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What is a tty on linux (and how to use the tty command)

What is a tty on linux (and how to use the tty command)

In this article, we’re talking about the tty command in Linux. The Linux operating system uses file system to represent everything. Not just the text files and images but even the hardware and the terminal. Yes, even the terminal you use to interact with Linux is actually a file.

tty is the command that displays information related to this terminal file.

tty is short for teletype. Historically the word ‘teletype’ comes from the word ‘teletypewriter’. A teletypewriter is an electromechanical device that sends and receives typed messages through various communication channels. That’s very similar to what a terminal does. In fact, in the early days, the first computer terminal was referred to as teletype terminal.

Table of Contents

How to use the tty command?

tty prints the name of the terminal file to standard output. To print the name just type ‘tty’ and hit enter.

Options with tty command

To know more about tty command you can use the –help as shown below:

What is a tty on linux (and how to use the tty command)

We can see that there are only two options available with tty command.

–silent option

When using the silent option along with tty command, no output is seen on the screen. It just returns the exit status.

We can print the exit status out to the screen by using the command :

What do different exit codes mean?

  • 0 : standard input is a terminal
  • 1 : standard input is not a terminal

Identify tty version

Using –version option along with tty command gives the version of tty you are using.

Conclusion

In this tutorial, we covered tty command. To learn more about the tty command refer to its man page. Although this tutorial covers everything there is to learn about the command.

What is a tty on linux (and how to use the tty command)

TTY what is the meaning of it? Why this short name? How to use this command actually? Many more questions you can do about this. Yes, we will go to talk about them. Let’s see.

What is TTY Linux?

At first, try to know what the meaning of TTY is. TTY is the short form of ‘Teletype.’ It is the most commonly known as a terminal. It is mainly a device that put into service as software at present. It permits you to work together with the process bypassing the data that you inputted to the method. It also is displaying output generate by the process.

TTY can be seen in different types. For instance:

  • Graphical Consoles – you will this access by the combination of the keys Ctrl+Alt+Fn.
  • Terminal Emulators – It’s like a Gnome terminal, and it runs inside the X session.

In Linux, the whole thing is a file. When any hardware tool added with the system, it’ll represent a especial file. But it would help if you did not surprise thinking that the Linux TTY terminal will also describe as the file. For this, there has an existed command named TTY works to display the information which is related to the terminal.

In the desktop version of Linux, you also can see a PTS TTY Linux that stands for Pseudo-Teletype multiplex, and it is the emulated Teletypes software. It can handle the connection from the terminal window PTS. If you need, you can learn more about what is TTY mode?

The repurpose of TTY

The TTY is the right contender as an input and output device. It is a device that permits you to type, encode, sent, receive, decode, and even print the essential messages. If the device connects with another teletype, as long as the encoding language will same to send and receive. It maintains the standard keyboard for this.

How TTY works Linux

Follow straight forward tips such as at first run the Linux TTY terminal with the output that will include the connected terminal for getting the standard output. This is the process of the TTY session to give the command its works to the users.

There have a few existed command line sections of –s for silences this command that no output produced. To recognize the existed status of TTY, you need to follow the below meaning.

  • 0 is if the standard input will the terminal
  • 1 is if the standard information won’t the terminal
  • 2 is if you get the wrong argument
  • 3 is if the writer wrong occurs

Summery

It is needless saying that this post has presented the right information on what is TTY Linux? We feel grateful that we have to talk and share with you about this and informed you of more important topics on it.

This brief guide describes how to switch between TTYs without using function keys in Linux operating systems. Before going further, we will see what TTY is. As mentioned in an answer in AskUbuntu forum, the word TTY came from TeleTYpewriter. Back in the early days of Unix, the user terminals connected to computers were electromechanical teleprinters or teletypewriters( tty in short). Since then, the name TTY has continued to be used for text-only consoles. Nowadays, all text consoles represents virtual consoles, not physical consoles. The TTY command prints the file name of the terminal connected to standard input.

Switch Between TTYs In Linux

By default, there are 7 ttys in Linux. They are known as tty1, tty2. tty7. The 1 to 6 ttys are command line only. The 7th tty is GUI (your X desktop session). You can switch between different TTYs by using CTRL+ALT+Fn keys. For example to switch to tty1, we type CTRL+ALT+F1.

This is how tty1 looks in Ubuntu 18.04 LTS server.

What is a tty on linux (and how to use the tty command)

If your system has no X session, just type Alt+Fn key. You don’t need to use CTRL.

In some Linux editions (Eg. from Ubuntu 17.10 onwards), the login screen now uses virtual console 1 . So, you need to press CTRL+ALT+F3 up to CTRL+ALT+F6 for accessing the virtual consoles. To go back to desktop environment, press CTRL+ALT+F2 or CTRL+ALT+F7 on Ubuntu 17.10 and later.

You know now we can easily switch between TTYs using CTRL+ALT+Function_Key(F1-F7). However, if you don’t want to use the functions keys for any reason, there is a simple command named “chvt” in Linux.

The “chvt N” command allows you to switch to foreground terminal N, the same as pressing CTRL+ALT+Fn. The corresponding screen is created if it did not exist yet.

Let us see print the current tty:

Sample output from my Ubuntu 18.04 LTS server.

Print current tty

Now let us switch to tty2. To do so, type:

Remember you need to use “sudo” with chvt command.

Now, check the current tty using command:

You will see that the tty has changed now.

Similarly, you can switch to tty3 using “sudo chvt 3”, tty4 using “sudo chvt 4” and so on.

Chvt command can be useful when any one of your function keys doesn’t work.

To view the total number of active virtual consoles, run:

As you can see, there are two active VTs in my system.

You can see the next unallocated virtual terminal using command:

A virtual console is unused if it is not the foreground console, and no process has it open for reading or writing, and no text has been selected on its screen.

To get rid of unused VTs, just type:

The above command deallocates kernel memory and data structures for all unused virtual consoles. To put this simply, this command will free all resources connected to the unused virtual consoles.

For more details, refer the respective command’s man pages.

Suggested read:

And, that’s all for now. Hope this was useful.

What is a tty on linux (and how to use the tty command)

In this article, we’re talking about the tty command in Linux. The Linux operating system uses file system to represent everything. Not just the text files and images but even the hardware and the terminal. Yes, even the terminal you use to interact with Linux is actually a file.

tty is the command that displays information related to this terminal file.

tty is short for teletype. Historically the word ‘teletype’ comes from the word ‘teletypewriter’. A teletypewriter is an electromechanical device that sends and receives typed messages through various communication channels. That’s very similar to what a terminal does. In fact, in the early days, the first computer terminal was referred to as teletype terminal.

Table of Contents

How to use the tty command?

tty prints the name of the terminal file to standard output. To print the name just type ‘tty’ and hit enter.

Options with tty command

To know more about tty command you can use the –help as shown below:

What is a tty on linux (and how to use the tty command)

We can see that there are only two options available with tty command.

–silent option

When using the silent option along with tty command, no output is seen on the screen. It just returns the exit status.

We can print the exit status out to the screen by using the command :

What do different exit codes mean?

  • 0 : standard input is a terminal
  • 1 : standard input is not a terminal

Identify tty version

Using –version option along with tty command gives the version of tty you are using.

Conclusion

In this tutorial, we covered tty command. To learn more about the tty command refer to its man page. Although this tutorial covers everything there is to learn about the command.

GoTTY is a simple GoLang based command line tool that enables you to share your terminal(TTY) as a web application. It turns command line tools into web applications.

It employs Chrome OS’ terminal emulator (hterm) to execute a JavaScript based terminal on a web browsers. And importantly, GoTTY runs a web socket server that basically transfers output from the TTY to clients and receives input from clients (that is if input from clients is permitted) and forwards it to the TTY.

Its architecture (hterm + web socket idea) was inspired by Wetty program which enables terminal over HTTP and HTTPS.

Prerequisites:

You should have GoLang (Go Programming Language) environment installed in Linux to run GoTTY.

How To Install GoTTY in Linux Systems

If you already have a working GoLang environment, run the go get command below to install it:

The command above will install the GoTTY binary in your GOBIN environment variable, try to check if that is the case:

Check GOBIN Environment

How To Use GoTTY in Linux

To run it, you can use the GOBIN env variable and command auto-completion feature as follows:

Else, run GoTTY or any other Go program without typing the full path to the binary, add your GOBIN variable to PATH in the

/.profile file using the export command below:

Save the file and close it. Then source the file to effect the changes above:

The general syntax for running GoTTY commands is:

Now run GoTTY with any command such as the df command to view system disk partitions space and usage from the web browser:

GoTTY will start a web server at port 8080 by default. Then open the URL: http://127.0.0.1:8080/ on your web browser and you will see the running command as if it were running on your terminal:

Gotty Linux Disk Usage

How To Customize GoTTY in Linux

You can alter default options and your terminal (hterm) in the profile file

/.gotty , it will load this file by default in case it exists.

This is the main customization file read by gotty commands, so, create it as follows:

And set your own valid values for the config options (find all config options here) to customize GoTTY for example:

You can set your own index.html file using the –index option from the command line:

How to Use Security Features in GoTTY

Because GoTTY doesn’t offer reliable security by default, you need to manually use certain security features explained below.

Permit Clients to Run Commands/Type Input in Terminal

Note that, by default, GoTTY doesn’t permit clients to type input into the TTY, it only enables window resizing.

However, you can use the -w or –permit-write option to allow clients to write to the TTY, which is not recommended due to security threats to the server.

The following command will use vi command line editor to open the file fossmint.txt for editing in the web browser:

Below is the vi interface as seen from the web browser (use vi commands here as usual):

Gotty Web Vi Editor

Use GoTTY with Basic (Username and Password) Authentication

Try to activate a basic authentication mechanism, where clients will be required to input the specified username and password to connect to the GoTTY server.

The command below will restrict client access using the -c option to ask users for specified credentials (username: test and password: @67890):

Gotty with Basic Authentication

Gotty Generate Random URL

Another way of restricting access to the server is by using the -r option. Here, GoTTY will generate a random URL so that only users who know the URL can get access to the server.

Also use the –title-format “GoTTY – << .Command >> (<< .Hostname >>)” option to define the web browsers interface title and glances command is used to show system monitoring stats:

The following is result of the command above as seen from the web browser interface:

Gotty Random URL for Glances Linux Monitoring

Use GoTTY with SSL/TLS

Because by default, all connections between the server and clients are not encrypted, when you send secret information through GoTTY such as user credentials or any other info, you have to use the -t or –tls option which enables TLS/SSL on the session:

GoTTY will by default read the certificate file

/.gotty.crt and key file

/.gotty.key , therefore, start by creating a self-signed certification as well as the key file using the openssl command below (answer the question asked in order to generate the cert and key files):

Then use GoTTY in a secure way with SSL/TLS enabled as follows:

Share Your Terminal With Multiple Clients

You can make use of terminal multiplexers for sharing a single process with multiple clients, the following command will start a new tmux session named gotty with glances command (make sure you have tmux installed):

To read a different config file, use the –config “/path/to/file” option like so:

To display the GoTTY version, run the command:

Visit the GoTTY GitHub repository to find more usage examples: https://github.com/yudai/gotty

That’s all! Have you tried it out? How do you find GoTTY? Share your thoughts with us via the feedback form below.

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There are 7 terminals that can be used in our system. tty7 is GUI based.

How can I check which tty I’m currently using?

8 Answers 8

There are several ways to find this out. I would go with the who am i (not who ) command:

When I’m in a graphical terminal, it would return something like:

Under ssh session using a graphical terminal result is the same, but instead of (:0), I will get my machine IP (192.168.x.x). other commands like w , who , pgrep , ps , etc are helpful too.

For example to find out at which tty my graphical interface is running:

Which in my case, because I don’t use any display manager like gdm or slim it will produce:

What is a tty on linux (and how to use the tty command)

Use tty command.

If I am right this is the reference:

Let’s take a step back and start with the confusion: what is a tty? Originally tty was an abbreviation of teletype which became glass teletype which became any terminal or the connection to one, specifically a serial port (These are still around, most commonly /dev/ttyS0, /dev/ttyUSB0 and sometimes /dev/ttyacm0). Then you got pseudo ttys and virtual ttys. old unix hands are familiar with pseudo ttys these are used for remote terminals (ssh and telnet), virtual terminals (xterm and the like), and terminal multiplexers (screen and tmux). Pseudo ttys have had various naming schemes over time but the current one uses names like /dev/pts/0. Virtual ttys on the other hand are associated with virtual consoles, specifically when you use control alt function keys you are switching virtual consoles each of which is paired with a virtual tty. The most famous virtual tty is /dev/tty7 which often used for graphical sessions (because the first six are usually text logins) there is nothing special about tty7 as you can run X servers on any virtual console (although running one on /dev/tty1 is really hard as the kernel opens it for boot logging, but I have done it) and you can do text logons on any virtual tty including tty7 (although init configuration is required and systemd’s dynamic allocation makes things interesting and switching to tty13 and up may need a change to the keyboard map).

So if you need to find your pseudo tty (or virtual tty when using text mode) there are all sorts of solutions like who am i or ps ax|grep $$ this is relatively easy to do as there are multiple ways to find out this as the pseudo tty is opened on standard io in most cases and there are other methods that work even when io is redirected. this also has the advantage of also doing the right thing when using serial ports and virtual ttys as long as you are not using graphical terminal emulators or terminal multiplexers.

But what if you are wanting to identify the virtual console? sudo fgconsole may be useful for interactive cases. Or what I do is just walk the consoles as switching is typically quick enough. I am not aware of a programmatic method that works reliably in noninteractive or nonforeground cases.

Let’s look at an example that is guaranteed to not be able to reliably answer the virtual console ever. The computer I am sitting in front of (alpha) has an Xserver running on tty2(:1), I have three windows open two xterms and a vncviewer (connected to bravo:2). One xterm is running screen, the other is running ssh charley. Screen has two windows open, ssh delta and who (who correctly identifies the pseudo tty in column two and provides the hint (:1:S0) in column five that tells us that the pseudo tty is connected to the first screen session which is connected to the second X server, but does not give any virtual console information). Running who over either ssh session gives the hint (alpha) which identifies the machine that the ssh session came from which is comparatively good for remote sessions. Although there is little information about what is connected to the pseudo tty (and absolutely no virtual console or even remote tty information is available) at least the remote host is identified. the information about screen can be wrong as screen sessions are detachable, and vnc provides no useful information at all as the only difference between a vnc session and a local session is the display number. In many cases you can assume that :0 is on tty7 but not always, and never on mine as bravo does not have a graphics card at all and :0 is a vnc session (which confuses who because it thinks it is the local console) and none of the machines use tty7 as a graphical session, because I (not just to be contrary) dump logs to tty7 (and tty5, tty6, and tty8 also) religating graphical sessions elsewhere. But wait screen can also act as a terminal program allowing you to establish a session over a serial cable. What does such a session report when who is run? Why naught but the serial port whether it be through vnc, xterm, ssh, screen and a usb serial adapter all at once or is connected to my televideo.

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TTY: What is? What’s the use? How to use it?

Very simple, TTY is an abbreviation for teletypewriter. Do not understand? You for sure have used .. If you use linux .. if you do not close that uses your internet explorer .. and look for a window to play. If you use MAC makeup and go for this PC formats. Jokes aside, TTY is when you use the shortcut key

, or even when you open a terminal on your OS.

Yes! TTY is simply a terminal to which you are connected. An interface from which you can give text commands to a machine.

In the case of terminal initiated within its interface like this:

What is a tty on linux (and how to use the tty command)

It is a virtual TTY, which simulates a direct command interface to the OS.

Command TTY

This command tells you what the file name connected to standard input. The term pts is the abbreviation for pseudo. If you run the command directly on a real TTY you have the following:

The number in the command output indicates that the machine it ran on standard input is associated with that number. If you open other terminals, they are numbered sequentially 6,7 … In some distributions few tty are blocked because they are associated with a manager like modem-manager or LightDM .

Beauty and serving me? Imagine that you are using more than one terminal in its distribution, common, and you want the result of a command from a tty appears in another tty. For example the listing of a directory appears in another terminal, you can use:

For more on the tty command, use on your tty command:

Subscribe to blog here to receive news and details about linux and other related software. In the next post to learn to conserve your pc memory TTY removing your computer’s unnecessary.

Table of Contents

How to enable tty for more than 6 console. How to disable all the tty terminals in Linux. systemd disable tty. systemd enable tty using getty service in Linux.

What is a tty on linux (and how to use the tty command)

I have written another article to understand the difference between /dev/tty and /dev/pts . In this article I will share the steps to disable tty and enable tty for specific terminal consoles in Linux.

Basic overview on TTY

  • tty consoles are managed by systemd in Red Hat Enterprise Linux 7 OS.
  • tty consoles are created on-the-fly upon access.
  • The allowed number of consoles can be configured in /etc/systemd/logind.conf file.
  • Set NAutoVTs= value in this file to desired number to have systemd capable of generating those many tty consoles.
  • By default there are 6 terminals available on a Linux system which can be accessed using Ctrl+Alt+F[1-6]

Disable TTY terminal console

To disable tty terminal make the below changes in /etc/systemd/logind.conf

Now since our aim is to disable all the terminals, we will leave the value as ” N ” for ReserveVT . With this step you have disabled all the available terminals. Now you can manually enable the required terminals.

Enable TTY terminal console

For the demonstration of this article I will enable console access for terminal 2 and 3 on my Linux host.

Create a symlink of a tty you want to enable in /etc/systemd/system/getty.target.wants .

Enable tty using systemctl:

Verify the changes

Next reboot the node to activate the changes

Once the node is successfully UP post reboot, attempt to connect to other terminals using Ctrl+Alt+F[4-6] and you will observe that all these terminals will be disabled although terminal 1-3 will be enabled because of our configuration.

Lastly I hope the steps from the article to enable or disable tty on Linux was helpful. So, let me know your suggestions and feedback using the comment section.

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Have you ever faced this situation, a lot of terminal connections to your server?

Before starting, we have a brief discussion on TTY. The word tty stands for teletype terminals. Some years ago, user terminals were connected to computers’ electromechanical teleprinters or teletypewriters (TeleTYpewriter, TTY), since then the name TTY has continued to be used as the name for the text-only console.

Here CryBit going to explain the command-line option to kill unwanted or unused or idle ttys.

We need the PID (Process ID) of that particular terminal (tty). First check the active connections server using the command “w.” Please see the sample output pasted below:

What is a tty on linux (and how to use the tty command)

Here, you can see three tty connections to your server, pts/0, pts/2 and pts/3 where PTS stands for pseudo terminal. You can also see which processes are currently executing for those tty connections. In this command we could not see the process ID (PID) of those ttys.

We can use the PS command to find out the process ID. Here is the sample output:

Example

Here You will get the user info and process ID. Then use kill command to terminate that tty connection.

For the above example

If the process doesn’t gracefully terminate, just as a last option you can forcefully kill by sending a SIGKILL

Another way; single command to kill tty connections

You can also use the PKILL command along with the switch “-t” to kill a tty connection forcefully. Please see the commend pasted below:

Example

How to check the current tty/pts session where you connected?

Yup, before going with the kill command, you must have an idea about your tty/pts session. This can be simply checked using the command ps or tty. See the usages pasted below:

Using ps

Using tty

tty is the best command!!

That’s it!! Go ahead and kill _/\_ Thanks!

Hooooray…. It’s time to relax!! Just watch A Breakfast Ride To Chota Ladakh

Also read:

  1. Setup/configure a three node Elasticsearch cluster on CentOS 7
  2. A quick jump into AWS EC2 features – overview

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Arunlal Ashok

SRE at NewFold Digital. Linux lover. Traveller. Father of two princesses.

Always happy for an open discussion! Write to arun ((@)) crybit ((dot)) com.

8 thoughts on “ How to kill or terminate unwanted tty/pts sessions in Linux? ”

I have been through the whole content of this blog which is very informative and knowledgeable stuff, I tried a lot to run command for kill or terminate unwanted tty/pts sessions in Linux but I failed. This post helps me.

Your system load average is over 1.0 and you haven’t rebooted in 234 days…what ARE you doing to that poor system? Not rebooting means you probably haven’t applied kernel updates, so there are probably some exploitable security vulnerabilities on that instance. Maxing out your uptime between reboots isn’t nearly as critical as applying all upstream kernel and security patches in a timely fashion. And the load average should be hanging around 0.1 even on a fairly busy system, which means you’ve got some CPU heavy code running on that system that desperately wants to be optimized (e.g. adding an index to a database table to deal with an expensive SQL query). A 2.0 load average is still somewhat usable but the system is hurting to the point of being noticeable by users and SSH is gonna start lagging like crazy. I keep all of my systems running smooth at a 0.1 (or less) load average and fully patched and I don’t allow massive resource hogs like WordPress to run on them.

Manny, can you explain to me the statement of system load average? i think you need to correct your views about it.
below a healthy system 🙂
top – 23:11:24 up 4 days, 20:50, 1 user, load average: 13.48, 13.62, 13.90
Tasks: 503 total, 1 running, 502 sleeping, 0 stopped, 0 zombie

1.0 is 100% CPU Usage on average.

13.48 means that – On average – Your CPU is backlogged 1348%

That is not a good thing. If your CPU is running at 100% usage 100% of the time, you probably have a rogue bitcoin miner you’re unaware about.

100% CPU usage is represented as 1.0 on a box that has 1 CPU. It is not uncommon to have the load average above 1.0 on a box running multiple CPUs. For example, a full load on a server with 12 cores and 2 CPUs per core would be 24.0.

And Gary is correct. The load always have to be checked together with the amount of cores.
I would change the wording a bit and say 2 sockets and 12 Cores per socket are 24 Cores 🙂

Also Manny Boros is correct – at least with the uptime 😉

I would prevent offering hostings in that environment.

How can I obtain TTY terminal/information on a cellular phone.
A deaf patient is harassing me daily with a TTY landline phone. The information is not showing on my cellular carriers phone logs.

Please advised how to locate this TTY.

Why kill the child and not the parent? On my side it worked only when I killed the parent process!