About system component

1. IT System Components

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IT System Components
 Operating Systems
 File Systems
 Processes and Job Control
 Devices and Controllers
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Operating Systems
 Software which shares and controls
hardware resources of a computer
 Shields user from low-level details
 Provides simple access to frequently
needed facilities
 Technical layer (kernel & drivers)
 File I/O
 User Interface
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Operating Systems
OS Users Tasks CPUs
MS/PC DOS S S 1
Windows 3X S NonPre-M 1
Mac System7 S NonPre-M 1
Windows 9X S M- 1
AmigaDOS S M- 1
Unix-like M M n
VMS M M n
NT/2000/XP M M n
OS390 M M n
Unix-Like OS Manufacturer Type
BSD Univ.California Berkeley BSD
SunOS (Solaris 1) Sun Microsystems BSD/Sys5
Solaris (2) Sun Microsystems Sys5/BSD
Ultrix DEC/Compaq BSD
OSF1/Digital Unix DEC/Compaq BSD/Sys5
HPUX Hewlett-Packard Sys5
AIX IBM Sys5/BSD
IRIX Silicon Graphics Sys5
GNU/Linux GPL Free Software Posix (SysV/BSD)
Unixware Novell Sys5
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Operating Systems
 Multi-programming (Processes/Threads) allows
logical concurrency: multi-user and
EventDriven systems, which yields
Client/Server architecture!
 User Interfaces
 Shell, CLI, GUI
 Logfiles, Audit trails, Policies:
accounting, security, reliability, performance
 Supervisor, Superuser, root user
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File Systems
Most OS’s are now multi-user and have
hierarchical file systems (Directories & Links)
 Unix or Windows File Hierarchy
 Directory structure related to function
 Link files – Symbolic (is a pointer or an alias to
another file) vs Hard Links (is a duplicate inode in a
filesystem)
 File Access Controls
 Owner, Group,Others method (permission bits)
 ACL method CS3063 (Sys & Net Admin)
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8. Unix File Hierarchy
 `/bin' Executable (binary) programs. On most systems
this is a separate directory to /usr/bin. In SunOS, this is a
pointer (link) to /usr/bin.
 `/etc' Miscellaneous programs and configuration les.
• This directory has become very messy over the history of UNIX and has
become a dumping ground for almost anything.
• Recent versions of unix have begun to tidy up this directory by creating
subdirectories `/etc/mail', `/etc/services' etc!
 `/usr' - This contains the main meat of UNIX.
 This is where application software lives, together with all of the
basic libraries used by the OS.
 `/usr/bin‘ - More executables from the OS.

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9. Unix File Hierarchy (Cont…)
 `/usr/local‘ This is where users' custom software is normally
added.
 `/sbin' A special area for statically linked system binaries.
 They are placed here to distinguish commands used solely by the system
administrator from user commands and so that they lie on the system root
partition where they are guaranteed to be accessible during booting.
 `/sys' This holds the con guration data which go to build the
system kernel.
 `/export‘ Network servers only use this. This contains the disk
space set aside for client machines which do not have their own
disks. It is like a `virtual disk' for diskless clients.
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10. Unix File Hierarchy (Cont…)
 `/dev, /devices‘ - A place where all the `logical devices' are
collected.
 These are called `device nodes' in unix and are created by mknod.
 Logical devices are UNIX's logicial entry points for writing to devices.
 `/home‘ - (Called /users on some systems.) Each user has a
separate login directory where les can be kept.
 These are normally stored under /home by some convention decided by the
system administrator.
 `/var' - System 5 and mixed systems have a separate directory
for spooling.
 Under old BSD systems, /usr/spool contains spool queues and system data.
/var/spool and /var/adm etc are used for holding queues and system log les.
 `/vmunix' - This is the program code for the unix kernel (see below).
On HPUX systems with le is called `hp-ux'. On linux it is called `linux'.
 `/kernel' - On newer systems the kernel is built up from a number of
modules which are placed in this directory.
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File Permission checking
 User OPEN(“filename”,mode) system call
mode = Create, Read, Write, Append, etc..
 System searches directory: locates “filename”
 Compares users name (UID) of program with
Owner of file. If not same, repeat for Group
(GID). Else use Other.
 Compares “mode” with files permBits: Error if
“mode” exceeds files allowed permissions.
eg. When mode=Read and permBits=rwx,-,- (700)
and UID not = Owner
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Access Control List checking
 Instead of permBits, directory entries for files
have ACLs
 ACLs are of the form:
user1:permBits, user2:permBits, …
Both user and permBits may be wildcards
 ACLs may be inherited from parent directory
 Checking involves a search of the list to
match the name of the user running the
program with the user in the ACL

13. 15/11/2023
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Network File Systems
For sharing file systems between hosts.
Methods include:
 Drive redirection
 NET USE in DOS/Windows
 MAP in Novell
 Directory redirection
 Mount in UNIX
 Share & Subscribe, Export & Mount
 Configured mount or Automount
 Distributed Directory systems

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Network File Systems
 Windows
 LAN Mgr, Workgroups (SMB),
 Unix NFS (originally by SUN)
 DFS (part of OSI DCE)
 Common Internet File System (CIFS) “Samba”
 Andrew File System
 Netware NDS by Novell
 Windows Advanced File System

15. Multi-Programming

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Processes
 Each process is a collection of resources:
instance of a running program in RAM, current
directory, open files with current position, User
and Group ID, limits, etc…
 Processes are “time-sliced” by OS Scheduler
 A process may also contain concurrent paths
of execution called Threads
 To see process hierarchy
Unix: ps –ef or tops
Windows: TaskManager

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Processes
Unix Process Hierarchy
 New processes are copy of existing ones
 “Parent” process may wait for “child”
processes to exit before proceeding
(synchronous model)
 When “parent” does not wait, “child” is said
to be “running in the background”
(asynchronous model)
 Processes send termination status message

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Process Environment
 Chains of processes share environment
 Environment may be implied or explicit
 Environment Variables are text strings
 Variables usually set by user or script
 Environment is inherited by new processes.
This is how command parameters are passed
from parent to child.
But changes to local environment are not passed
back to parent process

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Things of Special interest
to SysAdmins
 Logs and Audit Trails
 A detailed list of actions recorded by OS
 File system Logs used to reinstate data
 Usage Logs used for billing
 Auditing used for security
• Trace source of activity
• Provide non-repudiation

20. 15/11/2023
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Things of Special interest
to SysAdmins
 Privileged Accounts
 A user with power to configure/maintain
• root, Administrator, SysOp, etc..
 Can access or do anything !!
 Is actually very dangerous
 Should not be used as everyday login. . . .
use only when required
 Trusted host concept in TCP/IP can now be easily
circumvented because everyone has superuser
access on their own PC !!

21. 15/11/2023
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Things of Special interest
to SysAdmins
 Knowing how to care for your hardware
 Read the instructions!
 Understand interfaces & connectors
 Know capabilities and limitations of devices
• Speeds
• Capacities
• Compatibilities
 Know how to handle components
• Avoid damage due to Static Discharge
• Packaging and transport
• Assembly

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Things of Special interest
to SysAdmins
 Types of disk drives
 ATA-IDE
 SCSI
 Serial ATA
 Types of Memory devices
 Fast Page,EDO, SDRAM, ECC, etc…
 BIOS and NVRAM settings

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Things of Special interest
to SysAdmins
 Easy Systems Integration
 System built from identical parts
 Applies to hardware and software

24. IT System Components
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