昨晚我進行了升級，今天早上關機後我遇到了登入循環（即使我通常甚至沒有顯示登入畫面）。我檢查了 .xsession-errors 並發現以下內容：
openConnection: connect: No such file or directory
cannot connect to brltty at :0
upstart: gnome-session (Unity) main process (4070) terminated with status 1
upstart: unity-settings-daemon main process (4059) killed by TERM signal
upstart: logrotate main process (3887) killed by TERM signal
upstart: bamfdaemon main process (3973) killed by TERM signal
upstart: unity-panel-service main process (4077) killed by TERM signal
upstart: indicator-bluetooth main process (4110) killed by TERM signal
upstart: indicator-power main process (4111) killed by TERM signal
upstart: indicator-datetime main process (4113) killed by TERM signal
upstart: indicator-keyboard main process (4117) killed by TERM signal
upstart: indicator-sound main process (4118) killed by TERM signal
upstart: indicator-printers main process (4121) killed by TERM signal
upstart: indicator-session main process (4123) killed by TERM signal
upstart: Disconnected from notified D-Bus bus
我嘗試重新啟動 lightdm，mv .Xauthority 到備份檔案中，重新安裝 ubuntu-desktop 和 ubuntu-session，並 chown .Xauthority。
我認為這是一個圖形驅動程式問題，因為當我出現在登入畫面上時，我的顯示排列不正確（我有兩個顯示器）。
答案1
我自己想出來了。正如我所想，nvidia 驅動程式是問題所在。我查看了幾個目錄，仍然有 nvidia 367.27 圖形驅動程式的 .run 檔案。我刪除了目前的驅動程式：
sudo apt-get purge nvidia*
使用以下命令停止目前的 Xsession：
sudo service lightdm stop
最後從我的下載資料夾安裝了驅動程式：
sudo sh ~/Downloads/NVIDIA-Linux-*-367.27.run
運行 sudo restart，一切恢復正常。