The Runlevels

Many Windows users are familiar with different modes of execution of their operating system:
a. Safe mode
b. Command prompt only
c. Safe mode with network support
d. Safe mode with vga

And other such options that are presented during the boot-up process. Similarly, Linux has different modes of executing as well, which are known as runlevels. But unlike Windows, we can change runlevels on a fly.

Definition for runlevel : The term runlevel refers to a mode of operation in one of the computer operating system that implement Unix System V-style initialization. This system replaces the traditional /etc/rc and /etc/rc.local scripts used in BSD UNIX. Conventionally, seven runlevels exist, numbered from zero to six, plus an alias runlevel named 'S' and/or 's'.

Runlevels control services started by the initialization process. The number of runlevels and services started on those runlevels varies with Linux distributions. Information about the runlevels of a particular distribution is listed in file /etc/inittab.

The contents of the file include the following:

Default runlevel. The runlevels used by RedHat are :

# 0 - Halt (Do not set initdefault to this option.)

# 1 - Single User Mode

# 2 - Multi-user, without NFS (The same as 3, if you do not have networking)

# 3 - Full Multi-user Mode

# 4 - Unused

# 5 - X11

# 6 - Reboot (Do not set initdefault to this option.)

id:3:initdefault: # System initialization. si::sysinit:/etc/rc.d/rc.sysinit

l0:0:wait:/etc/rc.d/rc 0

l1:1:wait:/etc/rc.d/rc 1

l2:2:wait:/etc/rc.d/rc 2

l3:3:wait:/etc/rc.d/rc 3

l4:4:wait:/etc/rc.d/rc 4

l5:5:wait:/etc/rc.d/rc 5

l6:6:wait:/etc/rc.d/rc 6

Runlevel 0 : Is halt mode. Telling init to enter runlevel 0 will cause all processes to be killed off, the filesystems unmounted, and the machine to be halted. This is a perfectly acceptable way to bring down the system. On many laptops and modern desktop computers, this will also cause the machine to be turned off. Different commands to go to runlevel 0.

# halt

# init 0

# telinit 0

# shutdown -h

Now in the above command h is halting and now indicates shutdown the computer now it self no grace/trancision time for example you want to shutdown the command after 60 min so give the below command # shutdown -h +60.

Runlevel 1 : Runlevels 1 and 2 are generally used for debugging purposed only, and are not used during normal operations. Most desktop linux distributions boot into runlevel 5, which starts up the Graphical Login Prompt. This allows the user to use the system with X-Windows server enabled. Most servers boot into runlevel 3, which starts the text based login prompt. Linux runlevels can be changed on the fly using the init tool. If you want to switch from text based operations to the Graphical Interface, you just have to type in 'telinit 5' in the root prompt. This will bring up the Graphical Interface in your system. Each runlevel can be configured by the system administrator. The "/etc/inittab" file has information on which runlevel to start the system at and lists the processes to be run at each runlevel. Each runlevel has its own directory structure where you can define the order in which the services start. These directories are located in the /etc/rc.d/ directory, under which you have rc1.d, rc2.d, rc3.d…. rc6.d. Directories where the number from 0 to 6 that corresponds to the runlevel. Inside each directory are symbolic links that point to master initscripts found in /etc/init.d or /etc/rc.d/init.d. You can also change the runlevel at boot time. If your system uses LILO as the boot manager, you can append the runlevel to the boot command : LILO: linux 3 or LILO: linux 5. If your system uses GRUB, you can change the boot runlevel by pressing the `e’ key to edit the boot configuration. Append the runlevel to the end of the boot command as shown : kernel /vmlinuz ro root=/dev/hda1 5 different linux/unix disterbution's runlevels

Debian Linux :
Debian, as well as most of the distributions based on it, like Ubuntu, does not make any distinction between runlevels 2 to 5. See also the Debian FAQ on booting.
0 - Halt
1 - Single
2 - Full multi-user with display manager (GUI)
3 - Full multi-user with display manager (GUI)
4 - Full multi-user with display manager (GUI)
5 - Full multi-user with display manager (GUI)
6 - Reboot

Red Hat Linux
Red Hat as well as most of its derivatives uses runlevels like this.
0 - Halt
1 - Single
2 - Not used/User definable
3 - Full multi-user NO display manager
4 - Not used/User definable
5 - Full multi-user with display manager (GUI)
6 - Reboot

SUSE Linux
SUSE uses a similar setup as Red Hat :
0 - Halt
1 - Single
2 - Full multi-user with no networking
3 - Full multi-user NO display manager
4 - Not used/User definable
5 - Full multi-user with display manager (GUI)
6 - Reboot

Slackware Linux
Slackware Linux uses runlevel 1 for maintenance, as on other Linux distributions; runlevels 2, 3 and 5 identically configured for a console (with all services active); and runlevel 4 adds the X Window System.
0 - Halt
1 - Single
2 - Full multi-user NO display manager
3 - Full multi-user NO display manager
4 - Full multi-user with display manager (GUI)
5 - Not used/User definable
6 - Reboot

Gentoo Linux
0 - Halt
1 - Single
2 - No network
3 - Full multi-user with display manager
4 - Full multi-user with display manager (Alias for runlevel 3)
5 - Full multi-user with display manager (Alias for runlevel 3)
6 - Reboot

System V Releases 3 and 4
0 - shut down system, power-off if hardware supports it (only available from the console)
1 - single-user mode, all filesystems unmounted but root, all processes except console processes killed.
2 - multi-user mode
3 - multi-user mode with RFS (and NFS in release 4) filesystems exported
4 - multi-user, user-defined
5 - halt the operating system, go to firmware
6 - halt the system, reboot to default runlevel
s, S - identical to 1 except current terminal acts as the system console

Solaris
0 - operating system halted; (SPARC only) drop to OpenBoot prompt
S - single-user with only root filesystem mounted (as read-only)
1 - single-user mode with all local filesystems mounted (read-write)
2 - multi-user with most daemons started.
3 - multi-user, identical to 2 (runlevel 3 runs both /sbin/rc2 and /sbin/rc3), with filesystems exported, plus some other network services started.
4 - alternative multi-user, user defined
5 - shut down, power-off if hardware supports it
6 - reboot

HP-UX
0 - system halted
S - single-user, booted to system console only, with only root filesystem mounted (as read-only)
s - single user, identical to S except the current terminal acts as the system console
1 - single-user with local filesystems mounted (read-write)
2 - multi-user with most daemons started and Common Desktop Environment launched
3 - multi-user, nearly identical to runlevel 2 with NFS exported
4 - multi-user with VUE started instead of CDE
5 - user-defined
6 - user-defined


AIX
AIX does not follow the System V R4 (SVR4) run level specification. It defines run levels from 0 to 9, 0 and 1 are reserved, 2 is the default normal multiuser mode and run levels from 3 to 9 are defined by administrator.
AIX runlevels
ID
Name
Description
0
reserved
1
reserved
2
Normal multiuser mode
default mode
On AIX you can check the current runlevel with the following command: $ who -r

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Login To Root User In UBUNTU

This article totally deals with how to get access to root user in UBUNTU? So going in to topic, by default Ubuntu will not allow us to log in to root user because root user is super user and we can do any thing if we have root access.

Actually be default in Ubuntu root user is disable(means there is root user with out password set). So if we try to login to root user it will not allow us because there is no password set to that user.

So the solution to this problem is to set the password to root user so how to do that? A question arises?
Ans : In order to change the root password we have to log in to run level1.
if you are new to this run level concept you can get that one here. In order to go to run level.

Step1 : Reboot your Ubuntu system if its on other wise start your ubuntu

Step2 : Brake the timer when its displaying OS choice at the boot time. To brake the timer press any key. So now we will get 3 lines like below.

ubuntu, kernel 2.6.18-generic
ubuntu,kernel 2.6.18-generic(recovery mode)
ubuntu,MeM test86+

Like this you will find at the display. Select the first line by up/down arrows and then press "e" to edit that line. And here again you will get some 3 to 4 lines. Select the line with kernel at the starting and then press "e" again. Now press space bar and 1 at the end of that line and then enter. Then press b to boot. Now you will be in run level 1. Then type the below command to reset the root password
#passwd root

Then after resetting the password execute exit command. From now on words you will have a chance to log in as root user.

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History Of Linux

1950 : The history of computer operating systems starts in this year, with simple schemes for running batch programs(running programs in groups these prog will not interact with user) efficiently, minimizing idle time between programs.

1960's : Interactive use of systems started to gain ground. Not only interactive use, but having several people use the same computer at the same time(noting but multi user), from different terminals. Such systems were called time-sharing systems and were quite a challenge to implement compared to the batch systems.

1965's : There were many attempts at building good time-sharing systems. Some of these were university research projects, others were commercial ones. One such project was Multics, which was quite innovative at the time. It had, for example, a hierarchical file system, something taken for granted in modern operating systems. This multics was the project of combined effort of Bell Lab's, MIT,GE. The Multics project did not, however, progress very well. It took years longer to complete the anticipated and never got a significant share of the operating system market. One of the participants, Bell Labs, withdrew from the project. The Bell Labs people who were involved then made their own operating system and called it as Unix.

1969 : First UNIX 1 was released.

1970-1989 : So many flavers of unix came at this time depending on the lack of feature's in previous systems up to unix 7 was released in this time.

1990 : By this time, Unix had a strong position in the server market and was especially strong in universities. Most universities had Unix systems and computer science students were exposed to them. Many of them wanted to run Unix on their own computers as well. Unfortunately, by that time, Unix had become commercial and rather expensive. About the only cheap option was Minix, a limited Unix-like system written by Andrew Tanenbaum for teaching purpose. There was also 386BSD, a precursor NetBSD, FreeBSD, and OpenBSD, but that wasn't mature yet, and required higher end hardware than many had at home.

Into this scene came Linux, in October, 1991. Linus Torvalds, the author, had used Unix at the University of Helsinki, and wanted something similar on his PC at home. Since the commercial alternatives were way too expensive, he started out with Minix, but wanted something better and soon started to write his own operating system. After its first release, it soon attracted the attention of several other hackers. While Linux initially was not really useful except as a toy, it soon gathered enough features to be interesting even for people uninterested in operating system development.

first mail from linus to hacker community

From: torvalds@klaava.Helsinki.FI (Linus Benedict Torvalds)
Newsgroups: comp.os.minix
Subject: What would you like to see most in minix?
Summary: small poll for my new operating system
Message-ID: <1991aug25.205708.9541@klaava.helsinki.fi>
Date: 25 Aug 91 20:57:08 GMT
Organization: University of Helsinki

Hello everybody out there using minix -
I'm doing a (free) operating system (just a hobby, won't be big and
professional like gnu) for 386(486) AT clones. This has been brewing
since april, and is starting to get ready.I'd like any feedback on
things people like/dislike in minix, as my OS resembles it somewhat
(same physical layout of the file-system(due to practical reasons)
among other things). I've currently ported bash(1.08) and gcc(1.40),and
things seem to work.This implies that I'll get something practical within a
few months, and I'd like to know what features most people would want. Any
suggestions are welcome, but I won't promise I'll implement them :-)
Linus (torvalds@kruuna.helsinki.fi)
PS. Yes - it's free of any minix code, and it has a multi-threaded fs.
It is NOT protable (uses 386 task switching etc), and it probably never
will support anything other than AT-harddisks, as that's
all I have :-(.

Second mail to community:

From: torvalds@klaava.Helsinki.FI (Linus Benedict Torvalds)
Newsgroups: comp.os.minix
Subject: Free minix-like kernel sources for 386-AT
Message-ID: <1991oct5.054106.4647@klaava.helsinki.fi>
Date: 5 Oct 91 05:41:06 GMT
Organization: University of Helsinki
Do you pine for the nice days of minix-1.1, when men were men and wrote their own device drivers?
Are you without a nice project and just dying to cut your teeth on a OS you can try to modify for your
needs? Are you finding it frustrating when everything works on minix? No more all-nighters to get a nifty program working? Then this post might be just for you :-)
As I mentioned a month(?)ago, I'm working on a free version of a minix-lookalike for AT-386 computers. It has
finally reached the stage where it's even usable (though may not be depending on
what you want), and I am willing to put out the sources for wider distribution. It is just version 0.02 (+1 (very
small) patch already), but I've successfully run bash/gcc/gnu-make/gnu-sed/compress etc under it.
Sources for this pet project of mine can be found at nic.funet.fi (128.214.6.100) in the directory /pub/OS/Linux.
The directory also contains some README-file and a couple of binaries to work under linux
(bash, update and gcc, what more can you ask for :-). Full kernel source is provided, as no minix code has been
used. Library sources are only partially free, so that cannot be distributed currently. The system is able to compile
"as-is" and has been known to work. Heh. Sources to the binaries (bash and gcc) can be found at the
same place in /pub/gnu.

Linux itself is only the kernel of an operating system. The kernel is the part that makes all other programs run. It implements multitasking, and manages hardware devices, and generally enables applications to do their thing. All the programs that the user (or system administrator) actually interacts with are run on top of the kernel. Some of these are essential : for example, a command line interpreter (or shell), which is used both interactively and to write shell scripts (corresponding to .BAT files). Linus did not write these programs himself, and used existing free versions instead. This reduced greatly the amount of work he had to do to get a working environment. In fact, he often changed the kernel to make it easier to get the existing programs to run on Linux, instead of the other way around.

Most of the critically important system software, including the C compiler, came from the Free Software Foundation's GNU project. Started in 1984, the GNU project aims to develop an entire Unix-like operating system that is completely free. To credit them, many people like to refer to a Linux system as a GNU/Linux system. (GNU has their own kernel as well).

During 1992 and 1993, the Linux kernel gathered all the necessary features it required to work as a replacement for Unix workstations, including TCP/IP networking and a graphical windowing system (the X Window System). Linux also received plenty of industry attention, and several small companies were started to develop and distribute Linux. Dozens of user groups were founded, and the Linux Journal magazine started to appear in early 1994.

Version 1.0 of the Linux kernel was released in March 1994. Since then, the kernel has gone through many development cycles, each culminating in a stable version. Each development cycle has taken a year or three, and has involved redesigning and rewriting large parts of the kernel to deal with changes in hardware (for example, new ways to connect peripherals, such as USB) and to meet increased speed requirements as people apply Linux to larger and larger systems (or smaller and smaller ones : embedded Linux is becoming a hot topic). Now the latest version of linux is 2.6.33.3

Soon Linus faced some confrontation from none other than Andrew Tanenbaum, the great teacher who wrote MINIX. In a post to Linus, Tanenbaum commented:

"I still maintain the point that designing a monolithic kernel in 1991 is a fundamental error. Be thankful you are not my student. You would not get a high grade for such a design :-)" (Andrew Tanenbaum to Linus Torvalds)

Linus later admitted that it was the worst point of his development of Linux. Tanenbaum was certainly the famous professor, and anything he said certainly mattered. But he was wrong with Linux, for Linus was one stubborn guy who won't admit defeat. Tanenbaum also remarked that : "Linux is obsolete". Now was the turn for the new Linux generation. Backed by the strong Linux community, Linus gave a reply to Tanenbaum which seems to be most fitting:

Your job is being a professor and researcher: That's one hell of a good excuse for some of the brain-damages of minix. (Linus Torvalds to Andrew Tanenbaum)

And work went on. Soon more than a hundred people joined the Linux camp. Then thousands. Then hundreds of thousands. This was no longer a hackers toy. Powered by a plethora of programs from the GNU project, Linux was ready for the actual showdown. It was licensed under GNU General Public License, thus ensuring that the source codes will be free for all to copy, study and to change. Students and computer programmers grabbed it.

Soon, commercial vendors moved in. Linux itself was, and is free. What the vendors did was to compile up various software and gather them in a distributable format, more like the other operating systems with which people were more familiar. Red Hat , Caldera, and some other companies gained substantial amount of response from the users worldwide. While these were commercial ventures, dedicated computer programmers created their very own volunteer-based distribution, the famed Debian. With the new Graphical User Interfaces (like X-window System, )the Linux distributions became very popular.

Meanwhile, there were amazing things happening with Linux. Besides the PC, Linux was ported to many different platforms. Linux was tweaked to run 3Com's handheld PalmPilot computer. Clustering technology enabled large number of Linux machines to be combined into a single computing entity, a parallel computer. In April 1996, researchers at Los Alamos National Laboratory used Linux to run 68 PCs as a single parallel processing machine to simulate atomic shock waves. But unlike other Supercomputers costing a fortune, it was rather cheap. The do-it-yourself supercomputer cost only $152,000, including labor (connecting the 68 PCs with cables)-about one tenth the price of a comparable commercial machine. It reached a peak speed of 19 billion calculations per second, making it the 315th most powerful supercomputer in the world. And it was a robust one too. Three months later it still didn't have to be rebooted.

A Beaming Linus Today

The best thing about Linux today is the fanatic following it commands. Whenever a new piece of hardware is out, Linux kernel is tweaked to take advantage of it. For example, within weeks after the introduction of Intel Xeon® Microprocessor, Linux kernel was tweaked and was ready for it. It has also been adapted for use in Alpha, Mac, PowerPC, and even for palmtops, a feat which is hardly matched by any other operating system. And it continues its journey into the new millennium, with the same enthusiasm that started one fine day back in 1991.

Linus in 2002

As for Linus, he remains a simple man. Unlike Bill Gates, he is not a billionaire. Having completed studies, he moved to USA and landed a job at Transmeta Corporation. After conducting a top-secret research and development project, Transmeta launched the Crusoeâ„¢ processor. Linus was an active member of the research team. Recently married to Tove, he is the proud father of a girl, Patricia Miranda Torvalds. But he remains as the world's most favorite and most famous programmer to this date. Revered by Computer communities worldwide, Linus is by far the most popular programmer on this planet.

Addtional info related to OS's:

Different types of unix's

1BSD 2BSD 3BSD 4BSD 4.4BSD Lite 1 4.4BSD Lite 2 386 BSD Acorn RISC iX Acorn RISC Unix AIX AIX PS/2 AIX/370 AIX/6000 AIX/ESA AIX/RT AMiX AOS Lite AOS Reno ArchBSD ASV Atari Unix A/UX BOS BRL Unix BSD Net/1 BSD Net/2 BSD/386 BSD/OS CB Unix Chorus Chorus/MiX Coherent CTIX CXOs Darwin Debian GNU/Hurd DEC OSF/1 ACP DesktopBSD

Digital Unix DragonFly BSD Dynix Dynix/ptx ekkoBSD Eunice FireFly BSD FreeBSD FreeDarwin GNU GNU-Darwin Gnuppix GNU/Hurd-L4 HPBSD HP-UX HP-UX BLS IBM AOS IBM IX/370 Interactive 386/ix Interactive IS IRIS GL2 IRIX Linux Lites LSX Mac OS X Mac OS X Server Mach MERT MicroBSD Mini Unix Minix Minix-VMD MIPS OS RISC/os MirBSD Mk Linux Monterey more/BSD mt Xinu

MVS/ESA OpenEdition NetBSD NeXTSTEP NonStop-UX Open Desktop Open UNIX OpenBSD OpenDarwin OpenServer OpenSolaris OPENSTEP OS/390 OpenEdition OS/390 Unix OSF/1 PC-BSD PC/IX Plan 9 Plurix PWB PWB/UNIX QNX QNX RTOS QNX/Neutrino QUNIX ReliantUnix Rhapsody RISC iX RT SCO UNIX SCO UnixWare SCO Xenix SCO Xenix System V/386 Security-Enhanced Linux Silver OS Sinix Sinix ReliantUnix Solaris SPIX

SunOS Triance OS Tru64 Unix Trusted IRIX/B Trusted Solaris Trusted Xenix TS Tunis UCLA Locus UCLA Secure Unix Ultrix Ultrix 32M Ultrix-11 Unicos Unicos/mk Unicos/mp Unicox-max UNICS UniSoft UniPlus UNIX 32V UNIX Interactive UNIX System III UNIX System IV UNIX System V UNIX System V Release 2 UNIX System V Release 3 UNIX System V Release 4 UNIX System V/286 UNIX System V/386 UNIX Time-Sharing System UnixWare UNSW USG Venix Xenix OS Xinu xMach z/OS Unix System Services

Here is now some unixes that are not [yet] in my chart. Some web sites have listed them, like this site or this site. If you want to find more unixes, try Google :-)

ABCenix ACIX AD Altos System V ARIX AurOS BOS/X C Executive CLIX Consensys Unix Concentrix ConvexOS CPIX Cromix CX/UX DC/OSx Dell Unix

DG/UX DISTRIX DNIX DomainOS DRM System DTIX DVIX ENIX EP/IX Esix SVR4 Eurix FOR:PRO FreeMiNT FTX Genix HCR Helios

HEP-UPX HI-UX IDRIS INOS LSX LynxOS MachTen MacMach MAXION/OS MCS Micronix Microport SVR4 MicroPort Unix Mimos MMOS MP-RAS UNIX MST UNIX

Mulplix Munix NachOS NCR Unix NDIX News-OS NUXI Oasis ONIX OPUS OS 9 OS/MP OSx PCUNIX PNX QNIX Regulus

RT/EMT RTUX SORIX SOX Sphinx SPP-UX Stellix SUNIX Super-UX System B Thix TI System V TNIX Topix TOS Tropix UHC Unix

Umax Uniq Unisis Unity UNOS UTEK UTS UTX/32S UX UXP/DS UZIX VM/IX VOLVIX Xoftnix Zeus

home page's of different people who are resposiable for development of OS(unix and linux):

Brian Kernighan

http://cm.bell-labs.com/cm/cs/who/bwk/index.html

Dennis Ritchie

http://cm.bell-labs.com/cm/cs/who/dmr/index.html

Ken Thompson

http://plan9.bell-labs.com/who/ken/

The above three are responsable for unix first version.

Different types of Linux's

The below site will give u different types of linux's

www.distrowatch.com

The below guy responsable for linux develepment

Linus Torvalds

http://www.cs.helsinki.fi/u/torvalds/

And last but not least see the link below

http://www.catb.org/~esr/faqs/linus/

Q & A

1. When is first UNIX introduced?
Ans : 1969.

2. What is the present version of RedHat Enterprice Linux (by april 2007)?
Ans : RHEL5.

3. What is the present version of linux kernel (by april 2007)?
Ans : Precent version of linux kernel is 2.6.20.7.

4. What is the kernel type used bye linux?
Ans : Modular kernel (i will explain this in comming class ie in 133 classes).

5. State some Unix flavers you know?
Ans : Free BSD, NetBSD, OpenBSD, HP Unix(from HP), Solaries (from Sun micro systems).

6. State some Linux flavers you know?
Ans : RHEL, Fedora, CentOS, Ubuntu, Lindows(which have features of linux and MS window's), Suse, Debain etc.

7. What is the main difference between fedora and RHEl?
Ans : a.RedHat will give support to only for RHEL but not for Fedora with some charge.

b. Fedora is a open source no help is provided by RedHat user group's will provide help for this Fedora.

c. For every 2 years RHEL will be released where as Fedora is for very 6 months.

8. What is the different OS released from RedHat in the devision of RHEL side?
Ans : a. RedHat Desktop
b. RedHat Enterprice server
c. RedHat Advanced Server
d.RedHat work station.

9. What is the difference between Uinx and Linux?
a. unix is monolithic kernel where as linux uses modular kernel.
b. some commands will differ
c. unix is commersial where as linux is free
d. linux support different hardware you can install linux on notebook too.

10.What is the difference between linux and window's?
Ans : The given below link is enough
http://www.michaelhorowitz.com/Linux.vs.Windows.html

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