File Management

File Management

Wendell Taylor

4/14/15

Willie Love

POS/355

Many of the UNIX system that you know or have come across are based on the control pattern of file access associated with early version of UNIX system. Every user in UNIX are assigned a unique user identification that they will use to access the files saved in the memory. User can be identified two ways. The user is either part of a private group or they can be part of various group which they are identified by their group identification. Also, file belong to any group the user associated with otherwise the group of its parent directory has SetGID permission configed.SetGID are access right flag that allow User to run executable files with the permissions of the users group. There are a total of twelve protection bit set with each file.

The first 9 out of the 12 protection bits are prescribe to the users’ identification of the file which control writing, reading and execute permission. Then the nine protection bit form a system of ranking between the user, group and other identification. The ranking are accompany with the applicable file permission being used. In other word whatever file that has the highest priority. An example of this is when the file owner has both read and write permissions. This mean the owner can edit the file. Everyone else who is associated with that identification may will have only read permission. While everyone outside that identification will have no access right to the file.

The next 3 bits that is left over are used to define special behavior of file. Also two out of the three left over are set ID bits. They can be the Set User Id (SetUID) or the Set Group ID (SetGID) permission bits. For example the computer system may temporary let a user borrow some of permission of the user who created the file. This is when a userID with write permissions for file decide to execute. This is known as effective uses ID (EUID). It is also known as effective group ID (EGID)....