第8章 デスクトップの外観とブランディングのカスタマイズ

. Users must log out and back in again before the system-wide settings take effect.



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:_mod-docs-content-type: PROCEDURE
// Module included in the following assemblies:
//
// <List assemblies here, each on a new line>

// This module can be included from assemblies using the following include statement:
// include::<path>/proc_adding-extra-backgounds.adoc[leveloffset=+1]

// The file name and the ID are based on the module title. For example:
// * file name: proc_doing-procedure-a.adoc
// * ID: [id='proc_doing-procedure-a_{context}']
// * Title: = Doing procedure A
//
// The ID is used as an anchor for linking to the module. Avoid changing
// it after the module has been published to ensure existing links are not
// broken.
//
// The `context` attribute enables module reuse. Every module's ID includes
// {context}, which ensures that the module has a unique ID even if it is
// reused multiple times in a guide.
//
// Start the title with a verb, such as Creating or Create. See also
// _Wording of headings_ in _The IBM Style Guide_.
[id="adding-extra-backgrounds_{context}"]
= Adding extra backgrounds

You can make extra backgrounds available to users on your system.

.Procedure

. Create the `/usr/share/gnome-background-properties/extra-backgrounds.xml` file.

. In the new file, specify the extra background files and their appearance in the following format:
+
[source,xml, subs="+quotes"]

. The new backgrounds are now available to all users in the *Background* section of the *Settings* application.

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:_mod-docs-content-type: REFERENCE

[id="frequently-used-background-schema-keys_{context}"]
= Frequently used background schema keys

[role="_abstract"]
The following configuration controls the behavior of desktop backgrounds in the GSettings system.

.Frequently used GSettings and XML background keys
[options="header", cols="2,2,2a,3"]
|=======
|Key name |XML name |Possible values |Description
|`picture-options`
|`options` |
* `none`
* `wallpaper`
* `centered`
* `scaled`
* `stretched`
* `zoom`
* `spanned`
|Determines how the image set by `wallpaper_filename` is rendered.
|`color-shading-type`
|`shade_type` |
* `horizontal`
* `vertical`
* `solid`
|Determines the shade of the background color.
|`primary-color` |`pcolor` |default: `#023c88` |Left or Top color when drawing gradients, or the solid color.
|`secondary-color` |`scolor` |default: `#5789ca` |Right or Bottom color when drawing gradients, not used for solid color.
|=======

.An extra backgrounds file with one `<wallpaper>` element
====
[source,xml]

====

.An extra backgrounds file with two `<wallpaper>` elements
====
In one configuration file, you can specify multiple `<wallpaper>` elements to add more backgrounds as shown in the following example with two `<wallpaper>` elements, adding two different backgrounds.

[source,xml]

====

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:_mod-docs-content-type: PROCEDURE
[id="setting-the-screenshield_{context}"]
= Setting the screen shield

Screen shield is the screen that slides down when you lock the system. You can set a default screen shield picture for all users on the system.

.Procedure

. Create the [filename]`/etc/dconf/db/gdm.d/01-screensaver` file:
+
[subs="+quotes"]
....
[org/gnome/desktop/screensaver]
picture-uri='file://__/opt/corp/background.jpg__'
....
+
Replace [filename]`__/opt/corp/background.jpg__` with the absolute path to the image file that you want to use as the default screen shield. Supported formats are PNG, JPG, JPEG, and TGA. Note that the screen shield scales your image if necessary to fit the screen.

. Update the system databases:
+

. Users must log out and back in again before the system-wide settings take effect.

// Next time you lock the screen, the new Screen Shield will show in the background. In the foreground, time, date and the current day of the week will be displayed.

.Troubleshooting

* If the screen shield does not update:

.. Verify that you have updated the system databases:
+

.. Try restarting GDM:
+

+
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[WARNING]
--
////
Restarting GDM

This snippet explains the risks of restarting the `gdm` service. Include it next to all procedure steps that restart `gdm`.

This comment must stay inside the admonition block so that you can nest the snippet inside procedures.
////

Restarting the `gdm` service terminates all currently running GNOME sessions of all desktop users who are logged in. This might result in users losing unsaved data.
--

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:context: {parent-context-of-customizing-desktop-backgrounds}


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:_mod-docs-content-type: PROCEDURE

[id="customizing-the-branding-of-the-login-screen_{context}"]
= Customizing the branding of the login screen

[role="_abstract"]
You can change the logo that appears on the GNOME login screen (GDM) using a `dconf` profile.

.Prerequisites

* Prepare an image file in any of the supported formats: ANI, BPM, GIF, GTIFF, ICNS, ICO, JPEG, JPEG 2000, PCX, PNM, PBM, PGM, PPM, RAS, SVG, TGA, TIFF, WBMP, XBM, or XPM.
* The image must be around 48 pixels in height. If it is significantly larger, it will exceed the logo area.
* Store the image file in a location that the `gdm` user can access. For example, select a universally readable system directory such as `/opt/` or `/usr/local/`.

.Procedure

. Create the `/etc/dconf/db/gdm.d/01-override-logo` configuration file with the following content:
+
....
[org/gnome/login-screen]
logo='/path/to/logo.png'
....
+
Replace `__/path/to/logo.png__` with the full path to the image file that you want to use as the login screen logo.

. Update the system databases:
+

.Verification

. Log out or otherwise switch to the login screen.

. Check if it displays the logo that you selected.

. If the logo does not update, restart GDM:
+

+
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[WARNING]
--
////
Restarting GDM

This snippet explains the risks of restarting the `gdm` service. Include it next to all procedure steps that restart `gdm`.

This comment must stay inside the admonition block so that you can nest the snippet inside procedures.
////

Restarting the `gdm` service terminates all currently running GNOME sessions of all desktop users who are logged in. This might result in users losing unsaved data.
--

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////
[role="_additional-resources"]
.Additional resources

* This section is optional.
* Provide a bulleted list of links to other closely-related material. These links can include `link:` and `xref:` macros.
* Use an unnumbered bullet (*) if the list includes only one step.
////

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////
[role="_additional-resources"]
== Additional resources

* This section is optional.
* Provide a bulleted list of links to other closely-related material. These links can include `link:` and `xref:` macros.
* Use an unnumbered bullet (*) if the list includes only one step.
////

:context: {parent-context-of-customizing-desktop-appearance-and-branding}


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:parent-context-of-restricting-the-desktop-session: {context}

:_mod-docs-content-type: ASSEMBLY

[id="restricting-the-desktop-session_{context}"]
= Restricting the desktop session

:context: restricting-the-desktop-session

You can restrict and control various functionalities on the GNOME desktop environment. You can enforce specific configurations and restrictions to maintain system integrity and prevent unauthorized access.

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:_mod-docs-content-type: PROCEDURE

[id="disabling-user-logout-and-user-switching_{context}"]
= Disabling user logout and user switching


Disabling user logout and user switching can improve security, prevent user errors, and enforce a specific workflow. This can mitigate unauthorized access to sensitive data and disruptions to the workflow caused by users accidentally logging out or switching to another user.

.Prerequisites

* Administrative access.

.Procedure

. Create a plain text `/etc/dconf/db/local.d/00-logout` keyfile in the `/etc/dconf/db/local.d/` directory with the following content:
+
....
[org/gnome/desktop/lockdown]
# Disable user logut
disable-log-out=true

# Disable user switching
disable-user-switching=true
....

. Create a new file under the `/etc/dconf/db/local.d/locks/` directory and list the keys or subpaths you want to lock down:
+

. Apply the changes to the system databases:
+

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:_mod-docs-content-type: PROCEDURE

[id="disabling-printing_{context}"]
= Disabling printing

Disabling printing can prevent unauthorized access to sensitive documents and potential breaches and safeguard confidential information.

.Prerequisites

* Administrative access.

.Procedure

. Create a plain text `/etc/dconf/db/local.d/00-printing` keyfile in the `/etc/dconf/db/local.d/` directory with the following content:
+
....
[org/gnome/desktop/lockdown]
# Disable printing
disable-printing=true
....

. Create a new file under the `/etc/dconf/db/local.d/locks/` directory and list the keys or subpaths you want to lock down:
+
....
# Lock printing
/org/gnome/desktop/lockdown/disable-printing
....

. Apply the changes to the system databases:
+
....
# dconf update
....

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:_mod-docs-content-type: PROCEDURE

[id="disabling-filesaving_{context}"]
= Disabling filesaving

Disabling file saving can help to protect sensitive data from unauthorized access and protect against potential data leaks.

.Prerequisites

* Administrative access.

.Procedure

. Create a plain text `/etc/dconf/db/local.d/00-filesaving` keyfile in the `/etc/dconf/db/local.d/` directory with the following content:
+
....
[org/gnome/desktop/lockdown]
# Disable saving files on disk
disable-save-to-disk=true
....

. Create a new file under the `/etc/dconf/db/local.d/locks/` directory and list the keys or subpaths you want to lock down:
+
....
# Lock file saving
/org/gnome/desktop/lockdown/disable-save-to-disk
....

. Apply the changes to the system databases:
+
....
# dconf update
....

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:_mod-docs-content-type: PROCEDURE

[id="disabling-the-command-prompt_{context}"]
= Disabling the command prompt

Disabling the command prompt can simplify user interactions with the system, prevent inexperienced users from executing potentially harmful commands that might cause system instability or data loss, and  reduce the risk of unauthorized changes to system settings or configurations.

.Prerequisites

* Administrative access.

.Procedure

. Create a plain text `/etc/dconf/db/local.d/00-lockdown` keyfile in the `/etc/dconf/db/local.d/` directory with the following content:
+
....
[org/gnome/desktop/lockdown]

# Disable command prompt
disable-command-line=true