Pseudo terminal programming

Alien_Hominid · 01-10-2008, 05:55 AM

I was looking for information about writing a pseudo terminal but information is scarce at best. Actually, I don't need any escape codes emulation just STDIN, STDOUT support.

SciYro · 01-11-2008, 12:17 AM

?? Please clarify. Do you need a real terminal connection (such as is necessary for ncurses UI's), or just the ability to input data, and read data from a program (piping).

If its piping, then the best information is contained within the C library documentation from the glibc project. If its the other one, uhhh, i dono why you would do such a thing, but would suggest looking at terminal emulator source codes, such as from xterm, as it sounds like that might be a close match.

So, what exactly is it your trying to do?

Alien_Hominid · 01-11-2008, 02:24 AM

More like xterm. I found that all the pseudo terminals are based on xterm. But I wonder why it should emulate any of the terminals like vt100 (is it really necessary?). Can't it just act as virtual console (tty 1-6) but on X?

I am looking if it would be possible for me to write a minimalistic pseudo terminal (I didn't find better word to describe it).

There are:
Pseudo terminal
Terminal emulator
Text terminal
Virtual terminal
Virtual console

So I'm a bit confused, which defintion is the right one (or no one).

Thanks for response.

SciYro · 01-11-2008, 02:55 PM

ok, look at the libc documentation under "low level terminal interface"->"pseudo terminals" or something like that.

Is it really necessary? No, not really, but if it didn't, then the user couldn't manage the programs connected to the terminal (such as sending kill signals, and other signals). Even the Linux virtual terminals have some of this extra functionality (tho, im not sure if Linux emulates, or has its own terminal trickies).

Alien_Hominid · 01-12-2008, 06:17 AM

I've read that linux has its own codes, but they are mostly based on vt100. The reason why I don't want go with emulation is that I am afraid with complexity, which follows emulating some terminal types.

I've already looked at http://www.gnu.org/software/libc/man..._002dTerminals that's why I said that information is scarce. For example, when googling there is much more info about writing a shell. The only relevant link was a warning about the complexity of emulation: http://www.cs.utk.edu/~shuford/termi...ow_to_news.txt

Alien_Hominid · 01-20-2008, 04:19 AM

Quote:

CONSOLE(4) Linux Programmer's Manual CONSOLE(4)

NAME
console - console terminal and virtual consoles

DESCRIPTION
A Linux system has up to 63 virtual consoles (character devices with major number 4 and minor number 1 to 63), usually called /dev/ttyn with 1 <= n <= 63. The current console is also addressed by /dev/console or /dev/tty0, the character device with major number 4 and minor number 0. The device files /dev/* are usually created using the script MAKEDEV, or using mknod(1), usually with mode 0622 and owner root.tty.

Before kernel version 1.1.54 the number of virtual consoles was compiled into the kernel (in tty.h: #define NR_CONSOLES 8) and could be changed by editing and recompiling. Since version 1.1.54 virtual consoles are created on the fly, as soon as they are needed.

Common ways to start a process on a console are: (a) tell init(8) (in inittab(5)) to start a getty(8) on the console; (b) ask openvt(1) to start a process on the console; (c) start X -- it will find the first unused console, and display its output there. (There is also the ancient doshell(8).)

Common ways to switch consoles are: (a) use Alt+Fn or Ctrl+Alt+Fn to switch to console n; AltGr+Fn might bring you to console n+12 [here Alt and AltGr refer to the left and right Alt keys, respectively]; (b) use Alt+RightArrow or Alt+Left-Arrow to cycle through the presently allocated consoles; (c) use the program chvt(1). (The key mapping is user set- table, see loadkeys(1); the above mentioned key combinations are according to the default settings.)

The command deallocvt(1) (formerly disalloc) will free the memory taken by the screen buffers for consoles that no longer have any associated process.

PROPERTIES
Consoles carry a lot of state. I hope to document that some other time. The most important fact is that the consoles simulate vt100 terminals. In particular, a console is reset to the initial state by printing the two characters ESC c.
All escape sequences can be found in console_codes(4).

FILES
/dev/console
/dev/tty*

SEE ALSO
chvt(1), deallocvt(1), loadkeys(1), mknod(1), openvt(1), console_codes(4), console_ioctl(4), tty(4), ttyS(4),
charsets(7), getty(8), init(8), mapscrn(8), resizecons(8), setfont(8)

Linux 1994-10-31 CONSOLE(4)

What the hell? 14 years have passed but documentation is not updated. Should I go and read the source code or what?

What's the difference between virtual terminal and virtual console?