System Configuration for TCP/IP networking

Spring 2012, Fordham UniversityXiaolan Zhang

Outline

Unix overview Unix and TCP/IP: where are network func.

implemented? Different variants of Unix Pointers to resources

Introduction to Unix system administration Key commands for knowing system being

used Packaging utility

Unix and TCP/IP

Berkeley's Unix was first Unix to include libraries supporting  Internet Protocol stacks: Berkeley sockets. Integrate sockets with Unix operating

system's file descriptors, it became almost as easy to read and write data across a network as it was to access a disk.

Reference: TCP/IP Illustrated, Volume 2: The Implementation, by Gary R. Wright, W. Richard Stevens

Recall: Socket

a host-local, application-created OS-controlled interface (a “door” or “mailbox”) into which application process

can both send and receive messages

to/from another application process (remote or local)

Application 2-4

process

TCP withbuffers,variables

socket

host orserver

process

TCP withbuffers,variables

socket

host orserver

Internet

controlledby OS

controlled byapp developer

Socket API: interface for C programming socket(): creates a new socket of a certain socket

type, identified by an integer number, and allocates system resources to it.

bind(): server side, and associates a socket with a socket address structure, i.e. a specified local port number and IP address.

listen(): server side, causes a bound TCP socket to enter listening state.

accept(): server side, accepts a received incoming attempt to create a new TCP connection from remote client, and creates a new socket associated with the socket address pair of this connection.

Socket API: interface for C programming connect(): (client side) assigns a free local port

number to a socket. In case of a TCP socket, it causes an attempt to establish a new TCP connection.

send() and recv(), or write() and read(), or sendto() and recvfrom(), used for sending and receiving data to/from a socket.

close() causes system to release resources allocated to a socket. In case of TCP, the connection is terminated.

…

closeconnectionSocket

read reply fromclientSocket

closeclientSocket

Client/server socket interaction: TCP

wait for incomingconnection requestconnectionSocket =welcomeSocket.accept()

create socket,port=x, forincoming request:welcomeSocket =

ServerSocket()

create socket,connect to hostid, port=xclientSocket =

Socket()

Server (running on hostid) Client

send request usingclientSocketread request from

connectionSocket

write reply toconnectionSocket

TCP connection setup

Application 2-7

two socketsat server

outT

oSer

ver

to network from network

inFr

omS

erve

r

inFr

omU

ser

keyboard monitor

Process

clientSocket

inputstream

inputstream

outputstream

TCPsocket

Clientprocess

client TCP socket

Stream jargon

Stream: a sequence of characters that flow into or out of a process

input stream is attached to some input source for the process, e.g., keyboard, socket, file, …

output stream is attached to an output source, e.g., monitor, socket, file, …

Key: stream interface provides an abstraction, i.e., no matter what’s the actual source/dest, reading from input stream/writing to output stream are same

Application 2-8

This course

TCP/IP network administration on Unix/Linux system

Where are Network Func. Implemented? Link layer: implemented in device drivers TCP/IP: implemented in kernel Application layer protocols implemented in

command (software) DNS: dig, nslookup DHCP ssh ftp HTTP:

Will learn how to install/configure all these!

Origin of Unix

Dennis Ritchie (standing) and Ken Thompson begin porting UNIX to the PDP-11 via two Teletype 33 terminals.

Unix Lineage

Linux kernel versions

Unix Kernel Kernel: part of Unix operating system

that remains running at all times when the system is up

kernel executable image named unix (System V-based), vmunix (BSD-

based system), or something similar stored in or linked to root directory

• AIX /unix (actually a link to a file in /usr/lib/boot)• FreeBSD /kernel• HP-UX /stand/vmunix• Linux /boot/vmlinuz• Solaris /kernel/genunix

Linux distribution built upon standard kernels but are

packaged and bundled differently. collection of packages and how packages

were compiled and ultimately delivered are what make Linux distributions unique

Examples Linux Mint, linuxmit.com Ubuntu, ubuntu.com Fedora, federaproject.org Debian, redhat, …

For more complete list of distributions:

http://distrowatch.com/http://lwn.net/Distributions/

for system-specific guide, go to specificWebsite:help.ubuntu.comredhat.com/docs, …

Outline

Unix overview Unix and TCP/IP: where are network func.

implemented? Different variants of Unix Pointers to resources

Key commands for knowing system being used

Introduction to Unix system administration installation: compiling, driver, package

Interface/Routing configuration

System Administrator Resource General (for all distributions)

http://tldp.org/LDP/sag/html/index.html And much more

Distribution specific resource https://help.ubuntu.com/community/

SystemAdministration => We will use this as our example

And much more Essentials:

Using terminal and command lie AddUsersHowTo FilePermissions (permission bits and Access Control List) BackupYourSystem Software Management

Useful Commands

Focus on underlying commands (command line to use in terminal window), instead of GUI interface More ubiquitious More complete functionalities

First, one needs to know what kernel or distribution is running In order to find out relevant online info, get

help, …

System info

What’s Unix/Linux kernel version?zhang@mocha:~$ uname -aLinux mocha 2.6.32-38-generic #83-Ubuntu

SMP Wed Jan 4 11:13:04 UTC 2012 i686 GNU/Linux

What Linux distribution is used? zhang@mocha:~$ lsb_release -r -i -c -dDistributor ID: UbuntuDescription: Ubuntu 10.04.4 LTSRelease: 10.04Codename: lucid

Which version of command is used ? Almost all commands have a –v optionzhang@mocha:~$ nmap –vStarting Nmap 5.00 ( http://nmap.org ) at 2012-03-21 13:40 EDTNSE: Loaded 0 scripts for scanning.Read data files from: /usr/share/nmapWARNING: No targets were specified, so 0 hosts scanned.Nmap done: 0 IP addresses (0 hosts up) scanned in 0.07 seconds

Finding stuffs: where is …? which: locate a command whereis: locate binary, source, and manual

page files for a command locate, find: find files by names

Installing software

Suppose you want to install program dig Google “How to install dig on Ubuntu?” A resource:

Luckily this is easy to install, just not terribly intuitive or easy to find as it’s not a package known as dig:sudo apt-get install dnsutils

Software (or command) and Package

Software, a program which you can run on your computer Programs often need other resources to work Thousands of files may be required (and put in

exact location) Packages : store everything that a

particular program needs to run a collection of files bundled into a single file,

which can be handled much more easily contained special files called installation

scripts, which copy files to where they are needed (amongst other things)

Source Package and binary package

Source packages just include source code, and can be used on any type of machine if code is compiled in the right way

Binary packages have been made specifically for one type of computer, or architecture, e.g., x86 (i386 or i686), AMD64 and PPC Generally, correct binary packages will be

used automatically, so you don't have to worry about picking right ones

Installing new software (1)

Software you want => relevant software package locate command => findutils package named (DNS server) => BIND package

Know your packaging utilities Ubunto: APT (Debian Advanced Package Tool)

• E.g., apt-get install wget

RedHat: YUM• E.g., yum install wget

Solaris:• Pktutil –-install wget

Advanced Packaging Tool (APT)  apt-get command is a powerful

command-line tool installation of new software packages upgrade of existing software packages updating of the package list index Upgrading entire Ubuntu system.

Install/Remove package

Install a Package: e.g., to install the network scanner nmap:sudo apt-get install nmap

Remove a Package:sudo apt-get remove nmap --purge options to apt-get remove will remove the

package configuration files as well.

Multiple Packages: You may specify multiple packages to be installed or removed, separated by spaces.

Update Package Index

APT package index is essentially a database of available packages from repositories defined in  /etc/apt/sources.list file

deb http://us.archive.ubuntu.com/ubuntu/ lucid main restricteddeb-src http://us.archive.ubuntu.com/ubuntu/ lucid main restricted

## Major bug fix updates produced after the final release of the## distribution.deb http://us.archive.ubuntu.com/ubuntu/ lucid-updates main restricteddeb-src http://us.archive.ubuntu.com/ubuntu/ lucid-updates main restricted

To update local package index with latest changes made in repositories sudo apt-get update

Upgrade Packages

To upgrade your system, first update your package index as outlined above, and then type:sudo apt-get upgrade

sudo

allows a permitted user to execute a command as superuser (root) or another user, as specified in sudoers file.   Typically, sudo requires that users

authenticate themselves with a password  Once a user has been authenticated, a

timestamp is updated and the user may then use sudo without a password for a short period of time (15 minutes unless overridden in sudoers).

Outline

Unix overview Unix and TCP/IP: where are network func.

implemented? Different variants of Unix Pointers to resources

Key commands for knowing system being used

Introduction to Unix system administration installation: compiling, driver, package

Linux boot in a nutshell

System startup

When a system is first booted, or is reset, processor executes code at a well-known location For PC, this location is in

basic input/output system (BIOS), which is stored in flash memory on motherboard

BIOS must determine which devices are candidates for boot.

BIOS/Boot loader

BIOS searches for devices that are both active and bootable in the order of preference A boot device can be a floppy disk, a CD-

ROM, a partition on a hard disk, a device on network, or a USB flash memory stick

When booted from a hard disk, where Master Boot Record (MBR) contains the primary boot loader After the MBR is loaded into RAM, the BIOS

yields control to it.

Primary Boot Loader MBR, a 512-byte sector, first

sector on disk (sector 1 of cylinder 0, head 0)• contains both executable code and

error message text• partition table contains a record for

each of four partitions (sixteen bytes each).

• magic number: a validation check of MBR.

The job: to find and load secondary boot loader (stage 2)• Using partition tables

Second-stage boot loader, or kernel loader

a splash screen is commonly displayed, and Checks system hardware Enumerates attached hardware devices Mounts root device, and loads the necessary

kernel modules. Linux and an optional initial RAM disk

(temporary root file system) are loaded into memory.

When images are loaded, second-stage boot loader passes control to kernel image and kernel is decompressed and initialized

GRUB

first- and second-stage boot loaders combined Linux Loader (LILO) GRand Unified Bootloader (GRUB) in the x86

PC environment.

GRUB a three-stage boot loader Stage 1 (MBR) boots a stage 1.5 boot loader

that understands particular file system containing Linux kernel image

When stage 1.5 boot loader is loaded and running, stage 2 boot loader can be loaded.

With stage 2 loaded, GRUB displays a list of available kernels (defined in /etc/grub.conf, with soft links from /etc/grub/menu.lst and /etc/grub.conf).

kernel image and initrd image are loaded into memory. With images ready, stage 2 boot loader invokes kernel image.

multibooting

One boot disk (which as one MBR) Choose one boot loader to be the

“master” Use GRUB for Intel-based Unix/Linux

system

Kernel

prepares itself Uncompress itself Initialize internal tables, creating in-memory

data structures Complete hardware diagnostics Install loadable drivers for various hardware

devices present on system. creates a process (PID 1) to run init program

Command dmesg: display a copy of console messages generated during last boot at this stage

init process

the parent of all processes in the system, it is executed by kernel and is responsible for starting all other processes (including daemons, network services) System V startup model (sysvinit), book

talked about this Upstart, used on mocha Systemd, used on storm, erdos

After this, boot is complete, and the system is up and running normally.

Startup Runlevels

Indicate state of system when init process is complete 0: shuts down all processes and halt system 1: single-user mode, for sys. Admin. To

perform maintenance 2: special multi-user mode, no support for

file sharing 3: full multi-user mode, NFS file sharing 4: unused 5: dedicated X windows terminal 6: shuts down all processes and reboots

Configuration file, /etc/inittab

To set the default runlevel you can edit following line in your /etc/inittab file: id:X:initdefault:

where X is the runlevel. So to automatically startup X11, you would replace X with 5. Or if you're at the lilo prompt, you can enter linux X (where X again is the runlevel).

During the init process, the /etc/rc.sysinit file is run which in turn goes into the default runlevel from the /etc/inittab file.

Configuration file, /etc/inittab

Every runlevel runs available scripts in appropriate runlevel directory found in /etc/rcX.d where X is the runlevel.

If you're entering runlevel 3, scripts in /etc/rc3.d are executed. These files are symbolic links to main scripts located in /etc/init.d directory.

E.g., under /etc/init.3 K20nfs -> ../init.d/nfs S10network -> ../init.d/network S55sshd -> ../init.d/sshd

Upstart event-based replacement for

/sbin/init daemon which handles starting of tasks and services during boot, stopping them during shutdown and supervising them while the system is running. originally developed for Ubuntu but is

intended to be suitable for deployment in all Linux distributions as a replacement for venerable System-V init.

systemd system and service manager for Linux,

compatible with SysV and LSB init scripts. aggressive parallelization capabilities uses socket and D-Bus activation for starting

services offers on-demand starting of daemons keeps track of processes using Linux cgroups, supports snapshotting and restoring of the system

state maintains mount and automount points …

It can work as a drop-in replacement for sysvinit. 

Homework

Download and install Ubuntu http://www.ubuntu.com/download/ubuntu/downloadPlease use same release as mocha: Distributor ID: UbuntuDescription: Ubuntu 10.04.4 LTSRelease: 10.04Codename: lucid