在 Ubuntu 14.04 中，Evince 可以在 root 权限下打开。在 Ubuntu 16.04 中，我可以使用非 root 用户权限打开 evince，但在 root 权限下，我得到
# evince file.pdf
No protocol specified
Failed to connect to Mir: Failed to connect to server socket: Permission denied
Unable to init server: Could not connect: Connection refused
Cannot parse arguments: Cannot open display:
同样的事情也适用于其他几个实用程序，例如pdftk：
pdftk file.pdf cat 1down output file2.pdf
Error: Unable to find file.
Error: Failed to open PDF file:
1
Errors encountered. No output created.
Done. Input errors, so no output created.