NT1430 Linux Networking: Study Guide
Wed 21-November-2012

Linux Commands: Know these commands and what they do: • Directory and list commands o ls, ls –l o pwd o cd / o cd and cd~ (hint: both take you to your home directory) o cd .. (takes you up one directory • Know what cp and mv do and how to use them • File viewing commands: o cat o less and more (one page at atime) o vi and view o tail (shows the last 10 lines of a file) o head (shows the top 10 lines) • chmod for changing permissions on files and directories • know the differences in read write and execute for owner group and all • > to redirect output to a file (overwrites if file exists) • >> appends to a file • & puts a process in the background while fg brings it to the foreground. • ps –ef | grep programname locates a running process for you • grep is a program that searches for a string within a directory or command output • The pipe symbol ( | ) sends output from one command to the input of another. • Know what a Linux shell script is.

Direcories and file systems • / is the root of the entire file system • /usr stores program files • /home stores user home directories • /etc stores Linux configuration files • /var stores various miscellaneous files • /proc is a virtual directory that stores system performance metrics. It does not exist on disk and disappears when the system is turned off. • /tmp stores temporary files that disappear on system shutdown or reboot • The file /etc/fstab links physical disk partitions to the filesystem directories • The mount command links a new disk location to a new directory. • NFS (Network File System) allows you to share directories and files with other Linux systems. • The configuration for NFS is stored in /etc/exports

Runlevels • Know what each run level 0-6 does and how to change levels with the telinit command • Understand the differences between text based and graphical interfaces • Understand the difference between single user and multi user modes

DHCP: (Dynamic Host Configuration Protocol) • Client-server architecture • Assigns a lease on an IP address • Can be used to assign a staic IP • Assigns other network settings o Netmask o Broadcast address o Subnet mask o DNS Server • Example configuration file (/etc/dhcp/dhcp.conf on page 492
Installing software • Rpm installs individual packages; but does not check for prerequisites o Install with –i option ▪ rpm –i nano.1.3.rpm o Update with the –U option ▪ rpm –U nano.1.3 • Yum installs packages and all prerequisite packages o yum install package name ▪ example: yum install nano o yum update package name ▪ example yum update nano

CUPS (Common UNIX Printing System) (562-574) • Combines many differing printing protocols to make a very strong cross-platform printing system • Supports both the BSD Line Printer Daemon (LPD) and the System V Line Printer System (LPR) • Allows printing using the internet protocols (IPP) • Can print to windows using Samba (SMB) • Can be configured with a graphical GUI Applet, command line syntax, or a wb based interface. • If you cannot print from your Linux system, the first thing you should check is that CUPS is up and running. • Linux print drivers are traditionally given a .ppd extension

ssh (Secure Shell) and scp (secure copy) • Enables us to remotely log on to different Linux or UNIX systems from our local terminal. • Encrypts all network communication between servers to prevent eavesdropping. The older telnet utility transferred all network communications in clear text. • The implementation of ssh used in Fedora is openssh • Most ssh work is done using command line. But graphical display windows can be opened if the ssh server is configured to allow use of the –X flag (X windows GUI screens). • ssh uses a pair of public and private keys to encrypt communications. • A list of all servers for which you have established valid key pair relationships is stored in the ~/.ssh/known_hosts file. • The first time you connect to a server, it will ask you if you wish to exchange keys with this host. You will still need to enter the password each time however. • ssh syntax to connect is ssh username@servername o example: ssh loyd@dbserver • The configuration file for what ssh users can do when logged into YOUR computer is at /etc/ssh/sshd_config o Note: show example here • scp uses the same key pair encryption technology to allow secure transfer of files between computers o example syntax to securely copy file /home/george/budget.txt to server accounts as user Sally ▪ scp /home/george/budget.txt Sally@accounts

LDAP (Lightweight Directory Internet Protocol) • Enables us to use a common set of user accounts across multiple Linux systems without having to manually configure the users on each station. • Active Directory is an LDAP type system for Windows • In Fedora, we use OpenLDAP most frequently. • LDAP uses port 389 for traffic that is not encrypted or 636 for SSL Encrypted traffic. • LDAP uses a hierarchical structure to uniquely identify and classify all users. • Each full LDAP string used to unique key identify an individual is known as a DN (Distinguished Name). • The top of the LDAP hierarchy is known as the DSE (DSA-Specific Entry)

Email in Linux • Older command line based email packages such as mail and mailx are still very useful in Linux. • Sendmail is perhaps the most widely used Linux email server. You can set up a full open source email server as an alternative to Exchange. • Sendmail uses port 25 by default. Make sure you open this on your firewall. • Sendmail is configured in the sendmail.mc file. • If you only need to send and receive email from a Linux system, the Dovecot package provides both SMTP (outgoing) and POP (incoming protocols. • Multiple email clients exist for Linux, including Thunderbird and Evolution.

Samba • Allows use of windows network resources in linux • Includes the ability to share files between Linux and Windows based networks • Allows the use of Linux as a windows file share • Allows use of windows network printers from Linux • You can run many native Windows programs in Linux using the Wine emulator or by creating a VM within Linux. Note though that Wine is sometimes a resource hog.
BIND and iptables • The most common Linux based firewall program is iptables.
The Apache Web Server • The most common web server on Linux is Apache. It also exists in Windows and UNIX versions and is the most commonly used web server in the world. • You can use Apache to host a web site from your Linux system • The default http port for Apache to use on Linux is 80. • The Apache Web server is configured in the httpd.conf file. • The DocumentRoot Directive in httpd.conf tells Apache where you web files are stored.