Computer Science 447/647

Review for Exam II

Chapter 8 – Storage

SCSI is the standard for hard disks on UNIX servers (SATA on PCs)

Each SCSI has a device or target number between 0 and 7 or 15.

The SCSI controller counts as a device and is usually target 7

The SCSI bus needs to be terminated

Variations on SCSI:

Wide – more than one byte transferred at a time

Differential – uses two pins per signal (more noise resistant)

Disk Geometry

Disks are made up of one or more platters

Each platter has two surfaces

Each surface is broken down into tracks

Tracks are broken down into sectors (512 or 1024 bytes)

All tracks the same distances from the center are known as a cylinder

Large disks can be broken down into smaller partitions.

mkfs is used to create UNIX filesystems

It’s good to store a file’s data and inodes as close together as possible

The mount command tells UNIX to start using a new filesystem

Seek – moves the actuator arm to reposition the heads

Factors to look at when comparing disks:

Formatted capacity

Average access time = average seek + rotational latency

MTBF (Mean Time between Failure) the larger the better

Chapter 9 – Periodic Processes

Cron is used to schedule periodic processes

The command to setup cron jobs is crontab

Automate as many maintenance tasks as possible

Chapter 10 – Backups

Dump and restore are used to backup filesystems

tar, cpio and dd can also be used to backup files

Incremental backups only dump files that have changed since the last backup

Arrange things so all your incremental backups fit on one tape

Backups should be administered from a central location

Try to automate as much of your backup procedure as possible

Chapter 11 – Syslog and Log Files

Syslog is the system event logger: configured by syslog.conf

Chapter 12 – Software Installation and Management

Install software package using dpkg and apt-get

Minimize local compiles; Find packages whenever possible

Chapter 13 – Drivers and the Kernel

Reasons for reconfiguring the kernel

Installing a new system

Adding device drivers

Tuning table sizes

Adding or removing kernel capabilities

Loadable Kernel Modules – allow device drivers to be added

and removed from the kernel while it is running

Chapter 14 – TCP/IP

IP – Internet Protocol

ICMP – Internet Control Message Protocol

TCP – Transmission Control Protocol (guarantees delivery)

UDP – User Datagram Protocol (faster)

ARP – Address resolution protocol

NAT – Network Address Translation – Private addresses

PPP – Point-to-Point Protocol – IP on serial lines

DHCP – Dynamic Host Configuration Protocol

Each network layer adds a header to the outgoing packet

Topology: how your networks are connected

Addressing: Class A: 1-126 n.h.h.h

Class B: 128-191 n.n.h.h

Class C: 192-223 n.n.n.h

*Subnetting is used to break a network into smaller networks

*Repeaters, bridges, routers, and gateways are used to connect networks together

Chapter 15 – Routing

Routing is the process of directing packets between the source and destination.

netstat –nr is used to display the routing tables

Chapter 16 – Network Hardware

Main Ethernet flavors: 10BaseT, 100BaseT, 1000BaseT

Other: DSL

Ethernet uses the CSMA/CD Protocol

Carrier Sense – Multiple Access / Collision Detection

Collision - when two systems talk at the same time – each wait a random time and retry

Wire to use: Category 5e or 6 for 100BaseT & 1 Gig – Category 6a for 10Gig

When wiring a building:

Use high quality wire and network products

Run more wires than you think you will need

Plan for future expansion

It’s cheaper to do it once than to have to add wires later

The cost of materials is typically on 5-10% of the total cost

Chapter 17 – The Domain Name System DNS

Provides a hierarchical namespace – can use the same hostname in multiple domains

Distributed database for hostnames, IP Addresses and mail routing information

Second level domains need to be registered with the appropriate authority

Sites can create sub-domains beneath a registered domain

BIND is the DNS package on UNIX, contains both client and server

Client is the resolver – library – configuration file is /etc/resolv.conf

Server is called named – configuration file is /etc/named.boot

Main records in the DNS database: SOA NS A PTR MX CNAME

Test will have a DNS configuration and ask questions about it [page 622]

Types of servers: master, slave and caching

nslookup and dig are used to debug DNS

Chapter 18 – The Network File System NFS

NFS allows you to share filesystems between computers

Filesystems to export are listed in /etc/exports

Disk writes using NFS are significantly slower

Client must wait for writes to complete since NFS is stateless

automount is used to automatically mount NFS filesystems

Chapter 19 – Sharing System Files

Two schemes: copying files around or central database

rdist and rsync can be used to push system files

wget and rsync can be used to pull system files

Pull is more secure than push

LDAP – Lightweight Directory Access Protocol

NIS provides a central administrative database

NIS is not secure

IP Address Review

128.138.243.100