Operating System

1
Operating System

• VISC lab
• Na Young Lee
• 09-20-02

2
Agenda

• Operating System
• UNIX (standard UNIX)
• Window (2000)
• Manage Window

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Operating System (OS)

• Computer consists of Hardware and OS
• What is OS?
• Manager
• OS manages users, access rights and user
• interaction.
• OS manages resources
• Files, directories
• Devices
• Processes
• Memory
• I/O

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Operating System (OS)

• To understand OS what and how manage
• Process
• Memory
• I/O
• File System
• Security

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Operating System (OS)

• How manage
• User interaction command, GUI
• Device controllers bus
• Interrupts
• Tables fd
• Signals, messages system

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UNIX - Interfaces
Users
User mode
Standard Utility Program
Standard library
OS
Kernel mode
Hardware
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UNIX-User interaction

• User interaction
• Shell Command programming language
• providing an interface to the Unix OS.
• Modifiable
• compiler
• Kernel Core of the OS.
• Invoked by system call

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UNIX - Kernel
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UNIX Device

• Device Control
• Abstraction of the physical devices
• Input keyboard, mouse, CD-ROM
• Output Screen, printers
• I/O disk, tape, network
• Commands
• Lp, ioctl, sockio, streamio, tar

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UNIX process

• Abstraction of running program
• Address space that contains data, instruction,
  hardware resources.
• Running, ready, block status
• Interrupt from input (vector) current process's
  info pushed to stack hardware access the
  address to be assigned for interrupt device
  after process done, one of the processes in the
  ready status is scheduled.

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UNIX process

• Process table
• Process status, program counter, stack pointer,
  PID
• Scheduling parameters process priority, CPU
  running time, - decide next process
• Memory info how to find the process not in the
  memory (ready or block)
• Signals mask signal, effective signal

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UNIX process

• Kernel process start a series of processes
• -Daemons (started at system booting)
• ttymon watches various terminals for login
• ttymon starts new process for user shell
• Command
• ps, exit, kill, fork, wait, bg, fg, signal,
  sigset, alarm

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UNIX File System

• Hierarchical File System

/
System binary
sbin
var
usr
dev
home
tmp
etc
kernel
Device file
Data of sa
mail
spool
tmp
user2
user1
sbin
bin
Binary file
System files
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UNIX File System

• Command
• mkdir, link, mount, cd, rmdir, cp, mv, rm
• Create/open, close, read/write, pipe
• NFS (Network File System)

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UNIX - Security

• UNIX is designed for multi-user system
• UID (user ID) , GID (group ID)
• each process, file, and folder
• File and folder permission 9 bit
• SETUID
• Set on the program by superuser (root)
• chmod, setuid, setgid
• owner, superuser

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UNIX - Security

• Login is program with SETUID root
• Login asks the username and password
• Hash function h (username)
• Call setuid and setgid system call
• Open keyboard (fd 0), screen (fd 1), screen error
  (fd 2), start user shell (UID), and terminate
• All processes forked by shell inherit the UID

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Windows OS Structure

• Operating System Structure

Win32 program
Win32 subsystem
System Interface
System Service
Obj
Config
Process
Memory
Security
Cache
Power
Kernel
HAL
Hardware
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Windows OS Structure

• Kernel mode
• HAL present rest OS with abstract hardware
  device (winnt/system32/hal.dll)
• ex) map device address to logical
  system address (bus)
• interrupt service set the priority on
  the device

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Windows OS Structure

• Kernel present complete hardware independency
• ex) save the CPU register,
• flush CPU table
• System service accept windows system calls

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Windows OS Structure

• User mode provide each user process with system
  call interface
• Environment Subsystems win32 API (application
  programming interface)
• System Interface DLL (dynamic link libraries)
• Service processes

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Window - Manage

• Interrupt
• Direct memory
• access
• I/O
• Memory

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Window - Registry

• Registry
• Dont change if you have a plan to use machine
  again.
• Directory (key)
• Entry name, type, value

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Window - Registry

• All the win32 application include win32API
  functions
• ( RegCreateKeyEx, _Delete_, _Open_, etc)
• All the registry file is in the
  winnt/system32/confg
• Some file can not open, but if you succeed
  opening file (?), you can see the file start
  regf

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Windows

• Booting
• Boot sector first sector of the partition
  having the bootable OS and has ntldr
• ntldr look up boot.ini file to get the info on
  configuration
• ntoskrnl.exe, and bootvid.dll are loaded.
• Finally ntldr load all the drives needed to
  finish booting ( like mouse, keyboard) and load
  smass.exe
• winlogin.exe,

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Windows - Security

• Winlogin.exe create lass.exe (authentication
  manager) and services.exe (look in registry and
  start services)
• Services Printer server, File server,
  Telnet Daemon, DNS resolver,
• Event logger, Plug-and-play manager

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Windows - Security

• User SID (security ID)
• Process has access token

Expiration time
Groups
Default CACL
User SID
Group SID
Restricted SID
Header
Privilege
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Windows - Security

• Security descriptor
• Implementation
• Winlogon.exe give initial process access token
• lass.exe decides success of login and lookup
  registry to get correct user profile and start
  services.exe with access token
• Subsequent processes inherit parents access
  token.
• Thread usually inherit the processs access token.

Owners SID
Group SID
DACL
Deny access List
SACL
System Access Control List
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Manage Windows

• Why have to protect windows?
• Bugs Every software contains bugs
• Intruders Crackers find a vulnerability in the
  OS and exploit it to break into and control
• Virus Infections antivirus software
• Violation of your privacy spyware (software to
  collect data about you and secretly send it home)

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Manage Windows

• How to protect windows
• Service pack
• Windows update
• Installing Hotfixes
• Microsoft Baseline Security Analyzer
• Virus protection
• Firewall protection
• Malicious Script Protection

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Manage Windows

• Service packs
• contain hundreds of bug and security fixes and
  enable you to apply these fixes in one fell swoop
• Check the service pack version and download the
  newest version
• Windows Update
• Updates are being released constantly
• http//windowsupdate.microsoft.com/

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Manage Windows

• Installing hotfixs
• additional patches
• subscribe to Microsoft's Security Bulletin -
  http//www.microsoft.com/technet/security/bulletin
  /notify.asp - or the CERT Advisory Mailing List -
  http//www.cert.org/contact_cert/certmaillist.html
  . You will receive regular e-mail notifications
  about vulnerabilities and fixes you might need to
  apply to your system.

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Manage Windows

• Microsoft Baseline Security Analyzer
• MBSA allows you to check your Windows NT4, 2000,
  or XP installation for a number of security
  issues, i.e. Windows vulnerabilities, weak
  passwords, IIS vulnerabilities, SQL
  vulnerabilities, and missing hotfixes

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Manage Windows

• Virus protection
• Anti-virus program known virus , update
  virus definition
• Common sense
• unknown virus
• DON'T OPEN ATTACHMENTS FROM UNKNOWN SOURCES!
• DELETE IT!
• e-mail with an attachment from a person you know
  but didn't expect it - DO NOT OPEN IT - DELETE
  IT!

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Manage Windows

• Firewall Protection
• Internet connetion exposed to world
• DSL or cable modem with static IP
• Find out how vulnerable your machine is
• http//grc.com/default.htm
• click on Shield's UP!.
• Do Test My Shields! and Probe My Ports!.
• Check for obvious vulnerabilities of your PC.
• Chances are you have a number of open and/or
  visible ports that can make your machine a target
  for crackers

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Manage Windows

• Firewall protects machine by closing these
  security holes.
• Firewall software monitors your Internet
  connection and filters all traffic to keep
  undesired traffic out and only allow legitimate
  traffic through.
• recommend is ZoneLab's Zone Alarm
• http//www.zonelabs.com.
• After installing Zone Alarm, and perform another
  Shields UP! test and Port Probe.

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Manage Windows

• Spyware Protection
• What is Spyware
• come in form of software installed on your
  machine with or without your knowledge
• tracks and collects data about you and your
  computer and sends it back to a central database
  for processing and analyzing
• Lavasoft's Ad-aware http//www.lavasoftusa.com/.
• After installing this software you can scan your
  entire system including hard drives and registry
  for any traces of spyware.

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Manage Windows

• Lavasoft's Ad-aware

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Manage Windows

• Malicious Script Protection
• A lot of e-mail viruses are scripts.
• In order to function, they need to be executed.
• Prevent you from accidentally launching a
  malicious script that was not caught by your
  antivirus software by installing script
  monitoring software
• AnalogX's Script Defender http//www.analogx.com/c
  ontents/download/system/sdefend.htm

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Manage Windows

• Malicious Script Protection

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Manage Windows

• Email
• If possible, set the format as plain /text HTML
  mail is a potential risk and allows for snooping
  and malicious code infection
• Disable to running ActiveX , script
• ActiveX applets (or "controls" as they are
  called) are downloadable programs that are run by
  your system. Unlike the normal EXE files, ActiveX
  can be run transparently in your Internet
  Explorer to perform any action such as erasing
  files or stealing your passwords.
• Do not open EXE, BAT, VBS, and SCR type
  attachments ever
• Consider using a plain text (non-HTML) e-mail
  reader such as Eudora or The Bat!
• DOC file can be opened up in like WordPad to view
  the text contents without the risk of a macro
  virus infection.

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Manage Windows

• Perform frequent data backups.
• Disable file sharing.
• Create an emergency boot disk.

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Manage Windows -VISC

• Secure Shell

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Manage Windows - VISC
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Reference

• Modern operating systems Andrew S. Tanenbaum
• A practical Guide to Solaris Mark G. Sobell
• Lecture 2 Dr. Spring