chmod
chmod options file
The options are constructed by choosing one from each of these columns, with no blank between them:
Who
A combination of:
u user (file owner)
g group
o others
a all (same as ugo)
Operation
Permissions are:
= assigned
+ added
- subtracted
Permission
A combination of:
r read
w write
x execute
or one of the following
to copy permissions:
u user
g group
o other
or, to set user id:
s