Linux Tips • Page 37 of 113 • Getting you up to speed!

How To: Find Local Network Devices

Today’s article will be a bit of a weird one, as I share with you one way to find local network devices using the Linux terminal. I suppose network device discovery is typically seen as a dark art, something a malicious hacker might do, but it’s completely harmless (in and of itself). So, if you want to find local network devices, this article just might be for you!

What we’ll actually be doing is scanning a block of IP addresses to see what responds to our prodding. This is sometimes called IP Scanning or IP Sweeping. It’s also sometimes called Port Scanning, but we won’t be doing any real port scanning. I assure you, I am not secretly trying to turn you into a big bad hacker – but this is a pretty neat ‘hack’ (in the traditional sense of the word).

We will be learning just a single command (with a bit of explanation) with a single flag. It’s a very complicated tool and trying to cover it all would take a giant article or many smaller articles. You can guess which one we’re going to do!

The tool we’re going to use for this is called ‘nmap’. This is available in every major distro. It might be installed by default. It’s just the tool for the task at hand, so you need to install it before you can use it as this article will suggest. (I trust you to know how to do so at this point.)

Did you install nmap? If so, please continue. If not, read the last paragraph.

With nmap installed, you can check the man page to see that it’s described as:

nmap – Network exploration tool and security / port scanner

Now you’re ready…

Find Local Network Devices:

Picture this…

So, for some reason, one of my laptops has stopped answering on the .local domain when I want to connect to it with SSH. I have choices at this point. I could fire up Team Viewer and then connect to the laptop to find the IP address belonging to the said laptop. Another choice would be to get off my lazy butt and walk to the device, but that defeats the point of remotely controlling the device.

I suppose the best choice would be to just figure out why it’s stopped responding on the .local domain. Wouldn’t that be novel?

But, I have another tool! I have a tool that’s reasonably fast, very easy, and likely effective! That tool is, as suggested earlier, nmap.

The first thing I do is crack open a terminal to find my local IP address. That’s easy enough and the link will show you how to find your private (or local) IP address. Though it needn’t be private. Security by obscurity is not security – and it’s trivial to learn. But, that’s an article for another day.

I was able to quickly learn that my local IP address is 192.168.215.88. From this, I realize that the most common configuration will be for everyone to be on the same subnet and so my laptop likely falls within the 192.168.215.1 to 192.168.215.255 range.

We can use the asterisk to represent any of those numbers, as it’s a wildcard. This means the next command is obvious and will be simply:

nmap -sn 192.168.215.*

1	nmap -sn 192.168.215.*

The -sn flag would mean ‘do not do a port scan’, so it’s checking only for devices that return a ping. Make sense? (It’s a pretty speedy command when not also scanning ports.)

A Picture Of nmap:

I think that this is one of those instances where my text isn’t quite clear enough. So, what I’m going to do is show you a picture.

The nmap command I ran showed me a list of local network devices. As I already know the IP address of the device I’m using, I can exclude that from the list. The device I’m looking for (my laptop) is then a different IP address.

The process looks something like this (trimmed down to just have one device for simplicity’s sake):

using nmap to find local network devices — As I know my device’s IP address, I can exclude that from the list of possible IP addresses.

As you can see, I first tried to connect with the .local domain and found that it did not work. So, I ran the nmap command and used a wildcard to scan the entire IP address range (1 to 255).

Sure enough, the IP sweep with nmap found another device and showed the IP address. It showed the gateway, which I could also exclude. The process of elimination meant there was one IP address to try (it could have contained more devices). I tried to use SSH with that IP address and, sure enough, that’s my laptop!

See? I saved a trip across the room! I saved opening up a bulky application and waiting for it to do its thing before I could even try using it to connect to the laptop. In fact, I suppose I also saved the effort I could have spent just randomly guessing IP addresses and hoping I got the right one for my laptop eventually!

Closure:

I figure there’s a lesson in nmap in there somewhere. You never know when you’re going to need to find local network devices! Now, when you do need to do so you will know how.

I figured I’d try writing this one in a way that showed you how I benefit from knowing how to do this. I figured that it’d be interesting to show you how the command solves a real problem. There have been a few articles similar to this and they’re fun articles to write. They are articles that come from the real me, the me that is actively using and appreciating Linux (often in the terminal) in my day-to-day life.

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How To: Prevent A File From Being Deleted*

Today, we have another simple article, where we discuss how to prevent a file from being deleted. It’s not quite true and I’ll explain in a moment, but for the most part, it makes it so you can’t remove a file by accident or the like. So, if you want to prevent a file from being deleted* read on.

Now, let me be more clear. I’m a bit sorry for the cheesy headline, but there’s a reasonable character limit. I included an asterisk just to make sure. A user with root permissions (eg a user with sudo privileges) can still delete the file – but it takes an extra step to do so. They have to know and work at it to delete the file.

The tool we’re going to use is called chattr. While it looks like ‘chatter’ and I want to type ‘chatter’ every time I use it, it is a tool that you use to change a file’s attributes. It’s a handy tool but we’ll only be examining one specific use for chatter. If you’re curious, the man page defines chatter as:

chattr – change file attributes on a Linux file system

If you’re using a mainstream distro, you shouldn’t need to install chattr. You should find it already installed. Some of the more lightweight distros may not include it by default, but you can verify that it’s installed by running the following in your terminal:

which chattr

1	which chattr

If you do find that chattr isn’t installed, go ahead and install it. It’s in your default repos. I’m sure of it!

Prevent A File From Being Deleted:

You guessed it. You’ll need an open terminal for this one. That’s easy, just press CTRL + ALT + T and your default terminal should open. See? Pretty easy!

Now, I’m going to show you how to use chattr to set an immutable bit. It’s not difficult and just uses the +i flag. Let’s start with creating a file:

touch foo.txt

1	touch foo.txt

With the file created, let’s set the immutable bit with chattr:

sudo chattr +i foo.txt

1	sudo chattr +i foo.txt

Now, let’s try to remove it with the rm command:

rm foo.txt

1	rm foo.txt

No luck? Well, let’s grab a hammer. We’ll try to remove the file with sudo:

sudo rm foo.txt

1	sudo rm foo.txt

Surprise! You still can’t delete it, even with sudo or logging in as root. To delete the file, you have to first remove the immutable bit, like so:

sudo chattr -i foo.txt

1	sudo chattr -i foo.txt

After that, you can happily (and trivially) remove the file with:

rm foo.txt

1	rm foo.txt

In case that’s not very clear, I’ve made you an image. That should help!

prevent a file from being deleted — See? If the words aren’t useful, perhaps the picture will explain it better.

That should explain it well enough. The file can still be deleted, it just requires sudo and removing the immutable bit from the file’s attributes. Pretty neat, huh?

Closure:

Of course, there’s always a way for a root user to be able to remove a file. However, you can make it difficult should you want to prevent a file from being deleted. A skilled user will check the file’s attributes and know how to delete the file, so it’s more about protecting a file from being deleted unless you want to.

Let’s Update Ubuntu In The Terminal

Today’s article will be a nice basic article, where we discuss how to update Ubuntu in the terminal. It seems like a fine article to write and one that not everyone will be versed in. There are lots of folks who don’t use the terminal for much of anything. Then, there are people like me who use the terminal for all sorts of stuff.

If you know how to update Ubuntu in the terminal, this really won’t be a very interesting article. We’ll just be covering the basics and I’ll explain how I do it. You’ll see that I tend to throw caution to the wind and just blindly hope for the best. This strategy is fine for me, ’cause I can fix pretty much anything. (I can fix pretty much anything because I’ve broken pretty much everything.)

Of course, this article applies to Debian. This article applies to Linux Mint. This article should apply to anything that uses apt as the package manager. So, if your distro is related to Debian then this will probably work just fine for you.

Well, there’s no reason to make the intro any longer… I think I’ve covered all that you need to know to get started.

Update Ubuntu In The Terminal:

As you can guess, we need an open terminal if we’re going to update Ubuntu in the terminal. That only stands to reason… Press CTRL + ALT + T and your default terminal should open.

With your terminal now open, let’s update the list of software that’s available. Let’s see what software can be updated. To do that, you just run:

sudo apt update

1	sudo apt update

That will tell you the software that’s available to update. You can see what those updates are with the following command:

sudo apt list --upgradable

1	sudo apt list --upgradable

You can then upgrade those applications one by one if you want to. Some cautious people do this. Some businesses do this – and do this to a staging environment to test – ’cause they need to keep things running. If you want to upgrade just a single package, try this:

sudo apt --only-upgrade install <package_name>

1	sudo apt --only-upgrade install <package_name>

Now, most folks are probably going to want to upgrade all the software that has new versions. They get it easy, they just type:

sudo apt upgrade

1	sudo apt upgrade

This will give you the chance to see everything that’s going to be upgraded and the chance to decline or agree. Me? I automatically agree. You might want to be more cautious, but I like running the command closer to this:

sudo apt upgrade -y

1	sudo apt upgrade -y

That automatically says yes that I’d like to upgrade all the things. After all, even if stuff were to break, I’d have had to have upgraded to find it anyhow.

I go a step further and just tie the two commands together. The command I run would look closer to this:

sudo apt update && sudo apt upgrade -y

1	sudo apt update && sudo apt upgrade -y

That will find all the available upgrades and install them automatically, that is without any further input from me. I’ve done this for years and it hasn’t been a problem or any more of a problem any other method would cause me. So, in short, that works for me.

Closure:

I don’t know that you wanted to learn how to update Ubuntu in the terminal, but that’s today’s lesson. It’s not very complicated. I could keep going, as my actually command also includes the ‘clean’ option. I use an alias to tie it all together, rather than typing it out each time. There are also similar commands you can use for other distros with different package managers.

Make Applications Start Faster in Ubuntu

Today’s article is pretty specific as we discuss one way to make applications start faster in Ubuntu. However, I feel like I need to make you aware that this isn’t some sort of miracle software. The usage and results are pretty limited and I’m mostly covering this because it was in my notes and a question I saw recently on Reddit.

Now, for reasons, I’m not sure what format this article will take. I haven’t written it yet and the information I want to share is kinda mixed. I guess we could have a longer intro than normal.

So, the tool in question is called ‘Preload’. The man page describes Preload like this:

preload – Adaptive readahead daemon

Though I think it’s important to also quote this (also from the man page):

preload is an adaptive readahead daemon that prefetches files mapped by applications from the disk to reduce application startup time.

So, what is this Preload? It’s a daemon that runs in the background and monitors what you do. It pays attention to what applications you open (for example) and loads the various files into memory. Then, when you open the application it will open faster. This is mostly useful if you’ve opened the application, closed it, and wish to open it again. The second time you open the application, the theory is that it’ll open faster.

Does it work? I haven’t lied to you yet and I’m not going to start now. I haven’t tested it enough to claim it has any great benefits. Oh, I’ve installed it before and left it running. I just didn’t do any verification and I’m not going to cite my observations as factual without having data to back that up. I will say that I didn’t notice it slowing anything down. Of course, I have fast hardware, and using a stopwatch to test the results would be full of all sorts of inaccuracies.

Do I recommend it? Well, it doesn’t seem to hurt anything. It does seem faster when I close Thunderbird and open it back up again. I use an NVMe M.2 SSD, which is already pretty speedy, so I doubt I’d see much. I’ve never tried with a slower SSD nor on an older spinning platter HDD – which is where I’d expect this Preload to work best. If you’re using older disks, it may be worth trying Preload. But, you won’t break anything if you install it on more modern hardware.

Make Applications Start Faster:

So, installing Preload is pretty simple. Once you’ve installed Preload, you are done. There’s no need to tinker with settings. There’s no need to configure it. It should even automatically set itself up as a self-starting daemon.

Crack open your terminal (you know how to do that by now) and enter the following to install Preload in Ubuntu:

sudo apt install preload

1	sudo apt install preload

Agree to install and enter your password. That’s it. That’s all you need to do. You can check the man page:

man preload

1	man preload

See? I told you this would look like a weird article.

Closure:

Have you had good luck with Preload? Have you been using it all along? Did you use it back when you were using a spinning hard drive? Did it help to make applications start faster? Let me know in a comment. I mean, it’s not snake oil, but how much could it help an average user with modern hardware? I’m not sure how much it’ll help those folks.

How To: Encrypt A USB Drive

So, today’s article will be a bit different, as I answer a question posed to me by way of the contact form – which is how to encrypt a USB drive. Being the nice guy I am, I answered the question. As I’m also often busy (or lazy), I also decided to turn this into an article. Why not?

I normally frown on people asking me questions directly. My usual suggestion is that they visit a forum and ask there. I usually direct them to Linux.org, where there’s a good forum filled with all sorts of smart people. That’s usually a sufficient answer, but this time I had a few spare minutes and typed out a response to them.

First of all, this was their question (I’ve removed all the superfluous stuff):

How would you encrypt a USB drive?

There were several sentences, a preemptive thanks, and some commentary about reading the site regularly. I decided to tackle this question but I was limited strictly to text because I was using email as my format.

But, if we start with the question, we can see an immediate problem. The question was ‘how would you’… Well, I’d crack open the terminal and use a tool called cryptsetup. That’s what I’d do. It’s a great tool and I’m familiar with its use.

However… That’s not what I’d suggest to the person asking the question. I did mention this to them in my reply, leaving the door open for more questions or for them to hit up their favorite search engine. Instead, I detailed another way to encrypt a USB drive. Yes, they used the word ‘drive’ and not ‘thumbdrive’. That doesn’t matter.

How To Encrypt A USB Drive:

The first thing you’re going to need for this is ‘Gnome Disks’. So, let’s go ahead and ensure you’ve got that installed, open your terminal by pressing CTRL + ALT + T and install the application. If you’re using apt you’d use the following command, but you’ll need to edit it for your package manager. (It’s almost certainly available in your default repos.)

sudo apt install gnome-disk-utilities

1	sudo apt install gnome-disk-utilities

Using Gnome Disks is a good idea. It’s fairly ubiquitous, easy to install, and doesn’t pull in a ton of dependencies when you install it. That means you can easily use Gnome Disks with pretty much any desktop environment out there with ease and very little fanfare.

Now, insert the USB drive. Don’t worry if it automatically mounts. Gnome Disks is smart enough to deal with that. Any data on this disk will be lost. It will be irrevocably lost. There’s no ‘oops’ button involved.

With Gnome Disks now installed (do not ask me why the command to open the application is different than the command to install the application), you can open it with the following:

sudo gnome-disks

1	sudo gnome-disks

There you go, you’re in a GUI now. You won’t need the terminal for anything else. (This would be easier with images, but I couldn’t really include images in the email reply without a lot of work and them potentially never even seeing the images due to reading the email in plain text format.)

On the lefthand part of the Gnome Disks window, pick the USB drive you want to encrypt.

On the right-hand part of Gnome Disks, click on the ‘gears’ icon and select the ‘Format Partition’ option.

Add a name for your encrypted USB drive in the next window. Then, say it is an internal disk (it’s all good) and tick the button to password-protect the volume.

In the next window, you will type your password twice. You’ll type it once and then type it again below that. This is to make sure you typed it properly. It’s a good idea to remember this password, ’cause this isn’t something you can just back out of and still have your data.

At this point, Gnome Disks will give you a warning about data loss. In the upper right, click the ‘Format’ button. Be certain about what you’re doing because this will erase data. Gnome Disks doesn’t care if the drive contained the only copies of your child’s birthday pictures.

Gnome Disks is kinda like a wolverine. Approach it with caution because it does not give a crap about your feelings.

Assuming the winds are in your favor, you should now have an encrypted USB drive. Test this by unplugging your USB drive and plugging it back in. When you plug it back in, it should ask you for a password. Enter your password to ensure you typed it properly in an earlier step. If all goes well, enjoy your encrypted USB drive.

Closure:

By the way, happy Mother’s Day (for those who qualify).

And so, that was more or less my answer to the inquisitive user. I don’t mind questions. I just don’t always have time for that, and often don’t know the answers. Of course, I did make a few changes. The actual reply I sent them was worded a bit differently in places. I think the above reads better and is more concise.

In this case, I think I got it right and they were able to encrypt their USB drive. I haven’t heard back from them since. It’d be nice if they let me know but they left me hanging. Ah well… If it’s wrong, someone will leave me a comment!