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Chapter 8 System Startup and Shutdown

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Chapter 8 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). - PowerPoint PPT Presentation
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The Saigon CTT Chapter 8 System Startup and Shutdown
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Page 1: Chapter 8 System Startup and Shutdown

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Chapter 8

System Startup and Shutdown

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ObjectivesObjectives

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

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Standard Boot Process (LILO)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

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Standard Boot Process (LILO)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

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Boot ProblemsBoot 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

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Manual BootManual 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:

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Manual BootManual 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”

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Manual BootManual 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

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Startup Flow ControlStartup Flow Control

It used to run Linux system at level 3

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Run LevelsRun 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

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Run LevelsRun Levels

Runlevel 4 /etc/rc.d/rc4.d

User defined run level

Runlevel 5 /etc/rc.d/rc5.d

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)

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Run Levels UsingRun 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:

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The init Control File: /etc/inittabThe 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

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Structure of Structure of /etc/inittab/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

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Structure of Structure of /etc/inittab/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

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/etc/inittab/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

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Run Command ScriptsRun 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 …

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Run Command ScriptsRun 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

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Changing Run LevelsChanging 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

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Shuting DownShuting 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)

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Maintenance ModeMaintenance 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

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SummarySummary

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


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