-rwsr-x--- ............. rwx는 알겠는데.. s는 뭐죠?

b Block special file.
c Character special file.
d Directory.
l Symbolic link.
s Socket link.
p FIFO.
- Regular file.

1. If r, the file is readable; if -, it is not readable.

2. If w, the file is writable; if -, it is not writable.

3. The first of the following that applies:

S If in the owner permissions, the file is not exe-
cutable and set-user-ID mode is set. If in the
group permissions, the file is not executable and
set-group-ID mode is set.

s If in the owner permissions, the file is exe-
cutable and set-user-ID mode is set. If in the
group permissions, the file is executable and set-
group-ID mode is set.

x The file is executable or the directory is search-
able.

- The file is neither readable, writable, exe-
cutable, nor set-user-ID nor set-group-ID mode,
nor sticky. (See below.)

These next two apply only to the third character in the last group (other permissions).

T The sticky bit is set (mode 1000), but not execute
or search permission. (See chmod(1) or
sticky(8).)

t The sticky bit is set (mode 1000), and is search-
able or executable. (See chmod(1) or sticky(8).)