linux permissions
permission = read(4) + write(2) + execute(1)
ls -l [path]
---------- # file
d--------- # directory
-rwx------ # owner
----rwx--- # group
-------rwx # other
chmod [permissions] file
(u)ser, (g)roup, (o)ther, (a)ll
chmod o+rwx file # add rwx for other
chmod o=rw file # set rw for other
chmod og-x file # remove x from other and group
chmod a+r file # everyone can read
# Numeric
chmod 724 file # owner=everything, group=writing, other=reading