Transcript IT System Components - Pravin Shetty > Resume

Week 1: IT System Components
Operating Systems
File Systems
Processes and Job Control
Devices and Controllers
Readings
Burgess, Chapter 2
Mikalsen, Chapter 1
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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
MS/PC DOS
Windows 3X
Mac System7
Windows 9X
AmigaDOS
MTS
Unix-like
VMS
NT/2000/XP
Users
S
S
S
S
S
M
M
M
S/M
Tasks
S
NonPre-M
NonPre-M
MMM
M
M
M
CPUs
1
1
1
1
1
1
n
Unix-Like OS
Manufacturer
Type
1
BSD
Univ.California Berkeley
BSD
Sun Microsystems
BSD/Sys5
n SunOS (Solaris 1)
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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Comparing UNIX & Windows
• Compare Shell Commands
– See Table 2.1 in Burgess (Pg22)
• Compare Directory/File structure
– See Table 2.2 in Burgess (Pg23)
• Compare Software concepts
– See Table 2.3 in Burgess (Pg24)
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Comparing UNIX & Windows
UNIX-like OS
chmod
chown
chgrp
emacs
kill
ifconfig
lpq
lpr
mkfs/newfs
mount
netstat
nslookup
ps
route
setenv
su
tar
traceroute
Windows
CACLS
CACLS
No direct equivalent
Wordpad or emacs (in GNU tools)
kill (in resource kit)
ipconfig
lpq
lpr
format & label
net use
netstat
nslookup
pstat (in resource kit)
route
set
su (in resource kit)
tar (in Cygwin tools)
tracert
Table 2.1
Comparison of UNIX and
Windows Shell commands
Burgess Pg 22
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Comparing UNIX & Windows
UNIX-like OS
/usr
/bin or /usr/bin
/dev
/etc
/etc/fstab
/etc/group
/etc/passwd
/etc/resolv.conf
/tmp
/var/spool
Windows
%SystemRoot% usually points to C:\WINNT
%SystemRoot%\System32
%SystemRoot%\System32\Drivers
%SystemRoot%\System32\Config
No equivalent
%SystemRoot%\System32\Config\SAM* (binary)
%SystemRoot%\%\System32\Config\SAM* (binary)
%SystemRoot%\System32\DNS\*
C:\Temp
%SystemRoot%\System32\Spool
Table 2.2: Comparison of Unix and Windows directories and files, Burgess Pg 23
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Comparing UNIX & Windows
Unix-like OS
Standard libraries
Unix libraries
Symbolic/hard Links
Processes
Threads
Long filenames
Mount disk on directory
endl is LF
UID (User ID)
groups
ACLS (non standard)
Permission bits
Shared libraries
Environment variables
Daemons/services/init
Windows
WIN32 API
Posix compatibility library
Hard links (short cuts)
Processes
Threads
Long filenames on NTFS
Mount drive A: B: etc
endl is CR LF
SID (Subject ID)
groups
ACLs
(Only in ACLs or with Cygwin)
DLL's
Environment variables
Service control manager
Table 2.3 Comparison of UNIX and Windows software Concepts (Pg 24)
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Comparing UNIX & Windows
Unix-like OS
DNS/DHCP/bootp (free)
X windows
Various window managers
System Admin GUI (non-standard)
cfengine
Any client-server model
rsh
Free Software
Perl
Scripts
Shells
Primitive security
Dot files for configuration
Pipes with comm1 I comm2
Configuration by text/ascii files
Windows
DNS/DHCP (NT server)
X windows
Windows GUI
System Adrnin GUI (Standard)
cfengine as of 1.5.0
Central server model
limited implementation in server
Some free software
Perl + WIN32 module
Scripts
DOS Command window
Primitive security
System registry
Combinations comm1 l comm2
Config by binary database
Table 2.3 Comparison of UNIX and Windows software Concepts (Pg 24)
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File Systems
•
•
•
•
•
Most OS’s now have hierarchical file systems (Directories
and Links)
Unix File Hierarchy
File Names
File structure related to function
Link files
File Access Control
– Owner, Group, Other method (permission list)
– ACL method – user1 rwx, user2 rwx,…
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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,… (with wildcards!)
• ACLs may be inherited from parent directory
• Checking involves a search of the file’s ACL to match the
name of the user/group running the program, with the
user/group in the ACL
• If matched, the permission settings from the list are applied
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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 Manager, 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
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Multiprogramming…
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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, space and time limits,
etc…
• Processes are “time-sliced” by OS scheduler
– Various policies and queues of waiting processes
• A process may also contain concurrent paths of execution
called Threads
• To see process hierarchy
Unix:
Windows:
ps – ef or tops
taskmanager
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Processes
• Unix Process Hierarchy
– New processes are replicas 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”
– Processes may send termination status message to parent
process
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Processes
Windows/NT Process model
– Very similar to the Novell NLM model
– Background processes are detached
from foreground session
– Background jobs continue after logout
– Any console user may shutdown
– Shutdown terminates all processes
– Easier to manage concurrent functions as threads
within an existing program (not different objects)
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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 made in local environment are not returned back to
parent process environment.
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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
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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 !!
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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
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IT System Components
(end)
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