UNIX for Dummies Questions & Answers

I use Ubuntu Linux, and I'd like to become more familiar with the CLI. I have these questions:

1) How to remove a directory that is not empty? The only option in man rmdir is -p and that does not do what I need. rm -R needs sudo for some reason.

2) What is a CLI command to make all the files in a directory 644, and all the directories 755 (recursive to subdirectories)?

3) Some directories are listed as:
1 byte
8 byte
16 byte
32 byte
40 byte
4 KB
8 KB
This size has nothing to do with what is in them, either. What makes the different directories show as different sizes?

Thanks in advance.

Code:

rm -rf "$DIR"

Code:

find "$DIR" -type f -exec chmod 644 {} \;
find "$DIR" -type d -exec chmod 755 {} \;

The size of the directory entry, which includes all the file names.

‎Thanks. I should replace "$DIR" with the name of the directory in examples 1 and 2? In 1 it makes sense, but in 2 I need it to work on _all_ directories and files in the current directory. I understand that's what the find command does, but why would it need a "$DIR" argument?

For 3, where can I read the directory entry, or is that only available on the filesystem level?

Thanks for the answers. I really like the open, no-secrets thinking of Linux. No black magic, and everything can be explained.

Right.
The GNU/linux version of find assumes the current directory if you do not supply one. Other versions may require an explicit path (e.g., '.' for the current directory).

Code:

shopt -s dotglob  ## bash only
printf "%s\n" *   ## non-bash, add: .*

Or use ls.