tl;dr
如无特别的需求，尽量不要跨发行版安装新的Gnome，通过我的测试，Gnome 3.18/3.20/3.22都有或多或少的问题。而且会影响正常的使用，每次安装使用，无一例外的都会回滚到发行版自带的版本，至少Ubuntu是这样，Arch的同学可以尝试一下。
安装Gnome 3.18/3.20步骤
sudo add-apt-repository ppa:gnome3-team/gnome3
sudo add-apt-repository ppa:gnome3-team/gnome3-staging
sudo apt-get update
sudo apt-get dist-upgrade
dist-upgrade执行过程
ray@ray-ThinkPad-X250:~$ sudo apt-get dist-upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages will be REMOVED:
libcheese-gtk23 libcheese7 ubuntu-desktop unity-control-center
unity-control-center-signon
The following NEW packages will be installed:
dleyna-server gnome-control-center gnome-control-center-data
gnome-icon-theme gnome-icon-theme-symbolic gnome-online-accounts
gnome-settings-daemon gstreamer1.0-clutter-3.0 iio-sensor-proxy
libcamel-1.2-54 libcheese-gtk25 libcheese8 libcolord-gtk1
libdleyna-connector-dbus-1.0-1 libdleyna-core-1.0-3 libebook-contacts-1.2-2
libecal-1.2-19 libedata-cal-1.2-28 libedataserver-1.2-21
libgnome-desktop-3-12 libgoa-backend-1.0-1 libgtop-2.0-10 libgupnp-av-1.0-2
libgupnp-dlna-2.0-3 libjavascriptcoregtk-4.0-18 libwebkit2gtk-4.0-37
linux-headers-4.2.0-32 linux-headers-4.2.0-32-generic
linux-image-4.2.0-32-generic linux-image-extra-4.2.0-32-generic realmd
The following packages will be upgraded:
account-plugin-aim account-plugin-jabber account-plugin-salut
account-plugin-yahoo adwaita-icon-theme aisleriot baobab cheese
cheese-common dconf-editor empathy empathy-common eog evince evince-common
evolution-data-server evolution-data-server-common
evolution-data-server-online-accounts folks-common gedit gedit-common
gir1.2-freedesktop gir1.2-glib-2.0 gir1.2-goa-1.0 gir1.2-gtk-3.0
gir1.2-gtksource-3.0 gir1.2-pango-1.0 gir1.2-peas-1.0 gir1.2-totem-1.0
gir1.2-vte-2.91 gnome-accessibility-themes gnome-bluetooth gnome-calculator
gnome-contacts gnome-control-center-shared-data gnome-desktop3-data
gnome-disk-utility gnome-session-bin gnome-session-common
gnome-settings-daemon-schemas gnome-system-monitor gnome-terminal
gnome-terminal-data gsettings-desktop-schemas gvfs gvfs-backends gvfs-bin
gvfs-common gvfs-daemons gvfs-fuse gvfs-libs ifupdown libcairo-gobject2
libclutter-1.0-0 libclutter-1.0-common libclutter-gst-3.0-0
libclutter-gtk-1.0-0 libcogl-common libcogl-pango20 libcogl-path20 libcogl20
libdrm-amdgpu1 libebackend-1.2-10 libebook-1.2-16 libedata-book-1.2-25
libedataserverui-1.2-1 libevdocument3-4 libevview3-3 libfolks-eds25
libfolks-telepathy25 libfolks25 libgail-3-0 libgeocode-glib0
libgirepository-1.0-1 libgnome-bluetooth13 libgoa-1.0-0b libgoa-1.0-common
libgtk-3-0 libgtk-3-bin libgtk-3-common libgtksourceview-3.0-1
libgtksourceview-3.0-common libgtop2-common libgweather-3-6
libgweather-common libnautilus-extension1a libpango-1.0-0 libpango1.0-0
libpangocairo-1.0-0 libpangoft2-1.0-0 libpangoxft-1.0-0 libpeas-1.0-0
libpeas-common libpurple-bin libpurple0 libtotem0 libtracker-sparql-1.0-0
libvte-2.91-0 libvte-2.91-common linux-generic linux-headers-generic
linux-image-generic linux-libc-dev mcp-account-manager-uoa nautilus
nautilus-data python-gi python-gi-cairo python-gobject python3-gi
python3-gi-cairo totem totem-common totem-plugins ubuntu-session
115 upgraded, 31 newly installed, 5 to remove and 0 not upgraded.
Need to get 182 MB of archives.
After this operation, 554 MB of additional disk space will be used.
Do you want to continue? [Y/n] y
恢复到默认Ubuntu原始版本
安装ppa-purge工具，用于删除PPA源
sudo apt-get install ppa-purge删除Gnome 3.18/3.20
sudo ppa-purge ppa:gnome3-team/gnome3-staging
sudo ppa-purge ppa:gnome3-team/gnome3
sudo apt-get purge gnome-desktop gnome-shell恢复安装官方源中与Gnome3.18/3.20冲突的Unity系统包：
sudo apt-get install ubuntu-desktop unity-control-center unity-control-center-signon更新lightDM，删除gnome：
cd /usr/share/xsessions
sudo rm gnome-classic.desktop
参考URL：http://askubuntu.com/questions/81161/how-to-remove-session-entries-from-lightdm
Gnome 3.18/3.20问题收集（2016.04.25）
大家如果是老的Gnome用户可能就会知道，从3.16开始Gnome就将Tray bar移到屏幕左下角了，非常讨厌的一个小框，虽然会自动隐藏，但是隐藏后也会有一小块能看到，非常不爽：
从Reddit上的大神们的交流内容来看Gnome 3.16: Remove message tray on bottom left of screen，在GNOME内部对这个问题也是有很多的冲突观点，但无论如何现在就是这样的一个情况，而且GNOME 3.20也没有改变。
当前解决这个问题，可以使用一个叫做TopIcons的插件，可以将这个小框恢复到桌面右上角：
Gnome 3.20问题收集(2016.04.22)
-
不兼容GTK+ Theme
Gnome 3.20不向后兼容所有之前的Theme，所以需要临时切换为默认的theme，以正常显示GTK+界面：
问题界面
默认Adwaita主题
2.不兼容Gnome Shell Extension
从该Extension页面可以看到其他同学的解决方法：
https://extensions.gnome.org/extension/921/multi-monitors-add-on/
3.GDM不能登陆，ligthdm显示故障
未解决
Gnome 3.22问题收集（2017.02.23）
- 跨目录复制文件会导致Naultilus崩溃
没研究解决方法，直接回滚
参考URL：https://forum.antergos.com/topic/4204/after-update-to-gnome-3-20-i-have-many-problems
