System Startup and Shutdown

 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 m

 Explain single and multi-user run levels

 Identify and configure system startup files

mode

 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

 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

 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

 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:

 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”

 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

 It used to run Linux system at level 3

Reboot runlevel

Runlevel s/S

/etc/rc.d/rcS.d Single-user mode.

Runlevel a/b/c Pseudo states (rarely used)

 Use /sbin/runlevel to get current run level

 How to start X window ?

RedHat and TurboLinux : # init 5

 To manual set default run level at boot time, open

/etc/inittab and look for this line : id: 5 :initdefault:

 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

command Full path name and parameters of command to

be executed

 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

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

 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 …

 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

 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

 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)

 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

 Explain single and multi-user run levels

 Identify and configure system startup files

mode