Lecture #4 System Runlevels

Agenda

• Exercise: Install CentOS-5 onto the virtual machine named Computer 2 that you made last week. (Refer to last week's notes for partition information.)
• Boot a Linux system into System Maintenance mode.
• Shutdown a system in a safe and secure manner.
• Lecture on /etc/inittab file.
• Exercise: Configure your Computer2 as follows:
  • Disable ctr-alt-del reboot.
  • Password protect single user mode.
  • Remove these services from runlevel 2: isdn, pcmcia, apmd, sendmail, and anacron.
• Troubleshoot a system that won't root because of a failed system service

Assignment

• Read the first half of Chapter 11.
• Review PowerPoint Slides
• Labs 1 and 2 video

System Startup and Shutdown

1. Booting the System
   1. Power On Self Test (POST) - loads the BIOS
   2. BIOS loads the Master Boot Record
   3. MBR reads its partition table to determine which partition to boot into
   4. MBR loads the boot program in the active partition
   5. Boot program presents user with a boot prompt
   6. Based upon user selection, boot program loads the desired kernel along with any supplied boot options
   7. Kernel uncompresses and loads into memory
   8. Kernel detects hardware and initializes its data
2. Rooting the System
   1. Kernel mounts the root file system
   2. Kernel creates and starts the init process
   3. Init reads /etc/inittab for its instructions
   4. Init performs system initialization:
      • presents some kind of welcome banner
      • allows for an interactive startup
      • sets up keyboard mapping, system fonts, plug and play devices, ...
      • checks for dirty file systems, and cleans them if necessary
      • checks disk quotas and swap space
      • mounts all file systems
   5. Chooses which runlevel to come up in and executes those scripts via rc script
   6. daemons load
   7. getty processes are spawned on terminal devices
3. LILO, GRUB and Dual Booting
   • LILO boot manager
     • The/etc/lilo.conf file
     • The lilo command
   • GRUB boot manager
     • The /boot/grub/grub.conf file
     • stage1 and stage2 boot loaders
4. Init and Runlevels
   • The /etc/inittab file
     1. A two letter system identifier id
     2. A list of runlevels for specified actions
     3. An action - How and when should a command be run
     4. process - which command to run
   • Runlevels
     • Runlevel 0
     • Runlevel 1
     • Runlevel 2
     • Runlevel 3,4,5
     • Runlevel 6
     • rc scripts and/or rc.d directories for each runlevel
     • RC Script Naming conventions
       1. Start with S or K
       2. A number
       3. A daemon shell script
5. Shutting the System Down
   • Users log out
   • Services halt
   • Data is saved
   • File systems are unmounted
   • System powers off
   • Types of shutdowns:
     1. init 0 - no user warning
     2. shutdown [-hcr] time - warns users before shutting down
     3. halt and reboot - shortcuts for shutdown
     4. CTRL-ALT-DEL - shutdown behavior can be disabled.

Relevant Commands and Files