Customizing the user’s session

In this section, we will describe how the session startup in ThinLinc can be customized.

Session startup — the big picture

The session setup is constructed to be easy to use and configure yet still easy to customize for advanced use cases.

Fig. 23 Session startup procedure — on VSM Server

In Fig. 23, shows a (simplified) description of what happens on the VSM Server when a client connects to log in:

• The VSM Server checks if the user has an existing session.

• If a session exists, VSM Server contacts the VSM Agent running on the host where the session is running, and asks it to verify that the session is still alive.

• If the session was alive, VSM Server runs any scripts placed in /opt/thinlinc/etc/sessionreconnect.d. When all such scripts are completed, session information is returned to the client. The client proceeds by contacting the agent on which the session is running.

• If the existing session was not alive, or if there were no existing sessions at all, VSM Server finds out which VSM Agent has the least load, and contacts this agent to request a new session.

• When the agent responds that a new session has been created, VSM Server runs any scripts placed in /opt/thinlinc/etc/sessionstartup.d. When all such scripts are completed, session information is sent back to the client. The client proceeds by contacting the agent on which the session was started.

Scripts run at session startup/reconnect

Scripts in /opt/thinlinc/etc/sessionstartup.d and /opt/thinlinc/etc/sessionreconnect.d are run by the root user, on the VSM Server. Session information will not be sent back to the client until these scripts have completed. This makes it possible to ensure that commands have been run before the client connects to the VSM Agent.

If background execution is desired, place the command to be run in the background and make sure all file descriptors are closed. Here’s an example on how to execute a script in the background.

/opt/thinlinc/sbin/tl-limit-printers < /dev/null > /dev/null 2>&1 &

Session startup on VSM Agent

Fig. 24 Session startup procedure — on VSM Agent

Fig. 24 outlines what happens when an VSM Agent is contacted by VSM Server to request a new session. In detail, the following happens:

1. The VSM agent on the machine where the session will reside executes the script /opt/thinlinc/etc/xsession.

2. The file /opt/thinlinc/etc/xsession is a shell script that can be customized by advanced users. In its standard version, as delivered with ThinLinc, it will check if there is a file named ~/.thinlinc/xstartup in the user’s home directory. If there is such a file, it will be executed. If no such file exists, the file /opt/thinlinc/etc/xstartup.default is executed instead. See Profiles and the standard xstartup.default file for a description of the standard behavior of this file.

This system allows for experienced users to customize how their session startup should work by editing the file ~/.thinlinc/xstartup. On the other hand, at sites where users should not be able to customize their system startup, /opt/thinlinc/etc/xsession can be modified so that it doesn’t try to execute user-specific xstartup-files. The standard setup should however suit the needs of the majority of installations.

Profiles and the standard xstartup.default file

ThinLinc allows for different “profiles” when starting up a user session. The users will be presented with a menu after logging in, where they can choose for example between a desktop suited for engineering users, a desktop suited for the marketing department or a Windows desktop. The example configuration files that are delivered with ThinLinc have several different alternatives, however only those sessions that are actually available on the system are displayed. This is just an example configuration, meant to be customized for each individual ThinLinc installation.

Fig. 25 The ThinLinc profiles and xstartup.default

As described in Session startup — the big picture, /opt/thinlinc/etc/xstartup.default is executed if there is no ~/.thinlinc/xstartup for the user. This file, in its unmodified version as delivered with ThinLinc, executes three steps, as outlined in Fig. 25.

1. All files in /opt/thinlinc/etc/xstartup.d/ are executed. Files that have filenames ending with .sh will be sourced as shell scripts. Other files are executed normally. This way, environment variables that persist down to the session command can be set in *.sh files.

   If a specific execution order is needed for the scripts in the xstartup.d/ directory, let the names of the scripts begin with numbers, where a script with a lower number will be executed before one with a higher number. For example 10setuphomedir will be executed before 20copyfiles.

   By default, the script /opt/thinlinc/etc/xstartup.d/20-tl-select-profile.sh will let the user choose among the possible profiles. See Configuring available profiles for documentation on how to set up profiles. If only one profile is available, it will be selected without asking the user. The environment variable TLPROFILE is set to the name of the selected profile.

   Worth noting is that the environment variable TLPROFILE is available when running the scripts in xstartup.d, for decisions based on what profile will be run.

2. The command tl-run-profile is run. This runs the commands associated with the selected profile, for example startkde to start a KDE session.

3. When the commands run by tl-run-profile exits, xstartup.default runs scripts and commands located in the directory /opt/thinlinc/etc/xlogout.d. The same information that applies to files in xstartup.d (as documented in step 1. above) applies to files in this directory.

Note

Scripts in /opt/thinlinc/etc/xstartup.d and /opt/thinlinc/etc/xlogout.d are run on the agent, with the same rights as the user owning the session.

Session startup with a client supplied start program

If the client has requested that the session should be started with a command supplied by the client, VSM agent will set the environment variable TLCOMMAND to this command. In this case, the profile selection dialog will be disabled and tl-run-profile will execute the command specified by the client, instead of a profile command. To disable client supplied start programs, create the file /opt/thinlinc/etc/xstartup.d/00-no-startprog.sh, containing:

unset TLCOMMAND

Configuring available profiles

The available profiles are configured via Hiveconf, under the /profiles path. The default configuration includes a number of examples.

If the default parameter is present, it specifies the default profile. The profile chooser will have this entry selected when it starts, and it may also be used automatically for some error conditions.

The order parameter selects which profiles should be available for selection, and the order in which they are displayed. This is a space-separated list.

If the show_intro parameter is true, a configurable introduction text will be displayed and requires user input to proceed with the logon process. The introduction parameter is a text that will be displayed if introduction is shown. This text block also supports Pango Markup format styling for a fancier text layout.

Each profile is defined under a section named /profiles/<profile key>. For most desktop environments only the xdg_session parameter needs to be configured. For custom profiles more values need to be specified, mainly cmdline. Please see Parameters in /profiles/ for more details on the available options.

Configuring different Linux desktops based on the selected profile

Please read Building custom Linux desktops with the ThinLinc desktop customizer for documentation on how to configure different desktops with for example different menu and desktop icons depending on what profile is selected.

Speeding up session startup

If a user has a complicated session startup with many time-consuming operations, it can take quite a while before the user’s desktop environment (for example KDE or Gnome) begins to start. One example of when this happens is when mounting local drives.

One way of speeding up this process is to execute some of the operations in the background. Most often, there is no need to mount the local drives before starting KDE because it takes longer time to start KDE than it takes to mount the local drives. The two operations can easily run in parallel. The same goes for the example of mounting shared directories.

The easiest way to accomplish this is to add an & sign after commands run by scripts in /opt/thinlinc/etc/xstartup.d.

Make sure that commands that must be run before starting the window environment are run sequentially. For example, configuring desktops via TLDC must be done before starting KDE.

Configuring the language environment on the server based on the client language

The ThinLinc client reports the language settings on the client side when requesting a session. This can be used to configure the language on the server side. The idea is that in an environment where several languages are in use, a user could automatically get their preferred language based on what their client computer is configured for.

To activate this, a symlink needs to be created:

$ sudo ln -s /opt/thinlinc/libexec/tl-set-clientlang.sh \
   /opt/thinlinc/etc/xstartup.d/00-tl-set-clientlang.sh

Also, make sure no other parts of the startup environment are trying to set the LANG variable. For example, on Fedora, the files /etc/profile.d/lang.sh and /etc/profile/lang.csh will override the LANG variable set by tl-set-clientlang.sh.