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Mitesh Shah

Linux Enthusiast
System Administrator

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Overview

1. Network Configuration

  • Most networks use TCP/IP as the basic protocols for network communications. Regardless of the operating system you use.
  • Certain TCP/IP settings always need to be configured for your system to communicate with other systems.

Important Network Settings

  • Device Activation
  • IP Configuration
  • Default Gateway
  • DNS Configuration

Basics Of Network Setting

  • Network Interface Card’s IP Address
  • Subnet Mask
  • Network Number

  • In general these settings and more will be provided automatically by your network’s Dynamic Host Configuration Protocol (DHCP) Server.
  • Even when manual configuration is required, often the IP Address, which is used to identify your host, is the only one of these that needs to be set explicitly.

  • If you are not using DHCP Server, you will also need to specify:
  • Default Gateway
  • DNS Server

  • The Default Gateway is the IP Address of the Device or System to which Communications Destinated for Hosts on another Network.
  • It is the job of the gateway to see that such messages reach their intended destinations.

  • The DNS Server is used to translate Domain Names like google.com to IP Addresses like 216.58.196.110

Managing Ethernet Connections

  • Network interfaces are named sequentially: eth0, eth1, wlan0
  • Multiple addresses can be assigned to a device with aliases
  • Aliases are labeled: eth0:1, eth0:2, etc
  • Aliases are treated like separate interface

  • Every system has a special network interface called lo (LocalHost or LoopBack) with 127.0.0.1 IP Address.
Network Interface Configuration
ifconfig [interface]

NOTE!: By Default, ifconfig command print the information about all active interfaces.
If the interface name is passed as an argument, ifconfig command print the information about that interface only.


Example:

[mitesh@Matrix ~]$ ifconfig eth0
eth0	Link encap:Ethernet  HWaddr 00:09:6B:CD:2B:87
inet addr:192.168.0.254  Bcast:192.168.0.255  Mask:255.255.255.0
inet6 addr:fe80::209:6bff:fecd:2b87/64  Scope:Link
UP BROADCAST RUNNING MULTICAST   MTU:1500  Metric:1
RX packets:851525 errors:0 dropped:0 overruns:0 frame:0
TX packets:1132322 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:211140434 (201.3 MiB)  TX bytes:1113058956 (1.0 GiB)
Enable/Disable Network Interface
ifup ethX;	ifconfig ethX up
ifdown ethX;	ifconfig ethX down
Graphical Network Configuration:

System -> Preferences -> Network Connections

  • Add, Edit, Delete Network Interface
  • Assign IP Addresses/DHCP
  • Modify Gateway Address
  • Modify DNS Setting

NOTE!: The system-config-network also provides all the features listed above.


Network Configuration File

Ethernet Devices
  • Whether or not you use system-config-network to configure your network interfaces, All the Network Interface settings are stored in /etc/sysconfig/network-scripts/ directory.
  • The Network Interface Configuration is stored in a Text Files /etc/sysconfig/network-scripts/ifcfg-ethX

NOTE!: These files are read by system-config-network, ifup, ifdown and other tools that bring the Network Interface up and down.


Example:

/-------------------------------------------------------------------------------\
|	Dynamic Configuration		|	Static Configuration		|
|--------------------------------------------------------------------------------
|										|
|	DEVICE=ethX			|	DEVICE=ethX			|
|	HWADDR=00:09:6B:CD:2B:87	|	HWADDR=00:09:6B:CD:2B:87	|
|	BOOTPROTO=dhcp			|	IPADDR=192.168.0.123		|
|	ONBOOT=yes			|	NETMASK=255.255.255.0		|
|	TYPE=Ethernet			|	GATEWAY=192.168.0.254		|
|					|	ONBOOT=yes			|
|					|	TYPE=Ethernet			|
\-------------------------------------------------------------------------------/

NOTE!: The Network Interface file is just a collection of bash variables that define the interface’s setting. Remember the syntax of bash variable is VARIABLE=VALUE, with no spaces on either side of the =.


Network Interface Configuration

/-----------------------------------------------------------------------------------------------------------------------\
|	Setting		|	Meaning											|
|------------------------------------------------------------------------------------------------------------------------
|															|
|	DEVICE		|	Specify the Network Interface Name or Alias (Example eth0)				|
|															|
|	HWADDR		|	Hardwaare(MAC) Address.									|
|			|	This setting is optional & can cause problems,						|
|			|	when ethernet card is replaced								|
|															|
|	BOOTPROTO	|	Where IP Settings should be retrieved from.						|
|			|	Set to dhcp to use DHCP.								|
|			|	Leave the variable unset or set it to static for manual IP Settings.			|
|															|
|	IPADDR &	|	Basic IP Settings.									|
|	NETMASK		|	Only necessary when not using the DHCP Server.						|
|															|
|	GATEWAY		|	Only necessary when not using the DHCP Server.						|
|			|	The Gateway can also be set in /etc/sysconfig/network file.				|
|			|	If the Gateway is defined in the /etc/sysconfig/network and ifcfg file,			|
|			|	The Gateway defined in the most recently activated ifcfg file is used.			|
|															|
|	ONBOOT		|	Whether to bring the network interface up automatically when the system boots.		|
|			|	Set to yes or no. The default value is no.						|
|															|
|	USERCTL		|	Whether to allow non-root users to bring this interface up & down.			|
|			|	Set to yes or no. The default value is no.						|
|															|
|	TYPE		|	Specify the type of network interface.							|
|															|
\-----------------------------------------------------------------------------------------------------------------------/

Global Network Setting

  • Some Network Settings are defined globally, rather than on a per-interface basis.
  • The Global Network Settings are defined in the /etc/sysconfig/network

  • Many may be provided by DHCP Server.
  • GATEWAY can be overridden in ifcfg file.

Examples:

[mitesh@Matrix ~]$ cat /etc/sysconfig/network
NETWORKING=yes
HOSTNAME=server1.example.com
GATEWAY=192.168.2.254

NOTE!: If the Gateway is defined in the /etc/sysconfig/network and ifcfg file, The Gateway defined in the most recently activated ifcfg file is used.


DNS Configuration

  • Domain Name Service Translate Hostname to IP Address.
  • The DNS Server address is specified by DHCP or in /etc/resolv.conf
[mitesh@Matrix ~]$ cat /etc/resolv.conf
search example.com cracker.org
nameserver 192.168.0.254
nameserver 192.168.1.254
Explain DNS
  • When we type www.google.com into web browser, it initiates a DNS Lookup, in which it ask Local DNS Server what IP Address is assigned to that name.
  • If Local DNS Server does not know, it will try to find out which other DNS Server on the internet know about the google.com and will forward my request to one of them.
Local DNS Server
  • Local DNS Configuration is performed using the /etc/resolv.conf
  • Remember two things while creating or modifying /etc/resolv.conf file

search

  • The search specifies the Domain Name when incomplete DNS Name is give to the command.

  • If /etc/resolv.conf file contains the line: search example.com cracker.org
  • Now when we try to run following command ping server1
  • In this case system automatically convert server1 into server1.example.com
  • If the server1.example.com is not found then system try server1.cracker.org

nameserver

  • The nameserver is most important, as it specify the IP Address of the DNS Server that your system should use.
  • Multiple nameserver are added but remember that nameserver are tried in order, So be sure to put the fastest and available namesserver at first place.

2. Printing in Linux

  • Printing on Linux system is handled by the Common Unix Printing System (CUPS).
  • Printers May Be
    • Local (serial, parallel or usb)
    • Networked

Supported printer connections

  • Local (serial, parallel or usb)
  • Unix/Linux print server
  • Netware print server
  • Windows print server
  • HP JetDirect
  • IPP - Internet Printing Protocol

Queues

  • Print request are sent to the queues.
  • Different queues for the same printer may have different priority or output options.
  • Queued jobs are sent to the printer on a First Come First Served basis.

Jobs

  • Once a file has been sent to a queue for printing, it is called a job.
  • Jobs may be canceled before or during printing.

system-config-printer

  • A Graphical Configuration Tool is used to adding new printers to your systems.
  • To run this tools Select System -> Administration -> Printing OR Run the system-config-printer on the terminal

Printing Commands

lpr command
  • lpr Send job to the printer
  • Accepts ASCII, PDF, PostScript and other Formats
  • Most applications under Linux output PostScript Formats

Options

  • -P: Select the specific printer.
  • -#: Set the number of copies to print from 1 to 100.

Examples:

[mitesh@Matrix ~]$ lpr reports.txt

# Print 5 copies of the file reports.txt on the accounting printer
[mitesh@Matrix ~]$ lpr -P accounting -#5 reports.txt
lpq command
  • lpq Show printer queue status.

Options

  • -P: Select the specific printer.

Example:

[mitesh@Matrix ~]$ lpq

Printer:	ps@localhost
Queue:		no printable jobs in queue
Server:		no server active
Status:		job  'jay@localhost+916'  removed at 12:16:03.083
Rank	Owner/ID		Class	Job	Files		Size	Time
done	jay@localhost+185	  A	185	results		2067	08:38:04
lprm command
  • lprm: Removes a job from the print queue.

Options

  • -P: Select the specific printer.

Examples:

[mitesh@Matrix ~]$ lprm 916
Printer ps@localhost:
  • In this example, lprm responds with the name of the queue from which the job was removed.

NOTE!: A user may only remove his own jobs from the queue.


lpstat command
  • lpstat: Prints cups status information.

Options

  • -a: List Configured Printers.

Printing Utilities

  • evince: Views PDF Documents
  • ps2pdf: Converts PostScript to PDF
  • pdf2ps: Converts PDF to PostScript. Which makes it easy to print PDF Documents right from the command line.
  • pdftotext: Converts PDF to Plain Text
  • enscript, a2ps: Converts Text to PostScript
  • mpage: Prints multiple pages per sheet

Managing Printers With CUPS

  • Daemons: cups
  • Services: chkconfig cups on | off & service cups status | start | stop | restart

Configuration Files

  • /etc/cups/cupsd.conf
  • /etc/cups/printers.conf

Configuration Tools

  • CLI: lpr lpq lprm lpstat lpadmin lpinfo
  • GUI: system-config-printer System -> Administration -> Printing
  • Web Based: http://localhost:631

3. System’s Date and Time

GUI Method

  • system-config-date System -> Administration -> Date & Time

  • Can set Date/Time Manually or use NTP
  • Additional NTP Servers can be added
  • Can use Local Time or UTC

CLI Method

  • date [MMDDhhmm[[CC]YY][.ss]]

Examples:

[root@Matrix ~]# date 01011010		# 1st  Jan, at 10:10am.
[root@Matrix ~]# date 01010101.01	# 1st  Jan, at 01:01:01 am.
[root@Matrix ~]# date 12312359		# 31st Dec, at 11:59pm.
[root@Matrix ~]# date 123123592007	# 31st Dec 2007, at 11:59pm.
[root@Matrix ~]# date 123123592007.05	# 31st Dec 2007, at 11:59:05pm.

4. Shell Scripting

  • Taking Input With Positional Parameters:
  • Many commands and scripts can perform different tasks depending on the arguments supplied to the program.
  • Positional Parameters are special variables that hold the command-line arguments to the script.
  • The available Positional Parameters are: $0, $1, $2, $3, $4, $5, $6, $7, $8, $9, ${10}, ${11}…

NOTE!: $0 Specify the program name
$* Holds all command-line arguments
$# Holds the number of command-line arguments


Examples:

#!/bin/bash
# positionaltester
# Demonstrates the use of positional parameters

echo "The program name is $0"
printf "The first argument is %s and the second is %s\n" $1 $2
echo -e "All command line parameters are $*\n"
echo -e "Total number of command line parameters are $#\n"
[mitesh@Matrix ~]$ ./positionaltester Red Hat Enterprise Linux
The program name is ./positionaltester
The first argument is Red and the second is Hat
All command line parameters are Red Hat Enterprise Linux

Total number of command line parameters are 4

read command

  • Taking Input With Read Command
  • The read commands takes a line from the STDIN and breaks it down into individual words. (Usaually a word is defined as a character string surrounded by white space such as spaces and tabs).

  • The way the shell interprets words may be changed by setting the IFS variable.

NOTE! IFS=’:’ will tells the shell that words are separated by colons instead of white space).


  • The 1st word is assigned to the 1st variable The 2nd word is assigned to the 2nd variable and so on.

  • If there are more words than variables, All the remaining words are assigned to the last variable.

Options

  • -p: Designates prompt to display.

Examples:

#!/bin/bash
echo -n "Enter name ( first last ): "
read FIRST LAST
echo "Your first name is $FIRST and your last name is $LAST"

#!/bin/bash
read -p "Enter name ( first last ): " FIRST LAST
echo "Your first name is $FIRST and your last name is $LAST"

#!/bin/bash
read -p "Enter several values: " value1 value2 value3
echo "value1 is $value1"
echo "value2 is $value2"
echo "value3 is $value3"




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