System Init
- 2. Hardware Initialization After PC-type computer started: CPU initializes itself Sends signals to control other parts of computer BIOS performs power-on self test (POST) Checks memory and other hardware BIOS sends signal to SCSI controller card telling it to initialize itself SCSI controllers usually contain own BIOS
- 3. Hardware Initialization (continued) After PC-type computer started (continued): Other hardware components instructed to initialize themselves BIOS determines which devices to search for operating system BIOS loads boot loader into memory and passes control it
- 5. The Boot Loader Boot loader or boot manager Small program loaded by BIOS Commonly used LILO (Linux loader) GRUB (grand unified boot loader) Default on most systems BIOS looks for executable program in first sector of 3.5-inch disk or CD-ROM
- 6. The Boot Loader (continued)
- 7. Starting the Kernel Initial piece of kernel Loads rest of kernel into memory Uncompresses it dmesg command View messages stored by kernel during boot process
- 8. Starting the Kernel (continued) Kernel ring buffer Area of memory Stores messages from kernel
- 9. Configuring Boot Loaders Configuration files Created by installation program Examine how boot loader operates Usually no need to change
- 10. Using GRUB Installed by default for many versions of Linux /boot/grub/grub.conf Configuration file for GRUB Similar in layout and syntax to lilo.conf
- 11. init and its Scripts init program Master control program Starts many other programs Runs scripts to initialize system services Controlled by /etc/inittab configuration file Three main configuration files located in /etc/rc.d rc.sysinit rc rc.local
- 12. Understanding Run Levels Run level Numbered mode of operation Preconfigured set of services is activated Defined in /etc/inittab file Default run level 5 init or telinit command Change to different run level Commonly done only to restart or halt system
- 13. Understanding Run Levels (continued)
- 14. Understanding rc Scripts rc script Located in /etc/rc.d directory Started with parameter that includes run level Starts appropriate system services based on selected run level Each run level is associated with subdirectory Located in /etc/rc.d directory
- 15. Understanding rc Scripts (continued) Each file begins with K or S followed by two-digit number Begin with K ―s topped (killed) Begin with S ―s tarted Files symbolic links to scripts that stop and start services
- 16. Understanding rc Scripts (continued)
- 17. Controlling Services Many services listed in run-level directories relate to networking Scripts allow user to change almost anything on Linux system without restarting computer
- 18. Configuring System Services Initialization scripts in /etc/rc.d/init.d Typically use configuration information located in /etc/sysconfig directory and subdirectories Files in /etc/sysconfig Named for services Each file contains name-value pairs Define configuration options for service