CertiGuide to A+ (A+ 4 Real)  9  Chapter 5: The Linux Operating System       9  Basic Concepts and Procedures for Creating, Viewing and Editing Files and Directories            9  Common Commands

Common Commands 1 2 3 mkdir - Make Directories Command

Understanding Linux Permissions

The Linux file system uses the same permission model as UNIX. This has proved over the years to be a useful model, rich enough for most situations and yet relatively easy to understand and administer. User and a group own each file. Read, write, and execute permissions can be set individually for both of these users. Additionally a third set of permissions exist for all other system users that may want to see these files.

Looking at the listing above there is a string of 10 hyphens, r, w, or x’s. The first position is information about the type of file, a d will be used to indicate a directory or a - for normal files, immediately followed by the access permissions for the file’s user/owner, the group, then all others. If the character r,w, or x appears in the indicated area for the file user, then that user has those corresponding access permissions, read, write, or execute. A - implies that the permission associated to that location is denied. In other words for the files named ps in the above listing: the file“˜s user/owner has read and write permission, the group user has read and write permission and all other users have only read permission. These permissions can be changed by either the file’s user/owner or the system administrator.

For more information, the info pages for the ls command carries a detailed description on how the ls command displays access rights.

This permission scheme allows Linux to maintain a very high-level of security. The user or system administrator can protect information or grant access to information on a very granular basis. Proper control and maintenance of file and directory permissions will help insure proper system security.

Common Commands 1 2 3 mkdir - Make Directories Command