watch

Execute a command ever X seconds (default 2).
watch -n X who execute the who command every X seconds

ls

-a, --all
do not ignore entries starting with .

-h, --human-readable
with -l and -s, print sizes like 1K 234M 2G etc

-l
use a long listing format

-r, --reverse
reverse order while sorting

-t
sort by time, newest first

-i
display inode number

space / f
scroll forward one screen

enter
scroll forward one line

b
scroll backward one screen

d
scroll forward half a screen

h
display help

q
quit

/string
search string forward

?string
search string backward

n
find next occurrence

N
find previous occurrence (less only)

display lines (-l), words (-w), bytes (-c), characters (-m) of file

-b
remove all access acls

-d
apply default acl

-k
remove all default acls

-m
set or modify acls

-n
prevent automatic recalculation of mask

-R
apply recursive

-x
remove access acl