起源：http://superuser.com/questions/300500/ubuntu-unable-to-edit-bashrc-file-because-of-readonly
This is a vim issue, not a file permission issue. If you did not have read permission on the file, you’d see a “Permission denied” error.
Do you invoke vi/vim with the -R option? Are you calling view instead of vi or vim? Do you have set readonly in your .vimrc or in a file in ~/.vim/ftplugin?
In vim you can enter :set noreadonly to unset the readonly flag.
具体解决步骤：
1. 按 Esc 键，进入命令模式
2. 输出 :set noreadonly
3. 而后就能够输出 :wq 来保留文件了。