This book contains the introductory information about the operating system and the basics of Linux commands for graduation level studies. This book provides the concepts of operating system. It contains the fundamental concepts which are applicable to various operating systems. Unit-I explains what is operating system and how the concepts of operating system has developed, contains resource management, structure of operating system, services provided by operating system, types of operating systemit contains the common features of the operating system. Unit- II and III deals with the internal algorithm and structure of operating system, it contains Process concept, Process State, Threads, Concurrent process, CPU scheduling, Scheduling Algorithms. They provide a firm practical understanding of the algorithm used. Unit-IV contains File Concept, Operations on Files, Types of files, Access Methods, Allocation methods, Directory structure, Structure of Linux Operating System.Unit- V contains Shell related operations and basic Linux commands like Changing the running shell, Changing the shell prompt, Creating user account, Creating alias for long command, Input/output Redirection, Redirecting Standard Output/Input, Pipe lines, Filters, ls, cat, wc, Manipulating files and directories using cp, mv, rm, pwd, cd, mkdir, rmdir commands, vi Editor, Compressing files (gzip, gunzip commands), Archiving Files( tar), Managing disk space: df, du, Changing Your Password, File access permissions, Granting access to files: (chmod command), Creating group account, Communication commands like who, who I am, mesg, write, talk, wall.