1. Chapter 7: Using Network Clients
The Complete Guide To Linux System Administration

2. Objectives Log in to a Linux system over a network connection
Use command-line tools for common network services such as FTP and the Web
Perform simple network diagnostic checks
The Complete Guide to Linux System Administration

3. Remote Login Networking integrated into kernel Server Client
Easily log in across network
Perform virtually same work as if you were seated in front of Linux system
Server
Program running on Linux system listens for connections over network
Serves up information to another program
Client
Program making requests
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4. Remote Login (continued)
telnet
Most basic remote login capability
Set up by default on Red Hat Linux
Completely unprotected
r-utilities
Designed to access remote computers in order to:
Run programs
Transfer files
Perform other functions within trusted network environment
Designed for convenience, not security
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5. Remote Login (continued)
The Complete Guide to Linux System Administration

6. Remote Login (continued)
Secure shell (SSH)
Similar to telnet
Uses encryption so that everything transmitted over network is unreadable to other users
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7. The Telnet Remote Login Utility
Terminal emulation program
Log in to remote computer as if you were sitting at computer’s keyboard
Must have:
telnet client
telnet server
Command
telnet paris.mydomain.org
$ telnet paris .mydomain.org
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8. The Telnet Remote Login Utility (continued)
telnet session
Login
Execute commands on remote computer
telnet designed for text only
telnet program included with most versions of windows
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9. The Telnet Remote Login Utility (continued)
The Complete Guide to Linux System Administration

10. The telnet Remote Login Utility (continued)
To use telnet, need to know:
Remote host
For this field you can enter a host name such as
paris. mydomain. org or an IP address such as
Port number
By default, the Telnet port-23-is used.
Type of terminal to emulate
A standard choice is a VT100 terminal. Hundreds of terminal models exist, but VT100 is the mostwidely supported.
User name and password
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11. Using r-Utilities for Remote Execution
Not used much anymore
Useful for working with multiple computers in trusted network
Most effective when you can set up configuration file on multiple computers
/etc/hosts.equiv file
Contains hosts and user names permitted to access system using r-utilities
The Complete Guide to Linux System Administration

12. Using r-Utilities for Remote Execution (continued)
The Complete Guide to Linux System Administration

13. Using r-utilities for Remote Execution (continued)
rhosts file
List of hosts and user names that you want to permit to access account without password
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14. Secure Shell (SSH) Encrypted version of telnet
Data encoded so that only authorized recipient can read it
Can also act as complete networking toolkit
SSH consists of:
Client utility―ssh or slogin
Server program―sshd
Copy utility- sep
which acts like rep, letting you copy files between any two computers on your network with full encryption.
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15. Secure Shell (SSH) (continued)
SSH package also includes utilities
Openssh
Free version of SSH
Installed by default on many Linux systems
SSH can authenticate a connection using:
r-utilities files
User passwords
Public key encryption (preferred method)
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16. Secure Shell (SSH) (continued)
Public key encryption
Method of encrypting information
Establishes secure connection without sending key over network connection
In a way that compromises security of connection
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17. Data Services Tools for accessing Other network-based data services
Web
Other network-based data services
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18. Accessing the Web Lynx Text-based browser
Access Web sites when working on system that doesn’t have graphical interface
Very fast
Can be run from any command-line window
To start Lynx, enter lynx on any command line, followed by a Web page address
$ lynx or
$ lynx
Can download pages automatically using -dump option
The Complete Guide to Linux System Administration

19. This causes Lynx to act as a command-line utility, printing the HTML code from the page to STDOUT instead of displaying it as a formatted page.
For example, the following command saves the indicated page in the file nasa_home_page.htrnl:
$ lynx ·dump / index.html > nasa home page.html
You can combine the -dump Lynx option with other commands such as grep to search the contents of Web pages or compare versions of a Web page to see if updates have been made.
The Complete Guide to Linux System Administration

20. Accessing the Web (continued)
The Complete Guide to Linux System Administration

21. Accessing the Web (continued)
wget command
Download Web pages
Designed specifically for command-line downloading of Web pages
Example:
$ wget http: // .org/philosophy/ philosophy.html
Download recursively
Download Web page you indicate
Plus all pages referred to on page
Plus all pages linked to from those pages
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22. Accessing the Web (continued)
Mirroring
Process of copying entire Web site or FTP site
Mirror entire Web site
wget -m -k -K -E http// -o /tmp/gnu_site_log &
kget graphical utility
Enter one or more urls
Have them downloaded to system in background while you do other work
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23. The - m option sets mirroring, which turns on recursive downloading;
the -k and -K options convert links for use on your local system;
the -E option forces an .html ending on
downloaded pages, which is useful when the server is providing pages using .asp or another
format less commonly used by Linux;
the -0 option defines a log file where progress and any errors generated by wget are written.
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24. The Complete Guide to Linux System Administration

25. Accessing the Web (continued)
The Complete Guide to Linux System Administration

26. Accessing the Web (continued)
rsync utility
Uses SSH to transport files between systems
After first time files are copied, checks remote files to see what changes need to be updated
consider this command, which updates the files on oslo
# rsyne -avz stoekholm:does/ /data/does
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27. Accessing FTP Servers File transfer protocol (FTP)
Standard method used to move files between computers on Internet
Most publicly visible FTP servers support anonymous access
Log in using user name anonymous or FTP
Enter address as password
Browser provides login information automatically in background
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28. Accessing FTP Servers (continued)
The Complete Guide to Linux System Administration

29. Accessing FTP Servers (continued)
User name and password access
Administrator of FTP server must permit this type of connection
Access url:
Web browser starts connection and prompts for password
Graphical FTP clients
IglooFTP pro
gFTP
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30. Accessing FTP Servers (continued)
FTP utility
Text-mode program
Example: ftp ftp.ibiblio.org
Prompt changes to ftp>
Can transfer files in text mode or binary mode
To download a file using ftp, use the get command;
to upload a file , use the put command.
ncftp program
has a cleaner user interface and can be easier to use.
Similar to ftp
Preferred by administrators
Package includes other utilities (ncftpget, ncftpput)
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31. Accessing FTP Servers (continued)
The Complete Guide to Linux System Administration

32. Accessing FTP Servers (continued)
The Complete Guide to Linux System Administration

33. Accessing FTP Servers (continued)
The Complete Guide to Linux System Administration

34. Networking and Network Diagnostic Tools
Solve basic networking problems
Understand basics of networking
Use a few standard utilities
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35. Introduction to Networking
Internet protocol (IP)
Core of networking in Linux
Sends packets of information across network
Ethernet
Most widely used type of networking hardware
Other network hardware
Token ring
Wireless 80211b
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36. Introduction to Networking (continued)
IP address
Allows computers to locate each other on network
Each computer that uses IP must have address
Represented as series of four numbers
Each from 0 to 255
Network mask helps system route packets correctly between multiple networks
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37. Introduction to Networking (continued)
Routing
Moving packets of information efficiently through networks to reach correct destination
Only necessary when you have multiple networks that need to communicate
Gateway or router
Computer attached to multiple networks used by computers on one network can reach other networks
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38. Introduction to Networking (continued)
Transmission control protocol (TCP) provides stable connection between two computers
Domain name
Used by humans to address computers
Must be converted to IP address
Domain name system (DNS) converts domain names to IP addresses
Dynamic host configuration protocol (DHCP) issues IP addresses on request
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39. Introduction to Networking (continued)
ifconfig command
View active networking interfaces
Usually two network interfaces on Linux client
Local interface
Ethernet interface
Can also use graphical tools to set up or alter network configuration
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40. Using ping for System Testing
ping utility
Sends diagnostic data packet to specified computer
Verifies network connectivity
Example: ping
Use series of ping commands to test networking
ping to hosts further and further away from your system
ping with a host name:
$ ping ftp.xmission.com
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41. Using ping for System Testing
Can also be used for malicious attacks
“Flood ping”
“Ping of death”
Many computers on internet do not respond to ping to prevent attacks
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42. Using traceroute to Examine Routing Patterns
traceroute command
Carefully tracks each router between you and destination host
Lets you see
Exactly where packets are going
How long each hop takes
Tries a maximum of 30 hops to reach destination
Can change this value
The Complete Guide to Linux System Administration

43. Using traceroute to Examine Routing Patterns (continued)
Useful tool for diagnosing problems such as
Where packet stops
Where packet slows down
My traceroute program
Graphical interface in Red Hat
You can start this program by entering the command xmtr. After you provide the name of the host you want to reach
The Complete Guide to Linux System Administration

44. Using traceroute to Examine Routing Patterns (continued)
The Complete Guide to Linux System Administration

45. Summary Well-known methods of accessing Linux systems remotely
telnet
r-utilities
SSH suite of utilities
Command-line utilities provided in Linux to download Web pages and access FTP sites
Networking in Linux is based on IP
The Complete Guide to Linux System Administration

46. Summary (continued) Computers communicate across multiple networks by:
Relying on routing information
Sending data packets through routers or gateways
DNS servers convert domain names to IP addresses
ifconfig utility displays network interfaces in Linux
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47. Summary (continued)
ping command sends test packet to network location to determine if location is reachable
traceroute command shows computers that data packet traverses between your system and system you want to reach
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