class note: the syllabus is available on-line at: the syllabus is available on-line at:

Class Note:Class Note:

The Syllabus is available on-line at: The Syllabus is available on-line at: http://www.wildbill.org/rosehttp://www.wildbill.org/rose

System ProfilesSystem Profiles


When a user logs in a system profile When a user logs in a system profile is establishedis established• Set’s environment variablesSet’s environment variables

I.e. PATH=/bin;/usr/bin;I.e. PATH=/bin;/usr/bin;• Set’s alias’sSet’s alias’s

I.e. alias rm ‘rm –i’I.e. alias rm ‘rm –i’alias cp ‘cp –I’alias cp ‘cp –I’alias cls ‘clear’alias cls ‘clear’


Various system-wide profiles:Various system-wide profiles:• /etc/profile/etc/profile (bourne shell) (bourne shell)• /etc/bashrc/etc/bashrc (bash shell) (bash shell)• /etc/tcshrc/etc/tcshrc (c-shell) (c-shell)

User specific profiles (located in home User specific profiles (located in home dir)dir)• ~/.profile~/.profile• ~/.bashrc~/.bashrc• ~/.tcshrc~/.tcshrc

Shell ScriptsShell Scripts

A A shell scriptshell script is a group of commands, is a group of commands, functions, variables, etc., that can be run functions, variables, etc., that can be run from the shell prompt (command line)from the shell prompt (command line)

Chapter 12 gives an overview of how shell Chapter 12 gives an overview of how shell scripts work and can be used:scripts work and can be used:• Automate system choresAutomate system chores• Application startupApplication startup• Even generate web pagesEven generate web pages

http://www.wildbill.org/rose/spring07.cgihttp://www.wildbill.org/rose/spring07.cgi

• Those who attend Intro to UNIX should have a Those who attend Intro to UNIX should have a reasonable understanding of shell scripts.reasonable understanding of shell scripts.

Shell Scripts (/etc/init.d/*)Shell Scripts (/etc/init.d/*)

Many of the startup scripts are Many of the startup scripts are located in the located in the /etc/init.d/etc/init.d directory directory

Know and understand Know and understand symbolic linkssymbolic links A A symbolic Linksymbolic Link is where a file has is where a file has

one main name, but there's an extra one main name, but there's an extra entry in the file name table that entry in the file name table that refers any accesses back to the main refers any accesses back to the main namename

Symbolic LinksSymbolic Links

Symbolic links are set up using the ln Symbolic links are set up using the ln command with the -s option - so for command with the -s option - so for exampleexampleln -s filename1.txt ln -s filename1.txt filename2.txtfilename2.txt

System InitializationSystem Initialization

OverviewOverview Sequence of booting LinuxSequence of booting Linux Component descriptionComponent description Sequence of shutting down LinuxSequence of shutting down Linux ConclusionConclusion

Booting SequenceBooting Sequence

POSTPOST The principal duties of the main BIOS during POST The principal duties of the main BIOS during POST

are as follows:are as follows:• verify the integrity of the BIOS code itself verify the integrity of the BIOS code itself • determine the reason POST is being executed determine the reason POST is being executed • find, size, and verify system main memory find, size, and verify system main memory • discover, initialize, and catalog all system buses and discover, initialize, and catalog all system buses and

devices devices • pass control to other specialized BIOSes (if and when pass control to other specialized BIOSes (if and when

required) required) • provide a user interface for systems configuration provide a user interface for systems configuration • identify, organize, and select which devices are available identify, organize, and select which devices are available

for booting for booting • construct whatever system environment that is required construct whatever system environment that is required

by the target OS by the target OS

Bootstrap loaderBootstrap loader

Bootstrap loaderBootstrap loader In computing, In computing, bootingbooting is a is a bootstrappingbootstrapping

process that starts operating systems when process that starts operating systems when the user turns on a computer system. the user turns on a computer system.

A A boot sequenceboot sequence is the set of operations the is the set of operations the computer performs when it is switched on computer performs when it is switched on that load an operating system. that load an operating system. • Locate and start boot loader programLocate and start boot loader program• ROM BIOS ROM BIOS • Look for a boot sectorLook for a boot sector• Boot sectorBoot sector

First sector of the diskFirst sector of the disk 0xAA55 at byte 0x1FE (510)0xAA55 at byte 0x1FE (510) byte 510 (last two bytes of the sector)byte 510 (last two bytes of the sector)

• Load boot sector into memoryLoad boot sector into memory

Boot loader programBoot loader program

Boot loaderBoot loader Load the operating systemLoad the operating system into its into its

computer memory from its hard diskcomputer memory from its hard disk Master Boot RecordMaster Boot Record

• Special reserved areaSpecial reserved area• Beginning of the system diskBeginning of the system disk

First stage boot loaderFirst stage boot loader• Load and run second stage boot loaderLoad and run second stage boot loader

Second stage boot loaderSecond stage boot loader• Prompt to choose OSPrompt to choose OS• Loads the kernel of the chosen OSLoads the kernel of the chosen OS

Boot loaderBoot loader

Two primary Boot loader programs Two primary Boot loader programs for Linuxfor Linux• LILOLILO ( (LiLinux nux LoLoader)ader)• GRUBGRUB ( (GrGrand and UUnified nified BBoot loader)oot loader)

LILOLILO /etc/lilo.conf/etc/lilo.conf

• Location of kernelLocation of kernel• Disk partition to mount as root file Disk partition to mount as root file

systemsystem

Map installerMap installer• Read configuration fileRead configuration file• Write boot loaders, OS info to hard Write boot loaders, OS info to hard

diskdisk

GRUBGRUB

Boot time shellBoot time shell GRUB interactive command GRUB interactive command

promptprompt Run new configuration on the Run new configuration on the

flyfly Dynamic default configurationDynamic default configuration Can use to boot other OSCan use to boot other OS

GRUBGRUB /boot/grub/grub.conf/boot/grub/grub.conf

• # general section # general section • splashimage splashimage

(hd0,0)/grub/splash.xpm.gz(hd0,0)/grub/splash.xpm.gz• default 0 default 0 • timeout 30 timeout 30 • password -md5 password -md5 encoded-passwordencoded-password

• title Linux title Linux • root (hd0,0) root (hd0,0)

kernel /vmlinuz ro root=/dev/hda2 kernel /vmlinuz ro root=/dev/hda2

Compare LILO and GRUBCompare LILO and GRUB LILOLILO

• TraditionalTraditional• Need to be Need to be

reinstalled in the reinstalled in the master boot record master boot record after replacing the after replacing the kernel or changing kernel or changing the boot the boot configurationconfiguration

GRUB GRUB • NewerNewer• FlexibleFlexible• Interactive Interactive

command promptcommand prompt

Kernel InitializationKernel Initialization

Kernel initializationKernel initialization Checks system hardwareChecks system hardware Identifies devicesIdentifies devices

KernelKernel• Makes hardware do what the Makes hardware do what the

programs wantprograms want


Probe essential devicesProbe essential devices• CPU, Console, MemoryCPU, Console, Memory

Probe other hardware SubsystemProbe other hardware Subsystem• I/O buses, Network interfaces, Hard I/O buses, Network interfaces, Hard

disks, CD-ROM drives, Floppy disks, CD-ROM drives, Floppy drives, Storage devicesdrives, Storage devices


File System initializationFile System initialization• Logical volume manager subsystemLogical volume manager subsystem• RAIDRAID• SCSI DevicesSCSI Devices• Hard disk partitionsHard disk partitions

Change configuration of kernelChange configuration of kernel• /usr/src/linux/make menuconfig or /usr/src/linux/make menuconfig or

xconfigxconfig• rdevrdev• Boot loader parameterBoot loader parameter

Init programInit program

InitInit Location: Location: /sbin/init/sbin/init Uses functions from libraries written in CUses functions from libraries written in C Checks and mounts file systemChecks and mounts file system Starts up daemons to log system messagesStarts up daemons to log system messages Starts the Starts the gettygetty processes that put the processes that put the

login prompts on your virtual terminalslogin prompts on your virtual terminals NetworkingNetworking Serves web pageServes web page Listen to the mouseListen to the mouse

Inittab fileInittab file

Location: Location: /etc/inittab/etc/inittab xx:levels:action:processxx:levels:action:process XxXx

• Label for the entryLabel for the entry LevelsLevels

• Specific system operating modeSpecific system operating mode• Predefined set of system Predefined set of system

processesprocesses

Run levels in initRun levels in init 00: : Halted system (ready for powering Halted system (ready for powering

off) off) 11:: Conversion to/preparation for single Conversion to/preparation for single

user mode user mode 22:: Non-networked multiuser mode Non-networked multiuser mode 33:: Networked multiuser mode Networked multiuser mode 44:: Networked multiuser mode with Networked multiuser mode with

graphical login graphical login 66:: Reboot mode Reboot mode

Run levels in initRun levels in init SS,,ss:: Single user mode Single user mode UU,,uu:: Init process re-execution Init process re-execution

(pseudo run level) (pseudo run level) QQ,,qq:: Force reread of configuration Force reread of configuration

file (pseudo run level) file (pseudo run level) aa,,bb,,cc:: On-demand process On-demand process

initialization pseudo run levels initialization pseudo run levels

Inittab fileInittab file ActionsActions

• waitwait:: Start the process and wait for it to Start the process and wait for it to finish before going onto the next entry.finish before going onto the next entry.

• onceonce:: Start the process only if it is not Start the process only if it is not already running (don't wait).already running (don't wait).

• respawnrespawn:: Start the process (don't wait) Start the process (don't wait) and automatically re-start it if the and automatically re-start it if the process later dies.process later dies.

Inittab fileInittab file• bootwaitbootwait:: Execute the process only at Execute the process only at

boot time, waiting for it to finish.boot time, waiting for it to finish.• initdefaultinitdefault:: Specifies default run level. Specifies default run level.• ctrlaltdelctrlaltdel:: Execute the action when the Execute the action when the

Ctrl-Alt-Del key sequence is detected.Ctrl-Alt-Del key sequence is detected.• power*power*:: Several keywords are defined Several keywords are defined

for various power failure-related events for various power failure-related events (see examples below)(see examples below)

InittabInittab Program to interpret the Program to interpret the

initialization script – bashinitialization script – bash Script link to other scriptsScript link to other scripts Several scriptsSeveral scripts

• Initialization scriptInitialization script• Run-level scriptRun-level script

Initialization scriptInitialization script Initialization scriptInitialization script

• (Red hat) (Red hat) /etc/rc.d/rc.sysinit/etc/rc.d/rc.sysinit• File system get checked and mountedFile system get checked and mounted

/etc/fstab/etc/fstab

• Clock setClock set• Swap space enabledSwap space enabled• HostnameHostname

Shutting down sequenceShutting down sequence shutdownshutdown [ [-h-h//rr] ] (warning message)(warning message) Logins are blockedLogins are blocked All process are notified that the system is All process are notified that the system is

going down by signal SIGTERMgoing down by signal SIGTERM Process to exit cleanlyProcess to exit cleanly Signal the init process to change the run Signal the init process to change the run

level level • Default 1, -h flag 0, -r flag 6Default 1, -h flag 0, -r flag 6

Shutting down Shutting down unmount -aunmount -a unmounts all the unmounts all the

partitions listed in fstabpartitions listed in fstab shutdown -Fshutdown -F = Force fsck on reboot = Force fsck on reboot

• Journaling file systemJournaling file system saves a transaction log of file system saves a transaction log of file system

changeschanges replay when the system is restartedreplay when the system is restarted

AcknowledgeAcknowledge Two new links at Two new links at wildbill.org/rosewildbill.org/rose http://www.linuxforum.com/linux-introduction/ch04s02.htmlhttp://www.linuxforum.com/linux-introduction/ch04s02.html http://linux.about.com/library/cmd/blcmdl8_shutdown.htmhttp://linux.about.com/library/cmd/blcmdl8_shutdown.htm

class note: the syllabus is available on-line at: the syllabus is available on-line at:

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