Ubuntu14.04目前仍是非常不稳定，使用VNC的时候，只有一个终端，检查日志以后，发现了如下错误：
$ cat /home/brett/.vnc/bt-desktop:1.log
……
gnome-session-is-accelerated: No composite extension.
gnome-session-check-accelerated: Helper exited with code 256
gnome-session-is-accelerated: No composite extension.
gnome-session-check-accelerated: Helper exited with code 256
** (process:6694): WARNING **: software acceleration check failed: Child process exited with code 1
** (gnome-session:6694): CRITICAL **: We failed, but the fail whale is dead. Sorry....
……
简单看了下，可能是gnome-session无法识别到OpenGL硬件加速导致的。该问题普遍存在于DELL大部分系列的服务器上。这个帖子提供了一种解决办法，但我试了下，貌似是无效的。
解决办法：
$ sudo apt-get install gnome-panel gnome-settings-daemon metacity nautilus gnome-terminal
$ vim ~/.vnc/xstartup #修改此文件,写入以下内容
#!/bin/sh
export XKL_XMODMAP_DISABLE=1
unset SESSION_MANAGER
unset DBUS_SESSION_BUS_ADDRESS
[ -x /etc/vnc/xstartup ] && exec /etc/vnc/xstartup
[ -r $HOME/.Xresources ] && xrdb $HOME/.Xresources
xsetroot -solid grey
vncconfig -iconic &
gnome-session &
gnome-panel &
gnome-settings-daemon &
metacity &
nautilus &
gnome-terminal &
vncconfig -nowin &
然后重新启动VNC终端即可
也可以通过安装KDE/XFCE来解决：
$ sudo apt-get install gnome-core xfce4 firefox
$ vim ~/.vnc/xstartup #修改此文件,写入以下内容
#!/bin/sh
unset SESSION_MANAGER
unset DBUS_SESSION_BUS_ADDRESS
startxfce4 &
#gnome-session --session=gnome-flashback &
[ -x /etc/vnc/xstartup ] && exec /etc/vnc/xstartup
[ -r $HOME/.Xresources ] && xrdb $HOME/.Xresources
xsetroot -solid grey
vncconfig -iconic &
参考文章1
参考文章2
参考文章3
============================================
后续补充：
Ubuntu14.04真是很差劲，使用VNC连接成功上桌面以后，S键、D键与Alt功能键相反了。
解决办法：
#必须在图形界面的终端里操作，不能在远程的终端里操作
gsettings set org.gnome.desktop.wm.keybindings panel-main-menu "['<Alt>F1']"
gsettings set org.gnome.desktop.wm.keybindings switch-applications "['<Alt>Tab']"
gsettings set org.gnome.desktop.wm.keybindings show-desktop "['<Alt>d']"
gsettings set org.gnome.desktop.wm.keybindings maximize "['<Alt>Up']"
gsettings set org.gnome.desktop.wm.keybindings unmaximize "['<Alt>Down']"
#也可以运行dconf-editor在GUI界面中展开指定的项进行修改
2015.03.23补充：
VNC日志里出现如下错误：
error opening security policy file /etc/X11/xserver/SecurityPolicy
Could not init font path element /usr/share/fonts/X11/cyrillic, removing from list!
Could not init font path element /usr/share/fonts/X11/100dpi/:unscaled, removing from list!
Could not init font path element /usr/share/fonts/X11/75dpi/:unscaled, removing from list!
Could not init font path element /usr/share/fonts/X11/100dpi, removing from list!
Could not init font path element /usr/share/fonts/X11/75dpi, removing from list!
Could not init font path element built-ins, removing from list!
解决办法：
sudo aptitude install xfonts-100dpi xfonts-75dpi xfonts-scalable xfonts-cyrillic
2015.03.24，关于windows下无法连接Ubuntu 14.04 VNC的问题，在网上发现了一个解决办法（参考文章），但我试了下貌似不成功：
#必须在图形界面的终端里操作，不能在远程的终端里操作
sudo apt-get install dconf-tools
sudo dconf write /org/gnome/desktop/remote-access/require-encryption false
gsettings set org.gnome.Vino require-encryption false
更改背景图片：
#必须在图形界面的终端里操作，不能在远程的终端里操作
sudo dconf write /org/gnome/desktop/background/picture-uri file:///usr/share/backgrounds/Forever_by_Shady_S.jpg
gsettings set org.gnome.desktop.background draw-background false
gsettings set org.gnome.desktop.background picture-uri file:///usr/share/backgrounds/Forever_by_Shady_S.jpg
gsettings set org.gnome.desktop.background draw-background true
改成debian的背景图片
gsettings set org.gnome.desktop.background picture-uri file:///usr/share/images/desktop-base/joy-wallpaper_1920x1080.svg