Monitor Your Linux System With NMON

There are times when you want to see what’s going on with your devices and you can monitor your Linux system with nmon. If you’ve never heard of nmon, that’s okay. You’ll find that nmon is a handy application that lets you monitor all sorts of aspects of your system. You’ll also find that nmon is an application that’s used in the terminal, so be prepared for that.

This nmon application is available for most Linux systems and I’ll let you know how to install nmon in this article. You’ll find that nmon stands for ‘Nigel’s Monitor’ and has been around since the early IBM AIX days. It has since been made available for Linux.

You can read about nmon on Wikipedia.
You can also visit the nmon project page.

If you check the man page, you’ll see nmon described as:

nmon – systems administrator, tuner, benchmark tool.

We won’t be doing much of that. We’ll just be using nmon to monitor the system. You can then take that information and use it to administrate, tune, and benchmark the system. We’ll be using nmon to monitor CPU, RAM, your network usage, and things of that nature.

You can also learn more about nmon from the man page because I’ll only be covering how to monitor your Linux system with nmon. There’s almost always so much more! It’s almost a shame that I try to limit many of my articles.

Installing nmon:

You can use your usual GUI tools to find and install nmon. It’ll be available for most distros. It’s also possible to install nmon in the terminal. We’ll cover that, so just press CTRL + ALT + T to open up your terminal.

With your terminal now open, we’re ready to install nmon.

Debian/Ubuntu/etc:

Arch/Mandrake:

RHEL/CentOS:

SUSE/OpenSUSE:

Gentoo:

I think that covers the vast majority of distros out there. If you don’t see your distro, or if I got one wrong, please let me know in the comments. I don’t always get this section right. I wasn’t even planning on writing this article today. But… Here we are!

Monitor Your Linux System With NMON:

You should have a terminal open already, from when you were installing nmon. This is going to sound strange, but you’re new to nmon – or you probably wouldn’t be reading this article. Because you’re new, open up a second terminal.

In the first terminal, enter this:

In the second terminal, enter this:

Now, do you see why I had you open two terminals?

In the first terminal, look at your settings and options. In your second terminal, apply them. See, once you apply them you can no longer trivially refer to the material in the first terminal.

You can apply the monitoring options in any order you’d like and in any combination that you like. The nmon application makes it easy. You press c to monitor the CPU, m to monitor memory, n to monitor the network, and things like that.

So, pick what you want to monitor from the first terminal and press the appropriate key in the second terminal. It might look a bit like this:

nmon monitoring options
There are quite a few options to pick from and it’s straightforward.

Then, your monitoring terminal could look a bit like this:

monitoring system processes with nmon
See? That’s monitoring CPU, memory, the network, and top processes – all in one screen.

Of course, once you know how nmon works and what you’d like to monitor in your Linux system, you won’t need to have the first terminal open. There are a lot of options, but you’ll find they’re easy to remember. You can also use ? instead of a separate terminal window. I find the two-terminal method to be easier for me because I don’t run nmon often enough to recollect the myriad options.

I suppose you want to know how to get out of nmon without closing the terminal window and leaving nmon running in the background. Well, that’s easy. Just press CTRL + C to quit nmon and return to your regular terminal prompt.

Closure: 

I didn’t plan on writing this article today, but I’d cracked open nmon for one reason or another and decided that I’d write about nmon when I was thinking about it. It’s another one of those articles that scratches my own itch, but it’s also something worth sharing.

It’s a pretty easy task to monitor your Linux system with nmon. I figure anyone can do it and I tried to make it easier for new nmon users by suggesting they use two distinct terminal windows. It seems like a reasonable way to get started.

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Reboot From The Terminal

The weather has had a bit of an impact on my internet connection, so this is just going to be a quick article about how you reboot from the terminal. I want to schedule this as soon as possible, so it’ll be a fairly low-effort article. This should not take long!

There are times when you may want to know how to reboot from the terminal. Then, there are times when you can’t access a GUI, and using the terminal is the cleanest method of rebooting your computer. Knowing how to reboot from the terminal might be a skill worth having. I’ll show you a couple of quick and easy ways to do this.

As the title says, this is going to take place in the terminal. You can usually just press CTRL + ALT + T to open your default terminal. You could otherwise reboot with REISUB.

So, with your terminal open…

Reboot With systemd:

The first command we’ll use to reboot your computer. We’ll be using systemd. This will only work if you’re using a distro with systemd.

Reboot With shutdown:

It should be fairly obvious that the shutdown command can be used to reboot your computer. This is one of the generic utilities, so you won’t need to install anything.

(Check the man page because there are a lot of options available.)

Reboot With reboot:

Finally, we’ll use the reboot command to reboot your computer. This might be the easiest to remember and you shouldn’t need to install anything new. You need the following command:

In some distros, you can drop the ‘now’ and the command will still reboot your computer immediately. 

Closure:

So, there you have it. You have a new article and it should even be published on time. It’s not a long article. The subject is easy enough. You’ll never know when you need to reboot from the terminal, and now you do.

Ah well…

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Locate Your Home Directory

Today’s article will not be long, nor will it be a complicated article, as we learn how to locate your home directory. This is something you probably already know, but you may encounter a strange system where things are a little different. It can happen.

More importantly, this article is going to try something new. Rather than a very long article, it’s going to be a short article. Well, shorter than most – assuming I stop puffing it up with text such as this. Why? Well, I want to see the reception and the statistics.

So, basically, every user account you’re likely to use should have a home directory. This is where the user’s files, customizations, and settings reside. Not every user has a home directory, but the accounts you’d normally use (that is log into and operate) will likely have such a directory. However, you don’t have to have a home directory – though you can expect some weirdness without one.

How To: Create a New User Without a /home Directory

The usual home directory will be in /home/<user> and that’s pretty much the standard we’ve come to know and love. You really shouldn’t need to locate your home directory, but there comes a time when you just might want to.

So, that’s what this article covers. It covers how to…

Locate Your Home Directory:

So, we’ll be doing this in the terminal. That’s a nice place to do things. Press CTRL + ALT + T and your default terminal should open. If it doesn’t open, pick a better distro!

Nah, just open it from your application menu and love the distro you’ve chosen.

We’ll just be covering a couple of quick ways to locate your home directory. That’s all this article is and there’s no reason to turn it into a longer article. We’ll do them both with the echo command. See man echo for more details.

First, you can try this command:

As you should know by now, the tilde (~) is a shortcut for your home directory and it works just fine in this use case.

There’s another echo command you can memorize, but slightly longer:

That command uses both the echo command and an environment variable, specifically $HOME (obviously). This will happily echo the results, sending them to your standard output. This can be quite useful if you’re into scripting or the like.

See also:

How To: Show All Environment Variables

I told you that this wouldn’t be long or complicated. You can now locate your home directory from the Linux terminal.

Closure:

As I said, I figured I’d try the opposite of what I’ve been trying lately. My most recent articles have been quite long and quite detailed. I like them. I enjoy writing them. This time around, it seemed like a good idea to try something different with a subject that benefits from brevity.

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Set A Timeout Value In cURL

Today we’re going to discuss a topic you probably won’t ever need but is worth knowing, we’re going to set a timeout value in cURL. We’re telling the cURL application to quit trying if it takes too long. I suppose it is something worth knowing, so we might as well learn it.

How often do you need this? Well, that depends on you and your workflow. Me? Well, let’s just say that it’s in my notes. I’m not sure that I’ve ever actually used it productively, but it is in my notes. Now? Well, now it’s in your notes! Or, at least it’s here and searchable should you ever actually need to set a timeout value in cURL.

So, what is cURL? I’ve written about it before (some links to follow) but it’s a tool to transfer a URL. That’s exactly what the man page says. Specifically, it says:

If you want to see what the HTML looks like for this site, you can run this:

(That’s not particularly helpful, but you can do it.)

I mentioned that I’d written about cURL before and it may be of some benefit to read these articles (or at least skim them) if you’re unfamiliar with the cURL application.

Let’s Have a Limited Look at Linux’s cURL Application
How To: Make ‘curl’ Ignore Certificate Errors
How To: Add A New Line With CURL

You can see a couple of useful applications of cURL:

Weather In The Terminal? We can do that!
How To: Find Your IP Address Through Your Terminal

See? So, cURL has some use – even for a regular desktop user. If any of those things take too long, you can set a timeout value for cURL, which is what this article is all about.

Set A Timeout Value In cURL:

cURL is a terminal-based tool. Sure, some GUI applications use it in the background, but it’s a terminal tool. As such, you are going to need a terminal available. You should be able to press CTRL + ALT + T to access a terminal. If not, open one from your application menu.

With your terminal open, the syntax for setting one of the timeout values in cURL is pretty basic and easy to understand. Try this:

The time_limit value is in seconds. If you wanted to load the content of this site’s home page and set a timeout value of 10 seconds, you’d run this command:

(Again, not very useful.)

But, that timeout value is just for time-to-first-byte. So, the server will need to respond within 10 seconds else the cURL process will shut down.

There’s another timeout value for cURL. You can set the overall time limit, that is the entire process (including transferring of data) must be completed within that timeframe. If it isn’t, the cURL process will shut itself down. The syntax for that time of timeout value would be like so:

So, if you wanted to make sure the entire transfer of data was done in under 60 seconds, your command would look like this:

(Again, not very useful – but it should certainly take less than 60 seconds!)

I suppose you might find some of this useful if you’re cURLing files more weighty than a web page. You can cURL actual files and write that data to your terminal’s standard output. That’s what cURL does, after all. So, you might find a use for this command.

Closure:

Well, this wasn’t a very long article. It doesn’t cover a great deal and probably won’t be useful to 99 out of 100 people. That’s okay. Not all of my articles are meant for the 99% and sometimes you just gotta write what you feel like writing. This is what I felt like writing. It probably won’t do well for search engine results and that’s okay. Someday, somebody will want this information, type it into Google, and find this site. Or another one just like it, I suppose…

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Send A Message To Another Logged In User

Today’s article might be useful for system administrators or just for fun, as we learn to send a message to another logged-in user (in the terminal, of course). This shouldn’t be a complicated or lengthy article, though many of my recent articles have been significantly longer than usual.

If you’re just a regular desktop user, this might not be all that interesting, but you can still test it if you want. Besides, you never know when you will want to send a message to another logged-in user! It could happen.

Let’s say you have a server with people logged in via SSH. This could also be a single computer with multiple people logged in, should you wish to test this and play around with sending a message to another logged-in user. Let’s also say that you want to send them a message in the terminal.

Perhaps you’re going to log them off? Maybe you’re going to reboot the server? Who knows, maybe you want to give them some sort of directions and the easiest way to do so is to send them a message that pops up in their terminal. You can do that!

We’ll be using a few tools for this. None of them are all that complicated and these little tools (do one thing and do it well) are tools that make the Linux world go around. 

For starters, we’ll be using the ‘who’ command.

who – show who is logged on

We will also be making use of the ‘awk’ command.

gawk – pattern scanning and processing language

Next, we’ll be using the ‘echo’ command.

echo – display a line of text

There will also be the ‘write’ command.

write — send a message to another user

We will also be using a pipe. We will pipe the output from one command to another command. We’ve done that lots of times on this site, so regular readers will already be familiar with a pipe and how it works.

Briefly speaking, a pipe is just one way to take the output from one command for use in another command. It’s a pretty handy tool to add to your Linux toolbox if you haven’t already done so. It’s a simple tool, which is a good thing.

If all of the above looks complicated, don’t be alarmed. It’s not all that complicated and the commands I share will be simple enough for most anyone to follow. You’ll be able to adjust them to your needs quite easily.

Send A Message To Another Logged In User:

As mentioned in the intro, you’ll want an open terminal for this. So, open your default terminal emulator. You can usually just press CTRL + ALT + T and your default terminal will open. This isn’t always true, but it’s true in many cases. You will otherwise need to open the terminal on your own.

With your terminal now open, let’s find out who is logged in. To do that, we only need the following command:

However, we only care about the first two fields, so let’s narrow that output with the following command:

The output from that command is all we need for the next part. You use the first column to identify the username. That makes them easy to identify, or at least easier for most folks.

The other column is the 2nd one. That identifies their login method, basically which terminal they’re using, and is also what we will use to specify the recipient of our message. Next, to send a message to another logged-in user, you use a command similar to this:

Or, take a look at this:

identify and send a message to a logged in user.
See? It’s not complicated. It’s harder to describe than it is to do.

So, in that case, the syntax of the command is easy, it’s just like this:

You’ll notice that the output of the command isn’t on that screen. It was sent to the other screen, the screen where that user was logged in (specifically over SSH). It quite happily sends the message to the user logged in at that location.

You can’t use usernames alone, as it’s possible for more than one person to use the same username. This method identifies the user and the method/location they’ve used to log in. It’s a pretty handy command like that. It might look a bit complex, but it isn’t.

Closure:

So, if you’ve ever wanted to send a message to another logged-in user, you can now do that. It’s easier done than explained, but hopefully, you get the gist of it and can apply it to your personal computer usage.  

It’s not always that easy to come up with ideas for articles. I often pull them from my notes, but my notes are a mess, and not all of them would make good articles. If there’s something you’d like covered, and I know the subject, feel free to contact me and let me know. Of course, don’t forget that I take guest articles when they’re about Linux.

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 site. If you scroll down, you can sign up for the newsletter, vote for the article, and comment.

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