chmod command to set a file as permission denied

Question

I want my file not to be deleted by any user. Can I know the chmod mode command for the same?

I need to get this kind of msg (rm ctl_model_fact.csv: Permission denied)

Answer 1

root can always delete a file (at least on the chmod level; you need file system attributes or a Linux Security Module (SELinux, AppArmor) to prevent that).

For ordinary users you have to remove the write permission of the parent directory for all users.

Answer 2

As long as you're not trying to keep root from deleting the file, you actually need to modify the permissions on the directory in which ctl_model_fact.csv resides. chmod go-w [your directory] will do it, but it will affect all files in your directory, not just ctl_model_fact.csv. If you also want to make sure other users are unable to change the file, use chmod go-w ctl_model_fact.csv.

Answer 3

Deletion is a write operation so you need to remove write access from the directory that contains the file (using the file ~/foo/bar.txt as an example):

chmod a-w ~/foo/

or

chmod 666 ~/foo/

This, however still allows root to delete the file. If don't even want to allow that, things get more complex. As far as I know, the best way (and this is easily circumvented by reversing the command) is to set it to "immutable":

sudo chattr +i ~/foo/bar.txt

That will stop root from deleting the file but they can always just run chattr -i ~/foo/bar.txt again to undo it so it's more like a obstacle than a full block. It does, however, stop non-root users from deleting it and they won't have the right to run chattr -i on it so this is the easiest way since it does not affect all files in the directory.