Executable directory? And chmod o+w changing the terminal directory color?

Question

1. What is an executable directory?

2. If o+w is set the directory changes colors to a background green, what does this mean? Why doesn't it do it for ug+w, but only for o+w?

3. Additional question after reading the comments: Is making a directory executable a security risk? If so, why?

Answer 1

Colors

The coloring is controlled by the DIR_COLORS* files that reside under `/etc. For example on Fedora 19 I have the following 3 files:

$ ls -l /etc/DIR_COLORS*
-rw-r--r--. 1 root root 5004 Jan 20  2014 /etc/DIR_COLORS
-rw-r--r--. 1 root root 5682 Jan 20  2014 /etc/DIR_COLORS.256color
-rw-r--r--. 1 root root 4646 Jan 20  2014 /etc/DIR_COLORS.lightbgcolor

The coloring is completely cosmetic and keys off of the output that ls is generating. You can disable it like so:

$ ls --color=never <other options>

The DIR_COLORS* files can be viewed, they're just text, and have decent commenting, explaining their functionality. This line is why it's displaying as green:

OTHER_WRITABLE 34;42 # dir that is other-writable (o+w) and not sticky

Executable directories

Directories need to be executable so that user's can cd into them and run commands. Without that bit, the directories cannot be accessed.

$ mkdir adir
$ chmod 644 adir
$ cd adir
bash: cd: adir: Permission denied

The reasons behind this are already extensively discussed in this other U&L Q&A titled: Execute vs Read bit. How do directory permissions in Linux work?.