messaging Archives • Linux Tips

Today’s article will have limited use for my regular readers, as we talk about how you can send a message to logged-in users. The thing is, this is only valid for those users who are logged into the terminal. It doesn’t pop up a handy GUI window (like the old messenger service from Windows, though I’m sure there’s a way to do so). This is only valid for users who have logged into the terminal.

Got it?

Good!

So, who is this useful for? Well, those of you who have shell users. This is useful for system admins who want to send mass messages to the people who are currently logged in. For example, maybe you want to message folks to let them know that you’ll be doing routine maintenance and rebooting the system at a specific time.

While this is a bit archaic, it’s still useful under some circumstances.

Why do I include it if it’s so archaic and has limited use?

Well, because I can. You never know when someone doesn’t know something and will hit up their favorite search engine to learn something. I care that each article teaches you something, even if that something isn’t all that grandiose.

Plus, it’s nice to have an easy article now and then. This is going to be a pretty easy article! There are just a couple of tips that I have for folks and that’s the end of it.

Send A Message To Logged In Users:

You’ll need an open terminal if the opening wasn’t descriptive enough. After all, we’re sending messages to users who are logged in with the terminal. So, open said terminal. Most often, you can press CTRL + ALT + T and your default terminal should open.

With your terminal open, you can be reasonably sure that the wall command is available. Run this command to be certain that the wall command is available:

wall --v

wall --v

You can then check the man page to ensure that this is the correct tool for the job. As you’ll see, if you run man wall, this is the tool for the job:

wall – write a message to all users

See? It is the right tool for the job. The syntax is even remarkably simple:

wall "<message>"

1	wall "<message>"

Or, if you do this often and want consistency:

wall file_name.txt

1	wall file_name.txt

So, you can try something like:

wall "We'll be updating the system in 15 minutes. A reboot will be required."

1	wall "We'll be updating the system in 15 minutes. A reboot will be required."

Or, if you do this often, you can make a .txt file with your message and just reference that file in the wall command. That’d look like the above example.

See? That’s it. That’s all you need to know to send a message to logged in users. If you’re new to your admin job or maybe have started running a public-access shell, you’re now able to send those messages to your users.

Closure:

I figured it was a good day for a nice easy article. They can’t all be complicated, because not everything is complicated. Sometimes, it doesn’t take 1000+ words to describe a task. I could probably bloviate and digress, but that’d just make the article longer with no real value.

As much as it might seem otherwise, I value your time. I try to remain on topic and I try to include no more than the information you need – with just a bit of digression in the intro. I figure most of you skip the intro anyhow!

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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:

who -u

who -u

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

who -u | awk '{print $1, $2}'

1	who -u \| awk '{print $1, $2}'

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:

echo "<message>" | write <$1> <$2>

1	echo "<message>" \| write <$1> <$2>

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:

echo "this is a message" | write kgiii pts/3

1	echo "this is a message" \| write kgiii pts/3

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.