FILES:
------

Permissions
 Read      - Ability to open and view the contents of the file
 Write     - Ability to change and/or delete the file
 eXecute   - You can "run" the file

Refer to these permissions using the letters "r", "w" and "x".  This is called a permission
triple.

These permissions can be applied to three different access "levels".

 User ( Owner ) - Person that owns file
 Group          - Group that owns the file
 Other          - Neither the owner, nor the group

 UUUGGGOOO
-rwxrwxrwx - "Full perms"
-r-xr-xr-x - "Full read-only perms, with full execute perms"

Users: bob, alice, jack, nancy, joe
Groups:
 mgmt - bob, alice
 marketing - jack, bob
 devel - nancy, joe
 staff - bob, alice, jack, nancy, joe

-rw-r--r-- Announcement - owner: bob, group: marketing
 - Who can edit this file? Bob
 - Who can read the file? everyone
 - Who can execute this file? nobody!

-rw-rw---- index.html - owner: nancy, group: devel
 - Who can read this file? nancy and joe!
 - Who can edit this file? nancy and joe!
 - Who can execute? Nobody!
 - Who can delete this file? nancy and joe!

-rwxr-xr-x page - owner: joe, group: mgmt
 - Who can read this file? everybody!
 - Who can edit this file? joe!
 - Who can execute this file? everybody!

Common permission triples:
 rwx
 rw-
 r-x
 r--
 ---
 -w- -- "exists", but not useful
 -wx -- ditto
 --x -- ditto


DIRECTORIES:
------------

Permissions:
 Read:     Ability to list the contents of the directory
 Write:    Ability to create/delete/modify files in the directory
 eXecute:  Ability to "cd" into the directory ( make it CWD )

Common permission triples:
 rwx
 r-x
 ---   
 r--   Not common - it can be used, but only allows viewing of entries in directory - also,
       causes problems with some software..
 --x   Doesn't even make sense
 rw-   Ditto
 -w-   Ditto
 -wx   Ditto


Changing file permissions

1) Changing owners: "chown" command
# chown student /tmp/test

2) Changing group ownership: "chgrp" command
# chgrp students /tmp/test

3) Changing permission triples: "chmod" command
   Two ways of executing chmod:
   1) Uses octal numbers to specify specific triples
   # chmod 755 /tmp/test

rwx   Chart of octals:        Should memorize
---------------------------------------------
000   0    No perms           *
001   1    eXecute
010   2    Write
011   3    Write,eXecute
100   4    Read               *
101   5    Read,eXecute       *
110   6    Read,Write         *
111   7    Read,Write,eXecute *

755 - common for s/w ( programs )
644 - common for text files/documents/pictures/whatever

    2) Using an english interpretation
    # chmod u+rw,g-w,o=r /tmp/test
    User (u)
    Group(g)
    Other(o)
    u,g,o            +,-,=            r,w,x
    You can list multiple modifications by separating them with commas