Chattr according to Wikipedia;
“chattr is a Linux command that allows a user to set certain attributes on a file. Mostly chattr is used to make files immutable so that password files and certain system files cannot be erased during software upgrades.”

To set a file as immutable;
chattr +i file_name

To remove;
chattr -i file_name

http://en.wikipedia.org/wiki/Chattr

Categories: Linux