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Unity is an alternative shell for the GNOME desktop environment, developed by Canonical in its Ayatana project.

It consists of several components including the Launcher, Dash, Lenses, Panel and Indicators.

More info about its individual components can be found at Ubuntu's Unity article

Unity is currently a plugin of the Compiz window manager.

Under Canonical's developing convergence plans it will soon be a QT5 QML Desktop using their Mir display server.

Mir is being developed as an alternative display server to X or Wayland, more info about it can be found at Ubuntu's Mir article

Installation

You can install Unity by adding the unity-gentoo ebuild repository via eselect repository or layman:

root # eselect repository enable unity-gentoo

or

root # layman -a unity-gentoo

Select one of the 'unity-gentoo' profiles:

Warning

Ensure to keep the same profile version as the system starts with. New installs are 17.1 by default on amd64. Selecting a 17.0 profile from a 17.1 starting point will be disastrous once emerge installs files.

root # eselect profile list

Emerge unity-base/unity-build-env:

root # emerge -av unity-build-env

Finally, emerge unity-base/unity-meta:

root # emerge -uDNavt unity-meta

Usage

You should be starting it via a display manager or by setting XSESSION=unity for startx:

root # systemctl start lightdm

user $ XSESSION=unity startx

Technical

At its core Unity uses a lot of Gnome, and since >=gnome-3.8 systemd is required.

Project:GNOME/GNOME3-Upgrade-guide#Systemd

GNOME 3 requires systemd to be running to get it working properly, otherwise, you will get broken power management and multiseat handling, and also some more problems because upstream has moved away from the obsolete consolekit to logind (that needs systemd to be running to work).

Startup files

The display manager (lightdm) or XSESSION=unity and 'startx' uses the sys-apps/upstart desktop services daemon to start 'gnome-session --session=unity' This executes /usr/share/gnome-session/sessions/unity.session which starts compiz as the window manager. /etc/X11/xinit/xinitrc.d/65compiz_profile-on-session is sourced at Xsession startup and if $DESKTOP_SESSION=unity, it sets the COMPIZ_CONFIG_PROFILE=ubuntu variable. When compiz starts it checks the value of $COMPIZ_CONFIG_PROFILE and uses the 'ubuntu' entry located in /etc/compizconfig/config This 'ubuntu' entry sets the compiz profile to 'unity' and sets the compizconfig backend to use gsettings (dconf) which reads the compiz settings from the dconf registry. Default compizconfig settings find their way into the desktop user's dconf registry by way of /etc/xdg/autostart/compiz-migrate-to-dconf.desktop This is auto started at Xsession startup and actually copies the settings from the global gconf registry to the desktop user's dconf registry. Default compizconfig settings find their way into the global gconf registry when compiz is emerged. At src_install() time the compiz ebuild uses the 'update-gconf-defaults' tool to read all files in /usr/share/gconf/defaults/ and write them out to a gconf registry file located in /etc/gconf/gconf.xml.unity/ It then updates /etc/gconf/2/local-defaults.path to include the new /etc/gconf/gconf.xml.unity/ directory