System Startup and Shutdown

System Startup and Shutdown
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
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
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
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
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:
Manual Boot
List of some important boot prompt arguments :
Instead of typing them at each reboot, these arguments can be included into the lilo.conf :
append=“hdc=cdrom”
Manual Boot
More information about boot prompt and arguments can be found at:
http://www.tldp.org/HOWTO/BootPrompt-HOWTO.html
Refers to man 5 lilo.conf for a detailed information about arguments
Startup Flow Control
It used to run Linux system at level 3
Run Levels
Run Levels
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:
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
Structure of /etc/inittab
Each line has 4 fields seperated by colons:
id:level:action:command
Structure of /etc/inittab
The main inittab action keywords are:
/etc/inittab
# more /etc/inittab
...
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
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 …
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
Changing Run Levels
Use init command to change between run levels. Syntax :
init
Examples :
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
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
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