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Lecture 3: Unix installation&startup
Guntis Barzdins
Girts Folkmanis
Juris Krumins
Mājas Darbs #1
A. Izvēlēties iespēju robežās no citiem atšķirīgu *nix distribūciju (ar Ubuntu, Kubuntu vairāk
par 8 nevarēs dabūt) un to patstāvīgi instalēt un īsumā aprakstīt galvenos soļus, grūtības un tml.
Instalācijas procesa ekrānattēlu iegūšanai ieteicams lietot VirtualBox, Vmware vai citu
emulatoru.
B. Instalētajā *nix versijā panākt lai darbojas C kompilātors; tajā uzrakstīt, nokompilēt un
palaist vienkāršu "Sveika, pasaule!" programmiņu.
C. (Neobligātā daļa atzīmes 10 iegūšanai): nodemonstrēt buffer overflow ielaušanos datorā (Unix
shell piekļuvi vai kādas programmas izpildi) caur jūsu "Sveika, pasaule!" programmiņu, kas
satur scanf vai līdzīgu nedrošu C bibliotēkas funkciju. Pašu ielaušanos demonstrēt programmas
ievadā padodot negaidītus datus (bez ievainojamās programmas "pašuzlaušanas").
Praktiskas lietas
 Video lekcijas – padziļinātai izpratnei (angliski)



Kristaps Džonsons
http://students.mii.lu.lv/Lekcijas/OperetajsistemaUNIX/
Mājasdarba C-daļai skatīt
11stack1.mov (no 24-46 min)
 12stack2.mov (no sākuma)

Ieteicamās virtualiācijas vides
majas darbam
 VirtualPC (Win)
 VMWare (Win, Mac)
 VirtualBox (Sun, Oracle)
 Parallels (Mac)
 KVM (Linux)
Linux Distributions
 Debian GNU/Linux (Xandros, Knopix,...)

a free operating system that provides almost 4000 software packages for six
architectures (Intel, Motorola, Alpha, SPARC, PowerPC, ARM) and is developed
entirely by volunteers over the Internet
 Fedora/RedHat

a Red-Hat-sponsored and community-supported open source project. The goal of
The Fedora Project is to work with the Linux community to build a complete, general
purpose operating system exclusively from free software. Development will be done
in a public forum
 Mandrake Linux

a friendly Linux Operating System which specializes in ease-of-use for both servers
and the home/office. It is freely available in many languages throughout the world
 Slackware

a long running Linux distribution that descends from the SLS Distribution
 SuSE Linux

an extremely popular distro that features excellent documentation, thousands of
applications on a DVD/CD-ROM set
 Gentoo Linux

an optimized GNU/Linux distribution featuring 5 different pgcc-optimized builds,
including Intel Pentium, Pentium Pro/II/III and AMD K6 optimized
BSD Versions
 FreeBSD - Focusing on features and ease of use
 Darwin (OS X) - Focusing on the desktop and
multimedia with use of the Apple's Aqua Interface
 NetBSD - Focusing on portability
 OpenBSD - Focusing on security
Citi brīvi pieejami Unix
 Solaris


x64/x86
SPARC
 Minix
Linux, BSD
Minix
Unix Instalacija
no CD/DVD
Installing NetBSD
The main menu of the installation program
Installing NetBSD
Choosing the partitioning scheme
Installing NetBSD
fdisk
Installing NetBSD
Installing the boot selector
Installing NetBSD
The disklabel editor
System startup
System initialization
 Overview of the PC Boot Process

When a PC is powered on, the BIOS (Basic
Input-Output System) runs first, followed by
a boot loader and finally the operating
system initialization routine.
System initialization
 The BIOS


When power is initially applied to the computer this triggers
the RESET pin on the processor. This causes the processor to
read from memory location 0xFFFFFFF0 and begin executing
the code located there. This address is mapped to the ReadOnly Memory (ROM) containing the BIOS. The BIOS must poll
the hardware and set up an environment capable of booting
the operating system. BIOS functionality can be broken into
three areas: Power On Self Test (POST), Setup and Boot.
The last action of the BIOS is to execute the 19h interrupt,
which loads the first sector of the first boot device. Since this
is the location of the boot loader, execution of the 19h interrupt
transfers control to the boot loader.
Hard Drive Construction
Master Boot Record (MBR) Track 0,
Sector 1 (512bytes):
• Number of partitions and their
location (max 4 primary partitions or
3 primary + 1 Extended + 12
Logical)
• Pointer to partition with bootloader
struct master_boot_record {
char bootinst[446];
/* space to hold actual boot code */
char parts[4 * sizeof (struct fdisk_partition_table)];
ushort signature;
/* set to 0xAA55 to indicate PC MBR format */
};
System initialization
 The Boot Loader




Once the BIOS loads the first sector of the boot device into RAM,
the boot loader begins execution. In the case of a hard drive, this
first sector is referred to as the Master Boot Record (MBR). The
MBR contains the partition table describing the partitions defined on
the hard drive. It also contains a program, the boot loader, which
will load the first sector of the partition marked as active into RAM
and execute it.
The size of the MBR is limited to one sector on disk or 512 bytes,
since it is located within the first sector of the drive at cylinder 0,
head 0, sector 1.
Typically boot loaders have been highly integrated with the
operating system that they support. This integration cuts down on
the operations a boot loader must perform, making a 512 byte boot
loader feasible. When more functionality is required, a multi-stage
boot loader may be used.
A multi-stage boot loader provides more function and flexibility by
working around the 512 byte size limitation. Rather than consisting
of a single program which loads the operating system directly,
multi-stage boot loaders divide their functionality into a number of
smaller programs that each successively load one another.
Boot Block
The system’s primary disk unit contains a boot block that contains the
bootstrapping program that loads the OS to memory. This program is invoked by
the computer’s minimal bootstrap program in ROM.
This boot block is often called the Master Boot Record (MBR).
Different operating systems treat the MBR in very different ways. Some are flexible
enough to install a boot loader in the MBR, so that the disk can contain different
OS in different disk partitions. The loader for each OS is then stored at the
beginning of its own partition. Examples: Windows NT/2000/xp boot loader,
Linux lilo and grub.
A “bootable” disk is one on which a boot block has been installed.
How computer startup?
 Booting is a bootstrapping process that starts
operating systems when the user turns on a
computer system
 A boot sequence is the set of operations the
computer performs when it is switched on that
load an operating system
21
Booting sequence
1.
2.
3.
4.
5.
6.
Tern on
CPU jump to address of BIOS (0xFFFF0)
BIOS runs POST (Power-On Self Test)
Find bootale devices
Loads and execute boot sector form MBR
Load OS
22
BIOS (Basic Input/Output
System)
 BIOS refers to the software code run by a computer when first powered on
 The primary function of BIOS is code program embedded on a chip that
recognises and controls various devices that make up the computer.
BIOS on board
BIOS on screen
23
Boot loader
MBR (Master Boot Record)
 OS is booted from a hard disk, where the Master Boot Record
(MBR) contains the primary boot loader
 The MBR is a 512-byte sector, located in the first sector on the
disk (sector 1 of cylinder 0, head 0)
 After the MBR is loaded into RAM, the BIOS yields control to it.
25
MBR (Master Boot Record)
26
MBR (Master Boot Record)
 The first 446 bytes are the primary boot loader, which contains
both executable code and error message text
 The next sixty-four bytes are the partition table, which contains a
record for each of four partitions
 The MBR ends with two bytes that are defined as the magic
number (0xAA55). The magic number serves as a validation
check of the MBR
27
Extracting the MBR
 To see the contents of MBR, use this command:
 # dd if=/dev/hda of=mbr.bin bs=512 count=1
 # od -xa mbr.bin
**The dd command, which needs to be run from root, reads the first 512 bytes
from /dev/hda (the first Integrated Drive Electronics, or IDE drive) and writes
them to the mbr.bin file.
**The od command prints the binary file in hex and ASCII formats.
28
Boot loader
 Boot loader could be more aptly called the kernel loader. The task
at this stage is to load the Linux kernel
 Optional, initial RAM disk
 GRUB and LILO are the most popular Linux boot loader.
29
Other boot loader (Several OS)











bootman
GRUB
LILO
NTLDR
XOSL
BootX
loadlin
Gujin
Boot Camp
Syslinux
GAG
30
GRUB: GRand Unified
Bootloader








GRUB is an operating system independant boot loader
A multiboot software packet from GNU
Flexible command line interface
File system access
Support multiple executable format
Support diskless system
Download OS from network
Etc.
31
GRUB boot process
1.
The BIOS finds a bootable device (hard disk) and transfers control to the
master boot record
2.
The MBR contains GRUB stage 1. Given the small size of the MBR, Stage 1
just load the next stage of GRUB
3.
GRUB Stage 1.5 is located in the first 30 kilobytes of hard disk immediately
following the MBR. Stage 1.5 loads Stage 2.
4.
GRUB Stage 2 receives control, and displays to the user the GRUB boot menu
(where the user can manually specify the boot parameters).
5.
GRUB loads the user-selected (or default) kernel into memory and passes
control on to the kernel.
32
Example GRUB config file
33
LILO: LInux LOader
 Not depend on a specific file system
 Can boot from harddisk and floppy
 Up to 16 different images
 Must change LILO when kernel image file or
config file is changed
34
LILO v.s. GRUB
 LILO


Run LILO to modify mini-bootloader in the MBR
Cannot read file system itself
 GRUB


Multistage loader
Can read file-system itself
 Parameter passing (runlevel, init) to kernel

Actually hacking – modifies address and name inside kernel for
the process to start
Boot Terminology
 Loader:
Program that moves bits from disk (usually)
to memory and then transfers CPU control to the newly
“loaded” bits (executable).

 Bootloader / Bootstrap:

Program that loads the “first program” (the kernel).
 Boot PROM / PROM Monitor / BIOS:

Persistent code that is “already loaded” on power-up.
 Boot Manager:

Program that lets you choose the “first program” to load.
LILO: LInux LOader
 A versatile boot manager that supports:




Choice of Linux kernels.
Boot time kernel parameters.
Booting non-Linux kernels.
A variety of configurations.
 Characteristics:



Lives in MBR or partition boot sector.
Has no knowledge of filesystem structure so…
Builds a sector “map file” (block map) to find kernel.
 /sbin/lilo – “map installer”.

/etc/lilo.conf is lilo configuration file.
Example lilo.conf File
boot=/dev/hda
map=/boot/map
install=/boot/boot.b
prompt
timeout=50
default=linux
image=/boot/vmlinuz-2.2.12-20
label=linux
initrd=/boot/initrd-2.2.12-20.img
read-only
root=/dev/hda1
LILO interface
 Once LILO has successfully loaded, you will see a LILO
prompt.
 You may let LILO time out (after 10 seconds), which will
boot the default Linux partition.
 Second, you can press the TAB key, which will list a
selection of operating systems to boot from. For example
we would get "Linux" and "WindowsXP" as our options.

Typing either of these will load up that OS.
GRUB (GRand Unix Bootloader)
Master Boot Record
Partition 1: 100M
EXT3 (Linux)
/boot
MBR Passes control to
the /boot partition
GRUB
GRUB then boots to an
OS (Windows or Linux)
Partition 2: 10GB
NTFS (Windows XP)
Partition 3: 512MB
Linux Swap
Partition 4: 10GB
EXT3 (Linux)
/
Grub interface
Kernel is loaded into memory
GRUB decompresses the
Linux kernel and loads it
into memory
/boot
vmlinuz-2.6.12-1447_FC4
Memory
GRUB also passes
“kernel command line” (255bytes)
to the loaded Linux kernel
grub.conf
# grub.conf generated by anaconda
#
# Note that you do not have to rerun grub after making changes to this\
file
# NOTICE: You have a /boot partition. This means that
#
all kernel and initrd paths are relative to /boot/, eg.
#
root (hd0,1)
#
kernel /vmlinuz-version ro root=/dev/hdb3
#
initrd /initrd-version.img
#boot=/dev/hdb
default=0
timeout=10
splashimage=(hd0,1)/grub/splash.xpm.gz
title Linux Fedora (2.6.5-1.358smp)
root (hd0,1)
kernel /vmlinuz-2.6.5-1.358smp ro root=LABEL=/ rhgb quiet
initrd /initrd-2.6.5-1.358smp.img
title Linux Fedora-up (2.6.5-1.358)
root (hd0,1)
kernel /vmlinuz-2.6.5-1.358 ro root=LABEL=/ rhgb quiet
initrd /initrd-2.6.5-1.358.img
title Windows 2000
rootnoverify (hd0,0)
chainloader +1
Specifies the default boot image will
be the first hard entry
Grub will wait for 10 seconds for input from
the user before continuing to boot.
The root partition is the second partition
on the first hard drive.
Startup Sequence
Power-on
Boot
loader
LILO
Initialisation Scripts
Create
init
process
Linux
hardware
rc.sysinit
Load
Kernel
runlevel
0-6
rc.local
Ready
Changing runlevel at boot time
 LILO: append the runlevel to the boot command :


LILO: linux 3 or
LILO: linux 5
 GRUB: press the `e' key to edit the boot configuration


append the runlevel to the end of the boot command as shown:
kernel /vmlinuz ro root=/dev/hda1 5
Kernel starts the init process
Kernel passes
desired runlevel to the init
pocess as argument
Partition 4: 10GB
EXT3 (Linux)
/
If runlevel not specified, then
/etc
# Default runlevel
id:5:initdefault:
(Configuration files)
/etc/init.d
/etc/inittab
Resource (RC) scripts are
stored here and are called
depending on the system
runlevel
acpid*
anacron*
apmd*
atd*
auditd*
...
/etc/rc.d
rc5.d
Linux Run Levels





Linux defines 7 run levels
Each run level defines a set of commands that are run to stop and start
processes.
The actual commands are held in /etc/init.d directory
The run level directories rc0.d, rc2.d…rc6.d contain links to the actual
commands
Each command is prefixed with S or K and a number 00-99
 S prefix means that a process should be started e.g.
S10network
 K prefix means that a process should be stopped (killed)
K70syslog
 The numbers determine the order in which the commands are
run from lowest first to highest last
Linux Run Levels 0-2
 Runlevel 0 Directory /etc/rc.d/rc0.d

Actually shutdown sequence



Kill all processes
Turn off virtual memory system (i.e. swap partition)
unmounts swap and file systems
 Runlevel 1 /etc/rc.d/rc1.d


single user mode
used for maintenance by system administrators when they
need sole control of machine, e.g. reconfiguring hardware
installing software
 Runlevel 2 /etc/rc.d/rc2.d

Multi-user + networking (minus NFS)
Linux Run level 3-6
 Runlevel 3 /etc/rc.d/rc3.d


Default run level
multi-user + NFS
 Runlevel 4 /etc/rc.d/rc4.d

not defined ( available for customization)
 Runlevel 5 /etc/rc.d/rc5.d

Same as 3 under Redhat this but includes starting X windows
 Runlevel 6 /etc/rc.d/rc6.d


reboot
similar to 0 but allow allows option to shutdown (halt) or reboot
Shutdown
 shutdown allows...



users to be warned the systems is going down
the contents of disk caches to be written disk
file systems to be marked as having been closed properly (
avoid file system check on next startup)
 Access to the shutdown command is restricted (it is in
/sbin)
 eg shutdown -h now
h = halt
r = reboot
HD identification
 IDE drives



dev/hda
dev/hdb
...
Partition identification:
 SCSI



dev/sda
dev/sdb
...
brw-rw---- 1 root disk 3, 0 May 5 1998
hda
brw-rw---- 1 root disk 8, 0 May 5 1998
Note that /dev is not a real directory for
accessing the contents of disks –
it is rather a naming space for all hardware
devices (and their drivers) present in the
system, including keyboard, screen etc.
The contents of disks is made
available in other part of root / hierarchy.
File System Layout
Bootloader can be installed in different locations
(if bootloader not in MBR, the BIOS interprets MBR to find boot partition)
Mandatory partitions
 root


/dev/hda1 (recommended)
This is partition for the actual root / of the UNIX filesystem
 swap





/dev/hda2 (recommended)
4GB (max with 32bit x86 CPU)
RAM SIZE * 2 (recommended)
This partition is not visible in root / and is used only by kernel for
virtual memory page swapping (“raw” sectors, no structure)
Theoretically swap partition is optional, if enough RAM
Optional partitions or separate HD
 Typically on separate partitions

/home, /boot, /tmp, /var, /usr
 Reasons for separate partitions




logical or physical damage
reinstallation (affects only some partitions)
limit overflow effects
better performance
shared via network
# df
Filesystem 1K-blocks
/dev/hda1

/dev/hda3
none
Used Available Use% Mounted on
9070728 4701180
3908768
24950428
683412
22999584
257236
0
257236
55% /
3% /home
0% /dev/shm
File System Types

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







VFS
UFS / FFS
NFS
RFS
S5FS
VxFS
JFS
CFS
EXT2/EXT3
GFS
XFS
CXFS
QFS
HFS
NTFS
FAT16/ FAT32
GPFS
....
Virtual File System
UNIX File System – used interchangeably with FFS (Fast File System)
Network File System – developed by Sun
Remote File System – developed by AT&T
Original System V file system
Veritas Journaling File System
Journaled File System – AIX
Cluster file system – Tru64
2nd/3rd Extended File System – Linux systems
Global File System – Linux
Extended File System – SGI and others
Clustered Extended File System – SGI
64-bit very large file system – Sun Solaris
Hierarchical File System – S/390 UNIX, OS/2, MacOS X
Windows NT/2000/2003
Windows – several versions
IBM
File System Support
 Linux can interpret many
file system types,
including;






EXT2, EXT3,
UFS/FFS,
FAT16, FAT32
NTFS (read-only),
HPFS
ISO9660, UDF, UFS, etc.
 Win32 can interpret a few
file system types,
including;


FAT16, FAT32
NTFS
Creating Partitions: GNU Parted
Notes:
1.
2.
3.
4.
5.
For ext2, ext3: the start of the partition must stay fixed.
For ext2, ext3: the partition you copy to must be bigger or exactly the same size as the partition you
copy from.
For ext2 and ext3: the checking is limited to ensuring the resize and copy commands will be ok.
For fat: the size of the new partition after resizing or copying is restricted by the cluster size. Parted
can shrink the cluster size, so you can always shrink your partition. However, if you can't use
FAT32 for some reason, you may not be able to grow your partition.
Parted supports both FAT16 and FAT32. Parted can convert file systems between FAT16 and
FAT32, if necessary.
Linux
Partition Types
 Primary Partitions
 Swap Partitions
 Foreign Partition Types
 Logical Partitions
Linux
Device names
 IDE controller naming convention
drive name
drive controller
drive number
/dev/hda
/dev/hdb
/dev/hdc
/dev/hdd
1
1
2
2
1
2
1
2
Linux
partition names
drive name
drive controller drive number
partition type
partition
number
/dev/hda1
1
1
Primary
1
/dev/hda2
1
1
Primary
2
/dev/hda3
1
1
Primary
3
/dev/hda4
1
1
Swap
NA
/dev/hdb1
1
2
Primary
1
/dev/hdb2
1
2
Primary
2
/dev/hdb3
1
2
Primary
3
/dev/hdb4
1
2
Primary
4
Linux
Logical Partitions
drive name
drive controller drive number
partition type
partition
number
/dev/hdb1
1
2
primary
1
/dev/hdb2
1
2
extended
NA
/dev/hda5
1
2
logical
2
/dev/hdb6
1
2
Logical
3
passwd, shadow, group files
unix etc # ls -l passwd shadow group
-rw-r--r-- 1 root root 705 Sep 23 15:36 group
-rw-r--r-- 1 root root 1895 Sep 24 18:20 passwd
-rw------- 1 root root 634 Sep 24 18:22 shadow
unix etc #
unix root # more /etc/passwd
root:x:0:0:root:/root:/bin/bash
bin:x:1:1:bin:/bin:/bin/false
daemon:x:2:2:daemon:/sbin:/bin/false
adm:x:3:4:adm:/var/adm:/bin/false
lp:x:4:7:lp:/var/spool/lpd:/bin/false
sync:x:5:0:sync:/sbin:/bin/sync
shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
halt:x:7:0:halt:/sbin:/sbin/halt
...
guest:x:405:100:guest:/dev/null:/dev/null
nobody:x:65534:65534:nobody:/:/bin/false
girtsf:x:1000:100::/home/girtsf:/bin/bash
dima:x:1001:100::/home/dima:/bin/bash
guntis:x:1002:100::/home/guntis:/bin/bash
students:x:1003:100::/home/students:/bin/bash
unix root #
unix root # more /etc/shadow
root:$1$VlYbWsrd$GUs2cptio.rKlGHgAMBzr.:12684:0:::::
halt:*:9797:0:::::
...
guest:*:9797:0:::::
nobody:*:9797:0:::::
girtsf:$1$u6UEWKT2$w5K28n2iAB2wNWtyPLycP1:12684:0:99999:7:::
dima:$1$BQCdIBdV$xzzlj4s8XT6L9cLAmcoV50:12684:0:99999:7:::
guntis:$1$fiJF/0BT$Py9JiQQL6icajjQVyMZ7//:12684:0:99999:7:::
students:$1$wueon8yh$nLpUpNOKr8yTYaEnEK6OJ1:12685:0:99999:7:::
unix root #
unix root # more /etc/group
root::0:root
bin::1:root,bin,daemon
daemon::2:root,bin,daemon
sys::3:root,bin,adm
adm::4:root,adm,daemon
tty::5:girtsf
disk::6:root,adm
lp::7:lp
mem::8:
kmem::9:
wheel::10:root,girtsf
floppy::11:root
mail::12:mail
...
users::100:games,girtsf
nofiles:x:200:
qmail:x:201:
postfix:x:207:
postdrop:x:208:
smmsp:x:209:smmsp
slocate::245:
portage::250:portage
utmp:x:406:
nogroup::65533:
nobody::65534:
unix root #
Advanced Boot Concepts
 Initial ramdisk (initrd) – two-stage boot for flexibility:





First mount “initial” ramdisk as root.
Execute linuxrc to perform additional setup, configuration.
Finally mount “real” root and continue.
See Documentation/initrd.txt for details.
Also see “man initrd”.
 Net booting:


Remote root (Diskless-root-HOWTO).
Diskless boot (Diskless-HOWTO).
UUID
 A Universally Unique Identifier (UUID) is an identifier standard
used in software construction, standardized by the Open Software
Foundation (OSF) as part of the Distributed Computing
Environment (DCE).
 The intent of UUIDs is to enable distributed systems to uniquely
identify information without significant central coordination. Thus,
anyone can create a UUID and use it to identify something with
reasonable confidence that the identifier will never be
unintentionally used by anyone for anything else.
 A UUID is a 16-byte (128-bit) number. In its canonical form, a
UUID consists of 32 hexadecimal digits, displayed in 5 groups
separated by hyphens, in the form 8-4-4-4-12.
 UUIDs are often used to identify filesystems.
UUID
•
•
$ cat /proc/cmdline
BOOT_IMAGE=/boot/vmlinuz-2.6.32-24-generic-pae root=UUID=32fffc527a96-4acb-b94d-d743617ab0c1 ro quiet splash
•
•
•
$ sudo blkid
/dev/sda6: UUID="32fffc52-7a96-4acb-b94d-d743617ab0c1" TYPE="ext4"
/dev/sda7: UUID="f0a604b1-bfd4-4100-a963-401b0f2bdd82" TYPE="swap"
•
•
•
$ cat /etc/fstab
UUID=32fffc52-7a96-4acb-b94d-d743617ab0c1 / ext4 errors=remount-ro 0
1
UUID=f0a604b1-bfd4-4100-a963-401b0f2bdd82 none swap sw 0 0
•
•
$ uuidgen
8cd52053-1bdd-4192-8a90-788f9e972c88
LVM
 Logical volume management provides a higher-level view of the
disk storage on a computer system than the traditional view of
disks and partitions. This gives the system administrator much
more flexibility in allocating storage to applications and users.
 Storage volumes created under the control of the logical volume
manager can be resized and moved around almost at will,
although this may need some upgrading of file system tools.
 The logical volume manager also allows management of storage
volumes in user-defined groups, allowing the system administrator
to deal with sensibly named volume groups such as "development"
and "sales" rather than physical disk names such as "sda" and
"sdb".
 http://tldp.org/HOWTO/LVM-HOWTO/
LVM
•
•
# pvcreate /dev/sdd1
Physical volume "/dev/sdd1" successfully created
•
•
# vgcreate vgrupa2 /dev/sdd1
Volume group "vgrupa2" successfully created
•
•
# lvcreate -l100%FREE -n data2 vgrupa2
Logical volume "data2" created
•
•
# mkfs.ext3 /dev/vgrupa2/data2
...
•
pvdisplay, vgextend, lvresize, ...
md
 Software RAID devices are so-called "block" devices, like
ordinary disks or disk partitions. A RAID device is "built"
from a number of other block devices - for example, a
RAID-1 could be built from two ordinary disks, or from
two disk partitions.
 RAID modes: linear, 0, 1, 4, 5, 6.
 mdadm - manage MD devices aka Linux Software RAID.
 http://raid.wiki.kernel.org/
md
•
# mdadm --create /dev/md1 --level=raid1 --raid-devices=2 /dev/sdb
/dev/sdc
•
•
•
# cat /proc/mdstat
md1 : active raid1 sdb[0] sdc[1]
39070016 blocks [2/2] [UU]
•
# mdadm --stop /dev/md1
•
# mdadm --assemble /dev/md1 /dev/sdb /dev/sdc
Upstart
• Upstart is an event-based replacement for the /sbin/init daemon
which handles starting of tasks and services during boot, stopping
them during shutdown and supervising them while the system is
running.
• Known Users:
–
–
–
–
–
–
–
* Ubuntu 6.10 and later
* Fedora 9 and later
* Debian (as an option)
* Nokia's Maemo platform
* Palm's WebOS
* Google's Chromium OS
* Google's Chrome OS
Upstart
 Tasks and Services are started and stopped by events.
 Events are generated as tasks and services are started
and stopped.
 Events may be received from any other process on the
system.
 Services may be respawned if they die unexpectedly.
 Supervision and respawning of daemons which separate
from their parent process.
 Communication with the init daemon over D-Bus.
RedHat Boot Process
BIOS
GRUB
/etc/rc.d/
rc3.d
/etc/inittab
Linux
Kernel
init
/etc/rc.d/
rc.sysinit
/etc/rc.d/rc
Login
Shell
RL Specific
/etc/inittab
/etc/rc.d/
rc5.d
Source: http://nmc.nchu.edu.tw/linux/Linux_boot.htm
Fedora Boot Process
BIOS
GRUB
/etc/rc.d/
rc3.d
systemd
Linux
Kernel
Systemd
init
Login
Shell
/etc/
init/*.conf
RL Specific
/etc/rc.d/
rc5.d
Source: http://nmc.nchu.edu.tw/linux/Linux_boot.htm
Boot Process








Power On Self Tests (POST)
Run Boot Loader(s)
Load & initialize kernel
Detect & configure devices
Fork system processes
(Stop if Single User mode)
Run startup scripts
Start multiuser operations
Boot Loader
 ROM loads Master Boot program from disk
 Primary Bootloader


BIOS - Basic I/O, Program Loading
UEFI – Unified Extensible Firmware Interface
 2nd Boot Loader finds/loads kernel


Checks available memory
Initializes kernel internal data structures
 NTLDR – Microsoft Boot Loader
 GRand Unified Bootloader (GRUB/GRUB2)


Can boot multiple OS
Boot options can be edited at boot
GRUB Images (/boot/grub2)




boot.img – Loaded first on BIOS systems
diskboot.img – first sector of core image
cdboot.img – DVD version of diskboot.img
core.img



Main image
Includes kernel.img and module lists
Built with grub-mkimage
 kernel.img – Basic run-time functions
 *.mod – Dynamically loadable modules
Basic grub.cfg options
Shell script in /etc/boot2
set default=“0”
set timeout=“5”
menuentry ‘Fedora’ <options>
set root=‘(hd0,gpt2)’
linux /vmlinuz-<version> <options>
initrd /initranfs-<version>
Creating grub.cfg
 Compiled using grub2-mkconfig
 /etc/default/grub

Variables to change default settings
 /etc/grub.d/*



00_header
10_linux
40_custom
System Processes
 BSD Systems



swapper – PID 0
init – PID 1
pagedaemon – PID 2
 AT&T SVR4



sched – PID 0 (invisible under RedHat)
init – PID 1
/etc/inittab
Startup Services
 Hostname
 Timezone
 Check the hard drives
 Mount the hard drives
 Remove files from /tmp
 Configure network interfaces
 Start daemons and network services
BSD /etc/rc* Scripts
 /etc/rc


Master script
Executes supplemental scripts
 Example supplemental scripts (freeBSD)



/etc/defaults/rc.conf
/etc/rc.conf
/etc/rc.conf.local
/etc/inittab
 Initializes system for use
 Format: id:rl:action:process




id: uniquely identifies entry
rl: Run level entry applies to
action: How to execute process
process: process command line
 Ex: Setting the default Runlevel:
id:3:initdefault
 Replaced in Fedora with systemd
Systemd
 Becoming more prevalent in Linux Distros


Currently used by Fedora and OpenSUSE
Testing in Debian
 Mostly compatible with the init system


init scripts are read as alternative format
Established functionality such as fstab still supported
Systemd - Units
 Uses a dependency system between “units”




Requires/Wants
Conflicts
Before
After
 Encapsulate objects relevant to booting and
maintenance
 Configured in config files
 May be tied through symbolic links
Systemd – Unit Types
 Different unit types control different aspects of the
operating system







service: handles daemons
socket: handles network sockets
target: Logical grouping of units (example: runlevel)
device: expose kernel devices
mount: controls mount points of the files system
automount: mounts the file system
snapshot: references other units (similar to targets)
Systemd Unit File Section
 [Unit]






Description
Requires
Wants
Conflicts
Before
After
Systemd Service Section
 [Service]

Type=
simple|oneshot|forking|dbus|notify|idle




ExecStart
ExecReload
ExecStop
Restart=
no|on-success|on-failure|on-abort|always
Systemd Install Section
[Install]
 Wantedby=
Used to determine when to start
(e.g. Runlevel)
Startup Run Levels
RedHat
1 (S)
2
3
4
5
6
0
Mode
Single user
Multiuser (no networking)
Full Multiuser
Unused
X11
Reboot
Halt
Systemd – Runlevels
Runlevel is defined through a symbolic to one of the
runlevel targets
Runlevel Target


Runlevel 3:
/lib/systemd/system/multi-user.target
Runlevel 5:
/lib/systemd/system/graphical.target
Change Runlevel:

Remove current link /etc/systemd/system/default.target

Add a new link to the desired runlevel
Systemd - Virtual Consoles
Started in
/etc/systemd/system/getty.target \
.wants/getty@tty#.service
/sbin/agetty



agetty <port> <baud rate>
Alternative Linux getty
Opens tty port and prompts for login
Systemd - Virtual Consoles
 Example: [email protected]
[Unit]
Description=Getty on %I
BindTo=dev-%i.device
…
[Service]
Environment=TERM=linux
ExecStart=-/sbin/agetty %I 38400
Restart=always
RestartSec=0
UtmpIdentifier=%I
KillMode=process
…
/etc/init/*.conf directives
 exec
 script
 start on <event>
 stop on <event>
 task
 respawn
 See man 5 init for more
“Events”
 control-alt-delete
 power-status-changed
 startup
 runlevel <runlevel>
 started <job>
 stopped <job>
/etc/init - Virtual Consoles
 Started in /etc/init/start-ttys.conf
 tty restarts in /etc/init/tty.conf
 Example: /etc/init.d/tty.conf:
# tty - getty
#
# This service maintains a getty on the sepcified device.
stop on runlevel [016]
respawn
instance $TTY
exec /sbin/mingetty $TTY
/etc/init - Run Levels
 Started in /etc/init/rc[S].conf:
 Example (rc.conf):
start on runlevel [0123456]
stop on runlevel [!$RUNLEVEL]
task
export RUNLEVEL
console output
exec /etc/rc.d/rc $RUNLEVEL
Run Level Scripts
 Actual scripts - /etc/rc.d/init.d/
 /etc/rc.d/rc#.d/




Symbolic links to /etc/init.d scripts
S## - Start scripts
K## - Stop scripts
/etc/sysconfig/ - script configuration files
 chkconfig <script> on|off
 service <script> start|stop|restart
System Shutdown
 Turn off power – BAD!!!
 Reboot


reboot
shutdown –r
 Halting the system


halt
shutdown –h
 Changing the Run Level


telinit <mode>
shutdown –i<mode>
When to Shutdown
 Failures
 Maintenance and Upgrades
 Regularly Scheduled


Housecleaning
Window for Maintenance/Upgrades
 User Notification



/etc/motd
Email
Support web pages