Ch07-Startup and Shutdown

8/9/2019 Ch07-Startup and Shutdown

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SAIGONLAB 83 Nguyn Th Nh, P9, Q.Tn Bnh, Tp. HCM LPI 102

Chapter 7

System Startup and

Shutdown


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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


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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 tosingle-user or multi-user mode

After the bootstrap has loaded the kernel ( stored

in the /boot or / partition ) into memory, itrelinquishes control to this system


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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 otheruser processes

Before handing control over init, the kernel will

create any other kernel threads


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Boot Problems

Sometimes, lilo will not able to boot the system, it

prints the letters LILO on screen. The problems:

diskcorrupted, the information on diskgeometry 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 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,Its possible topass

configuration to the kernel through lilo at lilocommand line when booting:


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Manual Boot

List of some important boot prompt arguments :

root=/dev/hda1 Tell the kernel which device to be mounted as root filesystem

ramdisk_size=2MB Define maximum of ramdisk (up to 4MB )

single This actually is a parameter passed to init, causes thesystem to boot in single-usermode

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, thesearguments can be included into the lilo.conf :

append=hdc=cdrom


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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


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Startup Flow Control

It used to run Linux system at level 3


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Run Levels

Runlevel 0/etc/rc.d/rc0.d

Shutdown mode. Tasks: killing allprocesses and unmounting file systems

Runlevel 1

/etc/rc.d/rc1.d

Single-user mode, generally used by

system administrator when doingmaintenance/recovery of the system


Multi-user mode, some network servicesare not started : NFS,


Multi-user mode, all network services arestarted


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Run Levels


User defined run level


Multi-user X11 mode. All services thatare started in run level 3 are generallystarted


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 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/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 /etc/inittab

Each line has 4 fields seperated by colons:

id:level:action:command

id

Unique identifier for line (up to 4 alphanumericcharacters)

level Run level(s) to activate processs

action Keyword for how to run processcommand Full path name and parameters of command to

be executed


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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 processesare often started this way

respawn Run command; If process exists, then rerun it. Usedfor commands that have to start again aftercompletion, 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

# more /etc/inittab

...

id:3:initdefault:

#System initialization

si::sysinit:/etc/rc.d/rc.sysinit

l0:0:wait:/etc/rc.d/rc 0








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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 insub-directories under /etc/rc.d/

rc 0 looks in /etc/rc.d/rc0.d for runlevel 0



etc


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Run Command Scripts

These startup programs are symbolic links to the

actual scripts in the /etc/init.d/

The startup link names are formatted:firstcharacter

isS(started) orK(killed or stopped), the next two

digits identify the orderthat scripts are executed by

rc program


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Changing Run Levels

Use init command to change between run levels.

Syntax :

init

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 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 shutdownprocedure. 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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MaintenanceMode

When the system doesnt 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 tryto fix problems


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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

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Ch07-Startup and Shutdown

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