Linux Administration Cookbook

chattr

I'm starting to think we've been much too lenient here, so let's completely lock down the file so no one (even almighty root) can mess with it:

$ sudo chattr +i permissionfile

We've made the file immutable! 

$ echo "RFCs are great if boring." > permissionfile-bash: permissionfile: Permission denied

We can see this using the lsattr command:

$ lsattr permissionfile----i----------- permissionfile

And, not even root is able to modify the file:

$ sudo echo "RFCs are great if boring." > permissionfile-bash: permissionfile: Permission denied

There are various attributes that can be applied to a file with chattr, but I'd put money on the immutable option being the most commonly used.

To remove the attribute, use chattr again:

$ sudo chattr ...