what are tty's

e1000 · 12-12-2003, 11:18 PM

this problem has been nagging at me for a long time now so I figured I'd finally ask it. when I do "ps -ax" it spills out all the programs I have running but this one section from the output has me curious.

Code:

1454 tty1     S      0:00 -bash
1455 tty2     S      0:00 /sbin/agetty 38400 tty2 linux
1456 tty3     S      0:00 /sbin/agetty 38400 tty3 linux
1457 tty4     S      0:00 /sbin/agetty 38400 tty4 linux
1458 tty5     S      0:00 /sbin/agetty 38400 tty5 linux
1459 tty6     S      0:00 /sbin/agetty 38400 tty6 linux
1473 tty1     S      0:00 -su
1641 tty1     S      0:00 -su
20194 tty1     S      0:00 -su
20206 tty1     S      0:00 /bin/sh /usr/X11R6/bin/startx
20218 tty1     S      0:00 xinit /usr/X11R6/lib/X11/xinit/xinitrc --
20219 ?        R<L    1:15 X :0
20223 tty1     S      0:00 /usr/X11R6/bin/fluxbox

as you can see process 20219 is not a tty, but its the only program sandwiched inbetween them all, so I just figured I'd leave it.

so what are these "tty's" (especially agetty) and what do they do so specially to deserve their own notation?

2damncommon · 12-12-2003, 11:31 PM

Quote:

what are tty's

Basically, a user interface.
TTY actually means teletype terminal.
http://research.microsoft.com/~gbell...ine/quiz8w.htm

DrOzz · 12-12-2003, 11:37 PM

agetty man page
tty links

e1000 · 12-13-2003, 05:12 PM

"agetty opens a tty port, prompts for a login name and invokes the /bin/login command. It is normally invoked by init(8)"

thats its description, and as you might guess I still dont know what it is (in fact now I'm more confused). is a tty a port like say a port on the internet, like port 80 for http. Why doesnt the init script invoke "login" by its self, why does it need 5 instances of agetty going? I see that there are hella tty's in the /dev/ directory does that mean that agetty is treated like my keyboard or something?

teval · 12-13-2003, 05:31 PM

To get all this right you need to know a little history/what else you can do with Linux (nix in general)

At first they didn't have 1 computer/person, unix actually started as a nice way to share one computer among many users. A timesharing system. What happens is everyone can log on remotely using dumb terminals. agetty provides this capacity. Now.. when you log on to your own computer, it's as if you were logging on to a computer remotely except all connections are either redirected in a really fancy way or they use the loopback device (localhost).
When you have a non-graphical logon (a real logon

) login takes care of the authentication. agetty handles keyboard and outputting things to the screen.

A tty is the correct way of calling the text screen. The virtual ones made in things like Kconsole are called ptses.

Those columns that sometimes have a tty or a pts or a ? simply mean to were the process is attached to. Were it will send info to the screen and so on.