KMSCON - ArchWiki

Jump to content

# KMSCON

From ArchWiki

Related articles

- KMS
- systemd

From the project's git repository:

  Kmscon is a simple terminal emulator based on linux kernel mode setting. It is an attempt to replace the in-kernel VT implementation with a userspace console.

## Features

Kmscon can function as a drop-in replacement for the in-kernel linux-console. Features include:

- Full vt220 to vt510 implementation.
- Full internationalization support:
  - Kmscon supports printing full Unicode glyphs, including the CJK ones.
  - Kmscon provides internationalized keyboard handling through libxkbcommon, thus allowing it to use the full range of keyboard layouts supported in X keyboard.
- Hardware accelerated rendering.
- Scroll support.
- Mouse/Touchscreen support.
- On screen font resize support, including TTF fonts.
- Multi-seat capability.

## Installation

Despite its name, KMS is not a hard requirement for kmscon. Kmscon supports the following video backends: drm3d (Linux DRM hardware-rendering backend), drm2d (Linux DRM software-rendering backend), superseded fbdev (Linux fbdev video backend). Make sure one of them is available on your system.

Install the kmscon package.

Normally, there is a special systemd configuration for tty1. To be conservative, you can continue to run the traditional agetty on tty1 and only run kmscon on all the other virtual terminals. Or you can run kmscon on both tty1 and the other VTs.

To enable kmscon on tty1, disable `getty@tty1.service` and enable `kmsconvt@tty1.service`.

Note If you are using a display manager such as SDDM or GDM, replace `getty@tty1.service` with `kmsconvt@tty1.service` in the `Conflicts` and `After` fields of the display manager service file.

To enable kmscon on all virtual terminals, run:

    # ln -s '/usr/lib/systemd/system/kmsconvt@.service' '/etc/systemd/system/autovt@.service'

This will make systemd start kmscon instead of agetty on each VT. More precisely, this will make systemd-logind use `kmsconvt@.service` instead of `getty@.service` for new VTs. Additionally, all other systemd units that use `getty@.service` will not be affected by this change.

If kmscon cannot start for whatever reason, this unit will cause `getty@.service` to be started instead. Furthermore, if no VTs are available, this unit will not start anything.

Warning If you have replaced agetty on all terminals, take care to ensure kmscon presents you with a prompt before rebooting your machine, otherwise you may have to recover through a live CD.
Tip You can enable `getty@tty1.service` after enabling kmscon on all virtual terminals: this will allow the user to start a graphical session from the command line on tty1 while enjoying the benefits of kmscon on the remaining terminals.

## CJK support

Kmscon supports rendering CJK characters through the default font engine pango. However, fontconfig has to be globally configured to map the monospace font alias to proper CJK fonts. For Chinese users, the following template is provided and proved to result in satisfactory Chinese characters rendering:

    /etc/fonts/conf.d/99-kmscon.conf

    <?xml version="1.0"?>
    <!DOCTYPE fontconfig SYSTEM "fonts.dtd">
    <fontconfig>
    <match>
            <test name="family"><string>monospace</string></test>
            <edit name="family" mode="prepend" binding="strong">
                    <string>DejaVu Sans Mono</string>
                    <string>WenQuanYi Micro Hei Mono</string>
            </edit>
    </match>
    </fontconfig>

Alternatively, we can add the following line to `/etc/kmscon/kmscon.conf` for globally configuring kmscon using the fonts:

    /etc/kmscon/kmscon.conf

    font-name=DejaVu Sans Mono, WenQuanYi Micro Hei Mono
    font-size=14

See kmscon(1).

You need to have ttf-dejavu and wqy-microhei, both available from the official repositories, installed.

## Troubleshooting

### Root cannot login

If you cannot login as root check `/etc/pam.d/` files, if you have enabled `pam_securetty`. You need to disable the `pam_securetty` module by removing or commenting out the corresponding line eg. in `/etc/pam.d/login`.

### Window managers cannot be started from KMS console

Use the `kmscon-launch-gui` wrapper to launch your favourite desktop environment.

### Gnome Session does not start

You need to set the wayland type flag for your terminal. Add type=wayland to the pam_systemd.so line in `/etc/pam.d/system-login`

### Problems with switching between Xorg and kmscon

You may want to add `hwaccel` to `/etc/kmscon/kmscon.conf` if you have problems with switching between Xorg and kmscon. Another possibility would be editing the systemd service file.

### No audio control

As version 7, if you cannot control the audio, add your user to the `audio` user group. Be aware of the shortcomings of this choice.

### Vim does not clear terminal output

Vim might open without clearing the terminal output, it is still possible to edit the file but the text will not be visible until it is changed. As a workaround, try setting the environment variable `TERM=vt220`. Alternatively, another vim-like editor like Neovim might work.

Note Color support is not available if `TERM` is set to `vt220`.

### Automatic login

It is possible to login as user username automatically without asking for password by adding this to `/etc/kmscon/kmscon.conf`

    /etc/kmscon/kmscon.conf

    # Example: Login as user "username" without asking for password
    login=/bin/login -p -f username

Or as user root:

    /etc/kmscon/kmscon.conf

    # Example: Login as root in a bash shell without asking for password
    login=/bin/bash --login

### HiDPI support

You can change font size on the fly with `Ctrl++`, `Ctrl+Shift+=`, `Ctrl+-` shortcuts. Also you can set 'font-dpi' and 'font-size' in `/etc/kmscon/kmscon.conf` e.g. 'font-dpi=288' 288 is 96 * 3 that is 300% scaling. 96 is default.

Category:

- Terminal emulators

KMSCON
Add topic