A famous professor Andrew Tanenbaum developed Minix, a simplified version of UNIX that runs on PC.
Minix is for class teaching only. No intention for commercial use
In Sept 1991, Linus Torvalds, a second year student of Computer Science at the University of Helsinki, developed the preliminary kernel of Linux, known as Linux version 0.0.1
Free software, as defined by the FSF (Free Software Foundation), is a "matter of liberty, not price." To qualify as free software by FSF standards, you must be able to:
Run the program for any purpose you want to, rather than be restricted in what you can use it for.
View the program's source code.
Study the program's source code and modify it if you need to.
Share the program with others.
Improve the program and release those improvements so that others can use them.
Red Hat Linux : One of the original Linux distribution.
The commercial, nonfree version is Red Hat Enterprise Linux, which is aimed at big companies using Linux servers and desktops in a big way. (NJIT)
Free version: Fedora Project.

Debian GNU/Linux : A free software distribution. Popular for use on servers. However, Debian is not what many would consider a distribution for beginners, as it's not designed with ease of use in mind.

SuSE Linux : SuSE was recently purchased by Novell. This distribution is primarily available for pay because it contains many commercial programs, although there's a stripped-down free version that you can download.

Mandrake Linux : Mandrake is perhaps strongest on the desktop. Originally based off of Red Hat Linux.

Gentoo Linux : Gentoo is a specialty distribution meant for programmers.
A runlevel is a software configuration of the system which allows only a selected group of processes to exist
The processes spawned by init for each of these runlevels are defined in the /etc/inittab file
Init can be in one of eight runlevels: 0-6

Runlevel: defines number and type of daemons loaded into memory and executed init daemon responsible for changing runlevels
Often called initstates
Seven standard runlevels runlevel command: displays current and most recent runlevel init command: change OS runlevel telinit command: Alias to init command
Process of creating new user accounts
Add default files to be part of every user’s home directory to /etc/skel directory
Create home directory for all users
Configure default settings for all users
Create groups
Create user account for each person
Create valid password for each user
/etc/passwd file defines user accounts, including:
User name – Comment field
Password – User’s home directory
UID – User’s default shell
GID
vipw command edits /etc/passwd file passwd command defines password
Utilities to create new user accounts
Graphical tools
Command-line utilities system-config-users utility
Red Hat graphical user account creation tool
Information from /etc/passwd file shown in window
Can edit each fields
Edit password information stored in /etc/shadow
User Properties dialog, User Data tab
User name
Full name
Password and confirm password
Home directory
Login shell
User Properties dialog, Account Info tab
Enable account expiration
Lock local password
User Properties dialog, Password Info tab
View when user last changed password
Enable password expiration
Experts recommend changing password every 30 to 60 days
User Properties dialog, Groups tab
Lists groups from /etc/group file
Each user assigned primary group
User private group model
Used by Red Hat Linux and Fedora
User’s primary group has same name as user
Contains only user as member
Create new user system-config-users utility
Add User button
Enter information on dialog
Utility creates home directory based on user name
/etc/login.defs file
Stores settings used to create new users
Comments describe settings
Create new group
Click Add Group button
Enter group name
Delete user
Select user name on Users tab
Click delete button
Some administrators prefer to permanently disable, not delete useradd utility
Create new users
Must be logged in as root
Example: useradd -g sales -c “Raley Solomon" rsolomon
-D option displays the default settings
Edit /etc/default/useradd to change defaults passwd command
Change user’s password
Lock user account: passwd -l thomas
Unlock account: passwd -u Thomas groupadd command
Preferred method for adding new group
Example: groupadd managers usermod command
Modify user account
Uses same options as useradd command groupmod command
Modify group
-g option: change GID
-n option: change name
Directories and files are organized hierarchically
Ability to manipulate directory defined by rights
Superuser: arranges information anywhere
Regular user: is confined to a particular branch
Accessing the Fedora command line interface
Configure the system to open to the command line
Open a terminal window from the GUI
Home directory is starting directory for regular users
Example: /home/User01
Command [options] [parameter1] [parameter2]
[parameter3]

Data streams for ls -l, a sample command
Three methods for executing commands
– Same line, sequential command line processing
• Example: ls –l /etc ; pwd
– Piped, sequential command processing
• Example: ls –l /etc | more
• Pipe symbol pipes output from ls to more
– Batch file sequential processing

Example: ls –l /etc pwd
Use ls command to view list of directories and files
• ls default: display directory with files alpha sorted
• ls command syntax: ls [options] [location]
• Some ls command options
– a: shows hidden files
– l: a longlisting format • A few examples of many useful ls command options
– ls –l /etc/hosts: list details about a file or directory
– ls –S /etc/hosts: change the order of lines in a text file
Use more with ls to page through directories/files
– Example: ls –Rl /etc | more
• Use sort with ls to control order item appears in list
– Example: ls –l /etc | sort –k9 (sort by ninth field in list)
• sort command syntax: sort [options] [files]
• pwd command syntax: pwd [options]
– Displays full path filename of the current directory
• more command syntax: more [options]
Two wildcard characters identify groups of files
– The question mark (?): represents any character
– The asterisk (*), or star: represents any string
• Example with ? wildcard: ls host????
– Lists files consisting of host plus any four characters
– Possible matches: hostuser, hosthome, host1234
• Example using * wildcard: *.*
– Represents all filenames with any extension
Use the cd command to change current directory
– Page definition options are beyond scope of book
• cd command syntax: cd [options] [location path]
Two methods: change absolute path or relative path
• Other directory symbols
– “..” entry: points to the parent directory
• Change the directory with the absolute path method
– Type cd /college/business/accounting
• Refer to the previous directory using the relative path
– Type cd ../../business/accounting
• Back up one subdirectory and move up higher
– Type cd..
Users authorized to create directories with mkdir
– Superuser
– Regular user with write permission in parent directory
• mkdir syntax: mkdir [options] [directory name]
• mkdir command options:
– p: makes parent directories as needed
– v: displays a message for each created directory
• Navigating to arts directory, add printing directory
– cd /college/arts mkdir printing
Ownership permission or superuser logon required
• rmdir command syntax: rmdir [options] directory[s]
• rmdir command options:
– p: tries to remove components in path as needed
• Cannot be used if directories contain files
– v: displays a message for each removed directory
• Navigate to Printing directory, remove component
– cd /college/arts rmdir printing
• Remove full branch with rm command and r or R cp -A command utility that can be used to copy a file, including text and executable program (binary) files is the cp utility
Example:
cp tiles.conf /home/student/tiles1.conf

Tail - A command utility used to view the last ten lines of a file
Top – A command utility used to view the first ten lines of a file
Who – lists users who logged on to a specific terminal
Pwd- displays the pathname of the current working directory
Chmod – change ownership permissions of files and directories
To find files in the terminal

find <start-point> | grep <filename>

or locate if you prefer:

locate | grep <filename>

Each standard user account has a separate home directory under /home/ to store files specific to that user. This contains both their private data files, and the configuration files that define the user settings for each desktop application.
Locations for shared data
/srv/
/var/
/lost+found/
The root account uses the home directory /root/. This ensures that the root account may function normally when the /home/ directory is not accessible. Only store data files and scripts in /root/ if they are for the purposes of system administration. Each administrator should also have a standard user account for their own files.
Removable Storage
/media/
Network Directories
/mnt/
/net/
The connections made with /mnt/ and /net/ may be made available to all users on the system. Connections made with the desktop applications are not attached to the filesystem, and may only be accessed by the user that made those connections.
Location for Software
/bin/
The /usr/ heirarchy (and /usr/local/).
Specify /usr/share/ for shared documents and other resources relating to software.
The /sbin/ directory
The directory /sbin/ contains programs that are used by the system itself. Use the supplied configuration tools to modify your system, rather than the software in /sbin/.
Additional Software
/misc/
/opt/
System Configuration Files
Files for settings that apply to the entire system:
/etc/
Virtual files maintained by the system. These may be read or written to as if they were real files on the drive:
/proc/
/sys/
Virtual files are created on boot
All changes to virtual files are lost when your system reboots. If you wish to automatically change a value in a virtual file when the system starts, refer to Modifying the Startup Process.
Core System Directories
/boot/
/dev/
/lib/
/sbin/
/selinux/
/tmp/
Open a shell….
Type in the following and observe: w date man w (get more information on w command) whatis man whereis csh (lists the path) whoami hostname uname (linux) who (information about current user)

Linux Permissions
Permissions are set for user, group, and others
Each permission is set with a single digit from 0 to 7 based on the combination of permissions read = 4 write = 2 execute = 1
Using CHMOD to set permissions

Finding IP address
Use “uname”
Using grep command (or anything else) you can display the IP address and machine name

Text Editor
VIM – Has two modes: Command Mode Input Mode

Vim command Action :
:e filename Open a new file. You can use the Tab key for automatic file name completion, just like at the shell command prompt.
:w filename Save changes to a file. If you don't specify a file name, Vim saves as the file name you were editing. For saving the file under a different name, specify the file name. :q Quit Vim. If you have unsaved changes, Vim refuses to exit. :q! Exit Vim without saving changes. :wq Write the file and exit.
VIM
Moving around in the file j or Up Arrow Move the cursor up one line. k or Down Arrow Down one line. h or Left Arrow Left one character. l or Right Arrow Right one character. e To the end of a word.
E To the end of a whitespace-delimited word. b To the beginning of a word.
B To the beginning of a whitespace-delimited word. 0 To the beginning of a line.
H To the first line of the screen.
M To the middle line of the screen.
L To the the last line of the screen.
:n Jump to line number n. For example, to jump to line 42, you'd type :42

VIM Insert Mode i Insert before cursor.
I Insert to the start of the current line. a Append after cursor.
A Append to the end of the current line. o Open a new line below and insert.
O Open a new line above and insert.
C Change the rest of the current line. r Overwrite one character. After overwriting the single character, go back to command mode.
R Enter insert mode but replace characters rather than inserting.
The ESC key Exit insert/overwrite mode and go back to command mode.
VIM
x Delete characters under the cursor.
X Delete characters before the cursor. dd or :d Delete the current line.
Scripts
Shell scripts are short programs that are written in a shell programming language and interpreted by a shell process.
A shell is a program that provides the traditional, text-only user interface for Unix-like operating systems. The default shell on Linux is the very commonly used and highly versatile bash.
First Script
The following example, although extremely simple, provides a useful introduction to creating and using shell scripts. The script clears the monitor screen of all previous lines and then writes the text Good morning, world. on it.
All that is necessary to create this script is to open a text editor (but not a word processor), such as gedit or vi, and type the following three lines exactly as shown on a new, blank page:
#!/bin/bash
clear echo "Good morning, world."
Running a Script
After saving this plain text file, with a file name such as morning (or anything else desired), the script is complete and almost ready to run. Scripts are typically run by typing a dot, a forward slash and the file name (with no spaces in between) and then pressing the ENTER key.

./morning
Error Due to permissions
Sometimes an error message will appear on the screen such as bash: ./morning: Permission denied.
This is because the permissions for the file first have to be set to executable. (By default, the permissions for new files are set to read and write only.)
The problem can easily be solved by using the chmod command with its 755 option

chmod 755 morning
How Scripts Work
The first of the three lines tells the operating system what shell to use to interpret the script and the location (i.e., absolute pathname) of the shell. The shell is bash, which is located in the /bin directory (as are all shells); thus the line contains /bin/bash. This instruction is always preceded by a pound sign and an exclamation mark in order to inform the operating system that it is providing the name and location of the shell (or other scripting language).
The second line tells the shell to issue the clear command. This is a very simple command that removes all previous commands and output from the console or terminal window in which the command was issued.
The third line tells the shell to write the phrase Good morning, world. on the screen.
It uses the echo command, which instructs the shell to repeat whatever follows it.
(The quotation marks are not necessary in this case; however, it is good programming practice to use them, and they can make a big difference in more advanced scripts.)
In slightly more technical terms, Good morning, world. is an argument (i.e., input data) that is passed to the echo command.
Redirection
The term redirection encompasses the various ways you can cause the shell to alter where standard input of a command comes from and where standard output goes to. By default the shell associates standard input and standard output of a command with the keyboard and the screen as mentioned earlier.
You can cause the shell to redirect standard input or standard output of any command by associating the input or output with a command or file other than the device file representing the keyboard or the screen. This section demonstrates how to redirect input from and output to ordinary text files and utilities.
Redirecting Standard Output
The redirect output symbol (>) instructs the shell to redirect the output of a command to the specified file instead of to the screen
(Figure 7-6). The format of a command line that redirects output is command [arguments] > filename
Figure 7-6. Redirecting standard output where command is any executable program (such as an application program or a utility), arguments are optional arguments, and filename is the name of the ordinary file the shell redirects the output to.

$ cat > sample.txt
(Figure 7-6). The format of a command line that redirects output is command [arguments] > filename
Figure 7-6. Redirecting standard output where command is any executable program (such as an application program or a utility), arguments are optional arguments, and filename is the name of the ordinary file the shell redirects the output to.

$ cat > sample.txt
Redirecting Standard Input
Just as you can redirect standard output, so you can redirect standard input. The redirect input symbol (<) instructs the shell to redirect a command’s input to come from the specified file instead of from the keyboard (Figure 7-9). The format of a command line that redirects input is command [ arguments] < filename
Figure 7-10 shows cat with its input redirected from the supply_orders file that was created in Figure 7-8 and standard output going to the screen. This setup causes cat to display the sample file on the screen. The system automatically supplies an EOF (end of file) signal at the end of an ordinary file.
Figure 7-10. cat with its input redirected
$ cat < supply_orders
Appending Standard Output to a File
The append output symbol (>>) causes the shell to add new information to the end of a file, leaving any existing information intact. This symbol provides a convenient way of catenating two files into one. The following commands demonstrate the action of the append output symbol.
The second command accomplishes the catenation described in the preceding caution box:

$ cat orange this is orange
$ cat pear >> orange
$ cat orange this is orange this is pear
The shell uses a pipe to connect standard output of one command directly to standard input of another command. A pipe (sometimes referred to as a pipeline) has the same effect as redirecting standard output of one command to a file and then using that file as standard input to another command. A pipe does away with separate commands and the intermediate file. The symbol for a pipe is a vertical bar (|). The syntax of a command line using a pipe is command_a [arguments] | command_b [arguments]
You can use a pipe with any of the Linux utilities that accept input either from a file specified on the command line or from standard input.

$ ls | lpr

This will list all files in the local printer queue.
Network Configuration Files
/etc/resolve.conf-List DNS servers for internet domain name resolution.

/etc/hostsLists hosts to be resolved locally (not by DNS).

/etc/hosts /etc/nsswitch.conf-List order of host name search. Typically look at local files, then NIS server, then DNS server.

/etc/sysconfig/network-Specify network configuration. eg. Static IP, DHCP, NIS, etc.

/etc/sysconfig/network-scripts/ifcfg-device - Specify TCP network information.
/etc/network/interfaces - Specify network configuration and devices. eg. Static IP and info, DHCP, etc.
The easiest way to configure your network connection on Red Hat Linux is to run the 'netconfig' utility.
# netconfig
The netconfig utility will ask you if you would like to set up networking. Push the "Yes" button. (Use the tab key to move between items.) To have your computer configure itself automatically with DHCP simply select the item "Use Dynamic IP configuration" by pressing the space bar when that item is highlighted.
To configure you computer to use a static IP address, tab down the form and fill in the IP address, the Netmask (which will be 255.255.255.0), the Default gateway (which will be 143.229.xxx.1, where xxx is the subnet for your dorm or building), and the Primary Nameserver (which is 143.229.1.6).
To make the changes take effect you need to restart the networking service, with the command:
# service network restart
In Unix you do not need to reboot to change your network configuration. Remember though that you must be the root user to use the commands above. When you are done you should exit the root command shell or log out of the root account. ifconfig You can verify that the IP address and netmask have been set correctly using the ifconfig command:
# ifconfig
This will list the IP address (as "inet addr") and the subnet mask (as "Mask") for the network interface "eth0" (your ethernet card). It will also list other details, including the hardware address of your ethernet card (as "HWaddr"), which is sometimes refered to as the "MAC address". This is an identifier for your ethernet card (like a serial number) and is different from the IP address. (The ifconfig command will also give the status of the "loopback" device ("lo"), which is a simulated network connection from your computer back to itself. The IP address of the loopback device will be 127.0.0.1. You don't need to do anything to this interface.)
Default Route
You can verify that the gateway (default route) is set correctly by giving the route command:
# route -n The default "Destination", which is listed as 0.0.0.0, should have a "Gateway" of 143.229.xxx.1, where xxx the subnet for your dorm or building. The -n "numeric" flag prevents DNS lookup and reports addresses in numeric form.
/etc/sysconfig/network
These changes will go away after the next reboot. You can make permanent changes by editing the appropriate configuration files. Red Hat Linux keeps the network configuration information settings in the file /etc/sysconfig/network.
The file should look something like:
NETWORKING=yes
HOSTNAME=mandalay
BOOTPROTO=static
IPADDR=143.229.29.60 NETMASK=255.255.255.0 GATEWAY=143.229.29.1
The file /etc/sysconfig/network for a static IP address.
/etc/sysconfig/network-scripts
Sometimes some of this information will be recorded in the file ifcfg-eth0 in the directory /etc/sysconfig/network-scripts instead. I f you have more than one Network Interface Card (NIC), as for example a laptop with both a wired and wireless connection, then information for each NIC will appear in separate files in this directory with names of the form ifcfg-ethX for "eth0" and "eth1", etc. For example, to enable DHCP at boot for a wireless card which is "eth1" the file would contain:
DEVICE=eth1
ONBOOT=yes
BOOTPROTO=DHCP
Figure 2: The file /etc/sysconfig/network-scripts/ifcfg-eth1 for a wireless NIC, as in a laptop.
Printer Configuration Tool
Printer Configuration Tool allows users to configure a printer. This tool helps maintain the printer configuration file, print spool directories, print filters, and printer classes.
Red Hat Enterprise Linux 5.8 uses the Common Unix Printing System (CUPS).

Using Printer Configuration Tool requires root privileges. To start the application, select System (on the panel) > Administration > Printing, or type the command system-config-printer at a shell prompt.
Print Queues
The following types of print queues can be configured:
AppSocket/HP JetDirect — a printer connected directly to the network through HP JetDirect or Appsocket interface instead of a computer.
Internet Printing Protocol (IPP) — a printer that can be accessed over a TCP/IP network via the Internet Printing Protocol (for example, a printer attached to another Red Hat Enterprise Linux system running CUPS on the network).
LPD/LPR Host or Printer — a printer attached to a different UNIX system that can be accessed over a TCP/IP network (for example, a printer attached to another Red Hat Enterprise Linux system running LPD on the network).
Networked Windows (SMB) — a printer attached to a different system which is sharing a printer over an SMB network (for example, a printer attached to a Microsoft Windows™ machine).
Networked JetDirect — a printer connected directly to the network through HP JetDirect instead of a computer.
Adding Printers Through Command Line redhat-config-printer-tui --Xadd-local options

Options:
--device=node(Required) The device node to use. For example, /dev/lp0.
--make=make(Required) The IEEE 1284 MANUFACTURER
--model=model(Required) The IEEE 1284 MODEL
--name=name(Optional) The name to be given to the new queue. If one is not given, a name based on the device node (such as "lp0") will be used.
--as-default(Optional) Set this as the default queue.
Restart Print Services
After adding the printer, use the following command to start/restart the printer daemon: service cups restart
Print driver files always end in extension .ppd
Configuring Wireless
You can configure a wireless NIC by using system-config-network or iwconfig
Configuring Network Devices
You can configure network devices in Linux through Network Manager
Configuration Information
Configuration information is stored in

/etc/sysconfig/network

Directory
Configuration of network connections
Configuration of network connections is made through

nm-connection-editor
Network Manager
Configuration of network connections through Network Manager contains the below information:

IP Address
Subnet Mask
Gateway Address
Sendmail Configuration File
The configuration file is responsible for telling sendmail several important things about how it should handle mail: General configuration options, such as queue directory and timeout values
Definitions for each MDA, including pathnames and options
Rulesets for header processing/rewriting, and the "routing table" which determines which MDAs get used for which messages cf files vs .mc files
The /etc/mail/sendmail.cf file was designed to be quickly parsable by sendmail, not to be human-readable, and it's widely considered to be one of the most cryptic things a Unix administrator needs to deal with. So, starting with version 8, a set of macros for the m4 macro language were written to make it much easier to create, modify, and maintain all of the common configurations for the sendmail.cf file.
The file which contains these macros is called a .mc file.

The Structure of a .mc File
The basic structure of a .mc file is as follows: OSTYPE() Your .mc file must start with exactly one OSTYPE() macro, which tells m4 what platform you're running so that it can fetch the appropriate defaults from the cf/ostype/ostype.m4 file. For example, if you say
OSTYPE(linux), m4 will read the file cf/ostype/linux.m4. define() You can use zero or more define() directives to set variables which control the operation of the configuration macros. The syntax is: define(`variable', `value') Normally, both the variable and the value are quoted as shown to prevent their expansion by m4 itself.
FEATURE() Zero or more FEATURE() macros can be used to select which special features your configuration will use or support.
MAILER() One or more MAILER() macros must be used to define which MDAs are used by your configuration. Usually, you only need to define the local MDA and the SMTP MDA, like this: MAILER(smtp) MAILER(local)
Configuration Variables confSMTP_LOGIN_MSG This defines the one-line message which is displayed when a remote MTA connects to sendmail's SMTP port. Variable expansion is done for many variables, including:
$j local hostname
$v version of the sendmail binary
$Z version of the sendmail.cf file
$b current time confMAX_MESSAGE_SIZE This is the maximum message size allowed for local delivery. I recommend setting this to 5242880 (5MB) to avoid mail bombs. confPRIVACY_FLAGS This allows you to set some restrictions on what other users are allowed to find out about sendmail's operation.
Common values are: authwarnings Issue warnings about authenticity of header information. restrictqrun Only allow root to run the mail queue manually. restrictmailq Only allow root to see the contents of the mail queue. noexpn Do not allow the SMTP EXPN command, which allows remote users to see the result of an alias expansion on the local machine. novrfy Do not allow the SMTP VRFY command, which allows remote users to verify the existence of a user account on your machine. Multiple privacy flags can be specified, separated by commas. confQUEUE_LA Load average at which sendmail puts incoming email into the queue rather than attempt to deliver it immediately confREFUSE_LA Load average at which to stop accepting new incoming SMTP connections.
Sendmail
NAME sendmail - an electronic mail transport agent
Sendmail sends a message to one or more recipients, routing the message over whatever networks are necessary. Sendmail does internetwork forwarding as necessary to deliver the message to the correct place.
Sendmail uses port 25 for mail services.
With no flags, sendmail reads its standard input up to an end-of-file or a line consisting only of a single dot and sends a copy of the message found there to all of the addresses listed.
Senmails main configuration file is /etc/mail/sendmail.mc
Dovecot
Overview
Dovecot is an open sourceIMAP andPOP3 email server for Linux/UNIX-like systems, written with security primarily in mind. Dovecot is an excellent choice for both small and large installations. It's fast, simple to set up, requires no special administration and it uses very little memory.
Some of the most notable features of Dovecot include:

Dovecot is among the highest performing IMAP servers while still supporting the standardmbox and Maildir formats. The mailboxes are transparently indexed, which gives Dovecot its good performance while still providing full compatibility with existing mailbox handling tools.
Dovecots main configuration file is /etc/dovecot.dovecot.conf
Dovecot tries to be admin-friendly. Common error messages are made as easily understandable as possible. Any crash, no matter how it happened, is considered a bug that will be fixed.
Dovecot allows mailboxes and their indexes to be modified by multiple computers at the same time, while still performing well. This means that Dovecot works well with clustered filesystems.
Dovecot is easily extensible. Plugins can add new commands, modify existing behavior, add their own data into index files or even add support for new mailbox formats. For example quota and ACL support are completely implemented as plugins
Openssh
OpenSSH is a FREE version of the SSH connectivity tools that technical users of the Internet rely on. Users of telnet, rlogin, and ftp may not realize that their password is transmitted across the Internet unencrypted, but it is.
Encryption keys for users connecting to SSH servers are located in ~/.ssh
Directory.
Global configuration files for open ssh are located in /etc/ssh
The OpenSSH suite replaces rlogin and telnet with the ssh program, rcp with scp, and ftp with sftp.
Commands
Scp - scp allows files to be copied to, from, or between different hosts. It uses ssh for data transfer and provides the same authentication and same level of security as ssh.

Examples:
Copy the file "foobar.txt" from a remote host to the local host
$ scp your_username@remotehost.edu:foobar.txt /some/local/directory
Copy the file "foobar.txt" from the local host to a remote host
$ scp foobar.txt your_username@remotehost.edu:/some/remote/directory
Telnet – This command is utilized to connect to remote computers.
Mycomputer#> telnet host.com
The above example would open a telnet session to the domain host.com.
SSH
1. SSH Client Version:
Sometimes it may be necessary to identify the SSH client that you are currently running and it’s corresponding version number, which can be identified as shown below. Please note that Linux comes with OpenSSH.
$ ssh -V
OpenSSH_3.9p1, OpenSSL 0.9.7a Feb 19 2003
$ ssh -V
Login to remote host:
The First time when you login to the remotehost from a localhost, it will display the host key not found message and you can give “yes” to continue. The host key of the remote host will be added under .ssh2/hostkeys directory of your home directory, as shown below. localhost$ ssh -l jsmith remotehost.example.com
Host key not found from database.
Key fingerprint: xabie-dezbc-manud-bartd-satsy-limit-nexiu-jambl-title-jarde-tuxum
You can get a public key’s fingerprint by running % ssh-keygen -F publickey.pub on the keyfile. Are you sure you want to continue connecting (yes/no)? yes
The Second time when you login to the remote host from the localhost, it will prompt only for the password as the remote host key is already added to the known hosts list of the ssh client. localhost$ ssh -l jsmith remotehost.example.com jsmith@remotehost.example.com password: remotehost.example.com$ X11 forwarding
To run graphical programs through a SSH connection you can enable X11 forwarding.
To use the forwarding, log on to your server through ssh:
$ ssh -X -p port user@server-address
Installing and Removing packages with YUM
Yum stands for Yellowdog Updater Modified
To install a package, do ‘yum install packagename’. This will also identify the dependencies automatically and install them.
The following example installs postgresql package
# yum install postgresql.x86_64 Resolving Dependencies Install 2 Package(s) Is this ok [y/N]: y Package(s) data still to download: 3.0 M (1/2): postgresql-9.0.4-5.fc15.x86_64.rpm | 2.8 MB 00:11 (2/2): postgresql-libs-9.0.4-5.fc15.x86_64.rpm | 203 kB 00:00 ------------------------------------------------------------------ Total 241 kB/s | 3.0 MB 00:12 Running Transaction Installing : postgresql-libs-9.0.4-5.fc15.x86_64 1/2 Installing : postgresql-9.0.4-5.fc15.x86_64 2/2 Complete!
By default ‘yum install’, will prompt you to accept or decline before installing the packages. If you want yum to install automatically without prompting, use -y option as shown below.
# yum -y install postgresql.x86_64
To remove a package (along with all its dependencies), use ‘yum remove package’ as shown below.
# yum remove postgresql.x86_64

Resolving Dependencies ---> Package postgresql.x86_64 0:9.0.4-5.fc15 will be erased Is this ok [y/N]: y Running Transaction Erasing : postgresql-9.0.4-5.fc15.x86_64 1/1 Removed: postgresql.x86_64 0:9.0.4-5.fc15 Complete!
If you have a older version of a package, use ‘yum update package’ to upgrade it to the latest current version. This will also identify and install all required dependencies.
# yum update postgresql.x86_64
If you don’t know the exact package name to be installed, use ‘yum search keyword’, which will search all the packages that matches the ‘keyword’ and display it.

The following examples searches the yum repository for all the packages that matches the keyword ‘firefox’ and lists the available packages.

# yum search firefox Loaded plugins: langpacks, presto, refresh-packagekit ============== N/S Matched: firefox ====================== firefox.x86_64 : Mozilla Firefox Web browser gnome-do-plugins-firefox.x86_64 : gnome-do-plugins for firefox mozilla-firetray-firefox.x86_64 : System tray extension for firefox mozilla-adblockplus.noarch : Adblocking extension for Mozilla Firefox mozilla-noscript.noarch : JavaScript white list extension for Mozilla Firefox Name and summary matches only, use "search all" for everything.
Display additional information about a package using yum info

Once you search for a package using yum search, you can use ‘yum info package’ to view additional information about the package.
The following examples displays additional information about the samba-common package.

# yum info samba-common.i686
Loaded plugins: langpacks, presto, refresh-packagekit Available Packages Name : samba-common Arch : i686 Epoch : 1 Version : 3.5.11 Release : 71.fc15.1 Size : 9.9 M
Repo : updates Summary : Files used by both Samba servers and clients URL : http://www.samba.org/
License : GPLv3+ and LGPLv3+
Description : Samba-common provides files necessary for both the server and client : packages of Samba
View all available packages using yum list
The following command will list all the packages available in the yum database.

# yum list | less
List only the installed packages using yum list installed
To view all the packages that are installed on your system, execute the following yum command.

# yum list installed | less
All yum commands goes against one or more yum repositories. To view all the yum repositories that are configured in your system, do ‘yum repolist’ as shown below.
The following will display only the enabled repositories.

# yum repolist repo id repo name status fedora Fedora 15 - x86_64 24,085 updates Fedora 15 - x86_64 5,612
Execute yum commands interactively using Yum Shell

Yum provides the interactive shell to run multiple commands as shown below.

# yum shell
Setting up Yum Shell > info samba.x86_64 Available Packages Name : samba Arch : x86_64 Epoch : 1 Version : 3.5.11 Release : 71.fc15.1 Size : 4.6 M Repo : updates Summary : Server and Client software to interoperate with Windows machines URL : http://www.samba.org/ License : GPLv3+ and LGPLv3+ Description : : Samba is the suite of programs by which a lot of PC-related : machines share files, printers, and other information (such as : lists of available files and printers). The Windows NT, OS/2, and : Linux operating systems support this natively, and add-on packages : can enable the same thing for DOS, Windows, VMS, UNIX of all : kinds, MVS, and more. This package provides an SMB/CIFS server : that can be used to provide network services to SMB/CIFS clients. : Samba uses NetBIOS over TCP/IP (NetBT) protocols and does NOT : need the NetBEUI (Microsoft Raw NetBIOS frame) protocol. > yum.conf - Configuration file for yum

Description
Yum uses a configuration file at /etc/yum.conf.
Additional configuration files are also read from the directories set by the reposdir option (default is '/etc/yum.repos.d').

Parameters
There are two types of sections in the yum configuration file(s): main and repository. Main defines all global configuration options. There should be only one main section. The repository section(s) define the configuration for each repository/server. There should be one or more repository sections.
Name : wget
Product : Fedora 15 Version : 1.12 Release : 4.fc15
URL : http://www.gnu.org/software/wget/
Summary : A utility for retrieving files using the HTTP or FTP protocols

Description : GNU Wget is a file retrieval utility which can use either the HTTP or FTP protocols. Wget features include the ability to work in the background while you are logged out, recursive retrieval of directories, file name wildcard matching, remote file timestamp storage and comparison, use of Rest with FTP servers and Range with HTTP servers to retrieve files over slow or unstable connections, support for Proxy servers, and configurability.

This update can be installed with the "yum" update program.
Use su -c 'yum update wget' at the command line.
RPM command is used for installing, uninstalling, upgrading, querying, listing, and checking RPM packages on your Linux system.

RPM stands for Red Hat Package Manager.

With root privilege, you can use the rpm command with appropriate options to manage the RPM software packages
Installing a RPM package Using rpm –ivh

RPM filename has packagename, version, release and architecture name.

For example, In the MySQL-client-3.23.57-1.i386.rpm file:

MySQL-client – Package Name
3.23.57 – Version
1 – Release i386 – Architecture

When you install a RPM, it checks whether your system is suitable for the software the RPM package contains, figures out where to install the files located inside the rpm package, installs them on your system, and adds that piece of software into its database of installed RPM packages
Installing a RPM package Using rpm –ivh

RPM filename has packagename, version, release and architecture name.

For example, In the MySQL-client-3.23.57-1.i386.rpm file:

MySQL-client – Package Name
3.23.57 – Version
1 – Release i386 – Architecture

When you install a RPM, it checks whether your system is suitable for the software the RPM package contains, figures out where to install the files located inside the rpm package, installs them on your system, and adds that piece of software into its database of installed RPM packages. rpm command and options

-i : install a package
-v : verbose
-h : print hash marks as the package archive is unpacked.

The following rpm command installs Mysql client package.
# rpm -ivh MySQL-client-3.23.57-1.i386.rpm Preparing... ########################################## [100%] 1:MySQL-client ################################### [100%] Query all the RPM Packages using rpm –qa You can use rpm command to query all the packages installed in your system. # rpm -qa cdrecord-2.01-10.7.el5 bluez-libs-3.7-1.1 setarch-2.0-1.1 . . -q query operation -a queries all installed packages To identify whether a particular rpm package is installed on your system, combine rpm and grep command as shown below. Following command checks whether cdrecord package is installed on your system. # rpm -qa | grep 'cdrecord' Query a Particular RPM Package using rpm –q The above example lists all currently installed package. After installation of a package to check the installation, you can query a particular package and verify as shown below. # rpm -q MySQL-client MySQL-client-3.23.57-1 # rpm -q MySQL package MySQL is not installed Note: To query a package, you should specify the exact package name. If the package name is incorrect, then rpm command will report that the package is not installed. Which RPM package does a file belong to? – Use rpm –qf Let us say, you have list of files and you would want to know which package owns all these files. rpm command has options to achieve this. The following example shows that /usr/bin/mysqlaccess file is part of the MySQL-client-3.23.57-1 rpm. # rpm -qf /usr/bin/mysqlaccess MySQL-client-3.23.57-1

-f : file name Locate documentation of a package that owns file using rpm –qdf Use the following to know the list of documentations, for a package that owns a file. The following command, gives the location of all the manual pages related to mysql package. # rpm -qdf /usr/bin/mysqlaccess /usr/share/man/man1/mysql.1.gz /usr/share/man/man1/mysqlaccess.1.gz /usr/share/man/man1/mysqladmin.1.gz /usr/share/man/man1/mysqldump.1.gz /usr/share/man/man1/mysqlshow.1.gz

-d : refers documentation. Information about Installed RPM Package using rpm -qi rpm command provides a lot of information about an installed pacakge using rpm -qi as shown below: # rpm -qi MySQL-client Name : MySQL-client Relocations: (not relocatable) Version : 3.23.57 Vendor: MySQL AB Release : 1 Build Date: Mon 09 Jun 2003 11:08:28 PM CEST Install Date: Mon 06 Feb 2010 03:19:16 AM PST Build Host: build.mysql.com Group : Applications/Databases Source RPM: MySQL-3.23.57-1.src.rpm Size : 5305109 License: GPL / LGPL Signature : (none) Packager : Lenz Grimmer URL : http://www.mysql.com/ Summary : MySQL - Client Description : This package contains the standard MySQL clients. Upgrading a RPM Package using rpm –Uvh Upgrading a package is similar to installing one, but RPM automatically un-installs existing versions of the package before installing the new one. If an old version of the package is not found, the upgrade option will still install it. # rpm -Uvh MySQL-client-3.23.57-1.i386.rpm Preparing... ########################################## [100%] 1:MySQL-client ################################### [100%]