What is an Access control list?
Access control list (ACL) is used to identify individual or group user permissions in a computer system. The access control list is generally in table format, or some other software specific data structure. ACLs are a fundamental part of technology security systems
A Little More on Access Control Lists or ACLs
ACLs grants file access to different users or group without having to include them in the same category for them to have access permission – unlike in files and directories, where different permissions cannot be configured for different users.
Also, files and directories permission sets are configured for the owner of the data, the group to which the file owner belongs, and the other system users only.
ACLs, on the others hand, solve the limitation with files and directories by providing more precise control than file permissions alone, by giving the owner of an object the ability to grant or deny any user access.
ACL mechanism is available in most UNIX such as HP-UX, Solaris, and AIX, among others. However in other system ACL is not provided, for example, GNU / Linux, and one needs to install it as an additional package. GNU / Linux support 2 basic types of ACL:
- Standard ACL- They contains three ACLs entries, that is, owner, owner group, and other types. Theses ACL entries are equivalent with the files and directory mode permission bits.
- Extended ACL: They have more than three ACL entries. Theses ACLs also contain a mask entry and may comprise any number of named user and named group entries.
ACLs models define three classes of elements including User, group and mask permits that are configured with a set of permission. The permissions defined are read (r), write (w), and execute (x). For ACL to function optimally one needs to ascertain:
- Whether the computers kernel can support as well as allow mounting of extended attributes and ACL.
- Whether userspace utilities have been installed to establish the ACL: ACL package.
The kernel being a core the core of a computer’s operating system is where the ACL is activated for users of Ubuntu OS. Regarding the installation of userspace utilities, and in order to work with ACL in a particular file system (/ home) in the / etc / fstab file, one has to indicate it in as mentioned below: # cat / etc / fstab | grep home/ dev / sda2 / home ext4 defaults, acl 0 # cat /etc/fstab|grep home# /dev/sda2 /home ext4 defaults,acl 0 /dev/sda2 . To avoid rebooting the system, one can override the partition so that it uses ACL by executing the command below: # mount -o remount -o ACL /dev/sda2 /home# With this, the ACLs is ready for use in the system. We install the ACL package (can be done by default). # sudo apt-get install acl#
The following package contains the utilities that will allow one to establish and manage the ACLs.