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LPIC - 106 Configure GUI & Localization

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Objective


Configure X

The main GUI in Linux is the X Window System (The X Server). Few extra topics beyond basic X configuration:

  • Fonts
  • GUI login tools - Display Manager (e.g. GDM) - Control the graphical login
  • Desktop Environments (e.g. Gnome)
  • X for Remote Access
  • Accessibility - AccessX (acessibility control panels)

Serving the GUI component

The windows manager communicates with the display server on behalf of the UI

  • Desktop Environment (e.g. Gnome)
  • Windows Manager (e.g. Mutter, Kwin, Muffin, Metacity)
  • Display Server (e.g. X)
    • Compositor: Arrange display elements within a window to create a screen image

1 -X Basic

X is Linux’s GUI system. X isn’t a single program.


Features for configuration: (As an example)

  • Mouse

  • Keyboard layout

  • Screen resolution

  • Video refresh rate

  • Display color depth

  • Video card - X provides drivers that control the video card

    Most modern computers include video hardware on the motherboard

Both AMD & Nvidia drivers include Linux kernel drivers as a necessary component.
So if upgrade Linux kernel, need to reinstall drivers.


X Server options

  • XFree86 - Open source. Basis for X11
  • X11 - Open source
  • Accelerated-X - Commercial license, from Xi Graphics (Improvement on compatibility with video cards)

Config Notes

  • Cmdline Tools: sudo Xorg -configure (File location: /root/xorg.conf.new)
  • Main config file: /etc/X11/xorg.conf
  • X Accessibility
    • Magnifier (kmag) - Enlarges the area around the mouse cursor

Test X Config Changes

  • Boot Linux to text mode

    • Redhat - telinit 3
    • Debian - /etc/init.d/gdm stop (Shut down Display Manager)

  • Change config via command line

  • Start X server: startx 📌

  • Logout & Restore to GUI login mode

    • Redhat - telinit 5
    • Debian - /etc/init.d/gdm start

  • Can also boot into Graphics mode, then kill the X server.

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    # get X
    ps aux | grep X

    # kill by PID
    kill [PID]

X Config Options

Edit config file: Identify the feature that’s not working, and focus on the section that controls this feature.

An incorrect config of the video card is likely to cause failures in starting X.


1 - Module

  • Controls loading X server modules - drivers for specific features / hardware
  • If X configuration works, don’t adjust Module manually

2 - InputDevice (Keyboard + Mouse)

  • Identifier - ser defined label, to use in ServerLayout section
  • Driver - keyboard drivers: kbd, Keyboard, evdev

3 - Monitor

  • ModelName - user-defined name
  • HorizSync & VertRefresh 📌
    • Horizontal (kHz) & Vertical (Hz) refresh rates
    • Together define monitor’s max resolution & refresh rate
  • Modeline
    • Look through modeline to select a resolution
    • X11 supports Data Display Channel (DDC) - Monitor can communicate max refresh rates & mode lines to the computer

4 - Device (e.g. Video Card)

  • X sends data to monitor via video card - Video card also controls monitor resolution

  • Set device driver - Driver "nv"

    • Drivers location: /usr/lib64/xorg/modules/drivers/xx_drv.o
    • Nvidia - nv / nouveau
    • AMD - radeon
    • Intel - intel

  • Graphical video modes require some RAM on the video card (BIOS will reserve some system RAM)

    Modern video cards ship with large RAM to support 3D acceleration

5 - Screen

  • Combination of monitos + video cards
  • Choose between Display subsections: add option DefaultDepth

6 - ServerLayout

  • Links all above components - Usually Screen & Keyboard & Mouse
  • Multi-head display - multiple monitors combined to form one large desktop

X Display Info

  • xdpyinfo - display info for all available extensions

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    xdpyinfo -ext [name]

  • xwininfo - window info

    • Colormap
    • Bit Gravity State

Wayland Server

Wayland Website

Wayland is a replacement of X Windows System

  • Initial release was in 2009, now used by many desktop environments, e.g. Gnome Shell & KDE Plasma
  • Wayland native applications won’t use X at all
  • Fewer video card problems

Check if display server is Wayland

  • Method 1 - Check env var

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    echo $WAYLAND_DISPLAY

  • Method 2 - Use loginctl

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    # get GUI session number
    loginctl 

    # show type (Type=Wayland)
    loginctl show-session [session number] -p Type

Turn off Wayland

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# edit file: WaylandEnable=false
sudo /etc/gdm3/custom.conf

# Reboot
sudo reboot

More about Wayland

  • Compositor: Weston
    • Weston is a reference implementation - As a compistor requirements example
  • For backward compatibility: XWayland
    • Allows X-dependent applications to run on X server & display via Wayland session

If system running fine under X, but problems under Wayland

  • Check graphics card
  • Go to graphics card vendor’s website, check if the driver support Wayland

2 - X Fonts

Notes

  • X’s core font system can be setup form the X config file (managed directly by X)
  • Font server
    • Deliver fonts via network protocols
    • Integrate with X core fonts, but run as separate programs
  • Most modern program are using a new font system - Xft (to replace X core fonts)
    • Xft bypass the core font system to provide client-side fonts

Font Formats

  • Bitmap fonts
    • Each font must be optimized for display at a particular resolution
  • Outline fonts (Scalable)
    • Represent each character as a series of lines & curves in a high-resolution matrix
    • Scaling is imperfect - Scalable fonts often look slightly worse than bitmap fonts
    • Scaling takes more CPU time - But on modern CPU it’s not really an issue
    • Font rendering
      • Apple TrueType - freetype (.ttf)
      • Adobe PostScript Type 1 - type1 (.pfa, .pfb)

X Core Fonts

  • Font directory: /usr/share/X11/fonts

  • Store fonts elsewhere to prevent wiping from upgrade: /opt/fonts, /usr/local/fonts

  • Create font file

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    # create font.dir file for trutype
    ttmkdir

    # For type 1
    typelinst

    # Apply to both type1 & truetype
    mkfontscale

3 - Display Manager

X’s GUI login system uses XDMCP server. It starts X & manages X display

X is a network-enabled GUI

  • The login system uses a network login protocol - XDMCP (X Display Manager Control Protocol)
  • For remote login - XDMCP server listens for connections from remote X server
  • For local login - XDMCP starts the local X server

Common XDMCP servers (i.e. Display Managers)

  • XDM - oldest
  • MDM - recursive acronym. Derivative of GDM
  • GDM - for Gnome
  • KDM - for KDE
  • LightDM - bare-bone display manager for lightweight desktop environments like Xfce

Select Display Manager

  • Select via config file - /etc/sysconfig, set DISPLAYMANAGER=/bin/gdm
  • Select via systemd startup script

Configure Display Manager

  • XDM
    • Main config file - /etc/X11/xdm/xdm-config
    • Control remote access - /etc/X11/xdm/Xaccess
  • KDM
    • File location - /etc/X11/kdm, /etc/kde/kdm
    • Try searching KDM config files in kdm or kdebase package
    • Expands on XDM - User can select session type when login
    • Extra options - kdmrc file, [Xdmcp] section is for network operations
  • GDM
    • File location - /etc/X11/gdm
    • Set local options in custom.conf file
    • GDM settings tool - gdmconfig or gdmsetup

4 - Desktop Environment

KDE Plasma

  • Display Manager - SDDM (Simple Desktop DM)
  • File Manager - Dolphin
  • Windows Manager - Kwin

Gnome

  • Display Manager - GDM
  • File Manager - Gnome Files (Formerly: Nautilus)
  • Windows Manager - Mutter

Cinnamon

Fork of Gnome 3

  • Display Manager - LightDM
  • File Manager - Nemo (Fork of Nautilus)
  • Windows Manager - Muffin (Fork of Mutter)

Xfce

  • Display Manager - LightDM
  • File Manager - Thunar
  • Windows Manager - Xfwm (utilize its own compositor manager)

More about Xfce

  • Lightweight environment: Not much CPU & memory consumption compared to the above ones
  • Developed in 1996, as extension of CDE (Unix Common Desktop Environment)
    Use XForms graphical toolkit (Xfce)
  • Rewritten and no longer use codes from CDE / XForms, but remain to be lightweight

Other

Install MATE

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sudo tasksel install ubuntu-mate-desktop

5 - Remote Access

📌 只有 X Server 的 client-server model 是反过来的：Remote X clients access your X server.

X Server


X Client-Server

  • In most cases, X server & client are on the same computer
  • By default, X server only responds to local access requsts (as security measure)
  • xhost port: 6000 to 6063 (set firewall policy for connection to pass through)
  • xauth - add, remove & list remote hosts in X11 config file

Using Remote X Client

Access remote machine (remote) via machine (local)
Use compute resource on remote, while using GUI on local

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# local: connect to remote
xhost +remote

# remote: export display to local
export DISPLAY=local:0.0

# local: close connection
xhost -remote

Tunneling X via SSH

X11 forwarding - Remote GUI interactions within a secure channel


Encrypting X connection with SSH

  • Encryption might slow down X access - Enable SSH compression
  • Preferred & Secured: Tunneling X via SSH
  • Change SSH config (enable forwarding)
    • Client - /etc/ssh/ssh_config. Use SSH -X, set ForwardX11 yes
    • Server - /etc/sh/sshd_config, set X11Forwarding yes
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ssh -X user@remote

SSH can tunnel network connections: Carry another potocol via its own encrypted connection.

Never use SSH -Y, because it treats remote connection as trusted, which imposes security risks.


VNC

Notes

  • VNC - Virtual Network Computing
  • VNC is a cross-platform protocol, uses the RFB protocol (Remote Frame Buffer)
    • Allows client to send GUI commands (mouse clicks) to the server
    • Server sends desktop frames back to client
  • Ports
    • Server port -TCP 5900 + n (display number, usually port 5901)
    • Java-enabled browser - TCP 5800 + n

2 types of desktop UIs

  • Persistent - Persist GUI session state. Only available via browser access
  • Static - Does not save state. Always show the default desktop environment

Pros & Cons

  • Desktop is available for multiple users
  • VNC only handles mouse & keyboard input. Does not provide file / audio transfer
  • No traffic encryption by itself
  • Password stored in plaintext in server file

TigerVNC

  • Improvement of RealVNC
  • Server
    • Install - tigervnc-server
    • Control - vncserver, vncconfig
  • Client
    • Install - tigervnc
    • Control - vncviewer
  • Use SSH port forwarding for VNC server ports - Allow traffic via port 22

Remote Desktop

Xrdp

  • Alternative to VNC. Use RDP (Remote Desktop Protocol)

  • Standard RDP port - TCP 3389


NX

  • NX protocol, created by NoMachine in 2001
  • Compress X11 data - Excellent response time even over low-bandwidth connections
  • Faster than VNC-based connections
  • SSH tunneling by default
  • Support multiple simultaneous users via a single network port

SPICE (Simple Protocol for Independent Computing Environments)

  • X.org version - Xspice
  • Provide connections with KVM virual machines
  • Client uses multiple data socket connections
  • Consumes low amount of CPU
  • Strong security
    • Traffic encrypted using TLS
    • Authentication - SASL (Simple Authentication and Security Layer), supports Keberos

Both VNC & SPICE provide remote desktop connections to KVM vrirtual machines.



Localization

  • timedatectl - Manage time & date

  • localectl - Manage locale


1 - Time Zone

Linux uses UTC (Coordinated Universal Time) by default

  • Translate to local time (Not a plain text file, cannot directly edit)
    • Debian - /etc/timezone
    • Redhat - /etc/localtime

hwclock - Set Hardware clock (RTC)

  • Display internal BIOS / UEFI clock
  • Provide access to hardware clock built into the physical server

Verify local time

Time zone code reference

  • tzselect - determines timezone ✅

  • date - 3-letter TZ code (legacy command)

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    # Set time & date format
    date MMDDhhmm[[CC]YY][.ss]

Change Time Zone

  • Tools - tzsetup, tzselect, tzconfig

  • Create softlink from zonefile to localtime

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    # remove or rename original timezone
    sudo mv /etc/timezone /timezone.bkup

    # create softlink
    sudo ln -s /usr/share/zoneinfo/US/Pacific /etc/timezone

Use timedatectl

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# show time & date
timedatectl

# change time
sudo timedatectl set-time "2022-03-25 08:00:00"

Most Linux system use NTP (network Time Protocol) to sync time & date with centralized time server.
If use NTP, unable to alter time / date using date or timedatectl locally.


2 - Locale

Codeset / Charater set

  • ASCII (American Standard Code for Information Interchange), 7-bit

  • ISO-8859

  • Unicode - 3-byte code (24-bit) to represent every know character

  • UTF (Unicode Transformation Format)
    Transform long unicode value to 1-byte (UTF-8) or 2-bye (UTF-16) codes

    • UTF-8 (8-bit) ✅ New standard
      Adopt UTF-8 over ISO-8859: No need to specify a substandard

Locale: Specify language, country & related info for customizing display

  • Format - lang_country.codeset (e.g. en_US.UTF-8)

Locale options

  • File location - /usr/bin/locale

    • LC_PAPER - paper size. e.g. US letter, or standard A4
    • LC_MEASUREMENT - measuring units
    • LC_ALL - Master override (all previous settings)
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# Check available locale
locale -a

# show env var setting
locale -ck

Change locale

  • Temporary - Export both in current shell

  • Permanent - Add both lines in ~/.bashrc

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# need both LC_ALL & LANG
export LANG=en_GB.UTF-8
export LC_ALL=en_GB.UTF-8

Use localectl (systemd is enabled)

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# show current setting
localectl

# list all available locales
localectl list-locales

# change locale
localectl set-locale LANG=xx

Modify Text file codesets 📌 

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# get encoding list
iconv --list

# change from ISO-8859 to UTF-8
# -f (source), -t (destination)
iconv -f iso-8859-1 -t UTF-8 1.txt > 2.txt


Printing

Two major visual output tool on the computer: Monitor & Printer


1 - Linux Printing Architecture

The Linux print queue is managed by CUPS (Common Unix Printing System)

Linux printing is built around the concept of print queue

  • Print queue directory - /var/spool/cups
  • Network-oriented: Can accept print jobs from both remote & local systems

PostScript & GhostScript

  • PostScript - common printer language
  • Printer driver - Between application & print queue
  • Linux printer driver is part of GhostScript (translator for PostScript)
    • Some mid / low-end printers does not directly support PostScript
    • GhostScript takes PostScript input, and produces output in many different bitmap formats
    • Large GhostScript output file: Store briefly on hard disk
    • Fit Ghostcript into the print queue: Smart filter

2 - Network Printing

CUPS (act as both server & client)

  • Main config file - /etc/cups/cupsd.conf
  • Daemon runs in the background, watching for print jobs to be submitted
  • Client pass print jobs to other computers
  • Application can query CUPS about printer’s capabilities

CUPS Utilities

  • Access CUPS daemon in browser: At port 631 📌
  • Authentication: root (username) & root password

Network Printers

  • IPP - Internet Printing Protocol

  • Windows: SMB / CIFS (Server Message Block / Common internet File System)

  • Linux Samba server - Enable file sharing between machines in a single network

  • Two ways of printing to Windows from Linux

    • GhostScript - Windows SMB is non-PostScript, need a local Linux smart filter & GhostScript driver

    • PostScript - Print to Windows SMB queue from Linux via Samba (use PostScript driver)

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      # URI for SMB share
      smb://username:password@SERVER/SHARE

3 - Commands

Legacy BSD commands

  • lpr
  • lpq
  • lprm
  • lpc

lpr - Submit print jobs

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-P [queue]	// specify queue name
-J [job]	// job name
-m [user]	// notify user by email
-# [number]	// number of copies
    
// Example: print pdf in myqueue, 3 copies. Then notify user kk
lpr -P myqueue -# 3 -m kk file.pdf

lpq - Display info about print queue

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lpq -P myqueue

lprm - Remove print jobs

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# Get job ID
lpq -P xx

# remove by job ID
lprm 1630

lpc - Control print queue

  • Start, stop & reorder jobs within print queue
  • Other commands to control the queue
    • cupsenable - enable queue
    • cupsdisable - disable queue
    • lpmove - move job from one queue to anothe