Questions tagged [tty]

A representation of a device that asynchronously transmits and receives serial data.

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1261
votes
10answers
348k views

What is the exact difference between a 'terminal', a 'shell', a 'tty' and a 'console'?

I think these terms almost refer to the same thing, when used loosely: terminal shell tty console What exactly does each of these terms refer to?
227
votes
7answers
278k views

Why do I need a tty to run sudo if I can sudo without a password?

I have configured sudo to run without a password, but when I try to ssh 'sudo Foo', I still get the error message sudo: sorry, you must have a tty to run sudo. Why does this happen and how can I work ...
139
votes
3answers
138k views

Linux: Difference between /dev/console , /dev/tty and /dev/tty0

On a Linux system, what is the difference between /dev/console, /dev/tty and /dev/tty0? What is their respective use and how do they compare?
112
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2answers
118k views

Difference between pts and tty

Possible Duplicate: What is the exact difference between a 'terminal', a 'shell', a 'tty' and a 'console'? I always see pts and tty when I use the who command but ...
95
votes
16answers
425k views

How to connect to a serial port as simple as using SSH?

Is there a way to connect to a serial terminal just as you would do with SSH? There must be a simpler way than tools such as Minicom, like this $ serial /dev/ttyS0 I know I can cat the output from ...
63
votes
4answers
15k views

What are the responsibilities of each Pseudo-Terminal (PTY) component (software, master side, slave side)?

I am trying to figure out how a tty works1 (the work-flow and responsibilities of each elements). I have read several interesting articles about it, but there are still some blurry areas. This is ...
61
votes
2answers
10k views

Can a terminal emulator be as fast as TTY 1-6?

I've been trying various terminal emulators lately, from the built-in gnome-terminal, aterm, xterm, wterm, to rxvt. The test I've been doing is in this order: Open up a tmux window with 2 panes The ...
46
votes
8answers
103k views

How can I hook on to one terminal's output from another terminal?

I need to hook onto output of currently running terminal (tty1) from virtual terminal and capture it (running X server).
40
votes
5answers
151k views

Can I change the font of the text-mode console?

I have a Unix-like OS installed without a windowing environment; i.e., just a text-mode console and no GUI. Is it possible to change the font used by the console? To be clear, I am not talking about ...
39
votes
1answer
47k views

Is it okay to disable requiretty?

I'm trying to set up a deploy script using Capistrano At a step cap deploy:setup script is connecting to my server and trying to run commands that create directories. Then I see an error: msudo: ...
38
votes
1answer
3k views

What happens when Ctrl + Alt + F<Num> is pressed?

I am looking for an explanation of what happens in Linux when this key combination is pressed to change the current terminal. In particular, what software component intercepts this key combination and ...
34
votes
1answer
146k views

How to read/write to tty* device?

I have a device that sends information over USB to my computer. Arch Linux sets up this device by creating a file named ttyUSB0 in /dev/. I have been using GTKterm to receive this incoming information ...
34
votes
1answer
122k views

How to find which serial port is in use?

The Question: I plugged in a device (i.e. GSM modem) through a serial port (a.k.a. RS-232), and I need to see with which file in /dev/ filesystem this device was tied up, to be able to communicate ...
33
votes
4answers
51k views

Start a process on a different tty

After about an hour of Googling this, I can't believe nobody has actually asked this question before... So I've got a script running on TTY1. How do I make that script launch some arbitrary program ...
32
votes
2answers
15k views

How does a Linux terminal work?

If you fire up a terminal and call an executable (assuming one that's line oriented for simplicity) you get a reply to the command from the executable. How does this get printed to you (the user)? ...
29
votes
3answers
85k views

How to switch between tty and xorg session

My xorg session is on tty1 and if I want to issue a command from tty (because I cannot do it from xorg session for some reasons), I press Ctrl+Alt+F2, for example, and type a command. But I cannot ...
29
votes
3answers
2k views

Do programs run from an ssh session depend on the connection?

Does a program that is run from an ssh session depend on the connection to the client? For example when the connection is really slow. So does it actively wait until things are printed on the screen? ...
27
votes
5answers
28k views

How to get the tty in which bash is running?

In the second method proposed by this page, one gets the tty in which bash is being run with the command: ps ax | grep $$ | awk '{ print $2 }' I though to myself that surely this is a bit lazy, ...
27
votes
2answers
67k views

set baud speed for tty

How do I set the baud speed for a specific tty (in this case a serial port)? I tried using stty -F /dev/tty.iap ispeed 19200 But get the error Invalid argument for every speed I try (2400, 4800, ...
24
votes
1answer
16k views

What exactly is scrollback and scrollback buffer?

What are "scrollback" and "scrollback buffer" in programs like bash and screen, and how do they relate to the tty, the programs being run, and stdin/ stdout/ stderr? Here is the only definition of "...
23
votes
2answers
17k views

Why does awk do full buffering when reading from a pipe

I'm reading from a serial port connected to a gps device sending nmea strings. A simplified invocation to illustrate my point: $ awk '{ print $0 }' /dev/ttyPSC9 GPGGA,073651.000,6310.1043,N,...
23
votes
2answers
5k views

GNU Screen weird characters on click

I have a small problem in GNU screen. A GNU screen session runs on my RaspberryPi. Now sometimes, when I join it, if I click in the terminal (I'm using terminator on Fedora) I see weird characters ...
23
votes
2answers
3k views

Can the empty spaces/background in a terminal be replaced with a random(but pretty) pattern of ASCII characters?

Context and Question There are many ways to colorize the terminal and shell environment. The output of individual commands, such as ls and grep, can also be colorized. Not directly related but ...
22
votes
9answers
37k views

How to stop cursor from blinking

How do I make the cursor stop blinking when in a TTY? (or anywhere else). BONUS Points for one universal setting that stops the cursor blinking almost everywhere.
22
votes
5answers
11k views

Get ssh to forward signals

I want to be able to send signals (SIGINT is the most important) through ssh. This command: ssh server "sleep 1000;echo f" > foo will start sleep on server and after 1000 seconds it will put 'f\...
21
votes
4answers
13k views

Rebinding/disabling CTRL+ALT+F# Virtual Terminal/Console Switching

I have an application that binds CTRL+ALT+F7, but my linux machine seems to catch the keystroke. Is there a way to rebind/disable this key? A recompile of the kernel is an acceptable answer. The ...
19
votes
8answers
22k views

How can I run `watch` as a background job?

When I run: watch 'cmd >> output.txt' & the job gets suspended by the system: 3569 Stopped (tty output) Is there a workaround?
19
votes
1answer
3k views

Make program in a pipe think it has tty [duplicate]

Test environment: $ mkdir testdir $ cd testdir $ echo | tee "file name" Now, ls will print file?name (under Ubuntu GNU bash, at least), while ls | cat will print file and name in separate lines. ...
19
votes
4answers
21k views

Why are my virtual consoles completely blank?

When I go from my graphical session to a virtual console by Ctrl + Alt + F i (with i in 1 - 7 and 9-12) I see a completely black screen. Only on F8 I see the GUI. Not even a blinking coursor on the ...
18
votes
2answers
20k views

How to run builds in Docker containers from Jenkins

I am trying to use Jenkins to build a C++ project in a Docker container. I have no problem building in Jenkins, or building in a container outside of Jenkins. Below is what I tried. I am omitting the ...
17
votes
1answer
7k views

TTY On External Monitor

When using my laptop at home, I usually use an external monitor, keyboard, and mouse with my laptop's screen as a second monitor. This is all easily configured using a nice GNOME utility that I ...
16
votes
6answers
18k views

Show a notification across all running X displays

Using the command line, I'd like show a notification on every running X display. ( and running console ) Something like: notify-send-all 'Warning' 'Nuclear launch in 5 minutes, please evacuate' Is ...
15
votes
4answers
6k views

Construct a command by putting a string into a tty

I managed to do this echo -n "command" > /dev/tty1 The letters appear, and the cursor moves, but they are "ghosts" – if you hit Enter, nothing happens (they are not in stdin). Edit: In the ...
15
votes
1answer
3k views

Screenshot of X from tty

Using Xvfb I can launch an application and take a screenshot. What I'm wondering about is how to capture from an existing (dormant) X session. Say from tty or over ssh. From what I understand ...
14
votes
4answers
61k views

Pseudo-terminal will not be allocated because stdin is not a terminal

I'm trying to set up automatic SSH hopping through a server which doesn't have nc. This works from the command line: ssh -A gateway ssh steve@target (I have added my public key to the SSH agent). ...
14
votes
2answers
2k views

How does X11 interact with the kernel / perform login

As I understand for text-based interaction with the Linux kernel, a program called init starts getty (or agetty) which connects to one of the TTY devices under /dev and prompts for a username. After ...
14
votes
2answers
21k views

How to close a tty

I've opened several ttys and I don't know the key combination to use to close a tty. I'm using Arch Linux.
14
votes
3answers
24k views

How do I permanently change the console TTY font type so it holds after reboot?

I'm running Ubuntu 15.04 64-bit Desktop Edition (A Debian based Linux). I used sudo dpkg-reconfigure console-setup from the command line to change the default console font type to Terminus. ...
13
votes
2answers
4k views

What is `/dev/console` used for?

From this answer to Linux: Difference between /dev/console , /dev/tty and /dev/tty0 From the documentation: /dev/tty Current TTY device /dev/console System console /dev/tty0 Current ...
13
votes
2answers
6k views

How to get pinentry-curses to start on the correct tty?

I use gpg-agent for managing both PGP e SSH identities. The agent is started with a script like this gpg_agent_env="$XDG_CACHE_HOME/gpg-agent.env" export GPG_TTY="$(tty)" if ! ps -U "$USER" -o ...
13
votes
2answers
722 views

Possible to configure Login TTY over Audio device (Morse code or similar)?

One of the most miserable aspects of my day job is the need to occasionally investigate problems with machines scattered in remote locations all over the world that don't have network access to the ...
13
votes
1answer
610 views

Why does my terminal letter-spacing decrease when I disable a display return from using /dev/tty?

I've got a curious hardware situation, and I've run into a curious software quirk. I have a laptop with a broken screen that I have hooked up to an external display. I start up an X session and open a ...
12
votes
2answers
2k views

Why is this `grep -v` not functioning as expected?

I have a strange issue related to grep -v queries. Allow me to explain: To display connections I use who: $ who harry pts/0 2016-12-08 20:41 (192.168.0.1) james pts/1 2016-12-08 ...
12
votes
1answer
697 views

Why are two ^D presses necessary to exit `cat`? [duplicate]

Let's run cat and then type a then ^D - you will see that cat did not exit. Compare it with cat + a + Enter + ^D - now cat did exit. So, why two ^D presses are necessary to exit cat in the first ...
12
votes
2answers
7k views

Detect if running in a virtual terminal?

I'd like to autologin to tty1 on login and then use vlock to lock it. How can I detect from Bash if the current terminal is a console virtual terminal (e.g. tty1), so that I can put the vlock line ...
12
votes
2answers
3k views

How to get the real name of the controlling terminal?

How can one get the real name of the controlling terminal (if there is one, else an error) as a pathname? By "real name", I mean not /dev/tty, which cannot be used by other arbitrary processes to ...
12
votes
2answers
23k views

How to change tty login prompt?

To be clear, I am not referring to /etc/issue (shown before the prompt) or /etc/motd (shown after login), but the prompt itself, which is currently hostname login: For good measure, I am running ...
12
votes
1answer
3k views

Keep bash input on top line of screen

I'd like to keep the bash command prompt input at the top of the screen so that outputs from older commands are pushed downwards rather than up. How can I achieve this?
12
votes
2answers
411 views

Is there a way to mirror USB outputs?

I'm currently writing a program for a project. It is for a braille reading system where I have a braille display connected via USB that is controlled by a program called brltty. One of the ...
11
votes
4answers
847 views

ls command operating differently depending on recipient

How does commands like ls know what its stdout is? It seems ls is operating different depending on what the target stdout is. For example if I do: ls /home/matt/tmp the result is: a.txt b.txt c....

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