In the /etc, I found several commands with '-': -rw-r--r--. 1 root root  916 Jul  1  2015 group-----------. 1 root root  733 Jul  1  2015 gshadow--rw-r--r--. 1 root root 2261 Apr 25  2015 passwd-----------. 1 root root 1252 Apr 25  2015 shadow-of course, there are also their original ones. Since 'group' and 'passwd' are important, could anyone explain the meaning and the possible reason? Thanks. 
what is the meaning of '-' in file name?
security;filenames;passwd
Those are usually system-generated backup files. Feel free to ignore them.