Linux console
According to Wikipedia:
- The Linux console is a system console internal to the Linux kernel. 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.
This article describes the basics of the Linux console and how to configure the font display. Keyboard configuration is described in the /Keyboard configuration subpage. For alternative console solutions offering more features (full Unicode fonts, modern graphics adapters etc.), see KMSCON or similar projects.
Implementation
The console, unlike most services that interact directly with users, is implemented in the kernel. This contrasts with terminal emulation software, such as Xterm, which is implemented in user space as a normal application. The console has always been part of released Linux kernels, but has undergone changes in its history, most notably the transition to using the framebuffer and support for Unicode.
Despite many improvements in the console, its full backward compatibility with legacy hardware means it is limited compared to a graphical terminal emulator. The main difference between the Linux console and graphical terminal emulators is the shells in the Linux console are attached directly to TTY devices (/dev/tty*
), whereas the shells in a graphical terminal emulator are attached to pseudo-TTYs (/dev/pty*
).
Also, graphical terminal emulators can have many more features than the Linux console, including a richer set of available fonts, multiple tabs/windows, split views, scrollback buffers/sliders, background colors/images (optionally with transparency), etc. Some of these features can be used in the Linux console with terminal multiplexers, such as Tmux or GNU Screen, or in certain text user interface programs (TUI) typically relying on libraries such as ncurses and the like, e.g. Vim, nano, or Emacs. These can also be used in graphical terminal emulators, if desired.
Virtual consoles
The console is presented to the user as a series of virtual consoles. These give the impression that several independent terminals are running concurrently; each virtual console can be logged in with different users, run its own shell and have its own font settings. The virtual consoles each use a device /dev/ttyX
, and you can switch between them by pressing Alt+Fx
(where x
is equal to the virtual console number, beginning with 1). The device /dev/console
is automatically mapped to the active virtual console.
See also chvt(1), openvt(1) and deallocvt(1).
Text mode
Since Linux originally began as a kernel for PC hardware, the console was developed using standard IBM CGA/EGA/VGA graphics, which all PCs supported at the time. The graphics operated in VGA text mode, which provides a simple 80x25 character display with 16 colours. This legacy mode is similar to the capabilities of dedicated text terminals, such as the DEC VT100 series. It is still possible to boot in text mode (with vga=0 nomodeset
) if the system hardware supports it, but almost all modern distributions (including Arch Linux) use the framebuffer console instead.
Framebuffer console
As Linux was ported to other non-PC architectures, a better solution was required, since other architectures do not use VGA-compatible graphics adapters, and may not support text modes at all. The framebuffer console was implemented to provide a standard console across all platforms, and so presents the same VGA-style interface regardless of the underlying graphics hardware. As such, the Linux console is not a terminal emulator, but a terminal in its own right. It uses the terminal type linux
, and is largely compatible with VT100.
Keyboard shortcuts
Keyboard Shortcut | Description |
---|---|
Ctrl+Alt+Del
|
Reboots the system (specified by the symlink /usr/lib/systemd/system/ctrl-alt-del.target )
|
Alt+F1 , F2 , F3 , ...
|
Switch to n-th virtual console (not to be confused with Ctrl+Alt+Fn used in Xorg and Wayland)
|
Alt+Left
|
Switch to previous virtual console |
Alt+Right
|
Switch to next virtual console |
Scroll Lock
|
When Scroll Lock is activated, input/output is locked |
Ctrl+c
|
Kills current task |
Ctrl+d
|
Inserts an EOF |
Ctrl+z
|
Pauses current Task |
See also console_codes(4).
Fonts
The Linux console uses UTF-8 encoding by default, but because the standard VGA-compatible framebuffer is used, a console font is limited to either a standard 256, or 512 glyphs. If the font has more than 256 glyphs, the number of colours is reduced from 16 to 8. In order to assign correct symbol to be displayed to the given Unicode value, a special translation map, often called unimap, is needed. Nowadays, most of the console fonts have the unimap built-in; historically, it had to be loaded separately.
By default, the virtual console uses the kernel built-in font with a CP437 character set[1], but this can be easily changed. The kernel offers about 15 built in fonts to choose from, from which the officially supported kernels provide two: VGA 8x16 font (CONFIG_FONT_8x16
) and Terminus 16x32 font (CONFIG_FONT_TER16x32
). The kernel chooses the one to use based on its evaluation of the screen resolution. Another builtin font can be forced upon by kernel parameters boot parameter setting such as fbcon=font:TER16x32
.
The kbd package provides tools to override the kernel decision for virtual console font and font mapping. Available fonts are provided in the /usr/share/kbd/consolefonts/
directory; those ending with .psfu or .psfu.gz have a Unicode translation map built-in.
Keymaps, the connection between the key pressed and the character used by the computer, are found in the subdirectories of /usr/share/kbd/keymaps/
; see /Keyboard configuration for details.
eurlatgr
font. It includes a broad range of Latin/Greek letter variations as well as
special characters [2].Preview and temporary changes
$ showconsolefont
shows a table of glyphs or letters of a font.
setfont
temporarily changes the font if passed a font name (in /usr/share/kbd/consolefonts/
) such as
$ setfont lat2-16 -m 8859-2
Font names are case-sensitive. With no parameter, setfont
returns the console to the default font.
So to have a small 8x8 font, with that font installed like seen below, use e.g.:
$ setfont -h8 /usr/share/kbd/consolefonts/drdos8x8.psfu.gz
To have a bigger font, the Terminus font (terminus-font) is available in many sizes, such as ter-132b
which is large.
You can also append -d
for double size. This would be using a 64*64 font:
$ setfont -d ter-132n
- All font changing commands can be typed in "blind".
- The Terminus font names (
ter-*
) are explained in/usr/share/terminus-font/README
.
Persistent configuration
The FONT
variable in /etc/vconsole.conf
is used to set the font at boot, persistently for all consoles. See vconsole.conf(5) for details.
For displaying characters such as Č, ž, đ, š or Ł, ę, ą, ś using the font lat2-16.psfu.gz
:
/etc/vconsole.conf
... FONT=lat2-16 FONT_MAP=8859-2
It means that second part of ISO/IEC 8859 characters are used with size 16. You can change font size using other values (e.g. lat2-08
). For the regions determined by 8859 specification, look at the Wikipedia:ISO/IEC 8859#The parts of ISO/IEC 8859.
Since mkinitcpio v33, the font specified in /etc/vconsole.conf
gets automatically loaded during early userspace by default via the consolefont
hook, which adds the font to the initramfs. See Mkinitcpio#HOOKS for more information.
You may also need to restart systemd-vconsole-setup.service
after changing /etc/vconsole.conf
.
If the fonts appear to not change on boot, or change only temporarily, it is most likely that they got reset when graphics driver was initialized and console was switched to framebuffer. By default, all in-tree kernel drivers are loaded early, NVIDIA users should see NVIDIA#Early loading to load their graphics driver before /etc/vconsole.conf
is applied.
Cursor appearance
This subject is poorly documented. You should read the following articles:
- Software cursor for VGA
- Cursor Appearance in the Linux Console
- Disable Cursor Blinking on Linux Console
Hardware | Software | |
---|---|---|
Shape |
|
|
Blinking |
|
|
Color |
|
|
The console cursor can be adjusted with Device Attributes (DA) control function. The sequence of parameters must be preceded by a single question mark (despite console_codes(4) says the opposite).
Here is an example for full block non-blinking green cursor with black symbols under it:
$ printf "\x1b\x5b?16;$((8+4+2+1));$((32+0+8+4+2+1))\x63"
The same can be expressed with the octal and characters instead of hex codes:
$ printf '\033[?16;15;47c'
The same can be applied as permanent configuration with kernel parameter:
vt.cur_default=0x2f0f10
Cursor size
The first parameter, despite it's name cursor size, with number 16 (the rightmost two hex digits of the kernel parameter are 10) means "use software cursor."
If you want to change hardware cursor shape - use corresponding number (from 0 to 6, see the table above).
Toggle mask
The second parameter, called toggle mask, flips corresponding bits of the color.
Background
(cursor block) |
Foreground
(symbol under the cursor) | |||||||
---|---|---|---|---|---|---|---|---|
Bright (highlight)
or blinking |
Red | Green | Blue | Bright (highlight)
or blinking |
Red | Green | Blue | |
Decimals | 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1 |
Hex | 80 | 40 | 20 | 10 | 8 | 4 | 2 | 1 |
In our case the second parameter is 15 (the middle hex digits of the kernel parameter are 0f), so all four foreground (symbol) bits will be flipped. The most important rule is: toggling (the second parameter) is applied after the setting (the third parameter).
Set mask
The third parameter is called set mask. It sets corresponding character attribute bits. We use 47 (the leftmost hex digits of the kernel parameter are 2f) in our example, which means two things:
- (32) use pure green color for cursor block
- (8+4+2+1) set all four foreground (symbol color) bits. These bits will be toggled by the second parameter, so the color of the symbol under the cursor will be black (
0000
).
HiDPI
See HiDPI#Linux console (tty).
Audible tones
See PC speaker#Beep.