a is a shortcut for ugo, or “all.” So all the x permissions should now be unset.
rm myfile
With this command, you’re removing the file, but without write permissions. rm will ask if you’re sure by displaying the following message:
rm: remove ‘myfile’, overriding mode 0444?
You should respond by typing y and pressing Enter. This is a feature of rm, not a fact of permissions. Permission to delete a file comes from the directory permissions, and you have write permission in the directory. However, rm tries to be helpful, figuring that if you didn’t want to change the file (and thus remove write permission), you don’t want to delete it either, so it asks you.
What was that 0444 business in the question from rm? The permissions mode is a twelve-digit binary number, like this: 000100100100. 0444 is this binary number represented as an octal (base 8) number, which is the conventional way to write a mode. So you can type chmod 444 myfile instead of chmod ugo=r myfile.
7.2 Files Present and Their Locations
Now that you can navigate the directory tree, let’s take a guided tour of the files and directories you created when you installed Debian. If you’re curious, cd to each directory and type ls to see its contents. If the listing doesn’t fit on the screen, try ls | less, where | is the “pipe” character, generally found on the same key with backslash.
/ As already mentioned, this is the root directory, which contains every other directory.
/root But don’t get /confused with /root! /root is the home directory of the root user, or superuser. It’s a directory called /root, but it isn’t the root directory /.