[debian-edu-commits] [Debian Wiki] Update of "DebianEdu/Documentation/Bookworm/HowTo/NetworkClients" by WolfgangSchweer

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Sun Aug 29 23:17:29 BST 2021 

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The "DebianEdu/Documentation/Bookworm/HowTo/NetworkClients" page has been changed by WolfgangSchweer:
https://wiki.debian.org/DebianEdu/Documentation/Bookworm/HowTo/NetworkClients

Comment:
initial content (copy from the bullseye page w/ some adjustments)

New page:
<<Anchor(NetworkClients)>>
= HowTos for networked clients =
<<TableOfContents(3)>>

== Introduction to thin clients and diskless workstations ==

One generic term for both thin clients and diskless workstations is ''LTSP client''.

(!) Starting with Bullseye, LTSP is quite different from the previous versions.
This concerns both setup and maintenance. As one main difference, the SquashFS image for diskless workstations is now generated from the LTSP server file system. Also, thin clients are no longer supported.<<BR>>In case of a separate or an additional LTSP server required information for setting up the LTSP client environment isn't complete at installation time. Setup can be done once the system has been added with GOsa².

For information about LTSP in general, see the [[https://ltsp.org| LTSP homepage]]. On systems with ''LTSP server'' profile, {{{man ltsp}}} provides more information.

The ''debian-edu-ltsp-install'' tool is a wrapper script for {{{ltsp image}}}, {{{ltsp kernel}}} and {{{ltsp ipxe}}}. It is used to setup and configure diskless workstation support; in addition thin clients (both 64-Bit and 32-Bit PC) are supported using !X2Go. See {{{man debian-edu-ltsp-install}}} or the script content to see how it works. All configuration is contained in the script itself (here documents) to facilitate site specific adjustments.

Please note that the ''ltsp'' tool has to be used carefully. For example, {{{ltsp image /}}} would fail to generate the SquashFS image in case of Debian machines (these have a separate /boot partition by default), and {{{ltsp ipxe}}} would fail to generate the iPXE menu correctly (due to Debian Edu's thin client support).

Examples how to use the wrapper script ''debian-edu-ltsp-install'' instead:
 * {{{debian-edu-ltsp-install --arch amd64}}} creates 64-bit diskless workstation support.
 * {{{debian-edu-ltsp-install --arch amd64 --dist bullseye --thin_type bare}}} creates diskless workstation and 64-bit thin client support.
 * {{{debian-edu-ltsp-install --arch i386 --diskless_workstation no --thin_type bare}}} creates additional 32-bit thin client support.
 * {{{debian-edu-ltsp-install --diskless_workstation yes}}} updates the diskless workstation SquashFS image.
 * {{{debian-edu-ltsp-install --diskless_workstation no --thin_type bare}}} (re-)creates 64-bit thin client support.
 
Besides ''bare'' (smallest thin client system), also ''display'' and ''desktop'' are available options. The ''display'' type offers a shutdown button, the ''desktop'' type runs Firefox ESR in kiosk mode on the client itself (more local RAM and CPU power required, but server load reduced).

'''Diskless workstation'''

A diskless workstation runs all software locally. The client machines boot directly from the LTSP server without a local hard drive. Software is administered and maintained on the LTSP server, but runs on the diskless workstations. Home directories and system settings are stored on the server too. Diskless workstations are an excellent way of reusing older (but powerful) hardware with the same low maintenance costs as with thin clients. 

Unlike workstations diskless workstations run without any need to add them with GOsa².

'''Thin client'''

A thin client setup enables an ordinary PC to function as an (X-)terminal, where all software runs on the LTSP server. This means that this machine boots via PXE without using a local client hard drive.

Debian Edu still supports the use of thin clients to enable the use of very old hardware.

'''LTSP client firmware'''

LTSP client boot will fail if the client's network interface requires a non-free firmware.
A PXE installation can be used for troubleshooting problems with netbooting a machine; if the Debian Installer complains about a missing XXX.bin file then non-free firmware has to be added to the LTSP server's initrd.

Proceed like this on the LTSP server:
 First get information about firmware packages, run:
{{{
apt update && apt search ^firmware-
}}}
 Decide which package has to be installed for the network interface(s), most probably this will be firmware-linux-nonfree, run:
{{{
apt -y -q install firmware-linux-nonfree
}}}
 Update the SquashFS image for diskless workstations, run:
{{{
debian-edu-ltsp-install --diskless_workstation yes
}}}

=== LTSP client type selection ===

Each LTSP server has two ethernet interfaces: one configured in the main 10.0.0.0/8 subnet (which is shared with the main server), and another forming a local subnet (a separate subnet for each LTSP server).

In both cases ''diskless workstation'' or ''thin client'' can be chosen from the iPXE menu. After waiting for 5 seconds, the machine will boot as diskless workstation. 

The default boot menu item and it's default timeout can both be configured in {{{/etc/ltsp/ltsp.conf}}}. A timeout value of ''-1'' is used to hide the menu. Run {{{debian-edu-ltsp-install --diskless_workstation no}}} for any changes to take effect.

=== Use a different LTSP client network ===

192.168.0.0/24 is the default LTSP client network if a machine is installed using the LTSP profile. If lots of LTSP clients are used or if different LTSP servers should serve both i386 and amd64 chroot environments the second preconfigured network 192.168.1.0/24 could be used as well. Edit the file {{{/etc/network/interfaces}}} and adjust the eth1 settings accordingly. Use {{{ldapvi}}} or any other LDAP editor to inspect DNS and DHCP configuration.  

=== Add LTSP chroot to support 32-bit-PC clients ===

Run {{{debian-edu-ltsp-install --arch i386 --diskless_workstation no --thin_type bare}}}.
See {{{man debian-edu-ltsp-install}}} for details about thin client types.

=== LTSP client configuration ===

Run {{{man ltsp.conf}}} to have a look at available configuration options.
Or read it online: https://ltsp.org/man/ltsp.conf/

=== Sound with LTSP clients ===

LTSP thin clients use networked audio to pass audio from the server to the clients.

LTSP diskless workstations handle audio locally.

=== Use printers attached to LTSP clients ===

 * Attach the printer to the LTSP client machine (both USB and parallel port are supported). 

 * Configure the LTSP client with GOsa² to use a fixed IP address.
 
 * Configure the printer using the web interface {{{https://www.intern:631}}} on the main server; choose network printer type {{{AppSocket/HP JetDirect}}} (for all printers regardless of brand or model) and set {{{socket://<LTSP client ip>:9100}}} as connection URI.

== Modifying the PXE setup ==

PXE stands for Preboot eXecution Environment. Debian Edu now uses the [[https://www.ipxe.org/|iPXE]] implementation for easier LTSP integration.

=== Configuring the PXE menu ===

The iPXE menu item concerning system installations is generated using the script {{{debian-edu-pxeinstall}}}.  It allows some settings to be overridden using the file {{{/etc/debian-edu/pxeinstall.conf}}} with replacement values.

=== Configuring the PXE installation ===

The PXE installation will inherit the language, keyboard layout and mirror settings from the settings used when installing the main server, and the other questions will be asked during installation (profile, popcon participation, partitioning and root password). To avoid these questions, the file {{{/etc/debian-edu/www/debian-edu-install.dat}}} can be modified to provide preselected answers to debconf values. Some examples of available debconf values are already commented in {{{/etc/debian-edu/www/debian-edu-install.dat}}}. Your changes will be lost as soon as {{{debian-edu-pxeinstall}}} is used to recreate the PXE-installation environment. To append debconf values to {{{/etc/debian-edu/www/debian-edu-install.dat}}} during recreation with {{{debian-edu-pxeinstall}}}, add the file {{{/etc/debian-edu/www/debian-edu-install.dat.local}}} with your additional debconf values.

More information about modifying PXE installations can be found in the [[DebianEdu/Documentation/Bookworm/Installation#Modifying_PXE_installations|Installation]] chapter.

=== Adding a custom repository for PXE installations ===

For adding a custom repository add something like this to {{{/etc/debian-edu/www/debian-edu-install.dat.local}}}:

{{{
d-i     apt-setup/local1/repository string      http://example.org/debian stable main contrib non-free
d-i     apt-setup/local1/comment string         Example Software Repository
d-i     apt-setup/local1/source boolean         true
d-i     apt-setup/local1/key    string          http://example.org/key.asc
}}}

and then run {{{/usr/sbin/debian-edu-pxeinstall}}} once.

== Changing network settings ==

The debian-edu-config package comes with a tool which helps in changing the network from 10.0.0.0/8 to something else. Have a look at {{{/usr/share/debian-edu-config/tools/subnet-change}}}.  It is intended for use just after installation on the main server, to update LDAP and other files that need to be edited to change the subnet.

/!\ Note that changing to one of the subnets already used elsewhere in Debian Edu will not work. 192.168.0.0/24 and 192.168.1.0/24 are already set up as LTSP client networks. Changing to these subnets will require manual editing of configuration files to remove duplicate entries.

There is no easy way to change the DNS domain name.  Changing it would require changes to both the LDAP structure and several files in the main server file system.  There is also no easy way to change the host and DNS name of the main server (tjener.intern).  To do so would also require changes to LDAP and files in the main server and client file system.  In both cases the Kerberos setup would have to be changed, too.  

== Remote Desktop ==

Choosing the LTSP server profile or the combined server profile also installs the ''xrdp'' and ''x2goserver'' packages.

=== Xrdp ===

Xrdp uses the Remote Desktop Protocol to present a graphical login to a remote client. Microsoft Windows users can connect to the LTSP server running xrdp without installing additional software - they simply start a Remote Desktop Connection on their Windows machine and connect.

Additionally, xrdp can connect to a VNC server or another RDP server.

Xrdp comes without sound support; to compile (or re-compile) the required modules this script could be used.
Please note: The caller needs to be root or a member of the sudo group. Also, /etc/apt/sources.list must contain a valid deb-src line.

{{{
 #!/bin/bash
 set -e
  if [[ $UID -ne 0 ]] ; then  
     if ! groups | egrep -q sudo ; then
         echo "ERROR: You need to be root or a sudo group member."
         exit 1
     fi
 fi
 if ! egrep -q  ^deb-src /etc/apt/sources.list ; then
     echo "ERROR: Make sure /etc/apt/sources.list contains a deb-src line."
     exit 1
 fi
 TMP=$(mktemp -d)
 PULSE_UPSTREAM_VERSION="$(dpkg-query -W -f='${source:Upstream-Version}' pulseaudio)"
 XRDP_UPSTREAM_VERSION="$(dpkg-query -W -f='${source:Upstream-Version}' xrdp)"
 sudo apt -q update
 sudo apt -q install dpkg-dev
 cd $TMP
 apt -q source pulseaudio xrdp
 sudo apt -q build-dep pulseaudio xrdp
 cd pulseaudio-$PULSE_UPSTREAM_VERSION/
 ./configure
 cd $TMP/xrdp-$XRDP_UPSTREAM_VERSION/sesman/chansrv/pulse/
 sed -i 's/^PULSE/#PULSE/' Makefile
 sed -i "/#PULSE_DIR/a \
 PULSE_DIR = $TMP/pulseaudio-$PULSE_UPSTREAM_VERSION" Makefile
 make
 sudo cp *.so /usr/lib/pulse-$PULSE_UPSTREAM_VERSION/modules/
 sudo chmod 644 /usr/lib/pulse-$PULSE_UPSTREAM_VERSION/modules/module-xrdp*
 sudo service xrdp restart
}}}

=== X2Go ===

!X2Go enables you to access a graphical desktop on the LTSP server over both low bandwidth and high bandwidth connections from a PC running Linux, Windows or macOS. Additional software is needed on the client side, see the [[https://wiki.x2go.org/doku.php/doc:installation:x2goclient|X2Go wiki]] for more information.

Please note that the {{{killer}}} package should best be removed on the LTSP server if !X2Go is used, see DebianBug:890517.  

=== Available Remote Desktop clients ===

 * {{{freerdp-x11}}} is installed by default and is capable of RDP and VNC.
  * RDP - the easiest way to access Windows terminal server. An alternative client package is {{{rdesktop}}}.
  * VNC client (Virtual Network Computer) gives access to Skolelinux remotely.  An alternative client package is {{{xvncviewer}}}.
 * {{{x2goclient}}} is a graphical client for the !X2Go system (not installed by default). You can use it to connect to running sessions and start new ones. 

== Wireless clients ==

The ''freeRADIUS'' server could be used to provide secure network connections. For this to work, install the ''freeradius'' and ''winbind'' packages on the main server and run {{{/usr/share/debian-edu-config/setup-freeradius-server}}} to generate a basic, site specific configuration. This way, both EAP-TTLS/PAP and PEAP-MSCHAPV2 methods are enabled. All configuration is contained in the script itself to facilitate site specific adjustments. See [[https://freeradius.org/|the freeRADIUS homepage]] for details.

Additional configuration is needed to 
 * enable/disable access points via a ''shared secret'' (/etc/freeradius/3.0/clients.conf).
 * allow/deny wireless access using LDAP groups (/etc/freeradius/3.0/users).
 * combine access points into dedicated groups (/etc/freeradius/3.0/huntgroups)

(!) End user devices need to be configured properly, these devices need to be PIN protected for the use of EAP (802.1x) methods. And most important: users need to be educated to install the freeradius CA certificate on their devices to be sure to connect to the right server. This way the password can't be catched in case of a malicious server. The site specific certificate is available on the internal network.
 * https://www.intern/freeradius-ca.pem (for end user devices running Linux)
 * https://www.intern/freeradius-ca.crt (Linux, Android)
 * https://www.intern/freeradius-ca.der (macOS, iOS, iPadOS, Windows)
Please note that configuring end user devices will be a real challenge due to the variety of devices. For Windows devices an installer script could be created, for Apple devices a mobileconfig file. In both cases the freeRADIUS CA certificate can be integrated, but OS specific tools are needed to create the scripts.   

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