Hidden files

Hidden files under Linux are files that start with a dot. They are not included when using the * operator in bash:

# ls
.hidden  a.out  datei  main.cpp
# ls *
a.out  datei  main.cpp

Here is one example what this means for you:

Take care if you want to backup your home directory! Taking a backup with the command

tar cvzf backup.tar.gz *

will NOT save your dot files, better use

tar cvzf backup.tar.gz .