If you check most executables in /sbin and elsewhere, the permissions are set to 555. This prevents even root from making changes without specifically enabling them.

-Mark

There are several ways root can modify a write-protected file without changing its permissions, such as with output redirection ("echo foo > file") or with a text editor (which may prompt to overwrite read-only permission).

You can set a file's immutable flag to keep it from being modified, moved, deleted or having its permissions changed. Setting a file's system immutable flag is the most extreme because it can only be unset when the system is in single-user mode.

The Locked checkbox in a Finder Info window sets/clears the user immutable flag. The chflags command can set/clear others.

See "man chflags" and "man 2 chflags" for basic info about the different file flags.

I don't recommend using these unless you *really* understand the possible consequences.