1. System Startup and Shutdown
Chapter 8
System Startup and Shutdown

2. Objectives Define and explain bootstrap procedure
Explain single and multi-user run levels
Identify and configure system startup files
Perform a clean shutdown procedure
Explain and define the maintainance mode
Libraries provide functionality for programs compiled under Linux. Understanding how libraries work, the different types of linking, and how to identify andresolve library issues is important for maintaining a system

3. Standard Boot Process (LILO)
System load the Linux bootstrap from default boot device, LILO, which resides in Master Boot Record of hard drive
The bootstrap program has ability to boot Linux to single-user or multi-user mode
After the bootstrap has loaded the kernel ( stored in the /boot or / partition ) into memory, it relinquishes control to this system

4. Standard Boot Process (LILO)
The Linux system initializes physical devices, virtual memory controller, and its internal control tables for processes, files, ..
The init process is started and it starts all other user processes
Before handing control over init, the kernel will create any other kernel threads

5. Boot Problems
Sometimes, lilo will not able to boot the system, it prints the letters LILO on screen. The problems: disk corrupted, the information on disk geometry is incorrect, or since the new kernel image is installed
Troubleshooting: boot the system from bootable CD or floppy and try to repair disk problems or correct the /etc/lilo.conf

6. Manual Boot
There are times when lilo has loaded the kernel but the kernel does NOT work properly because some of hardware can not be found,…It’s possible to pass configuration to the kernel through lilo at lilo command line when booting:

7. Manual Boot List of some important boot prompt arguments :
root=/dev/hda1
Tell the kernel which device to be mounted as root file system
ramdisk_size=2MB
Define maximum of ramdisk (up to 4MB )
single
This actually is a parameter passed to init, causes the system to boot in single-user mode
mem=192MB
Tell the kernel amount of memory ( RAM size )
aha1542=0x334
Set the I/O port address for SCSI Interface Card
hdc=cdrom
Specifies the third disk device is a CD-ROM
Instead of typing them at each reboot, these arguments can be included into the lilo.conf :
append=“hdc=cdrom”

8. Manual Boot
More information about boot prompt and arguments can be found at:
Refers to man 5 lilo.conf for a detailed information about arguments

9. Startup Flow Control
It used to run Linux system at level 3

10. Run Levels Runlevel 0 /etc/rc.d/rc0.d
Shutdown mode. Tasks: killing all processes and unmounting file systems
Runlevel 1 /etc/rc.d/rc1.d
Single-user mode, generally used by system administrator when doing maintenance/recovery of the system
Runlevel 2 /etc/rc.d/rc2.d
Multi-user mode, some network services are not started : NFS, …
Runlevel 3 /etc/rc.d/rc3.d
Multi-user mode, all network services are started

11. Run Levels Runlevel 4 /etc/rc.d/rc4.d User defined run level
Multi-user X11 mode. All services that are started in run level 3 are generally started
Runlevel 6 /etc/rc.d/rc6.d
Reboot runlevel.
Runlevel s/S /etc/rc.d/rcS.d
Single-user mode.
Runlevel a/b/c
Pseudo states. (rarely used)

12. Run Levels Using Use /sbin/runlevel to get current run level
How to start X window ?
RedHat and TurboLinux : # init 5
Debian : # init 2
SuSE and Caldera: # init 3
Slackware : # init 4
Reboot : # init 6
Shutdown : # init 0
To manual set default run level at boot time, open /etc/inittab and look for this line : id:5:initdefault:

13. The init Control File: /etc/inittab
The init process uses /etc/inittab as its control file :
This is a text file, can be edited by the system admin
init must be told about changes to /etc/inittab by: # init q
One line per process to run at define run levels
Lines starting with ‘#’ are comments
Processes run from /etc/inittab are daemons
Init read /etc/inittab every time the run level is changed

14. Structure of /etc/inittab
Each line has 4 fields seperated by colons:
id:level:action:command id
Unique identifier for line (up to 4 alphanumeric characters)
level
Run level(s) to activate processs
action
Keyword for how to run process
command
Full path name and parameters of command to be executed

15. Structure of /etc/inittab
The main inittab action keywords are:
off
Do not run this command. Used to retain an entry but to disable it.
wait
Run command and wait for completion
once
Run command but do not wait. Daemons processes are often started this way
respawn
Run command; If process exists, then rerun it. Used for commands that have to start again after completion, like getty and ttymon
sysinit
Run command at first init
boot
Run command at boot time but do not wait
bootwait
Like boot but wait for completion
initdefault
Defines default boot level

16. /etc/inittab # more /etc/inittab id:3:initdefault:
...
id:3:initdefault:
#System initialization
si::sysinit:/etc/rc.d/rc.sysinit
l0:0:wait:/etc/rc.d/rc 0
l1:1:wait:/etc/rc.d/rc 1
l2:2:wait:/etc/rc.d/rc 2
l3:3:wait:/etc/rc.d/rc 3
l4:4:wait:/etc/rc.d/rc 4
l5:5:wait:/etc/rc.d/rc 5
l6:6:wait:/etc/rc.d/rc 6

17. Run Command Scripts
The run commands scripts are kept under /etc/rc.d/ and are initiated by init with directions from /etc/inittab
The script called rc itself runs startup programs in sub-directories under /etc/rc.d/
rc 0 looks in /etc/rc.d/rc0.d for runlevel 0
rc 1 looks in /etc/rc.d/rc1.d for runlevel 1
rc 2 looks in /etc/rc.d/rc2.d for runlevel 2
etc …

18. Run Command Scripts
These startup programs are symbolic links to the actual scripts in the /etc/init.d/
The startup link names are formatted: first character is S (started) or K (killed or stopped), the next two digits identify the order that scripts are executed by rc program

19. Changing Run Levels
Use init command to change between run levels. Syntax :
init <runlevel>
Examples :
# init 0
Shutdown system
# init 6
Reboot system
# init 3
Change to runlevel 3, multi-user text mode
# init 5
Change to runlevel 5, multi-user X11 mode

20. Shuting Down
Use shutdown commansd. It differs from “init 0” when allowing to specify time to exit, warn users what happens, …
Make sure that you follow the proper shutdown procedure. Do NOT simply shut off the power
# shutdown
Default system shutdown (run level 1)
# shutdown –r now
Reboot the system now (run level 6)
# shutdown –h 2:00
Halt the system at 2:00AM (run level 0)

21. Maintenance Mode
When the system doesn’t work because problems. The simplest and best solution is to shut down the system to maintenance mode (run level 1) or reboot the system to single-user mode (run level S) and try to fix problems

22. Summary Define and explain bootstrap procedure
Explain single and multi-user run levels
Identify and configure system startup files
Perform a clean shutdown procedure
Explain and define the maintainance mode
Libraries provide functionality for programs compiled under Linux. Understanding how libraries work, the different types of linking, and how to identify andresolve library issues is important for maintaining a system