1. Linux File Security

2. What is Permission ? Specifies what right are granting to users to access the resources available in the computer. So that important files are protected from unauthorized users.

3. Permission Precedence If UID matches, user permission apply If GID matches, group permission apply If neither match other permission apply

4. Methods of Implementing Permission Symbolic Method Numeric Method

5. Permission- Symbolic Method Four symbols are used when displaying permissions: r: permission to read file or list a directory’s contents. w: permission to right a file or create and remove files from directory. x: permission to execute a program or change into a directory and do a long listing listing of the directory. -: no permission

8. Applying Permission with Symbolic Method chmod command is used to change access modes. chmod u+w,go-w filename (grants write access to owner but denies it to group and other.) chmod u=wr filename (grants read and write permission to the owner) chmod +r filename (make the file world-readable) Note: +,- and = are operators to, add, remove or overwrite the permissions.

9. Permissions- Numeric Method Four number are used when displaying or applying permissions. 4: permission to read file or list a directory’s contents. 2: permission to write a file or create and remove files from directory. 1: permission to execute a program or change into a directory and do a long listing listing of the directory. 0: no permission

10. Applying Permission with Numeric Method chmod command is used to change the access mode. chmod 664 filename (grants read and write access owner and group but read only it to other. chmod 600 filename ( sets read and write permission to owner chmod 444 file (make file world-readable)

11. Examining File Permissions File permissions may be viewed using ls –l File type and permissions represented by 10 character string.

12. Changing File Ownership Only root can change a file’s owner Only root or the owner can change file’s group Ownership is changed with chown chown username file/directory Group-ownership is changed with chgrp: chgrp groupname file/directory