System console in the context of Console application

In computer programming, standard streams are preconnected input and output communication channels between a computer program and its environment when it begins execution. The three input/output (I/O) connections are called standard input (stdin), standard output (stdout) and standard error (stderr). Originally I/O happened via a physically connected system console (input via keyboard, output via monitor), but standard streams abstract this. When a command is executed via an interactive shell, the streams are typically connected to the text terminal on which the shell is running, but can be changed with redirection or a pipeline. More generally, a child process inherits the standard streams of its parent process.

The Linux console is a system console internal to the Linux kernel. A system console is the device which receives all kernel messages and warnings and which allows logins in single user mode. The Linux console provides a way for the kernel and other processes to send text output to the user, and to receive text input from the user. The user typically enters text with a computer keyboard and reads the output text on a computer monitor. The Linux kernel supports virtual consoles – consoles that are logically separate, but which access the same physical keyboard and display. The Linux console (and Linux virtual consoles) are implemented by the VT (virtual terminal) subsystem of the Linux kernel, and do not rely on any user space software. This is in contrast to a terminal emulator, which is a user space process that emulates a terminal, and is typically used in a graphical display environment.

The Linux console was one of the first features of the kernel and was originally written by Linus Torvalds in 1991 (see history of Linux). There are two main implementations: framebuffer and text mode. The framebuffer implementation is the default in modern Linux distributions, and together with kernel mode setting, provides kernel-level support for display hardware and features such as showing graphics while the system is booting. The legacy text mode implementation was used in PC-compatible systems with CGA, EGA, MDA and VGA graphics cards. Non-x86 architectures used framebuffer mode because their graphics cards did not implement text mode. The Linux console uses fixed-size bitmap, monospace fonts, usually defaulting to 8x16 pixels per character.