1. Unix Startup procedure
Boot strap
ROM
Kernel Initialization,
Hardware probing.
Single User Mode
Creation of
Init executes
Swapper&init
rc scripts
single or
multi-user?
/etc/ttys
/etc/inittab
Init reads terminal
(BSD)
configuration file
(System V)
Getty process started
Getty process started 1

2. ROM & Boot strap
ROM: that contains a program the machine executes when the power first comes on.
IBM PC
UNIX hardware has some form of prompt to allow administrator to
specify where to boot the machine from (boot partition corrupt, then from another HD, CD-ROM, floppy, tape drive)
come up in single user or multi-user mode. 2

3. ROM & Bootstrapping The Bootstrap Program
The code stored in the boot block is referred to as a bootstrap program, executed by ROM
responsible for locating and loading the kernel of UNIX operating system into memory from disk.
On some systems, it also performs some additional hardware probing. 3

4. Kernel Initialization
Test RAM & reserve part of RAM for kernel, or print available RAM
initialize its internal data structures, 4

5. Kernel Initialization
Perform some further hardware checking for major devices supposed to be connected,
Probe bus for devices and ask drivers. If no positive response, disable it.
Create the following so called spontaneous processes, because they are not created by fork().
PID=0: swapper/sched (BSD/Sys V)
PID=1,init/init
PID=2,pagedaemon/various handler (BSD/System V)
Under Linux
no visible PID 0,
init & kflushd,kupdate, kpiod, kswapd 5

6. System Processes process 0 (swapper) & process 1 (init)
swapper process is actually part of the kernel and is not a "real" process
init process is the ultimate parent of all processes executing on a UNIX system
Going into multi-user mode,init process must execute many system startup scripts. These startup scripts are Bourne shell scripts stored under the /etc directory
One of the last steps performed by init is to enable user logins (getty processes) 6

7. Single/Multi-User All UNIX machine can be in 2 basic states
multi-user mode
standard mode for a UNIX machine.
Multiple users are allowed to log in, all the daemons and all the services provided by the machine are available.
single user mode.
system maintenance mode.
In single user mode only the bare minimum of services are available. 7

8. Single/Multi-User single user mode.
Only one user (the root user) will be able to log in, only the root file system will be mounted automatically (others may be able to be mounted manually) and most of the daemons and services will not be available.
two reasons to come up in single user mode
root wanted to perform system maintenance.
the boot procedure has failed, caused by some errors in the initialisation files or by fsck detecting errors that it could not fix by itself. 8

9. Operator Intervention,manual boot only(RH)
The init process is notified via command-line flag passed in by kernel. (e.g. typing ‘I’ during boot up or single-user mode in RedHat)
Entering a shell if root password is correctly entered or continuing with the boot process if ^D or exit is pressed.
Able to execute all commands except those mounted on other filesystem than /, /bin,/sbin,/etc
the daemon processes like mail will not work correctly .
(Red Hat automatically mount all the filesystems)
fsck must be run by hand, if required. 9

10. Startup Scripts Startup Scripts Multi-User Operation
The init process runs sh to interpret the scripts.
They are kept in /etc directory and have names starting with rc (BSD), and /etc/init.d, /etc/rc1.d… (ATT).
Multi-User Operation
The init spawns the several getty (mgetty in Red Hat) processes to listen the users' login request. 10

11. System V Run Levels
Later versions of System V based Unix added a number of different run levels shown in Table.
Run level
classify the scripts into groups by level
command “who -r” can be used to display the run level 11

12. System V Run Levels Function 1 2 3 4 5 6 s,S State
prepare the machine for turning off power, if the
machine can turn the power off tell it to do so 1
system administrator mode, all file systems
mounted, only small set of kernel processes
running, single user mode 2
multi-user mode 3
multi-user mode with remote file sharing,
processes, and daemons 4
user definable system state 5
shutdown to ROM 6
shutdown and reboot
s,S
single-user mode, only root file system mounted 12

13. System V Run Levels (cont.)
As system boots, it will move through the various run levels (s, 1, 2, 3) under the control of init.
Each run level has associated with it various initialisation scripts that will be executed as the machine enters that run level.
On SysV based machines init goes through run levels is controlled by file /etc/inittab. 13

14. System V Run Levels (cont.)
Entry format of /etc/inittab
id:run-state:action:process
When init receives notification of an event, it examine inittab and execute the process specified for that event, controlled by action. 14

15. System V Run Levels (cont.)
Entry format of /etc/inittab
id:run-state:action:process 15

16. System V Run Levels (cont.)
Example values for action include
respawn:If process doesn’t exist, create it but don't wait for termination,carry on immediately. If at any stage the process terminates, restart it (getty for terminals).
Wait:start the process and wait for the process to finish.The process is never executed again until the system receives notification of the event again (This is how system execute initialisation scripts.) 16

17. System V Run Levels (cont.)
once: start the process when entering the run level, but not wait for it to complete, not restart it if it dies
boot: process the entry only on boot up
sysinit: process the entry before accessing the console and wait for it to complete 17

18. System V Run Levels (cont.)
initfefault: process whem init is initially invoked - sets the default run-level to enter
bootwait:Execute the process only when the system first goes multi-user and wait for its finish.
powerfail:Execute only when init receives a power fail signal. 18

19. The /etc/inittab file in SunOS
ap::sysinit:/sbin/autopush -f /etc/iu.ap
ap::sysinit:/sbin/soconfig -f /etc/sock2path
fs::sysinit:/sbin/rcS >/dev/console 2<>/dev/console </dev/console
is:3:initdefault:
p3:s1234:powerfail:/usr/sbin/shutdown -y -i5 -g0 >/dev/console 2<>/dev/console
s0:0:wait:/sbin/rc0 >/dev/console 2<>/dev/console </dev/console
s1:1:wait:/usr/sbin/shutdown -y -iS -g0 >/dev/console 2<>/dev/console</dev/console
s2:23:wait:/sbin/rc2 >/dev/console 2<>/dev/console </dev/console
s3:3:wait:/sbin/rc3 >/dev/console 2<>/dev/console </dev/console
s5:5:wait:/sbin/rc5 >/dev/console 2<>/dev/console </dev/console
s6:6:wait:/sbin/rc6 >/dev/console 2<>/dev/console </dev/console
fw:0:wait:/sbin/uadmin 2 0 >/dev/console 2<>/dev/console </dev/console
of:5:wait:/sbin/uadmin 2 6 >/dev/console 2<>/dev/console </dev/console
sc:234:respawn:/usr/lib/saf/sac -t 300
co:234:respawn:/usr/lib/saf/ttymon -g -h -p "`uname -n` console login: " -T sun -d /dev/console -l console -m ldterm,ttcompat
ml:23456:once:su abaqus57 -c '(umask 022; /usr/local/abapre/bin/flexlm lmgrd)' 19

20. The Startup Scripts Init’s responsible run sys. startup scripts.
scripts are executed after the kernel initialised but before normal users are allowed to log on.
These scripts will typically
check the integrity of the machine’s file systems using fsck,
mount the file systems,
designate paging and swap areas,
check disk quotas, 20

21. The Startup Scripts
clear out temporary files in /tmp and others,
start up system daemons for printing, mail, accounting, system logging, networking, cron,
enable user logins by running getty processes, a number of other tasks.
BSD format: usually called /etc/rc and perhaps /etc/rc.local.
System V:init reads the file /etc/inittab and as the system enters each associated run level it runs a specified shell script. 21

22. BSD Startup Scripts Most BSD systems will have at least
/etc/rc
The system startup script that is executed as the system goes multi-user. It will typically run /etc/rc.local.
/etc/rc.local.
The startup script that contains procedures deemed to be specific to your local site.
Some systems will add additional scripts /etc/rc.boot, /etc/rc.single that are run under various circumstances. 22

23. SysV Startup Scripts
Under SysV, /etc/inittab informs init which startup scripts it should execute. Each run level associate a particular startup script.
generally the format /etc/rcL (these files may be located in /sbin on later versions).
The purpose of these scripts is to execute all the shell scripts stored in a directory called with the name /etc/rcL.d. 23

24. SysV Startup Scripts
i.e.: When system enters run level 3 init will execute /etc/rc3 (/sbin/rc3 on later machines). This script will in turn execute all the scripts in /etc/rc3.d
The rcL.d directories will contain scripts with filenames that either start with, an K, or S
The "K files" are used to kill processes.
The "S files" are used to start processes and other initialisation procedures.
init will execute all the "K files" in a directory in alphabetical order first and then execute all the "S files" in alphabetical order. 24

25. The init Process in SunOS
Init executes the scripts for entries with sysinit in the action field, eg /sbin/rcS, and then /sbin/rc2, /sbin/rc3, … according the run level.
Those rc scripts will execute the scripts in the directories /etc/rcS.d/, /etc/rc2.d/, /etc/rc3.d/, … respectively.
The scripts in the /etc/rc#.d/ directories begin with either the letter K or S. These scripts have names of the form:
[K,S][ ]filename
The K (kill) files are run first for killing the existing processes,
The S (start) files run next to start the various daemons needed for that run level. 25

26. Why Won't My System Boot? Possible reasons include hardware problems,
Both hardware failure and problems caused by human error (e.g. the power cord isn't plugged in, the drive cable is the wrong way around)
defective boot floppies, drives or tapes,
damaged file systems,
improperly configured kernels,
A kernel configured to use SCSI drives won't boot on a system that uses an IDE drive controller.
errors in the rc scripts. 26

27. Why Won't My System Boot?
Solution: Systems Administration maxim:Always keep a separate working method for booting the machine into at least single user mode.
a boot floppy, CD-ROM or tape, format doesn't matter. What does matter that at anytime you can bring the system up in at least single user mode so you can perform some repairs. 27

28. Hardware Problems Some guidelines to solving hardware problems
check the power supply and its connections,
Don’t laugh, there are many cases I know of in which the whole problem was caused by the equipment not being plugged in properly or not at all.
check the cables and plugs on the devices,
check any fault lights on the hardware, 28

29. Hardware Problems
power cycle the equipment (power off, power on),there is an old Systems Administration maxim. If something doesn’y work turn it off, count to 10 very slowly and turn it back on again (usually with the fingers crossed).
try rebooting system without selected pieces of hardware,
It may be only one faulty device that is causing the problem. Try isolating the problem device.
use any diagnostic programs that are available, or as a last resort, call a technician or a vendor. 29

30. Hardware Problems Damaged File Systems Improperly Configured Kernels
First always have backups of all file systems so that you can quickly recover some information.
Try using fsck to fix the problem.
If worse comes to worse resort to your backups.
Improperly Configured Kernels
Reasons why you might change the kernel will be discussed in a later chapter.
When you do change the kernel you should always keep a backup working version of kernel that you can use to reboot the system. 30

31. Daemons
A daemon is a process that runs in background, is independent of control from all terminals, and spends much of its time waiting for some event to occur.
Once the event occurs, the daemon wakes up and performs some predefined action.
The action is sometimes controlled by a configuration file. 31

32. Daemons Ways to start a daemon common daemons on a UNIX machine.
from rc, start up script, root
From inet superserver
from cron
from at command
use & sign
<error messages to syslogd>
common daemons on a UNIX machine.
Init: itself can be classed as a daemon.
Inetd:the main network server 32

33. Daemons
named:Name server, provides dynamic hostname data for TCP/IP networking
timed:Time daemon used to synchronise different system clocks
sendmail:the mail daemon, responsible for delivering mail locally and to remote hosts
nfsd:nfs file exporting daemon
ypbind&ypserv:NIS (yellow pages) daemons
syslogd:System logging daemon, records various events. 33

34. Shutting the System Down
You should not just simply turn a UNIX computer off or reboot it. Doing so will usually cause some sort of damage to system especially to file system.
tasks that have to be performed for a UNIX system to be shutdown cleanly
tell the users the system is going down,
Telling them 5 seconds before pulling the plug is not enough. Wherever possible the users should know at least a couple of days in advance that the system is going down. 34

35. Shutting the System Down
signal all the currently executing processes that it is time for them to die,
Hopefully these processes will all die gracefully (given some time) and will not do anything nasty to the system in the process.
place the system into single user mode, and
perform sync to flush the file systems buffers so that the physical state of the file system matches the logical state. 35

36. Shutting the System Down
Some of the reasons why you may wish to shut a UNIX system down include
general housekeeping,
Every reboot will perform some important housekeeping tasks, including deleting files from the temporary directories and performing checks on file systems.
Rebooting will get rid of zombie processes.
general failures (problems that can only be solved by shutsown) include:
hanging logins,
unsuccessful mount requests, 36

37. Shutting the System Down
dazed devices,
runaway processes filling up disk space or CPU time,preventing useful work being done
system maintenance and additions.
There are some operations that only work if the system is rebooted or if the system is in single user mode, i.e. adding a new device. 37

38. Shutting the System Down
The following command is an example of what not to do. shutdown -g0
On a SVR4 box this results in a message like this appearing on user's terminal
THE SYSTEM IS BEING SHUT DOWN NOW!
Log off now or risk your files being damaged.
Guidelines of how and when to perform shutdowns 38

39. Shutting the System Down
shutdowns should be scheduled,
If users know the system is coming down at specified times they can organise their computer time around those times.
perform a regular shutdown once a week,
A guideline, so that the housekeeping tasks discussed above can be performed. If it's regular the users get to know when the system will be going down.
use /etc/motd: the message users see when they first log onto a system use it to inform users of the next scheduled shutdown. 39

40. Shutting Down/ Rebooting
the shutdown command: The most used
The command can display messages at preset intervals warning the users that the system is coming down.
the BSD haltcommand
Logs the shutdown, kills the system processes, executes sync and halts the processor.
the BSD rebootcommand
Similar to halt but causes the machine to reboot rather than halting. 40

41. Commands Shutting Down/ Rebooting
sending init a TERM signal
init will usually interpret a TERM signal (signal number 15) as a command to go into single user mode. It will kill user processes and daemons. The command is kill (It may not work or be safe on all machines.)
BSD fasthalt or fastboot commands
Shell scripts which create a file /fastboot before calling halt or reboot. When the system reboots and it finds a file /fastboot it will not perform a fsck on the file systems. 41

42. The AT&T shutdown The format is
shutdown -ggrace_period -iinit_state [-y]
grace_period: # of seconds to wait before beginning the shutdown (default of 60)
init_state: The init state (run level) to put the system into
some cases ask for confirmation just before performing the shutdown. This question can be pre-answered by using -y option.
Shutdown -y -g120 -i0 42

43. The BSD shutdown The format is Parameters Meaning:
shutdown [-fhknr]time [warning-message]
actually calls on the halt command to perform the actual work of halting the system.
It just displays messages before calling halt.
Parameters Meaning:
f:file systems will not be checked on system restart (create /fastboot file)
k:simulate shutdown, WON'T actually do it
h:simply halt the system (same as halt) 43

44. The BSD shutdown Command
r:reboot the system (same as reboot)
n:don't execute sync before shutting down
time:has two formats either
+number:system down in number mins
hour:min: in 24 hour format
Warning messages are displayed at periodic intervals and logins are disabled five minutes before shutdown
warning-message: message to display to the users 44

45. The BSD shutdown
The halt and reboot commands are actually used by the shutdown command.
The halt command performs a sync on the disks and stops the processors. The format of halt is.
halt [-nqy]
-n:don't sync the disks before stopping
-q:do a quick halt (create /fastboot file so that file systems are not fscked on reboot)
-y:halt the system 45

46. The BSD shutdown reboot shuts system down and restarts it:
reboot [-dnq][boot arguments]
-d:dump a copy of the kernels memory (system core) before rebooting (some machines recognize this but don't do anything)
-n avoid the sync call.
-q reboot quickly and ungracefully
boot arguments:specify how system should restart (e.g. single user mode). Some machines ignore these arguments. 46

47. Sun PROM and SGI Indy Sun PROM
Interact with PROM by holding down the “STOP” key (L1 key on older KB) and pressing “a” key
“break” key if terminal keyboard
ok prompt
specify boot device:
b device(controller#,unit#,file#)pathname args OR 47

48. Sun PROM and SGI Indy
boot device(controller#,unit#,file#)pathname args
example:
ok boot or ok boot -s
ok probe-scsi
SGI Indy PROM
printenv
setenv
>> boot dksc(controller#,unit#,file#)pathname 48

49. Boot Up Sequence in x86 Linux
BIOS
run level 5
xdm
X-login
MBR
Linux Kernel
LILO
init
Shell
Console login
First 512-byte segment of the first boot disk
run level 3
getty
Other OS 49

50. Using LILO in Linux
LILO (LInux LOader) is a separate boot loader which resides on your hard disk. (it is not an OS)
It is executed when the system boots from the hard drive (Master Boot Record, MBR). boot manager capable of booting MS-DOS, or Windows.
Installing and Reconfiguring LILO:
Editing the lilo.conf file
Run the /sbin/lilo command to update the boot sector and create the /boot/map file.
Examples of LILO’s boot time options:
root=/dev/foo tells kernel to use /dev/foo as the root device.
single enter single user mode
init=/sbin/init tells kernel to use /sbin/init as its init program. 50

51. The /etc/lilo.conf file
# Tell LILO to modify the boot record on /dev/had (the first non-SCSI
# hard drive). If you boot from a drive other than /dev/had, change the
# following line.
boot=/dev/hda
# /boot/map contains information the LILO uses during the boot process
map=/boot/map
# Set the delay in milli-seconds. This is the time you have to press
# the 'SHIFT' key to bring up the LILO Boot: prompt if you haven't
# specified the 'prompt directive'
delay=60
# Name of the boot loader.
install=/boot/boot.b
# This forces LILO to prompt you for the OS you want to boot. A 'TAB'
# key at the LILO: prompt will display a list of the OSs available to
# boot according the the names given in the 'label=' directive below.
prompt
# Tell LILO to wait for .10 seconds before booting the first image.
timeout=50 51

52. The /etc/lilo.conf file (con't)
# Set the default booting image.
default=linux
# Different entries of OSs
password=Linux # password for entering the boot image (case-sensitive)
image=/boot/vmlinuz
label=linux
initrd=/boot/initrd img #file for initial RAM disk
read-only # mount read only
root=/dev/hda1 # location of root partition
restricted # require password only for command line input
Other=/dev/hda2
label=msdos
table=/dev/hda # location of partition table for /dev/hda2
Read the files under /usr/share/doc/lilo directory for more information. 52

53. RunLevel-Red Hat The following runlevels are defined in Red Hat Linux:
0 — Halt
1 — Single-user mode
2 — Not used (user-definable)
3 — Full multi-user mode
4 — Not used (user-definable)
5 — Full multi-user mode (with an X-based login screen) .
6 — Reboot 53