobody can delete them, not even root.

Undoing this is the same command, only instead of +i, you must use -i.

Closure:

And there you have it, a fairly well written article that I didn’t do much to other than some basic formatting. If there’s an error, don’t blame me! Ha! It looks right to me and jives with what I know on the subject, but I did not actually go through and test this. I trust the author to know what they’re talking about.

By the way, if you have a favorite subject and want to write an article, it really is that easy. Up in the upper right, click on the ‘contribute’ and I’ve made it even easier. (Don’t worry if it won’t let you pick a category, it’ll go through – and I still have to pick a category for it anyhow. All that does is save it as a draft for me to work on. It certainly doesn’t publish anything without my intervention. That’d just be silly talk!)

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Let’s Have A Look At The free Command

If the title wasn’t enough, today’s article has us taking a look at the free command. Once again, this will be a nice and easy article. I wanted to write a witty title, but Google doesn’t like witty titles for stuff like this and Google has been mad at me for a couple of months! Either way, it’s a good time for an easy article.

If  you’ve somehow never used the free command, you’re in luck! That’s what this article is going to be about! It should be relatively short, as there’s really only a few ways you’ll want to use the command.

What is the free command? Well, it’s an application that you run in the terminal (like oh so many of my articles) and it gives you some needed information about memory usage. It’s not fine-grained information, it’s about total usage. 

You can get this information all sorts of ways. Both top and htop will happily spit this information out. There are any number of GUI ways to get this information, such as your task and process manager may have a tab to tell you about memory usage. 

Us? No, we’ll be using the free command. The man page happily describes the free command as:

free – Display amount of free and used memory in the system

See? It’s another one of those terminal applications that does exactly what it says it’s going to do! Imagine that!

The Free Command:

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.

You can just run the command with nothing else:

That’s the same as you’d get if you ran free -w, by the way.

You can pick the display units as flags. Just look into man free to learn how to do that, but the easiest output for most people to read will be to display the units in megabytes or in ‘human readable’ form. You do those with:

Or the human-readable format:

Or if you prefer base ten:

Next, as you can see there’s a swap and regular memory section. If you have swap enabled, you can get some small benefit from seeing the total memory used. To do that, try this:

Finally, you can run the command periodically and get a running output so that you can monitor memory usage over time. That one’s pretty simple. The -s means seconds, so the following will refresh every ten seconds:

There’s more that can be done with the free command, so be sure to run man free in the terminal. However, those are the most common ways I use the command, so it’s likely to be fairly similar usage needs for you.

Closure:

There you have it, we have an article about the free command. It’s a good way to monitor memory usage, unless you need something more fine grained. If you want, there are are tools for that – including top and htop. But, those are fine article ideas for another time.

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.

Let’s Take A Look At Logged In Users

Today is a good day to learn how to take a look at logged in users. The vast majority of my readers are desktop users, so you can mostly skip this article. On the other hand, when you take a look at logged in users, you might find users you didn’t know were logged in and discover a problem like unknown users.

Yeah, most of you – including me at the moment (which makes it difficult to do things like take useful screenshots) are using Linux (mostly) as a single user. You have a user and you login to that user account when you start your system up.

While you do have other system-configured users, you don’t generally login as those users. As such, you probably spend very little time thinking about the users you have. Those system users aren’t generally logged in but are there for permissions purposes, so they’re out of mind for most of us.

Well, for the rest of you, you can use this article to learn how look logged in users – even getting a glimpse at what they’re doing. I mentioned some difficulty in taking screenshots, so I’ll provide you with just one. Cherish it, as it’s the only one you’re getting!

Here it is:

looking at other users
See? I’ll reference some of this below, in the article itself. I might as well…

Have A Look At Logged In Users:

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.

As you can see from the image above you can see all the logged in users with the first command. The following command will list them:

You’ll see the same thing, with a bit more information, when you use the following command:

Now, in the image above, you can see where I used it once and then ran it again. What you don’t see is that, in between those two commands, I opened up another TTY and logged in again as ‘kgiii’. If you want to replicate that, just press CTRL + ALT, then F3 to F6, and login at the prompt with any user(s) you happen to have.

Finally, you can get a look at what they’re doing – like one has a desktop session open and two of those login instances just have bash sessions open in TTY sessions. To do that,  you just use:

That should be easy enough for you to remember! By the way, if you did login as an additional TTY instance, run ‘users‘ again and you’ll see the output for that command has changed accordingly. The command’s output will may also give you a good idea about how long the system has been up and what the system resources are like.

Closure:

There you have it. You have learned how to have a look at logged in users so that you can have an idea of what’s going on with your system. If you spot a user you don’t recognize, that might be indicative of a problem. If you spot a user you don’t recognize, you’ll need to do some more investigating. By the way, if you have ‘finger’ installed you can always run ‘finger <username>‘.

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 Few Ways To Count CPU Processors Or Cores

So, in today’s article we’re going to learn a few ways to count CPU processors or cores. This is something you might already know about the system in front of you, but may want to verify with a remote system.

To the Linux system, there’s little difference between an individual processor or a core, or even a thread. Each core will appear as its own processor – and that’s exactly how it should be. Linux will treat each as its own processor and do its best to take advantage of multi-core/multi-CPU systems.

Now… Hmm… I shouldn’t need to explain this, but your computer has a processor called a CPU. It may have more than one, though that’s unlikely in a personal computer. Instead, your CPU may have multiple processors on it – each functioning more or less independently as ‘cores’. Additionally, your CPU cores may have multiple threads and each of those threads will appear as its own CPU.

That’s a very simplistic overview and I have to do things like limit how many characters are in the title of the article – and I don’t really want to try to explain everything. 

For example, you could have a 4 core CPU that’s dual threaded. 4 x 2 = 8, so your system will see 8 CPUs. There’s only one physical processor, but you’re effectively working with 8 of them. (By the way, you can *sometimes* compile software optimized by the number of cores available.)

Count CPU Processors Or Cores:

(or threads, I suppose)

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.

Now, there are so many ways that you can count the CPU processors or cores. We’re just going to cover a few of them. Feel free to leave other solutions as a comment. I’ll approve the comments as quickly as I can.

Solution #1

We just recently used the ‘cpuinfo‘ file to learn about your CPU. So, we’ll start with that one first. We’ll process it with ‘grep’ and then do some counting:

It might look something like this:

output showing there are 8 CPUs available
You’ll have to use your imagination for the rest. I’m only making one screenshot.

Now, those are individual threads that it’s counting – on the same physical CPU. But, to the system they appear to be individual CPUs. I can assure you, I do not have 8 physical CPUs in my laptop.

Solution #2:

Now, your computer does technically know if it’s a physical CPU, CPU core, or CPU core thread. It just normally doesn’t much care. If your CPU and OEM vendor did things properly, you can learn that information using ‘dmidecode‘.

They do not always implement this properly and you will sometimes find mistakes when using ‘dmidecode‘. Let’s hope for the best when we run this more convoluted command:

That one uses egrep and picks out multiple words to include. If you run that command, you should find out that your computer really can tell the difference between cores and threads – and physical CPU count (though not with this command).

Solution #3:

This final solution is nice and easy. If you’re gonna memorize one of these, this would be the one to memorize. In fact, if you’re going to need to count CPU processors or cores, you might just as well use this one. It’s easy and effective.

That one will output the total number of CPUs, cores, or threads. That’s all it will output, just a single number. That number is how many CPUs (effectively) your computer sees – and that’s it. It’s pretty much perfect.

Closure:

There you go. You have another article, this one explaining how to count CPU processors or cores (or threads, really). It’s handy information to know, though you probably already know it. Like I mentioned above, you can optimize C/C++ code to run on the specific number of cores – and there are other reasons you might want to know this. 

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One Way To See CPU Information

Today, we’re going to explore one way to see CPU information. On the original site, I had a couple of articles about this sort of stuff but we didn’t cover this method. It’s a short and sweet process, though I’ll show you a couple of ways to process the output.

The date that this will be published is July 4th. That’s a holiday in the United States. Not only do I live here, the vast majority of my readers live here (according to the stats I have). So, this will be a nice and easy article. For those of you who reside elsewhere, you’re welcome. You won’t have to work too hard today to understand what’s going on.

Anyhow, we’re not going to use any special tools. We’re not going to use any applications that you don’t already have installed. While we likely could, there really isn’t any need to. This being Linux, the information we’re after is already in a file. All we need to do is read that file.

So, let’s get to it…

How To See CPU Information:

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.

With your terminal now open, let’s go ahead and read the file we need if we want to see the CPU information:

That’ll output a ton of text. You can read it as it is, or you can actually get it in a more readable form using the ‘less’ command. To do that, you just change out the ‘cat’ command, like so:

Now, just use the arrows on your keyboard to scroll down (or back up) through the text. When you want to close the output and return to the terminal, just press Q and it will close.

Closure:

That’s it. That’s all there is to this article that tells you how to see CPU information. It’s not a very tough article, and it’s quick. So, I met those goals! Yay me! Enjoy your holiday, even if the holiday is just a nice quick article that doesn’t require much thinking. Me? I’ll drink some beer and char some dead animal flesh.

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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