The Saigon CTT
Chapter 8
System Startup and
Shutdown
The Saigon CTT
 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 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)
 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 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 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 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
single
Define maximum of ramdisk (up to 4MB )
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 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
Shutdown mode. Tasks: killing all
/etc/rc.d/rc0.d processes and unmounting file systems
Runlevel 1
Single-user mode, generally used by
/etc/rc.d/rc1.d system administrator when doing
maintenance/recovery of the system
Runlevel 2
Multi-user mode, some network
/etc/rc.d/rc2.d services are not started : NFS, …
Runlevel 3
Multi-user mode, all network services
/etc/rc.d/rc3.d are started
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 Run Levels
Runlevel 4
User defined run level
/etc/rc.d/rc4.d
Runlevel 5
Multi-user X11 mode. All services that
/etc/rc.d/rc5.d are started in run level 3 are generally
started
Runlevel 6
Reboot runlevel.
/etc/rc.d/rc6.d
Runlevel s/S
Single-user mode.
/etc/rc.d/rcS.d
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
level
Unique identifier for line (up to 4 alphanumeric
characters)
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 /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
bootwait
Run command at boot time but do not wait
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 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 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 Levels
 Use init command to change between run levels.
Syntax :
init <runlevel>
 Examples :
# init 0
# init 6
Shutdown system
Reboot system
# init 3
# init 5
Change to runlevel 3, multi-user text mode
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 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 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
The Saigon CTT
 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