Now, I wonder why people do not use ACLs as much as they should. Most Linux distributions do not mount the file system with ACLs support by default. You need to add the option "acl" to the fstab entry in order to enable it, or just remount the partition:

# mount -o remount,acl /

Let's see some examples on how to use ACLs (works on both: OpenSolaris and Linux):

- Create a test directory and read the ACLs

alo@ferrari:~/tmp$ mkdir test
alo@ferrari:~/tmp$ getfacl test 
# file: test
# owner: alo
# group: alo
user::rwx
group::r-x
other::r-x

alo@ferrari:~/tmp$ setfacl -m d:u::rwx,d:g::r-x,d:o:---,d:m:rwx test 
alo@ferrari:~/tmp$ setfacl -m d:u:www-data:rwx test 
alo@ferrari:~/tmp$ getfacl test 
# file: test
# owner: alo
# group: alo
user::rwx
group::r-x  
mask:r-x
other:r-x
default:user::rwx
default:user:www-data:rwx
default:group::r-x
default:mask:rwx
default:other:---

alo@ferrari:~/tmp$ touch test/file
alo@ferrari:~/tmp$ getfacl test/file 
# file: test/file
# owner: alo
# group: alo
user::rw-
user:www-data:rwx 
group::r-x        
mask:rw-
other:---

alo@ferrari:~/tmp$ setfacl -m u:dummy:r-- test/file

alo@ferrari:~/tmp$ getfacl test/file 
# file: test/file
# owner: alo
# group: alo
user::rw-
user:dummy:r--
user:www-data:rwx
group::r-x
mask::rwx
other::---