6.6 Access Control 2

6.6 Access Control 2

1. File modes in unix are written as 10 positions -rwxrwxrwx

   • First entry is special use, next 3 are owner, followed by 3 for group and 3 for world
     • IE -rw-r----- = owner can read and write, group can read, world have no permissions

2. making access decisions

   • its possible that an owner of a file is also a member of the group so which permissions apply?
     • Permissions apply to the most specific catagorisation of the user requesting access
       • If the user is the owner then owner permissions apply
         • Otherwise if a user is a member of a group the group permissions apply and if no then the world permissions apply

3. Directory permissions

   • make use of the first character in the set denoting it with D IE: d rwxr-xr--
   • RWX for directories
     • read allows you to list the contents of a directory
     • write allows you to add or remove files from a directory
     • execute allows you to enter a directory
       • if you have execute but not read then you can enter a directory but cant list the names of files, files can only be accessed if the name is already known

4. Directory vs file permissions

   • Rule: In order to access a file, permissions on the file itself and each directory from / down to where the file resides in the directory tree must allow access
     • the directory permissions take precedence over the files that are within it