touch testfile
ls -l testfile
-rw-r--r-- 1 yourname yourname 0 2011-04-05 05:44 testfile
chmod u+wx testfile
ls -l testfile
-rwxr--r-- 1 yourname yourname 0 2011-04-05 05:44 testfile
chmod ug-x testfile
ls -l testfile
-rw-r--r-- 1 yourname yourname 0 2011-04-05 05:44 testfile
chmod a-r testfile
ls -l testfile
--w------- 1 yourname yourname 0 2011-04-05 05:44 testfile
Which user?
u user/owner
g group
o other
a all
What to do?
+ add this permission
- remove this permission
= set exactly this permission
Which permissions?
r read
w write
x execute