Chapter 7. GUI System
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Chapter 7. GUI System

Table of Contents

7.1. GUI desktop environment
7.2. GUI communication protocol
7.3. GUI infrastructure
7.4. GUI applications
7.5. User directories
7.6. Fonts
7.6.1. Basic fonts
7.6.2. Font rasterization
7.7. Sandbox
7.8. Remote desktop
7.9. X server connection
7.9.1. X server local connection
7.9.2. X server remote connection
7.9.3. X server chroot connection
7.10. Clipboard

7.1. GUI desktop environment

There are several choices for the full featured GUI desktop environment on the Debian system.

Table 7.1. List of desktop environment

task package popcon size description
task-gnome-desktop I:196 9 GNOME desktop environment
task-xfce-desktop I:90 9 Xfce desktop environment
task-kde-desktop I:95 6 KDE Plasma desktop environment
task-mate-desktop I:36 9 MATE desktop environment
task-cinnamon-desktop I:39 9 Cinnamon desktop environment
task-lxde-desktop I:23 9 LXDE desktop environment
task-lxqt-desktop I:17 9 LXQt desktop environment
task-gnome-flashback-desktop I:11 6 GNOME Flashback desktop environment

[Tip] Tip

Dependency packages selected by a task metapackage may be out of sync with the latest package transition state under the Debian unstable/testing environment. For task-gnome-desktop, you may need to adjust package selections as follows:

  • Start aptitude(8) as sudo aptitude -u.

  • Move cursor to "Tasks" and press "Enter".

  • Move cursor to "End-user" press "Enter".

  • Move cursor to "GNOME" press "Enter".

  • Move cursor to task-gnome-desktop and press "Enter".

  • Move cursor to "Depends" and press "m" (manually selected).

  • Move cursor to "Recommends" and press "m" (manually selected).

  • Move cursor to "task-gnome-desktop and press "-". (drop)

  • Adjust selected packages while dropping problematic ones causing package conflicts.

  • Press "g" to start install.

This chapter will focus mostly on the default desktop environment of Debian: task-gnome-desktop offering GNOME on wayland.

7.2. GUI communication protocol

GUI communication protocol used on the GNOME desktop can be:

Please check freedesktop.org site for how Wayland architecture is different from X Window architecture.

From user's perspective, differences can be colloquially summarized as:

  • Wayland is a same-host GUI communication protocol: new, simpler, faster, no setuid root binary

  • X Window is a network-capable GUI communication protocol: traditional, complex, slower, setuid root binary

For applications using Wayland protocol, the access to their display contents from a remote host is supported by the VNC or RDP. See Section 7.8, “Remote desktop”

Modern X servers have the MIT Shared Memory Extension and communicate with their local X clients using the local shared memory. This bypasses the network transparent Xlib interprocess communication channel and gains performance. This situation was the background of creating Wayland as a local-only GUI communication protocol.

Using the xeyes program started from the GNOME terminal, you can check GUI communication protocol used by each GUI application.

 $ xeyes

  • If the mouse cursor is on an application such as "GNOME terminal" which uses Wayland display server protocol, eyes don't move with the mouse cursor.

  • If the mouse cursor is on an application such as "xterm" which uses X Window System core protocol, eyes move with the mouse cursor exposing not-so-isolated nature of X Window architecture.

As of April 2021, many popular GUI applications such as GNOME and LibreOffice (LO) applications have been migrated to the Wayland display server protocol. I see xterm, gitk, chromium, firefox, gimp, dia, and KDE applications still use X Window System core protocol.

[Note] Note

For both the xwayland on Wayland or the native X Window System, the old X server configuration file "/etc/X11/xorg.conf" shouldn't exist on the system. The graphics and input devices are now configured by the kernel with DRM, KMS, and udev. The native X server has been rewritten to use them. See "modedb default video mode support" in the Linux kernel documentation.

7.3. GUI infrastructure

Here are notable GUI infrastructure packages for the GNOME on Wayland environment.

Table 7.2. List of notable GUI infrastructure packages

package popcon package size description
mutter V:0, I:30 221 GNOME's mutter window manager [auto]
xwayland V:250, I:343 2541 An X server running on top of wayland [auto]
gnome-remote-desktop V:110, I:246 2215 Remote desktop daemon for GNOME using PipeWire [auto]
gnome-tweaks V:19, I:238 1145 Advanced configuration settings for GNOME
gnome-shell-extension-prefs V:8, I:153 82 Tool to enable / disable GNOME Shell extensions

Here, "[auto]" means that these packages are automatically installed when task-gnome-desktop is installed.

[Tip] Tip

gnome-tweaks is the indispensable configuration utility. For example:

  • You can force "Over-Amplification" of sound volume from "General".

  • You can force "Caps" to become "Esc" from "Keyboard & Mouse" -> "Keyboard" -> "Additional Layout Option".
[Tip] Tip

Detail features of GNOME desktop environment can be configured with utilities started by typing "settings", "tweaks", or "extensions" after pressing Super-key.

7.4. GUI applications

Many useful GUI applications are available on Debian now. Installing software packages such as scribus (KDE) on GNOME desktop environment are quite acceptable since corresponding functionality is not available under GNOME desktop environment. But installing too many packages with duplicated functionalities may clutter your system.

Here is a list of GUI applications which caught my eyes.

Table 7.3. List of notable GUI applications

package popcon package size type description
evolution V:26, I:236 492 GNOME Personal information Management (groupware and email)
thunderbird V:46, I:111 273862 GTK Email client (Mozilla Thunderbird)
kontact V:1, I:11 2258 KDE Personal information Management (groupware and email)
libreoffice-writer V:117, I:439 33053 LO word processor
abiword V:0, I:5 3576 GNOME word processor
calligrawords V:0, I:5 6937 KDE word processor
scribus V:1, I:14 32052 KDE desktop publishing editor to edit PDF files
glabels V:0, I:2 1283 GNOME label editor
libreoffice-calc V:111, I:435 28164 LO spreadsheet
gnumeric V:3, I:11 9958 GNOME spreadsheet
calligrasheets V:0, I:4 13593 KDE spreadsheet
libreoffice-impress V:92, I:434 2469 LO presentation
calligrastage V:0, I:4 6017 KDE presentation
libreoffice-base V:24, I:82 5031 LO database management
kexi V:0, I:0 7565 KDE database management
libreoffice-draw V:92, I:434 10985 LO vector graphics editor (draw)
inkscape V:12, I:86 113183 GNOME vector graphics editor (draw)
karbon V:0, I:5 3962 KDE vector graphics editor (draw)
dia V:1, I:19 4086 GTK flowchart and diagram editor
gimp V:45, I:232 32135 GTK bitmap graphics editor (paint)
shotwell V:15, I:255 6334 GTK digital photo organizer
digikam V:1, I:9 302 KDE digital photo organizer
darktable V:4, I:12 35873 GTK lighttable and darkroom for photographers
planner V:0, I:5 1400 GNOME project management
calligraplan V:0, I:3 19241 KDE project management
gnucash V:2, I:7 29748 GNOME personal accounting
homebank V:0, I:1 3196 GTK personal accounting
lilypond V:0, I:6 16924 - music typesetter
kmymoney V:0, I:2 18826 KDE personal accounting
librecad V:1, I:15 9100 Qt-app computer-aided design (CAD) system (2D)
freecad I:20 110 Qt-app computer-aided design (CAD) system (3D)
kicad V:3, I:15 163802 GTK electronic schematic and PCB design software
xsane V:10, I:135 1512 GTK scanner frontend
libreoffice-math V:83, I:437 1904 LO mathematical equation/formula editor
calibre V:7, I:27 65174 KDE e-book converter and library management
fbreader V:0, I:7 3783 GTK e-book reader
evince V:79, I:300 963 GNOME document(pdf) viewer
okular V:41, I:135 4415 KDE document(pdf) viewer
x11-apps V:31, I:467 2461 pure X-app xeyes(1), etc.
x11-utils V:217, I:565 651 pure X-app xev(1), xwininfo(1), etc.

7.5. User directories

Default names for user directories such as "~/Desktop", "~/Documents", ..., used by the Desktop environment depend on the locale used for the system installation. You can reset them to the English ones by:

 $ LANGUAGE=C xdg-user-dirs-update --force

Then you manually move all the data to the newer directories. See xdg-user-dirs-update(1).

You can also set them to any names by editing "~/.config/user-dirs.dirs". See user-dirs.dirs(5).

7.6. Fonts

Many useful scalable fonts are available for users on Debian. User's concern is how to avoid redundancy and how to configure parts of installed fonts to be disabled. Otherwise, useless font choices may clutter your GUI application menus.

Debian system uses FreeType 2.0 library to rasterise many scalable font formats for screen and print:

The following table is compiled in the hope to help users to chose appropriate scalable fonts with clear understanding of the metric compatibility and the glyph coverage. Most fonts cover all Latin, Greek, and Cyril characters. The final choice of activated fonts can also be affected by your aesthetics. These fonts can be used for the screen display or for the paper printing.

Table 7.4. List of notable TrueType and OpenType fonts

package popcon size sans serif mono note on font
fonts-cantarell V:180, I:302 213 59 - - Cantarell (GNOME 3, display)
fonts-noto I:158 31 61 63 40 Noto fonts (Google, multi-lingual with CJK)
fonts-dejavu I:405 35 58 68 40 DejaVu (GNOME 2, MCM:Verdana, extended Bitstream Vera)
fonts-liberation2 V:71, I:239 15 56 60 40 Liberation fonts for LibreOffice (Red Hat, MCMATC)
fonts-croscore V:21, I:39 5274 56 60 40 Chrome OS: Arimo, Tinos and Cousine (Google, MCMATC)
fonts-crosextra-carlito V:18, I:102 2696 57 - - Chrome OS: Carlito (Google, MCM:Calibri )
fonts-crosextra-caladea V:10, I:97 347 - 55 - Chrome OS: Caladea (Google, MCM:Cambria ) (Latin only )
fonts-freefont-ttf V:78, I:209 14460 57 59 40 GNU FreeFont (extended URW Nimbus)
fonts-quicksand V:207, I:460 392 56 - - Debian task-desktop, Quicksand (display, Latin only)
fonts-hack V:32, I:140 2507 - - 40 P A typeface designed for source code Hack (Facebook)
fonts-sil-gentiumplus I:30 14345 - 54 - Gentium SIL
fonts-sil-charis I:29 6704 - 59 - Charis SIL
fonts-urw-base35 V:189, I:536 15560 56 60 40 URW Nimbus (Nimbus Sans, Roman No. 9 L, Mono L, MCAHTC)
fonts-ubuntu V:2, I:5 4339 58 - 33 P Ubuntu fonts (display)
fonts-terminus I:4 452 - - 33 Cool retro terminal fonts
ttf-mscorefonts-installer V:0, I:43 85 56? 60 40 Downloader of Microsoft non-free fonts (see below)

Here:

  • "MCM" stands for "metric compatible with fonts provided by Microsoft"

  • "MCMATC" stands for "metric compatible with fonts provided by Microsoft: Arial, Times New Roman, Courier New"

  • "MCAHTC" stands for "metric compatible with fonts provided by Adobe: Helvetica, Times, Courier"

  • Numbers in font type columns stands for the rough relative "M" width for the same point size font.

  • "P" in mono font type columns stands for its usability for programming having clearly distinguishable "0"/"O" and "1"/"I"/"l".

  • The ttf-mscorefonts-installer package downloads Microsoft's "Core fonts for the Web" and installs Arial, Times New Roman, Courier New, Verdana, ... . These installed font data are non-free data.

Many free Latin fonts have their lineage traced to URW Nimbus family or Bitstream Vera.

[Tip] Tip

If your locale needs fonts not covered well by the above fonts, please use aptitude to check under task packages listed under "Tasks" -> "Localization". The font packages listed as "Depends:" or "Recommends:" in the localization task packages are the primary candidates.

Debian uses FreeType to rasterize fonts. Its font choice infrastructure is provided by the Fontconfig font configuration library.

Table 7.5. List of notable font environment and related packages

package popcon size description
libfreetype6 V:578, I:996 1021 FreeType font rasterization library
libfontconfig1 V:569, I:831 624 Fontconfig font configuration library
fontconfig V:459, I:708 681 fc-*: CLI commands for Fontconfig
font-manager V:2, I:7 1121 Font Manager: GUI command for Fontconfig
nautilus-font-manager V:0, I:0 39 Nautilus extension for Font Manager

[Tip] Tip

Some font packages such as fonts-noto* install too many fonts. You may also want to keep some font packages installed but disabled under the normal use situation. The multiple glyphs are expected for some Unicode code points due to Han unification and unwanted gliphs may be chosen by the unconfigured Fontconfig library. One of the most annoying case is "U+3001 IDEOGRAPHIC COMMA" and "U+3002 IDEOGRAPHIC FULL STOP" among CJK countries. You can avoid this problematic situation easily by configuring font availability using Font Manager GUI (font-manager).

You can list font configuration state from the command line, too.

  • "fc-match(1)" for fontconfig font default

  • "fc-list(1)" for available fontconfig fonts

You can configure font configuration state from the text editor but this is non-trivial. See fonts.conf(5).

7.7. Sandbox

Many mostly GUI applications on Linux are available in binary formats from non-Debian sources.

[Warning] Warning

Binaries from these sites may include proprietary non-free software packages.

There is some raison d'être for these binary format distributions for Free Software aficionados using Debian since these can accommodate clean set of libraries used for each application by the respective upstream developer independent of the ones provided by Debian.

The inherent risk of running external binaries can be reduced by using the sandbox environment which leverages modern Linux security features (see Section 4.7.5, “Linux security features”).

  • For binaries from AppImage and some upstream sites, run them in firejail with manual configuration.

  • For binaries from FLATHUB, run them in Flatpak . (No manual configuration required.)

  • For binaries from snapcraft, run them in Snap . (No manual configuration required. Compatible with daemon programs.)

The xdg-desktop-portal package provides a standardized API to common desktop features. See xdg-desktop-portal (flatpak) and xdg-desktop-portal (snap) .

Table 7.6. List of notable sandbox environment and related packages

package popcon size description
flatpak V:97, I:103 8284 Flatpak application deployment framework for desktop apps
gnome-software-plugin-flatpak V:29, I:40 285 Flatpak support for GNOME Software
snapd V:67, I:70 71722 Daemon and tooling that enable snap packages
gnome-software-plugin-snap V:1, I:2 144 Snap support for GNOME Software
xdg-desktop-portal V:359, I:442 2169 desktop integration portal for Flatpak and Snap
xdg-desktop-portal-gtk V:326, I:441 715 xdg-desktop-portal backend for gtk (GNOME)
xdg-desktop-portal-kde V:78, I:111 2688 xdg-desktop-portal backend for Qt (KDE)
xdg-desktop-portal-wlr V:1, I:6 160 xdg-desktop-portal backend for wlroots (Wayland)
firejail V:1, I:4 1759 a SUID security sandbox program firejail for use with AppImage

This sandbox environment technology is very much like apps on smart phone OS where apps are executed under controlled resource accesses.

Some large GUI applications such as web browsers on Debian also use sandbox environment technology internally to make them more secure.

7.8. Remote desktop

Table 7.7. List of notable remote access server

Access to the desktop and applications which use Wayland protocol and run on the remote host is supported by the GNOME Remote Desktop on the remote host through VNC or RDP to the local client.

Access to the desktop capabilities of all QEMU virtual machines is supported by the SPICE (the Simple Protocol for Independent Computing Environments) protocol.

package popcon size protocols description
gnome-remote-desktop V:110, I:246 2215 RDP GNOME Remote Desktop server
xrdp V:25, I:28 4506 RDP xrdp, Remote Desktop Protocol (RDP) server
x11vnc V:8, I:41 1835 RFB (VNC) x11vnc, Remote Framebuffer Protocol (VNC) server
tigervnc-standalone-server V:4, I:14 2967 RFB (VNC) TigerVNC, Remote Framebuffer Protocol (VNC) server
gnome-connections V:5, I:112 1599 RDP, RFB (VNC) GNOME remote desktop client
vinagre V:1, I:30 4249 RDP, RFB (VNC), SPICE, SSH Vinagre: GNOME remote desktop client
remmina V:14, I:65 971 RDP, RFB (VNC), SPICE, SSH, ... Remmina: GTK remote desktop client
krdc V:1, I:17 4052 RDP, RFB (VNC) KRDC: KDE remote desktop client
virt-viewer V:5, I:46 1278 RFB (VNC), SPICE Virtual Machine Manager's GUI display client of guest OS

7.9. X server connection

There are several ways to connect from an application on a remote host to the X server including xwayland on the local host.

Table 7.8. List of connection methods to the X server

package popcon size command description
openssh-server V:752, I:808 3501 sshd with option X11-forwarding SSH server (secure)
openssh-client V:902, I:996 5131 ssh -X SSH client (secure)
xauth V:183, I:970 81 xauth X authority file utility
x11-xserver-utils V:306, I:537 559 xhost server access control for X

Access to the local X server by the local applications which use X core protocol can be locally connected through a local UNIX domain socket. This can be authorized by the authority file holding access cookie. The authority file location is identified by the "$XAUTHORITY" environment variable and X display is identified by the "$DISPLAY" environment variable. Since these are normally set automatically, no special action is needed, e.g. "gitk" as the following.

username $ gitk
[Note] Note

For xwayland, XAUTHORITY holds value like "/run/user/1000/.mutter-Xwaylandauth.YVSU30".

Access to the local X server display from the remote applications which use X core protocol is supported by using the X11 forwarding feature.

This method can display the output from a remote X client as if it were locally connected through a local UNIX domain socket.

See Section 6.3, “The remote access server and utilities (SSH)” for SSH/SSHD.

[Warning] Warning

A remote TCP/IP connection to the X server is disabled by default on the Debian system for security reasons. Don't enable them by simply setting "xhost +" nor by enabling XDMCP connection, if you can avoid it.

Access to the X server by the applications which use X core protocol and run on the same host but in an environment such as chroot where the authority file is not accessible, can be authorized securely with xhost by using the User-based access, e.g. "gitk" as the following.

username $ xhost + si:localuser:root ; sudo chroot /path/to
# cd /src
# gitk
# exit
username $ xhost -

7.10. Clipboard

For clipping text to clipboard, see Section 1.4.4, “Mouse operations”.

For clipping graphics to clipboard, see Section 11.6, “Graphic data tools”.

Some CLI commands can manipulate character clipboard (PRIMARY and CLIPBOARD), too.

Table 7.9. List of programs related to manipulating character clipboard

package popcon package size target description
xsel V:7, I:43 55 X command line interface to X selections (clipboard)
xclip V:13, I:74 62 X command line interface to X selections (clipboard)
wl-clipboard V:6, I:22 162 Wayland wl-copy wl-paste: command line interface to Wayland clipboard
gpm V:9, I:10 545 Linux console a daemon that captures mouse events on Linux console

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