Tag: networking

Monitor Network Usage On A Per-Application Basis

Today’s article is going to tell you how to use Nethogs to monitor network usage on a per-application basis. It’s actually easier than one might think and we’ll even show you how to install Nethogs on a variety of distros.

Why would you want to monitor this? Well, you may want to know which applications are eating up most of your bandwidth. Not everyone has unlimited bandwidth after all. You might also be looking for rogue applications/malware that’s using up some of your bandwidth. There are all sorts of reasons to monitor your network usage at this level. Feel free to leave a comment telling us how you intend to use Nethogs.

As stated, we’ll be using Nethogs. The man page describes it as:

nethogs – Net top tool grouping bandwidth per process

I suppose that’s mostly useful to those who know what ‘top‘ is. (There’s a future article about top and htop, when I get to it.) But, Nethogs is like a system monitor, except it’s a network monitor with some visual similarity with top. (Yes, that’s an ugly, ugly sentence.)

We’ll be using ‘sudo’ for all of these commands. It’s possible to use Nethogs without sudo, but we won’t be covering that here. If that’s something you’re interested in doing, a search engine will help you get there.

Monitor Network Usage:

Nethogs is a terminal-based application. As such, you’ll need an open terminal. Just press CTRL + ALT + T and your default terminal emulator should open right up.

Once your terminal is open, you can go ahead and install Nethogs. Pick the command that works with your system’s package manager.

Debian/Ubuntu:

RHEL/CentOS (will need to enable EPEL):

Fedora:

Arch/Derivatives: 

Once you have Nethogs installed, you can check the help files. In this case, the help files are better than the man files (I think) so just enter the following into your terminal:

Now, to run Nethogs, we’ll use sudo and just run it in the terminal. Believe it or not, this mode is generally just fine for anything you’re going to do.

That’ll open Nethogs and start monitoring your network usage on a per-application basis. It looks something like this:

Nethogs running in the terminal.
As you can see, bandwidth monitoring on a per-application basis. Tada!

Now, if you’re going to leave it open, you can change the refresh rate. That’s done with the -d <seconds> flag. If you want it to refresh every 15 seconds, your command would look like this:

By the way, if you want to exit Nethogs, you just press Q and it closes – like top and htop do.

If you want, you can specify the network interface you want to use. It doesn’t require any flags, just the network interface name. (Read Also: how to change your network interface name.) An example of that command would be:

While the application is running, you can do some sorting/display changes with the M, R, and S keys. But it’s usually not all that complicated and sorting isn’t needed. If you’re dealing with hundreds of collections, then you may want to start sorting. Really, that’s about all you’ll ever need.

Closure:

And there you have it! You have another article to read. This one is about monitoring your network usage on a per-application basis, a pretty handy skill/tool to have. It’s pretty easy and the output is clear enough for all but the newest Linux users. If you find the tool useful, or already use the tool, please feel free to comment.

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Better Network Diagnostics With MTR

This article will show you how to get better network diagnostics with MTR, a tool called “My Traceroute” that combines both traceroute and ping into a single tool. MTR is a pretty handy tool that’s likely installed by default and a tool that even regular users should have in their toolbox.

You may remember that I wrote an article about traceroute. If you don’t know what traceroute is, it’d be in your best interest to go read that article, as I will not really be duplicating the work that went into writing that article.

As of yet, I have not yet written an article about ping. Ping is a terminal-based tool, used to time how long it takes for your device to send and receive packets to and from another device. It’ll also tell you if there are packets being dropped along the way. You can use it pretty easily. Here’s a very basic ping command:

(You can use CTRL + C to stop the running process.)

The output from that command is pretty self-explanatory. The numbers you’re probably most interested in are all the way on the right, and denote how long it took for a round-trip message to complete in milliseconds. Online gamers are often interested in their ping times. This is because a higher ping may mean they may lag behind their competitors. In this case, lower is better.

Well, MTR combines the two, traceroute and ping. It’s pretty awesome. You’ll see!

Network Diagnostics With MTR:

So long as you understand both ping and traceroute, there’s not much more this article can teach you. MTR is pretty basic in its output, easily understood by all but the novice users. Anyone with any networking history will immediately grasp the importance of MTR.

MTR isn’t a new tool, having been around since 1997. I won’t be covering how to install it. MTR’s likely already installed. If not, it’ll be easy enough to install it. If anything, this article is largely just an excuse to make people aware of it.

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, with your terminal open, try:

It should look something like this:

mtr in action
I really don’t need to explain the columns, do I? I’m sure you can figure it out!

There’s some options while it is running. The H, D, R, O, and Q keys all have functions, listed right there after “Keys:”! There are a few options when starting MTR, a whole lot of options. You can find those options by running man mrt. I’ll cover a couple of interesting options here.

If you want to limit the number of pings, you use the -c flag and then add the number. In the example below, I have chosen 5.

You can also just show IP addresses, not resolving the hostname. Like so:

If you want to show both IP addresses and resolved hostnames, the flag is -b.

There’s more that you can do with it, but mostly you can use it to find where along the line the traffic stops. If it’s on your end, you get to do something about it. Otherwise, I suppose you’re at the whim of the MITM. So, give the man pages a look and let me know in a comment if you already use this tool and how you use it.

Closure:

And there’s another article. Woohoo! It’s not just another article, but it’s an article about doing network diagnostics with MTR. It’s not as hard as one might think to come up with ideas for articles. Sometimes, I just use a tool and then realize it may make for a good article. That’s what happened in this case.

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How To: Find Your IP Address Through Your Terminal

The answer to the question, “What is my IP address?” can have different answers. In practice, you likely have more than one IP address. This article will explain how and will tell you how to use your terminal to find your IP address(es).

What is an IP address?

An IP address is a numerical designation given to computers on a network. This number is used to identify the computer. You can also identify a computer by their hostname, but the hostname is resolving to an IP address. Computers that are connected to a network will have an IP address.

There are two types of IP addresses to be curious about these days. There’s IPv4 and IPv6. IPv4 predates IPv6 and is still in use, but has run out of numbers. IPv6 solves that by enabling a whole lot more combinations. IPv6 has a potential of 340,282,366,920,938,463,463,374,607,431,768,211,456 addresses – which is a whole lot of ’em, especially when compared to IPv4’s paltry ~4.3 billion addresses.

IPv4 addresses have technically already been exhausted, and have been since early 2011. The addresses still exist, but they’re all assigned to various entities. The IPv6 roll-out has been slow. Odds are good that you’re using IPv4 right now, in fact I know you are – as this site has an IPv4 address. Still, your router is likely handing out IPv4 addresses and your ISP is likely still using IPv4 addresses.

Additionally, in most cases, you would be concerned with two IP addresses. You’re likely connected to a router/modem that’s connected to the internet. As such, you will have a private IP address and you’ll have a public IP address. The first is (usually) assigned to your computer by your router and the second is assigned to your router by your ISP. This article will explain a little about each and how to find both of them.

Find Your Private IP Address:

Your private IP address will be in a reserved section of the IP address space. It will probably be handed down by DHCP (Dynamic Host Configuration Protocol), but many routers will both let you pick your IP address (from the reserved space) or will just assign the same IP address to the same device based on the MAC address (Media Access Control). 

The reasons you’d want to know it are your own, but it’s handy if you want to connect to a specific computer. As I know my laptop is 192.168.1.5, I can just SSH into it using that address. I know my media server is a different address, and I can connect to it with the IP address as well.

There are a number of ways to find your private IP address. I’ll share two of them that are quick and easy. For this, you’re going to want to open your terminal, which you can do by pressing CTRL + ALT + T and it should open right up.

First try:

You can also try:

In both cases, you look for ‘inet’ AND your device. You’re not looking for ‘loopback’, as that will likely list your IP address as 127.0.0.1 – which isn’t the address you’re after for reasons beyond the scope of this article.

You’re looking for your device, maybe named ‘eth0’ or ‘wlo1’ or similar, and then you’re looking for ‘inet’. Your IP address is the next four sets of digits (or alphanumeric combinations in the case of IPv6). For example:

example IP address
I’m not so sure the underlining matters.

One or both of those methods should work for you with any major distribution. There are surely many other ways to find your IP address, so feel free to leave a comment indicating how you do it.

Find Your Public IP Address:

The next kind of address is your public IP address. This is the IP address your ISP assigns you. If you wanted to connect to your computer over the world-wide-web, you’d be able to do so (with obvious caveats and proper configuration) with your public IP address.

It’s also the address I see (unless you’re using a VPN) in my server logs when you visit my site. That’s perfectly normal – as my site needs to know where to send the return packets. If my site didn’t know an address to send data to, it simply wouldn’t work.

You can think of this as the IP address assigned to the public side of your router, and your router then passes that information along via the private IP address that originated the request. This lets you have multiple devices using the same public IP address. (Read about NAT here.)

My understanding is that some ISPs are NATing public IPv4 addresses so that multiple routers can actually have the same IP address (not necessarily a good thing). However, that too goes beyond the scope of this article and isn’t want this site is actually about.

Anyhow, there are numerous public servers out there that you can ‘cURL‘ and those will give you your public IP address right there in the terminal. Just like above, you can open your terminal by using your keyboard and pressing CTRL + ALT + T. Once open, you can try:

Or you can try:

It should look a little something like this:

my public IP address
Yes, that’s my public IP address. No, I don’t care.

There are numerous other sites that’ll spit out the same info. The top-most example was recently handed over to Cloudflare, just so folks are aware.

Closure:

And, there you have it. You now know how to find your public IP address and how to find your private IP address from within the terminal. There are also many dozens of websites that will tell you your public IP address, but we might as well stick to the terminal for this one. Why not? You can do a lot in the terminal.

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Enable x11 Forwarding With SSH (Remotely Use GUI Applications)

In the last article, I explained how to enable SSH. In today’s article, we’re going to learn how to forward GUI application windows with SSH. x11 forwarding is easy and beneficial. Once you learn how, you may decide to stop using VNC or TeamViewer.

Just to quickly clear up a misconception, x11 forwarding works just fine with Wayland. Way back in the earliest days of Wayland development, it was agreed that it should retain backwards compatibility with x11 forwarding.

What is this strange thing, this x11 forwarding?

Well, when you’re connected to another computer via SSH you can use the terminal to control the computer. That’s great, but what if you want to use a GUI application? Sure, you could set up some sort of remote desktop application, such as VNC. Or, alternatively, and often more simply, you can just forward graphic applications over SSH. It’s remarkably easy!

Perhaps a picture is in order. Check this:

gedit in action
That’s GEdit running on a different computer, but forwarded to this one. Pretty neat, huh?

That’s right. That’s GEdit running on my laptop. I’ve just forwarded the GUI application to this computer. If I write something and save it, it’d be saved on the computer that I’m connected to and not the computer that I’m using.

Amusingly, I used this exact process just recently. I had to move a complex password to my laptop and I was being lazy. So, I opened GEdit remotely and pasted in my password, transferring my new password to the other device. See? It comes in handier than you might think.

Let’s Enable x11 Forwarding:

How do you do this? Well, first you need to crack open your terminal. To do that, you just press CTRL + ALT + T on your keyboard and your default terminal emulator should open.

Now, in said terminal, you need to run the following command:

Once you have that file opened with nano, you just need to remove the appropriate pound sign (“uncomment” it out) for the right line. Look for the line that says:

And change it to:

Then save the file with nano by pressing CTRL + X, then Y, and then ENTER. (You may want to learn that, as that’s how you save files in nano.)

Next up, you’ll restart the SSH service and be done with it:

And that’s it! You can now use x11 forwarding over SSH. To do so, you just need to add the -X switch. That’s not as complicated as you might think. Nothing in this article is all that difficult.

To try to make sense of that above command, if I were to remotely connect to the MSI laptop, then my command would look just like:

You can also use the IP address, instead of the hostname, just like we discussed in the previous article about SSH. To do that, it looks like this:

x11 Forwarding in Action:

Once you’re there, just go ahead and start an application. For example, open gedit by typing just that into the terminal. You may find some applications won’t work, often due to ownership and permissions issues, but you’ll find many that work just fine. If you find one that doesn’t work, you can always check any errors thrown and go from there.

Firefox forwarded over SSH
See? Note the carefully drawn arrow that shows where it was forwarded from. Tada!

That’s an example of Firefox forwarded over SSH using x11 forwarding and you may notice the washed out look. I haven’t really dug into it, but I am reasonably confident that washed out look is because of compression. I’ve never needed to dig into that and, amazingly enough, I don’t know everything.

Conclusion:

Anyhow, there you have it. One more article in the books and one more bit of knowledge plastered across the internet. Thanks for reading! If you want to help, you can donate, you can share the site on social media, you can vote to show what type of articles you enjoy, and sign up for the newsletter. You can even buy inexpensive hosting and start your own site while supporting this site or write your own article!

Install SSH to Remotely Control Your Linux Computers

If this article’s headline looks vaguely familiar, it’s probably because I previously wrote an article that told you how to install SSH. That article was on the earlier site. This article will show you how to install SSH, so that you can remotely control your Linux computers.

The old site, while up, will redirect to this address. It’s also a bit of a misnomer. We’ll be installing ‘OpenSSH‘ and enabling SSH. SSH is the protocol, OpenSSH is the application, specifically the ‘openssh-server’.

Let’s say your computer is in another room, in another state, over in another country, or perhaps on another continent entirely. How are you going to manage it? Servers are scattered across the world and it is not even remotely economical to send a person to administer each one of them in person. You’ll need to manage these devices remotely.

One of the best tools for this job is SSH.

As a home-use note; SSH is perfectly suitable to manage my own router. It’s quick, easy, lightweight, effective, doesn’t require an attached monitor, and more. What’s not to like? I SSH into my computers all the time! In fact, right this minute I’m connected to two other computers via SSH!

SSH has been around since 1995 and it lets you issue commands on a remote computer. In fact, the man page describes it like this:

ssh — OpenSSH remote login client

Which, as you can guess, means it lets you login to remote computers so that you can control them. It’s a pretty handy tool to have in your toolbox and it’s actually simple to install.

Install SSH:

SSH is really the protocol, and you can do many things over it. OpenSSH is the application that we’ll really be installing. Once that’s installed, you can login to the computer remotely and manage it that way. I use it quite often.

My homemade router doesn’t have a keyboard attached. It doesn’t even have a monitor attached. It’s not like I can just easily walk over and deal with it. I just got a laptop that, and it’s only used to test Lubuntu. I don’t always want to have to go over to the device and physically use it to start the test.

There’s also my dedicated server in Las Vegas – and I live in Maine. It wouldn’t be practical to fly out to Vegas every few days to run updates on the server. It wouldn’t make financial sense to go out there every time the server needed to be rebooted!

Those are all situations where you can use SSH. It’s available in pretty much every default repository out there. I’m surprised more people don’t use it. To get started, you just open your terminal (press CTRL + ALT + T on your keyboard) and enter the following:

If you’re using a distro with apt:

If you’re using a distro with yum:

Simply adjust that for your distro. For example, in OpenSUSE you may have installed it during the OS installation process. If it wasn’t installed during the initial OS installation then it’s just called ‘openssh’ – if you want to install a few of the applications surrounding openssh. You can also do a ‘sudo zypper install openssh-server’ like the rest of us.

Anyhow, once you’ve installed it, you may not even need to start it. If you install it on Ubuntu, you can go right ahead and test it immediately. If your distro requires that you start it manually, you should do that.

Once you’re done, you can test it easily enough. Try this:

If that works, you’ve properly installed openssh-server and can now make use of SSH. You may also need to enable it in  your firewall. Chances are that your firewall knows what SSH is.

To connect to your device from a remote computer, you’d do:

You can use a specific username in that command, like demonstrated in the testing command just above this command. It’s not mandatory, but doing so will skip a step.

Closure:

You can expect a couple more SSH articles, as this is woefully incomplete. A lot more can be done with SSH, plus SSH should be properly secured. For most of you, behind a NATed router, you don’t really have to worry too much unless you enable port forwarding. If you’re making the port available to the world-wide-web, you’re definitely going to need to add some security. Otherwise, there are a few nifty things you can do once SSH is enabled. We’ll cover those in future articles.

You can also connect with your hostname – probably. In many instances, you’d do this (distro-dependent):

For example, to connect to my testing laptop, I use the following command:

Go ahead and play around with it. There’s a number of ways to help secure SSH and we’ll go over some of that in a future article. I’ve been maintaining the ‘article every two days’ thing for a while now. I see no reason to expect that to not continue.

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