Neil Greenwood wrote:
> The reason that the directories 'vanished' is that execute permission
> is used to indicate that directories can be browsed i.e. listed in ls
> or Nautilus. When you did the chmod 664 it also worked on the
> directories, and then you couldn't look into them.
Neil >>> This was perhaps one of the most important things I learned,
and I had not seen it in any of the books: to see the directories at
all you have to have exec permission, so at least the owner's octal has
to be odd. Not knowing this, I thought 664 would be simplest (Ockham's
razor!).
I see now why the Ubuntu default is 755 (all the digits odd) -
everyone can, for starters, see the directories and their contents.
So it wasn't that I got mixed up by using the octal method for
permissions (pace, Robert!); rather, I just didn't know enough about
how permissions work. In fact, like you Neil, I find the octal system
simpler and neater to use for ordinary purposes: u/g/o maps to the digit
positions, and their values map the rwx settings as 4/2/1 - easy-peasy
(especially if you're fairly comfortable with maths!). But perhaps
there's some other reason (maybe to do with administering servers?) for
using the letter notation?
I do have one remaining question. In the following compound command
find ~/music -type f -group diana -exec sudo chgrp root {} \; -exec
sudo chmod 755 {} \;
what is the function of ' {} \; '?
I've gleaned that the last term is an escaped semi-colon. I guess
this indicates the end of a specific group of commands; and the
semi-colon has to be escaped to show that it's a delimiter, rather than
just the sign that the commands continue on the next line without a
break? But is the syntax more complex - maybe command sequences
delimited by -exec...\; show that they all act on the output of the
first command in the line (in this case, 'find ~/music -type f -group
diana')? As you see, I'm just guessing here - I'd be interested to
understand what the syntax really is.
Best wishes
--
Diana
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