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8/9/2019 Ch07-Startup and Shutdown
1/22
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
Runlevel 2/etc/rc.d/rc2.d
Multi-user mode, some network servicesare not started : NFS,
Runlevel 3/etc/rc.d/rc3.d
Multi-user mode, all network services arestarted
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Run 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 thatare started in run level 3 are generallystarted
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 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
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 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
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 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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