Postfix Pre-Installation on RHEL

Postfix Pre-Installation Steps

Sendmail Stop

The first step before installing Postfix is to make sure that Sendmail is not already running on your system. You can check for this using the following command:

#/sbin/service sendmail status

If sendmail is not running the following output will be displayed:

#sendmail is stopped

If sendmail is running you will see the following:

#sendmail (pid 2138) is running

If sendmail is running on your system it is necessary to stop it before installing and configuring Postfix. To stop sendmail run the following command as super user:

#/sbin/service sendmail stop

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Finnix 107

Ryan Finnie has announced the release of Finnix 107, a small, self-contained, bootable Linux CD distribution for system administrators, based on Debian's testing branch: "Today I am pleased to announce the release of Finnix 107, only two months from the previous release, but packed with new functionality and bug fixes. Finnix 107 includes Linux kernel 3.6, and includes a fix for the (overhyped, it seems) ext4 corruption bug. Average Finnix startup times have been reduced even further by the cleanup of legacy code. In addition, the shutdown procedure, which largely has not changed in years, got a revamp and is now noticeably quicker. The x86 ISO is now being built with the isohybrid method, meaning you can now write the ISO directly to a USB flash drive at the block level to boot it.

Download: finnix-107 free Download

NetBSD 6.0.1

Jeff Rizzo has announced the release of NetBSD 6.0.1, the first security and bug-fix update of the project's 6.0 branch: "The NetBSD project is pleased to announce NetBSD 6.0.1, the first security and bug-fix update of the NetBSD 6.0 release branch. It represents a selected subset of fixes deemed important for security or stability reasons. Please note that all fixes in security and bug-fix updates (i.e., NetBSD 6.0.1, 6.0.2, etc.) are cumulative, so the latest update contains all such fixes from the corresponding minor release (in this case, 6.0). Major changes: posix_spawn() - fix processes with attributes; resolve races between vget() and vrele() resulting in vget() returning dead vnodes.

Download: NetBSD 6.0.1  free Download

Calculate Linux 13

Alexander Tratsevskiy has announced the release of Calculate Linux 13, a Gentoo-based distribution for desktops and servers: "We are proud to announce the final release of Calculate Linux 13. Main changes and fixes: meta-packages are no longer used to manage default dependencies; Portage files will be unpacked when booting for the first time; better identification of NTFS partitions; fixed the user profile configuration for VMware; Composite enabled by default for VMware; should you want to replace main applications, their launch icons will be created correctly; in case the user modified the local Portage overlay repositories, those can now be restored; Calculate Utilities were updated to 3.1; full French translation now available.

Download: Calculate Linux 13 free Downlaod

openSUSE 12.3 Milestone 2 release

Milestone 2 of openSUSE 12.3 is out and ready for testing: "A month's work since milestone 1 shows that the new release team is hitting its stride, as they it reviewed and checked in more than 470 updated packages. The biggest update is in LibreOffice, which jumps from 3.5.4 to 3.6.3. This new version of the office suite fixes a lot of annoying bugs and improves DOCX compatibility. Also this release includes a lot of new functionality, like adding the Lanczos image algorithm for resizing, which reduces aliasing in resized images. In Calc, there are several new functions, like support for color scales and data bars in XLSX and ODS document formats. In a change to policy, KDE 4.10 Beta 2 has been added to Factory already.

Download: openSUSE 12.3 Milestone 2

How to Create ISO Images from Command-Line

For this tutorial we’ll use the genisoimage utility, developed as part of the cdrkit project. genisoimage is a command-line tool for creating ISO 9660 filesystem images, which can be burnt after to a CD or DVD using some other burning tool. To install it open a terminal and type the following as root:

Ubuntu and Debain
$ sudo apt-get install genisoimage (for Centos and redhat )

For Redhat and Centos
$ yum -y install genisoimage

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GParted Live 0.14.1-1 Downlaod

Curtis Gedak has announced the release of GParted Live 0.14.1-1, a bug-fix update of the project's utility live CD containing tools for disk management and data rescue tasks: "The GParted team is proud to announce the stable release of GParted Live 0.14.1-1. This is a maintenance release that includes important bug fixes and it also adds more language translation updates. Two important bugs fixed in this release are: fix Linux software RAID device detection; fix logical partition grow overlaps extended partition end. The

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Calculate Linux 13 Beta 1 Downlaod

Alexander Tratsevskiy has announced the availability of the first beta release of Calculate Linux 13, a distribution based on Gentoo Linux: "We are happy to announce the release of the first Calculate Linux 13 beta version. Main changes: meta packages are no longer used to manage default dependencies; each Calculate Linux edition is now featuring its own appearance theme; Portage files will be unpacked when booting for the first time; Calculate Utilities were updated to 3.1 beta 2; a new tool, calculate-update - for the time being, it only handles the world file, but will be able to do much more soon; KDE was updated to

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Vyatta 6.5 Free Download

Stephen Harpster has announced the release of Vyatta 6.5, an updated version of the project's specialist distribution for firewalls and routers: "I'm pleased to announce that Vyatta Core (VC) release 6.5 is now available for download. Release 6.5 of the Vyatta Network OS adds significant enhancements including: support for Microsoft Hyper-V; Policy-Based Routing (PBR) which allows incoming packets to be forwarded based on policies, rather than just on the destination address; Virtual Tunnel Interface (VTI) which is a way to represent policy-based IPsec tunnels as virtual interfaces; BGP Multipath enables the installation of multiple BGP paths to a destination into the IP routing table; IPsec support for IPv6 using Internet key management protocol IKEv1; the VRRP (Virtual Router Redundancy Protocol) operational mode commands have been modified to improve usability...."

Download: vyatta-livecd_VC6.5R1_i386.iso  vyatta-livecd_VC6.5R1_amd64.iso

Linux Mint 14 Free Downlaod

Clement Lefebvre has announced the final release of Linux Mint 14, code name "Nadia", in MATE (version 1.4) or Cinnamon (version 1.6) editions: "The team is proud to announce the release of Linux Mint 14 'Nadia'. For the first time since Linux Mint 11, the development team was able to capitalize on upstream technology which works and fits its goals. After 6 months of incremental development, Linux Mint 14 features an impressive list of improvements, increased stability and a refined desktop experience. We're very proud of MATE, Cinnamon, MDM and all the components used in this release, and we're very excited to show you how they all fit together in Linux Mint 14.

Download: linuxmint-14-mate-dvd-32bit.iso  linuxmint-14-mate-dvd-64bit.iso

Redo Backup & Recovery 1.0.4 Free Download

Redo Backup & Recovery 1.0.4 has been released. Redo is an Ubuntu-based live CD featuring backup, restore, and disaster recovery software, with an easy-to-use graphical program for running bare-metal backup and recovery of hard disk partitions. What's new in this release? "Base upgrade to Ubuntu 12.04 LTS; percent complete now based on part sizes rather than total number of parts; Windows now have title bars to ease minimizing, maximizing and closing; time is now synced to localtime (hardware clock) after boot; widget theme changed to Bluebird for GTK+ 3 compatibility; now has a helpful beep to indicate when long processes are finished; added alsamixergui to enable mixer button on volume control; drive reset utility can now operate on multiple drives simultaneously; removed Synaptic and boot-repair packages to reduce image size.

Download: redobackup-livecd-1.0.4.iso

IPFire 2.11 Core 64 Free Download

 
Michael Tremer has announced the release of IPFire 2.11 Core 64, a specialist firewall distribution, with updated intrusion detection software and fixed MAC rules: "Today, we are releasing the 64th Core Update for IPFire 2.11. The Intrusion Detection program Snort has been updated to version 2.9.3.1, the corresponding daq library to version 1.1.1. This enables Snort to work with the latest VRT rule set. Outgoing firewall - the broken MAC rules have been fixed. It was impossible to use the MAC rules to allow hosts to access the Internet. A bigger rewrite of the code fixes this problem and makes the outgoing firewall a bit more performing. Minor bugs and feature enhancements: update accelerator - the path to the delete icon has been fixed; pakfire can now use the XZ compression.

Download: ipfire-2.11.i586-full-core64.iso

LinuxCBT PostgreSQL Edition Free CBT Download

LinuxCBT PostgreSQL Edition Free CBT Download

LinuxCBT DBMS Edition feat. PostgreSQL focuses on the implementation of PostgreSQL DBMS.

PostgreSQL is a widely used open source ORDBMS engine due to its: non-commercial implications, flexible license, long academic development history @ UC Berkeley, object-oriented and relational nature, cross-platform prowess and considerable scalability.

If you are/will be responsible for PostgreSQL and/or an environment of SQL flavors (MS SQL, Oracle, MySQL, etc.), broaden your knowledge of SQL implementations by exploring PostgreSQL. The benefits will be realized in any SQL arena.

Let LinuxCBT DBMS Edition feat. PostgreSQL cost-effectively strengthen your SQL skills.

Course Objective

PostgreSQL - DBMS

    Introduction - Topology - Features

        Identify key systems to be used

        Discuss key PostgreSQL features

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Installing and Configuring PhpMyAdmin-3.5.1

Installing and Configuring PhpMyAdmin-3.5.1

PhpMyAdmin is a tool written in PHP intended to handle the administration of MySQL over the World Wide Web. Most frequently used operations are supported by the user interface (managing databases, tables, fields, relations, indexes, users, permissions, while you still have the ability to directly execute any SQL statement. It comes with an intuitive web interface, support for most MySQL features.

Install phpMyAdmin

Type the following command:

# yum search phpmyadmin

# yum -y install phpmyadmin

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Installation of MySQL on Linux

MySQL

MySQL is a relational database management system (RDBMS) that runs as a server providing multi-user access to a number of databases. This is guide, howto install or upgrade MySQL Community Server latest and greatest version 5.5.28 on CentOS 6 and Red Hat (RHEL) 6.

Install MySQL Database 5.5.28 on CentOS 6/5, Red Hat (RHEL) 6/5

1. Change root user

su -

CentOS and Red Hat (RHEL)

Run the following command defined with your Operating system

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Installing PostgreSQL9.2 on Redhat (RHEL5 & 6)

Installing PostgreSQL9.2 on Redhat (RHEL)

the same installation you can use for CentOS

1. Install PostgreSQL 9.2.1 Database Server on CentOS/Red Hat (RHEL)

1.1 Change root user or login as a root

su –

Example: su - root

1.2 Red Hat (RHEL)

Add exclude to /etc/yum/pluginconf.d/rhnplugin.conf file [main] section:

[main]

...

exclude=postgresql*

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Ubuntu 12.10 has been released

Ubuntu 12.10 has been released. Featuring many popular open-source applications, up-to-date Unity desktop and new cloud-related features, the latest version of Canonical's Linux distribution for desktops and servers is ready for download: "Ubuntu 12.10 introduces innovations that bring together desktop and cloud-based experiences, representing the next stage in the transition to a multi-device, cloud-based world. New Previews give large, clear previews of content as it appears in the Dash search results, giving users a quick way to get more information to help find what they are looking for. The new Web Apps feature makes frequently used web applications available through the desktop.


Download: Official Website
ubuntu-12.10-desktop-i386.iso
ubuntu-12.10-desktop-amd64.iso

Protecting Against Intruders with Security- Firewall

As an administrator in today’s world of networked computing and easy access to the Internet, security both internally and externally must be the first and last issue considered. Denying unauthorized access is the first step to keeping your system secure. The mechanism to prevent access to all or some network services on a system is called a firewall.

Every operating system allows for the implementation of a firewall differently. Red Hat Enterprise Linux uses IPTables, a network packet-filtering mechanism in the Linux kernel. IPTables can be used to allow or deny packets based on numerous factors including their destination, their source, which port they are trying to access, the user ID of the process that created the packet, and more.

Install the iptables RPM package to use IPTables. It includes utilities to configure which packets to filter. The IPTables configuration consists of a series of rules. Each rule must be for a specific table, with each table having its own set of chains. A chain is a list of rules, which are compared to the packets passed through the chain. If a set of packets matches a chain, the target of the rule tells the system what to do with the packets, including passing it along to a different chain.

This section discusses how to write and enable IPTables rules. It also discusses the Red Hat Enterprise Linux security levels, which are predefined sets of IPTables rules. They can be used to quickly implement a basic firewall.

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Protecting Against Intruders with Security- Enhanced Linux

On a system without Security-Enhanced Linux (SELinux) enabled, discretionary access control (DAC) is used for file security. Basic file permissions are used to grant file access to users. Users and programs alike are allowed to grant insecure file permissions to others. For users, there is no way for an administrator to prevent a user from granting world-readable and world writable permissions to his files. For programs, the file operations are performed as the owner of the process, which can be the root user, giving the program access to any file on the system.

SELinux is a mandatory access control (MAC) mechanism, implemented in the kernel. Programs protected by SELinux are only allowed access to parts of the filesystem they require to function properly, meaning that if a program intentionally or unintentionally tries to access or modify a file not necessary for it to function or a file not in a directory controlled by the program, file access is denied and the action is logged. The ability to protect files with SELinux is implemented in the kernel. Exactly what files and directories are protected and to what extent they are protected is defined by the SELinux policy. This section gives instructions on how to enable the SELinux protection mechanism, describes the SELinux policies available in Red Hat Enterprise Linux, tells you how to read the SELinux permissions of a file, shows how the SELinux Troubleshooting Tool alerts you of SELinux errors, and steps you through how to change the security context of files.

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Windows 8 Installation Step by Step

Window 8 Installation

Step 1:

The first thing you should do is head to Windows 8 and downloads the installation image for your chosen architecture. The image used in the creation of this guide is the 64-bit (x64) ISO.

Step 2:

Using your disc burning software, burn the .iso you downloaded to a DVD.  and boot form your CD-ROM Drive.

Step 3: 

Once loaded you will see the following screen.

Select your location, keyboard and regional language settings as required and click "next" to continue and you'll see the following box:

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Google Chrome for Linux

Google Chrome is a browser that combines a minimal design with sophisticated technology to make the web faster, safer, and easier. It has one box for everything: Type in the address bar and get suggestions for both search and web pages. Will give you thumbnails of your top sites; Access your favorite pages instantly with lightning speed from any new tab.

Download: Google Chrome

Frozen Bubble game for linux

Frozen Bubble

Colorful 3D rendered penguin animations, 100 levels of 1p game, hours and hours of 2p game, nights and nights of 2p/3p/4p/5p game over LAN or Internet, a level-editor, 3 professional quality digital soundtracks, 15 stereo sound effects, 8 unique graphical transition effects, 8 unique logo eye-candies.

Download: Frozen Bubble

Quantum GIS (QGIS) Software for Redhat, Fedora and Centos

Quantum GIS (QGIS) is a user friendly Open Source Geographic Information System (GIS) licensed under the GNU General Public License. QGIS is an official project of the Open Source Geospatial Foundation (OSGeo). It runs on Linux, Unix, Mac OSX, Windows and Android and supports numerous vector, raster, and database formats and functionalities.
QGIS is available on Windows, MacOS X, Linux and Android. Binary packages are provided for the current version. The current version is QGIS 1.8.0 and was released in June 2012.

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NetBSD 6.0 RC2 Release Free Download

NetBSD 6.0 RC2

Jeff Rizzo has announced the availability of the second release candidate for NetBSD 6.0: "On behalf of NetBSD's developers, I'm happy to announce the availability of the second release candidate of NetBSD 6.0. Adding a little more polish before the 6.0 release,

 

Fixes since NetBSD 6.0_RC1
Adding a little more polish before the 6.0 release, RC2 fixes these additional issues:
 •The vax port shared library issue is resolved, and vax is once again bootable
 •ntpd(8) broadcast transmission is fixed
 •i486 support is fixed in the i386 port.
 •Interrupt issues on some PowerPC machines are fixed
 •X.org display on a Xen amd64 DOM0 is now working again
 •a pmap_growkernel() issue which causes some systems to reset very early in the boot process is fixed.

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avast! Linux Home Edition - Antivirus software for Linux

avast! Linux Home Edition represents an antivirus solution for the increasingly popular Linux platform.
The Home Edition is offered free of charge but only for home, non-commercial use. Both of these conditions should be met.

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How to Manually Mount a USB Flash Drive on Redhat Enterprise Linux

1.       Login as a root redhat Enterprise linux or Centos distribution then enter the appropriate password when prompted.

2.       Enter the command lsusb at the command line.  Thankfully for Plug-N-Play, your computer should recognize your USB drive. 

3.       If it does not, try plugging into another USB drive and re-issuing the lsusb command. 

4.       Look for the device assignment.  Generally, this is done by ‘searching’ using the dmesg command.  After issuing the dmesg | grep ‘disk’ command, I found my device assignment as shown in the output /dev/sdb.

5.       Now, let’s create a folder in the Linux file directory to act as a mount point for our USB flash drive.  I am going to create a folder in the /mnt directory called /usbflash’ by issuing the "mkdir /mnt/usbflash" command.

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Fedora 18 Has Been Released

 

The delayed alpha build of Fedora 18 has been released: "The Fedora 18 'Spherical Cow' alpha release is plumping up! This release offers a preview of some of the best free and open-source technology currently under development. Features: NetworkManager hotspots improve the ability to use a computer's WiFi adapter to create a network hot spot; the redesigned installation system adds flexibility to the installation process while simplifying the user interface; desktop updates galore - GNOME 3.6, KDE Plasma Workspace 4.9, Xfce 4.10, Sugar 0.98, and the introduction of the MATE Desktop in Fedora." Read the release announcement and release notes for more information.
 

Download (torrents): Fedora-18-Alpha-i686-Desktop.iso 

The xinetd Super Server

Not all services have their own initialization script for starting, stopping, and checking the status of the daemon. Some network services are controlled by xinetd, also known as the super server. Running services through xinetd allows the administrator to utilize xinetd features such as access control, custom logging, and the incoming connection rate. The xinetd service listens on all ports used by the daemons it controls. When a connection is requested, xinetd determines if the client is allowed access. If the client is allowed access, xinetd starts up the desired service and passes the client connection to it. The xinetd RPM package must be installed to use this super server. If it is not, install it via Red Hat Updates.

Configuring the xinetd Server

The xinetd super daemon uses the /etc/xinetd.conf file as the master configuration file and the /etc/xinetd.d/ directory for configuration files per service controlled by xinetd. This section discusses how to use these files to configure xinetd and its services.

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How to install Firefox 15 on Linux Redhat, Ubuntu, Debian, CentOS, Fedora or any other Linux distribution.

This howto explains how to install Firefox 15 on Linux, with or without replacing an existing Firefox installation.

1. Download

Download the release from the official channels page:
www.mozilla.com/firefox/channels/
A 64 bit build is also available in the x86_64 directory of Mozilla's FTP.

This how-to supposes that the downloaded file is saved in the “Downloads” directory situated in your home directory.

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Securing Remote Logins with OpenSSH Server

OpenSSH is the open source version of SSH, or Secure Shell. Connectivity tools such as Telnet and FTP are well-known, but they send data in plain text format, which can be intercepted by someone using another system on the same network, including the Internet. On the other hand, all data transferred using OpenSSH tools is encrypted, making it inherently more secure. The OpenSSH suite of tools includes ssh for securely logging in to a remote system and executing remote commands, scp for encrypting files while transferring them to a remote system, and sftp for secure FTP transfers. OpenSSH uses a server-client relationship. The system being connected to is referred to as the server. The system requesting the connection is referred to as the client. A system can be both an SSH server and a client. OpenSSH also has the added benefits of X11 forwarding and port forwarding. X11 forwarding, if enabled on both the server and client, allows users to display a graphical application from the system they are logged in to on the system they are logged in from. Port forwarding allows a connection request to be sent to one server but be forwarded to another server that actually accepts the request. This section discusses how to use OpenSSH, both from the server-side and the client-side.

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Configuration of Apache HTTP server

Creating a Web Server with the Apache HTTP Server

Apache Configuration step by step click here

When you view a web page over the Internet, the code to create that page must be retrieved from a server somewhere on the Internet. The server that sends your web browser the code to display a web page is called a web server. There are countless web servers all over the Internet serving countless websites to people all over the world. A web server can also be set up on an internal network so that it is only accessible by the computers inside the private network. If this internal network is inside a company or corporation, it is often called an intranet. Whether you need a web server to host a website on the Internet or to host a company portal inside its internal network, a Red Hat Eterprise Linux server can function as a web server using the Apache HTTP server. The Apache HTTP server is a popular, open source server application that runs on many UNIX-based systems as well as Microsoft Windows. This section explains how to get a web server up and running on Red Hat Enterprise Linux.

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Granting Network Connectivity with DHCP Server

DHCP, or Dynamic Host Configuration Protocol, allows an administrator to configure network settings for all clients on a central server. The DHCP clients request an IP address and other network settings from the DHCP server on the network. The DHCP server in turn leases the client an IP address within a given range or leases the client an IP address based on the MAC address of the client’s network interface card (NIC). If an IP address is assigned according to the MAC address of the client’s NIC, the same IP address can be leased to the client every time the client requests one.

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Samba configuration Step by Step Part-3

Connecting Samba Clients and Users

Now that all your Samba shares are set up, you can access them from one of the client systems (Client02). Be aware that you need to install the client Samba packages before you can connect to any Samba shares.

Step 1. Install the client packages:

# yum install -y samba-client samba-common

Step 2. Verify that the install was successful:

# rpm -qa | grep samba

samba-client-3.5.4-68.el6.x86_64

samba-winbind-clients-3.5.4-68.el6.x86_64

samba-common-3.5.4-68.el6.x86_64

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Samba configuration Step by Step Part-2

Samba the Use SELinux and Firewall Configuration

If you are accustomed to Windows systems, you should already know what ports you need to open on the firewall.

Step 1. Use the iptables command to create your firewall rules:

# iptables -I INPUT 5 -p tcp -m tcp --dport 137 -j ACCEPT

# iptables -I INPUT 5 -p udp -m udp --dport 138 -j ACCEPT

# iptables -I INPUT 5 -p udp -m udp --dport 139 -j ACCEPT

# iptables -I INPUT 5 -p tcp -m tcp --dport 445 -j ACCEPT

Step 2. Save the rules you just created:

# service iptables save

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Samba configuration Step by Step Part-1

Samba

Samba, which uses the CIFS/SMB protocol, is commonly brought up when you want Linux and Windows machines to be able to share files together. Aside from the file sharing uses, Samba also has some built-in functionality to run as a member server on a Windows domain, print server, or file server. Let’s get started with the setup.

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Installing and configring nfs-server step by step part 4

Connecting Clients Via NFS

Setting up a client to use NFS is relatively simple when you have the NFS server in place. Let’s set up the Client01 system to use a share on the RHEL01 NFS server.

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Installing and configring nfs-server step by step part 3

NFSD Firewall and SELinux Configuration

NFS is one of the many Red Hat services that can take advantage of TCP Wrappers as well as firewall rules for security. We don’t use TCP Wrappers here, but should you run into trouble on the exam with the NFS service not working, don’t forget to check to see whether anything is being filtered by TCP Wrappers. Because you are using NFS version 4 here, you need to create only a single firewall rule.

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Installing and configring nfs-server step by step part 2

Now export the file to network

If you already started the services before creating an /etc/exports file, you can also use the exportfs command to manually export any new resources added to the /etc/exports file.

Syntax: exportfs [options]

Options:

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Installing and Configring NFS Server step by step Part 1

Installing and Configring NFS Server step by step

Follow these steps to install an NFS server.

Step 1. To begin the NFS server setup, install the required packages:

# yum install -y nfs-utils nfs4-acl-tools

Step 2. Verify the package installation:

# rpm -qa | grep nfs

nfs4-acl-tools-0.3.3-5.el6.x86_64

nfs-utils-1.2.2-7.el6.x86_64

nfs-utils-lib-1.1.5-1.el6.x86_64

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Samba Server Configuration

Samba File Sharing

Samba is the file-sharing protocol used by the Microsoft Windows operating system. Because some network environments include more than one operating system, Red Hat Enterprise Linux provides a way to use alternative file-sharing methods. If only sharing between Linux and other UNIX variants, it is recommended that NFS be used instead. For additional information on Samba, refer to the /usr/share/doc/samba-<version>/ directory.

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Connecting & Mounting to the NFS Share Folders

Connecting to the NFS Share Folders

There are three ways to mount an NFS export on a client system, assuming the server has given the client permission to do so:

1.     Use the mount command along with the server name, exported directory, and local mount point.

2.     Add the export to /etc/fstab so it is automatically mounted at boot time or is Available to be mounted.

3.     Use the autofs service to mount the share when a user attempts to access it from a client.

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Redhat Enterprise linux 5 NFS-Part3

Redhat Enterprise linux 5 NFS-Part2

Redhat Enterprise linux 5 NFS-Part1

Configuring the NFS Server on the Command Line

To configure a Red Hat Enterprise Linux system as an NFS server via the command line, make sure the nfs-utils RPM package is installed.

The server configuration file, /etc/exports, uses the following format:

shared_directory allowed_hosts(options)

where shared_directory is the name of the directory to be shared, allowed_hosts is the IP address range of the allowed clients, and options is a list of NFS options for the exported directory. Obviously, the exported directory must exist. You must be root to modify this file.

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NFS and SELinux Configuration

NFS and SELinux

In Red Hat Enterprise Linux 5 & 6, NFS is protected by the default Security-Enhanced Linux (SELinux) policy, known as the targeted policy. By default, this targeted policy allows NFS connections to the server by setting the nfs_export_all_ro and nfs_export_all_rw SELinux booleans to 1.

If you are sharing home directories over NFS while using SELinux, you must set

use_nfs_home_dirs boolean to 1 on each client connecting to the NFS server sharing the home directories. Execute the following command as root:

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What is NFS server

Network File Sharing

In an enterprise computing environment, it is common to share files between computers or allow several users to access the same set of files on a central server and have all changes be visible to all users immediately. In a pure UNIX environment, including those consisting solely of Red Hat Enterprise Linux systems, this can be achieved via Network File System (NFS). If sharing files between Red Hat Enterprise Linux and Microsoft Windows systems is desired, Samba can be used to achieve connectivity.

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Understanding PAM, or Pluggable Authentication Modules

PAM, or Pluggable Authentication Modules, is an authentication layer that allows programs to be written independent of a specific authentication scheme. Applications request authentication via the PAM library, and the PAM library determines whether the user is allowed to proceed. If an administrator wants to implement a different authentication scheme, he just changes the PAM configuration files and the existing programs work seamlessly.

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Automation with crontab

Automation with crontab

In any operating system, it is possible to create jobs that you want to reoccur. This

process, known as job scheduling, is usually done based on user-defined jobs. For

Red Hat, this process is handled by the cron service, which can be used to schedule tasks (also called jobs). By default, Red Hat comes with a set of predefined jobs that occur on the system (hourly, daily, weekly, monthly, and with arbitrary periodicity). As an administrator, however, you can define your own jobs and allow your users to create them as well.

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Scheduling Tasks with Cron job

Now that you understand the basics of automating tasks with a script or program, the next step is to know how to schedule the tasks so they are executed at a specific time or on a set schedule. Some scripts such as removing users may not need to be scheduled, but others such as performing backups might work better on a schedule so users can anticipate them or so they can be run during a time when they won’t interfere with the daily workload of the system.

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Executing Commands in a Bash Script

To execute a series of commands in a Bash script, list each command on a separate line. For example, Listing shows the very basic Bash script that gathers information about system resources.

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Writing Scripts with Bash

The GNU Bourne Again Shell (Bash) scripting language is useful when trying to automate a sequence of commands or when you want to execute the same command over and over again until a certain limit is reached.

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Emergency Mode & Filesystem Repairing

Emergency Mode

Emergency mode is similar to single-user mode except the root filesystem is mounted read-only and runlevel 1 is not used. Boot into emergency mode using the same method as single-user mode except replace the word single with emergency in the boot method.

Because the filesystem is mounted read-only, files can not be changed or repaired, but files can be retrieved off the system.

Filesystem Repair

If one or more filesystem are corrupt, boot into rescue mode and do not mount the filesystem. Even if you can boot into single-user mode, do not use it because the filesystem cannot be repaired if it is mounted.

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Single-User Mode

Single-user mode is equivalent to runlevel 1 on the system. If runlevel 1 is not configured properly, you will not be able to boot into single-user mode. Rescue mode requires a boot media, but single-user mode is specified as a kernel option using the installed boot loader and does not require additional boot media. However, it does require that the boot loader is working properly and that the filesystem be mounted. It does not provide the ability to start a network connection.

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Recovery and Repair Linux system

To analyze or repair a system failure, you might need to boot into the system. But, what if the boot loader is corrupt or what if the filesystem can’t be mounted anymore? Red Hat Enterprise Linux includes alternative boot methods for system repair: rescue mode, single user mode, and emergency mode.

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The rsync Utility

The rsync Utility

When developing backup scripts, consider using the rsync utility. The rsync utility allows you to copy from the local system to a remote system or copy between two local directories. If the files exist in the destination directory, rsync only transfers the differences in the files, which is ideal for backups. The rsync RPM package is required and should already be installed on your system.

After the rsync command-line arguments are listed, the first directory listed is the source, and the second directory listed is the destination. If either directory is preceded by a hostname and a colon (:), the directory is a remote directory. For example, to transfer all home directories to the backup/ directory on the remote server backup.example.com:

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The tar Utility and compression

 The tar Utility

When backing up data that is no longer being used or data that is not frequently changed, consider creating a compressed archive file using the tar archive utility in combination with one of the compression tools such as gzip or bzip2. Creating a compressed archive file results in one file that must be decompressed and unarchived before files can be restored from it. The compression of the files saves room on the backup media. To use tar, the tar RPM package must be installed. It should be installed on your system unless you chose to only install a specific set of packages. The tar utility does not preserve access control lists.

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Techniques for Backup and Recovery

When hardware components or security measures fail, every administrator must be prepared to recover a system as quickly and efficiently as possible. Preparing for a disaster means having a solid backup procedure and a well- tested recovery process.

Because you can’t always detect when a failure will occur, it is important to create backups on a regular basis depending on how often the data changes and how much time it takes to complete the backup. All the files on the system.

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What are Users and Groups in Linux

What Are Users and Groups?

In addition to a Red Hat Enterprise Linux system having a username for each user allowed access to a system, each system has user groups. A user group is a group of one or more users. A user can be a member of more than one group.

User groups can be any grouping of users on which you decide: groups of users in a functional department, groups in the same physical location, or groups based on security access. It is important to plan the user groups for your company carefully before implementing them because changing them means changing the groups associated with files, which can sometimes lead to incorrect group permissions if they are not changed correctly.

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RHEL-6 LVM Introduction Part 2

RHEL-6 LVM Introduction Part1

Creating a Physical LVM

Creating a Physical Volume

To create a new physical volume from free hard drive space or a hard drive partition, use the pvcreate command:

pvcreate <disk>

Replace <disk> with the device name of the hard drive:

pvcreate /dev/sda

or the partition name:

pvcreate /dev/sda1

The <disk> specified can also be a meta device or loopback device, but using an entire hard disk or partition is more common. After creating a physical volume, you can either add it to an existing volume group or create a new volume group with the physical volume.

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Adding Additional Disk Space LVM

Adding Additional Disk Space

One big advantage of using LVM is that the size of a logical volume can be increased and logical volumes can be added to create additional mount points. To modify the LVM configuration post-installation, the lvm2 package needs to be installed.

To increase the size of an existing logical volume or to add a logical volume, you first need free disk space. This free disk space can either be disk space that already exists in the system as unpartitioned space (not part of an existing logical volume), an unused partition, physical volume that is not already a member of a logical volume, or disk space as a result of installing one or more additional hard drives to the system. The disk space can come from removing a logical volume to create space in the logical volume group, however, this is not common because if the LV already exists, it is most likely already being used and cannot be easily deleted without losing data.

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What is LVM (logical Volume manager)

Understanding LVM (logical Volume manager)

Logical Volume Manager, or LVM, is a storage management solution that allows administrators to divide hard drive space into physical volumes (PV), which can then be combined into logical volume groups (VG), which are then divided into logical volumes (LV) on which the file system and mount point are created.

A logical volume group can include more than one physical volume, a mount point can include more than one physical hard drive, meaning the largest mount point can be larger than the biggest hard drive in the set. These logical volumes can be resized later if more disk space is needed for a particular mount point. After the mount points are created on logical volumes, a filesystem must be created on them.

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