Commercial Linux
Linux Boot Process
1.BIOS(Basic Input/Output System)
2.MBR(Master Boot Record)
3.LILO or GRUB
LILO:-LInux LOader
GRUB:-GRand Unified Bootloader
4.Kernel
5.init
6.Run Levels
1.BIOS:
i.When we power on BIOS performs a Power-On Self-Test (POST) for all of the different hardware components in the system to make sure everything is working properly
ii.Also it checks for whether the computer is being started from an off position (cold boot) or from a restart (warm boot) is
stored at this location.
iii.Retrieves information from CMOS (Complementary Metal-Oxide Semiconductor) a battery operated memory chip on the motherboard that stores time, date, and critical system information.
iv.Once BIOS sees everything is fine it will begin searching for an operating system Boot Sector on a valid master boot sector
on all available drives like hard disks,CD-ROM drive etc.
v.Once BIOS finds a valid MBR it will give the instructions to boot and executes the first 512-byte boot sector that is the first
sector (“Sector 0″) of a partitioned data storage device such as hard disk or CD-ROM etc .
2.MBR
i. Normally we use multi-level boot loader.Here MBR means I am referencing to DOS MBR.
ii.Afer BIOS executes a valid DOS MBR,the DOS MBR will search for a valid primary partition marked as bootable on the hard disk.
iii.If MBR finds a valid bootable primary partition then it executes the first 512-bytes of that partition which is second level MBR.
iv. In linux we have two types of the above mentioned second level MBR known as LILO and GRUB
3.LILO
i.LILO is a linux boot loader which is too big to fit into single sector of 512-bytes.
It is divided into two parts :an installer and a runtime module.
iii.The installer module places the runtime module on MBR.The runtime module has the info about all operating systems installed.
iv.When the runtime module is executed it selects the operating system to load and transfers the control to kernel.
v.LILO does not understand filesystems and boot images to be loaded and treats them as raw disk offsets
GRUB
i.GRUB MBR consists of 446 bytes of primary bootloader code and 64 bytes of the partition table.
ii.GRUB locates all the operating systems installed and gives a GUI to select the operating system need to be loaded.
iii.Once user selects the operating system GRUB will pass control to the karnel of that operating system.
See below what is the difference between LILO and GRUBThe original file is /etc/grub.conf of which you can observe a symlink file at /boot/grub/grub.conf
Sample /boot/grub/grub.conf
4.Kernel
i.Once GRUB or LILO transfers the control to Kernel,the Kernels does the following tasks
i.The kernel, once it is loaded, finds init in sbin(/sbin/init) and executes it.
ii.Hence the first process which is started in linux is init process.
iii.This init process reads /etc/inittab file and sets the path, starts swapping, checks the file systems, and so on.
i.There are 7 run levels in which the linux OS runs and different run levels serves for different purpose.The descriptions are
given below.
Many people might have no idea about Commercial Linux Distribution. Some think that it is like Microsoft or Apple. NO but it is different, Commercial Linux Distribution is free to use but if you want their support you need to pay.
Best example for Commercial Linux is Redhat Linux, it is free to use it, But if you need their support you have to pay for it.
There are million of companies use linux in their server system and also many educational institute use linux based server.
These Server system are difficult to configure for a individual so for that purpose there is Commercial linux Distribution.
If you are using Commercial linux Distribution for free and if you stuck with any problem in the linux Distribution you can subscribe it and take their help.
CentOS / Red Hat Enterprise Linux
Red Hat Enterprise Linux is a commercial Linux distribution intended for servers and workstations. It’s based on the open-source Fedora project, but is designed to be a stable platform with long-term support.
Red Hat uses trademark law to prevent their official Red Hat Enterprise Linux software from being redistributed. However, the core software is free and open-source. CentOS is a community project that takes the Red Hat Enterprise Linux code, removes all Red Hat’s trademarks, and makes it available for free use and distribution. It’s a free version of RHEL, so it’s good if you want a stable platform that will be supported for a long time. CentOS and Red Hat recently announced they’re collaborating, so CentOS is now part of Red Hat itself.
Open Source Linux
Ubuntu
Ubuntu is probably the most well-known Linux distribution. Ubuntu is based on Debian, but it has its own software repositories. Much of the software in these repositories is synced from Debian’s repositories.
The Ubuntu project has a focus on providing a solid desktop (and server) experience, and it isn’t afraid to build its own custom technology to do it. Ubuntu used to use the GNOME 2 desktop environment, but it now uses its own Unity desktop environment. Ubuntu is even building its own Mir graphical server while other distributions are working on the Wayland.
Ubuntu is modern without being too bleeding edge. It offers releases every six months, with a more stable LTS (long term support) release every two years. Ubuntu is currently working on expanding the Ubuntu distribution to run on smartphones and tablets.
Mint is a Linux distribution built on top of Ubuntu. It uses Ubuntu’s software repositories, so the same packages are available on both. Originally Mint was an alternative distribution loved mainly because it included media codecs and proprietary software that Ubuntu didn’t include by default.
This distribution now has its own identity. You won’t find Ubuntu’s own Unity desktop here — instead, you get a more traditional Cinnamon or MATE desktop. Mint takes a more relaxed approach to software updates and won’t automatically install critical software updates. Controversially, this has led some Ubuntu developers to label it insecure.
Debian
Debian is an operating system composed only of free, open-source software. The Debian project has been operating since 1993 — over 20 years ago! This widely respected project is still releasing new versions of Debian, but it’s known for moving much more slowly than distributions like Ubuntu or Linux Mint. This can make it more stable and conservative, which is ideal for some systems.
Ubuntu was originally founded to take the core bits of stable Debian and improve on them more quickly, packaging the software together into a user-friendly system that’s more frequently updated.
Fedora
Fedora is a project with a strong focus on free software — you won’t find an easy way to install proprietary graphics drivers here, although third-party repositories are available. Fedora is bleeding edge and contains the latest versions of software.
Unlike Ubuntu, Fedora doesn’t make its own desktop environment or other software. Instead, the Fedora project uses “upstream” software, providing a platform that integrates all this upstream software without adding their own custom tools or patching it too much. Fedora comes with the GNOME 3 desktop environment by default, although you can also get “spins” that come with other desktop environments.
Fedora is sponsored by Red Hat, and is the foundation for the commercial Red Hat Enterprise Linux project. Unlike RHEL, Fedora is bleeding edge and not supported for long. If you want a more stable release that’s supported for longer, Red Hat would prefer you use their Enterprise product.
openSUSE / SUSE Linux Enterprise
openSUSE is a community-created Linux distribution sponsored by Novell. Novell purchased SuSE Linux in 2003, and they still create an enterprise Linux project known as SUSE Linux Enterprise. Where Red Hat has the Fedora project that feeds into Red Hat Enterprise Linux, Novell has the openSUSE project that feeds into SUSE Linux Enterprise.
Like Fedora, openSUSE is a more bleeding edge version of Linux. SUSE was once one of the great user-friendly desktop Linux distributions, but Ubuntu eventually took that crown.
Mageia / Mandriva
Mageia is a fork of Mandriva Linux created in 2011. Mandriva — known as Mandrake before that — was once one of the great user-friendly Linux distributions.
Like Fedora and openSUSE, this is a community-created project to create an open-source Linux distribution. Mandriva SA no longer creates a consumer Linux distribution for desktop PCs, but their business Linux server projects are based on Mageia code — just like how Fedora and openSUSE provide code to their enterprise equivalents.
Arch Linux
Arch Linux is more old school than many of the other Linux distributions here. It’s designed to be flexible, lightweight, minimal, and to “Keep it Simple.” Keeping it simple doesn’t mean Arch provides tons of graphical utilities and automatic configuration scripts to help you set up your system. Instead, it means Arch dispenses with that stuff and gets out of your way.
You’re in charge of configuring your system properly and installing the software you like. Arch doesn’t provide an official graphical interface for its package manager or complex graphical configuration tools. Instead, it provides clean configuration files designed for easy editing. The installation disc dumps you at a terminal, where you’ll need to enter the appropriate commands to configure your system, partition your disks, and install the operating system yourself.
Arch uses a “rolling release” model, which means any installation image is just a snapshot of the current software. Every bit of software will be updated over time without you needing to upgrade to a new “release” of Arch.
This distribution has a bit in common with Gentoo, which was popular at one time. Both Linux distributions are designed for users who know how their systems work or who are at least willing to learn. However, Arch uses binary packages while Gentoo had an (unnecessary) focus on compiling every bit of software from source — this means it’s quick to install software on Arch as you don’t have to spend CPU cycles and time waiting for software to compile.
Slackware Linux
Slackware is another institution. Founded in 1993, Slackware is the oldest Linux distribution that’s still maintained and putting out new releases today.
Its pedigree shows — like Arch, Slackware dispenses with all those unnecessary graphical tools and automatic configuration scripts. There’s no graphical installation procedure — you’ll have to partition your disk manually and then run the setup program. Slackware boots to a command-line environment by default. It’s a very conservative Linux distribution.
Puppy Linux
Puppy Linux is another fairly well-known Linux distribution. Previous versions have been built
on Ubuntu, but the latest is built on Slackware. Puppy is designed to be a small, lightweight operating system that can run well on very old computers. The puppy ISO file is 161 MB, and Puppy can boot from that disc in a live environment. Puppy can run on PCs with 256 MB or RAM, although it does recommend 512 MB for the best experience.
Puppy isn’t the most modern and doesn’t have all the flashiest bells and whistles, but it can help you revive an old PC.
These aren’t the only Linux distributions out there. Distrowatch lists many and tries to rank them by popularity.
The choice is yours
Linux Boot Process
1.BIOS(Basic Input/Output System)
2.MBR(Master Boot Record)
3.LILO or GRUB
LILO:-LInux LOader
GRUB:-GRand Unified Bootloader
4.Kernel
5.init
6.Run Levels
1.BIOS:
i.When we power on BIOS performs a Power-On Self-Test (POST) for all of the different hardware components in the system to make sure everything is working properly
ii.Also it checks for whether the computer is being started from an off position (cold boot) or from a restart (warm boot) is
stored at this location.
iii.Retrieves information from CMOS (Complementary Metal-Oxide Semiconductor) a battery operated memory chip on the motherboard that stores time, date, and critical system information.
iv.Once BIOS sees everything is fine it will begin searching for an operating system Boot Sector on a valid master boot sector
on all available drives like hard disks,CD-ROM drive etc.
v.Once BIOS finds a valid MBR it will give the instructions to boot and executes the first 512-byte boot sector that is the first
sector (“Sector 0″) of a partitioned data storage device such as hard disk or CD-ROM etc .
2.MBR
i. Normally we use multi-level boot loader.Here MBR means I am referencing to DOS MBR.
ii.Afer BIOS executes a valid DOS MBR,the DOS MBR will search for a valid primary partition marked as bootable on the hard disk.
iii.If MBR finds a valid bootable primary partition then it executes the first 512-bytes of that partition which is second level MBR.
iv. In linux we have two types of the above mentioned second level MBR known as LILO and GRUB
3.LILO
i.LILO is a linux boot loader which is too big to fit into single sector of 512-bytes.
It is divided into two parts :an installer and a runtime module.
iii.The installer module places the runtime module on MBR.The runtime module has the info about all operating systems installed.
iv.When the runtime module is executed it selects the operating system to load and transfers the control to kernel.
v.LILO does not understand filesystems and boot images to be loaded and treats them as raw disk offsets
GRUB
i.GRUB MBR consists of 446 bytes of primary bootloader code and 64 bytes of the partition table.
ii.GRUB locates all the operating systems installed and gives a GUI to select the operating system need to be loaded.
iii.Once user selects the operating system GRUB will pass control to the karnel of that operating system.
See below what is the difference between LILO and GRUBThe original file is /etc/grub.conf of which you can observe a symlink file at /boot/grub/grub.conf
Sample /boot/grub/grub.conf
default=0
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
title Red Hat Enterprise Linux Server (2.6.18-194.26.1.el5)
root (hd0,0)
kernel /vmlinuz-2.6.18-194.26.1.el5 ro root=/dev/VolGroup00/root clocksource=acpi_pm divisor=10
initrd /initrd-2.6.18-194.26.1.el5.img
title Red Hat Enterprise Linux Server (2.6.18-194.11.4.el5)
root (hd0,0)
kernel /vmlinuz-2.6.18-194.11.4.el5 ro root=/dev/VolGroup00/root clocksource=acpi_pm divisor=10
initrd /initrd-2.6.18-194.11.4.el5.img
title Red Hat Enterprise Linux Server (2.6.18-194.11.3.el5)
root (hd0,0)
kernel /vmlinuz-2.6.18-194.11.3.el5 ro root=/dev/VolGroup00/root clocksource=acpi_pm divisor=10
initrd /initrd-2.6.18-194.11.3.el5.img4.Kernel
i.Once GRUB or LILO transfers the control to Kernel,the Kernels does the following tasks
- Intitialises devices and loads initrd module
- mounts root filesystem
i.The kernel, once it is loaded, finds init in sbin(/sbin/init) and executes it.
ii.Hence the first process which is started in linux is init process.
iii.This init process reads /etc/inittab file and sets the path, starts swapping, checks the file systems, and so on.
- Executes the system to boot into the run level as specified in /etc/inittab
# Default runlevel. The runlevels used by RHS are:
# 0 - halt (Do NOT set initdefault to this)
# 1 - Single user mode
# 2 - Multiuser, without NFS (The same as 3, if you do not have networking)
# 3 - Full multiuser mode
# 4 - unused
# 5 - X11
# 6 - reboot (Do NOT set initdefault to this)
#
id:5:initdefault:6.Runleveli.There are 7 run levels in which the linux OS runs and different run levels serves for different purpose.The descriptions are
given below.
- 0 – halt
- 1 – Single user mode
- 2 – Multiuser, without NFS (The same as 3, if you don’t have networking)
- 3 – Full multiuser mode
- 4 – unused
- 5 – X11
- 6 – Reboot
Below are given some few important differences about LILO and GRUB
| LILO |
GRUB
|
| LILO has no interactive command interface | GRUB has interactive command interface |
| LILO does not support booting from a network | GRUB does support booting from a network |
| If you change your LILO config file, you have to rewrite the LILO stage one boot loader to the MBR | GRUB automatically detects any change in config file and auto loads the OS |
| LILO supports only linux operating system | GRUB supports large number of OS |
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