Access Control Lists (ACLs) offer more precise control of file ownership than the traditional Unix file permissions. ACLS are difficult to use and unexpected, so use iof ACSL is discouraged. But in certain places, ACLS can help provide a permissions set not available with just chmod, chown, and chgrp.

Here's a case where ACLS are recommended. BCN's "Human Service" center (/htdocs/human-social) is co-owned by Catherine Weldon and Paul Tiger. Depending on how one of the owners edits a file, group-write may not be set. So I made Catherin the owner and used ACLS to give Paul write access.

The output of "ls -l" lets you know ACLs apply if a plus sign is added to the permissions. 

bcn> ls -ld .
drwxrwsr-x+ 34 weldon   dipp        1536 Apr 23 19:27 .
The "getfacl" command will then display information about the ACLs on file(s). 
bcn> getfacl .

# file: .
# owner: weldon
# group: dipp
user::rwx
user:ptiger:rwx  #effective:rwx
group::rwx  #effective:rwx
mask:rwx
other:r-x
To set an ACL 
setfacl -m user:ptiger:rwx test_index.html
setfacl -m mask:rw- test_index.html
For more information about SOlaris ACLs, see http://www.samag.com/documents/s=1151/sam0105g/0105g.htm