The process involves several steps.
1. Loading UNIX into Memory: When system is powered ON, computer accesses a small ROM based start-up routine that performs elementary system verifications. (Assuring HDD and networks) the boot routine does more sophisticated hardware verifications and then loads kernel file UNIX from systems root directory to system RAM.
2. Executing the kernel: Once loaded into the memory, the kernel starts working. It sets up the information table needed to control UNIX environment, checks system hardware, checks memory available, hardware devices and then creates the swapper process.
3. Swapper process: Swapper process is identified as process 0. It monitors memory management overhead, when overhead, swapper removes entire process from memory till system performance becomes acceptable.
4. Init process: init initializes system processes, places system in multi-user mode unless single user mode is specified, sets the computer name and environment variables such as PATH and HOME checks the file system with fsck command, deletes temporary files, initiates network services and starts the /etc/getty process.
5. Getty: Initiates individual terminal lines. It periodically checks for terminals that are switched ON. After terminal is ON, it prints the login prompt, prompting for users login name, once user enters a login name, getty spawns or starts the login process for that terminal.
6. Login: The login process prompts the user for a password. It validates the login name and the password against the entry in the /etc/passwd file and the /etc/shadow file. The users shell specified in the Home directory.
7. Shell: The shell prints the Unix prompt and executes user commands when user logs out, sh is taken over by login to allow the next user to log in.
0 Comments