RED HAT ENTERPRISE LINUX ESSENTIALS

Location of various system configuration related files :part-1

2008-09-27T03:36:00.000-07:00

We know that Linux Operating systems are totally distributed as a open source codes operating system.Here if we know about all the commands and variable definitions then we are very much able to change the configuration files as needed for our different purposes.Here the locations of different configuration related files are given below.In my next post i will discuss about how can we modify all the commands.

"Installing Red Hat Enterprise Linux 5.0 in Graphical Mode"

2008-09-18T12:07:00.000-07:00

Instructions:
1.Boot your system from the CD,this will start anaconda,the Red Hat Enterprise Linux installer
2.Press Enter at the boot:prompt
3.Choose the appropriate language for your region.
4.Choose the appropriate keyboard for your region
5.Choose NFS image for the installation method
6.You will now be prompted to do some network configuration.Select "Use dynamic IP configuration(DHCP)".Deselect IPv6 support
7.Enter the following information to configure the installation source:
# NFS Server Name:192.168.0.254
# Red Hat Enterprise Linux directory:/var/ftp/pub
8.At this point Anaconda will retrieve the necessary installation image and probe the system for its monitor and mouse type.
9.Select "Skip entering Installation Number" and click next.Confirm by clicking Skip
10.Anaconda next checks if Red Hat Enterprise Linux is already installed on this system.If yes,it will offer you the option to perform an Upgrade instead of a fresh installation.
11.Choose "Install Red Hat Enterprise Linux" and Click Next
11.Create default layout & follow here my previous post of "Size allocation of different partition".and click Next
12.Use the default Boot0Loader settings
13.Choose "DHCP for networking" and Check "the active on boot checkbox"
14.choose Enable Firewall
15.Set the time Zone
16.Set the root password
17.Use the default set of packages
18.Click Next to begin installation
19.Once you have successfully completed the installation,log in as root and examine the following :
[cat /root/install.log]
[cat /var/log/messages]
[cat /var/log/dmesg]

"LINUX RESCUE"

2008-09-17T07:03:00.000-07:00

Suppose you have two Operating systems "Windows & Linux" in parallel.Somehow if windows becomes corrupted.Then what should you do?Reinstalling the previous OSs again is not the solution.Here is a solution.
If windows becomes corrupted then you should recover your previous grub-Boot-Loader.If you can recover it then you will be able to rescue your Existing Linux OS.

First you have to insert your Linux-Bootable disk.
And there type [linux rescue]
then there will appear some messages.
then type [/mnt/sysimage]
then [chroot/mnt/sysimage]
then [grub-install /dev/hda]

Thus this will install newly Grub-boot-loader to MBR(Master Boot Record)
Then type [reboot]
After a successful rebooting a boot-loader will be appeared.Then select the first Linux OS.And press'e' button.Here 'e' for editing.
then type exactly the following codes (without third bracket).
[ root (hd0,7)
kernel /vmlinuz-2.6.18-8.el5 ro root=LABEL=/ rhgb quiet crashkernel=128M@16M
initrd /initrd-2.6.18-8.el5.img ]
then press 'b' button to boot your selected Linux OS.

"Defferent Run Levels "

2008-09-17T01:22:00.001-07:00

Run Level is considered as a System state.In Linux Operating systems there are 7 Run Levels [0-6]

Run level 0 =power off

Run level 1 =Single user mode

Run level 2 =Network without NFS

Run level 3 =Text mode (multiUser)

Run level 4 =Not defined

Run level 5 =X11 (graphical interface,its our default)

Run level 6 =Reboot

here are Run level related commands:
[ls /etc/rc.d/] ---to see rc directory for individual run level
[ls /etc/rc.d/rc.5.d] ----to see run level 5 contents.we can see other run level contents replacing rc.0,rc.1,rc.2 etc.

All the run level files are stored in /etc/init.d

"Linux Booting Process"

2008-09-17T01:22:00.000-07:00

How does actually Linux OS boot? Here is the process of Booting Linux Operating Systems.

Step 1:POST (power on self test)
Step 2:Boot-Loader (Examples of Boot-loader are 'GRUB','LILO')
Step 3:Kernel starts
Step 4:Init services starts
Actually Kernel starts all the Init processes.

"few Very Basic Commands"

2008-09-14T12:32:00.000-07:00

The following commands are the basic commands of Red Hat Linux.To execute the commands open the terminal window or console window at your Red Hat Linux Desktop.

[adduser student] to create a user named 'student'
[passwd student] to change the password for user named 'student'
[man command] to Show command details in brief
[what command] what is the command actually
[where command] location of the command
[which command] to Show exactly from where the command runs
[date] to show date
[cd directory] to change to the directory
[ls -a directory] to show hidden files
[ls -l directory] to show files of the directory
[touch file] to make a file
[cat file] to read the file
[mkdir directory] to make a directory
[who] to show who are logged in which terminals.
[cp source destination] to copy a source file to its destination directory.
[mv ] to move a source file to its destination directory.
[rm -i file] to remove a file
[rm -r directory] to remove directory

"Minimum Size allocations of Different partitions"

2008-09-14T12:23:00.000-07:00

In Linux operating systems all the hard disk partitions are also referred as individual directory.Minimum Size allocations are given below.These sizes must be maintained in partitioning hard drives while installing the Linux OS.

/ = 512MB
/boot = 100MB
/home = 512MB
/var = 512MB
/usr = 3000M
/swap = RAM*2[double of RAM size]

"Different Directories of Linux"

2008-09-14T12:13:00.000-07:00

/=top most directory
/root=roots home directory
/home=users home directory
/bin=users binary program
/sbin=super users binary program
/var=Log+mail+printer directory
/usr=doc+man+program files
'/tmp=temporary files
/opt=optional files
/etc=Global configuration files
/lib=Shared library files
/boot=kernal+boot loader
/media=foreign file system
/dev=all device file

BASIC COMMANDS of Consoles"

2008-09-14T12:08:00.000-07:00

* A typical Linux System will run six virtual Consoles and one graphical console.Switch among virtual consoles by typing:Ctrl+Alt+f[1-6]
Access the graphical console by typing:Ctrl+Alt+f7

"About REDHAT ENTERPRISE LINUX"

2008-09-14T11:32:00.000-07:00

The Red Hat Enterprise Linux product family is designed specially for organizations planning to use Linux in production settings.All products in the Red Hat enterprise Linux family are built on the same software foundation and maintain the highest level of ABI/API compatibility across releases and errata.Extensive support services are available: a one year support contract and Update Module entitlement to Red Hat Network are included with purchase.Various Service agreements are available that may provide up to 24x7 coverage with guranteed one hour response time.Support will be available for up to seven years after a particular release.

RedHat Enterprise linux is released on an eighteen to twenty-four month cycle.It is based on code developed by the open source community and adds performance enhancements,intensive testing and certification on products produced by top independent software and hardware vendors such as Dell,IBM,BEA and Oracle.Red Hat Enterprise Linux provides a high degree of standardization through its support for seven processor architectures (Intel x86-compatible,Intel Itanium 2,AMD AMD64/Intel EM64T,IBM PowerPC on server iSeries and eServer pSeries and IBM mainframe on eServer zSeries and S/390.)