KDE

KDE & Qt Applications

General

• kdesvn, when used with KDE < 3.5.6 can cause an error message with the context menu (although this is inoffensive), telling about DCOP errors. The fix is in KDE 3.5.6.

• Some applications are much better opened only once if they support tabs. For example, Quanta and Kate. Generally, they have a command-line option to tell them to use an existing instance. Open the KDE control panel and change the file association, so that the application is launched with this option. For Kate it is -u.

• By default, KDE uses all key shortcuts control+F5, control+F6, etc... for virtual desktop switching. This prevents these keys from working in Firefox for example. The best is to disable these key shortcuts. KDE Control Center -> Regional & Accessibility -> Keyboard Shortcuts -> Shortcut Sequences.

• This is not specific to KDE, but KDE / Gentoo seems to use XDG to manage the creation of directories on the HOME folder (directories such as Desktop, Downloads, Documents...). To change those directories to what is needed, edit /etc/xdg/user-dirs.conf (or /etc/xdg/user-dirs.defaults).

Advanced KDE configuration

• First, using the KDE control center should *never* mess up with the KDE base installation/configuration, except when it asks for administration rights.

• The user directories used by KDE 4 under Gentoo:

~/.kde4/
~/.local/
~/.config/

The last directory (.config) seems more related to Qt stuff and themes. It also contains data about the Kmenu, but that's not the only place.

• UPDATE: Not sure .config is still used by KDE (only by Qt).

KMenu Entries

• The KMenu is built unfortunately from a number of different places. System-wide, /usr/share/applications for example. For one user, it is in config/menus/applications-kmenuedit.menu (probably deprecated place), as well as .local/share/applications.

• The KMenu entries in a user home directory will override the system ones. So using the user ones is dangerous as you may override Portage's data.

• If an entry does not appear in the KMenu, try to delete all the stuff in /var/tmp/kde-cache (and in /tmp). You can also run kbuildsycoca4 with various options. If nothing works, try to run the menu editor and to reset the menu to the system one. It will rebuild correctly everything but will remove user defined stuff.

• If an application still does not appear, check that the binary is present on the system and the user can actually execute it (eg, no permission problems).

• If a .desktop file has no categories, the icon will probably appear in Lost+Found in the KDE menu.

Wallet Subsystem

• You can disable the subsystem entirely.
• If KDE keeps asking for the wallet key, and you forgot the key, it's pretty easy to remove the ~/.local/share/kwalletd directory. The system will ask you for a new password, and you can set it to the empty password, which will usually solve the issue (it will stop asking for the unlocking of the wallet, probably because it will be auto-unlocked).
• In order for Kopete not to keep asking you for the wallet password, you can deny Kopete any access to the wallet subsystem. This will force it to use the unsafe password storing option (in the configuration file). Edit the file ~/.kde/share/config/kwalletrc.

Brightness

• The default brightness (restored when KDE starts up) depends on your power management profile. Thus you can change that by configuring your power management profile.

Volume keys

• These will work in KDE if you install kmix.

Screen Locking & Screen Saving

• Chromium can prevent the screen from locking when some sites are opened. This seems to happen on Youtube for instance. Not sure how to prevent this yet.

Input Actions

• In KDE 5, you can configure those in System Settings -> Shortcuts. You can also associate hotkeys to KMenu entries (eg, launch applications this way).
• If you create a custom script (for instance in /usr/local/bin/) that will be launched via a shortcut, make sure you add a shebang (ie #!/bin/sh) at the beginning, else it just won't work.

Issues

• In KDE-4.2, if you uncheck the "Confirm Logout" checkbox in Session Manager, the computer reboots when you simply choose to logout.

KDE Frameworks

Baloo

• Baloo is the new indexing framework replacing nepomuk. You can configure it (exclude some paths from indexing) in System Settings -> Desktop Search. It can be useful to disable content indexing, this will make indexing 100 times faster / lighter. This is now possible easily via the GUI.
• Baloo does not follow symlinks, so indexing directories containing symlinks won't work. You need to specify the real directories in the configuration.

• Useful commands:

balooctl status # shows how many files are indexed and indexing process
balooshow /path/to/file # shows if file is indexed
baloosearch ExampleWord
balooctl check # checks for any unindexed file (this should normally not happen, but I had to manually issue this one time)
balooctl monitor # prints what the indexer is currently doing (indexing). If nothing happens, it means the indexer is stuck / idle

• Sometimes the database is not up to date and contain wrong, old entries. The easiest way is to remove it at ~/.local/share/baloo/, logout then relog, Baloo will build a new one.

Search in Dolphin

• If searching via Baloo does not work in Dolphin (unfortunately, for me Baloo is still very unstable and works one time out of ten), disabling File Search (in System Settings -> Search > File Search) will make Dolphin revert to standard search features and not use Baloo. This will make search work in the end.

Nepomuk

• Nepomuk is obsolete and no longer used, you can remove its database at ~/.kde4/share/apps/nepomuk if it is still present.

KDE Compositor and Vertical Sync

• KDE 5 / Plasma uses a Compositor, but it seems it can be disabled. The configuration is available at Hardware -> Display and Monitor -> Compositor. You can enable / disable the compositor at startup and choose the rendering backend (I select OpenGL 3.1 but not sure it is the best option).

• Screen tearing can be a real problem on KDE (apparently especially with Nvidia cards) and can be configured there as well (via vertical sync). Choosing everything on the vsync select box except "Never" or "Automatic" seems to solve the tearing problem. However, some settings seem to make Plasma extremely buggy / unstable / slow (for instance "Re-use screen content"). I chose "Only when cheap" which seems to work well.

• Note that screen tearing occurs in certain applications and not others. For instance, mpv / vlc with a vdpau or opengl video output don't suffer from tearing, whereas Chromium (and the Plasma desktop itself, for instance when moving a window around) do have intense tearing (if vsync is disabled in the Compositor configuration panel). In many applications, vertical sync can be configured directly. Starcraft 2 under Wine had very important tearing in videos: it could be removed either by choosing a vsync configuration on KDE, or directly on Starcraft 2 options.

• What's not clear is that it seems vsync is independent of actually running the compositor or not. Even if compositor is disabled, if the vsync option is changed, it can remove screen tearing.

• Note that you can also try to change nvidia driver options / Xorg configuration, by enabling "ForceFullCompositionPipeline = On" (this is suggested in the Gentoo wiki). I did not do that as it seems it can negatively affect performance in games or cause other problems. Moreover, according to comments on forums, the screen tearing problems are really dependent of the model of the nvidia card used.