• BIOS stands for Basic Input/output System
• Performs some system integrity checks
• Searches, loads, and executes the boot loader program.
• It looks for boot loader in floppy, cd-rom, or hard drive. You can press a key (typically F12 of F2, but it depends on your system) during the BIOS startup to change the boot sequence.
• Once the boot loader program is detected and loaded into the memory, BIOS gives the control to it.
• So, in simple terms BIOS loads and executes the MBR boot loader.

• MBR stands for Master Boot Record.
• It is located in the 1st sector of the bootable disk. Typically /dev/hda, or /dev/sda
• MBR is less than 512 bytes in size. This has three components 1) primary boot loader info in 1st 446 bytes 2) partition table info in next 64 bytes 3) mbr validation check in last 2 bytes.
• It contains information about GRUB (or LILO in old systems).
• So, in simple terms MBR loads and executes the GRUB boot loader.

• GRUB stands for Grand Unified Boot loader.
• If you have multiple kernel images installed on your system, you can choose which one to be executed.
• GRUB displays a splash screen, waits for few seconds, if you don’t enter anything, it loads the default kernel image as specified in the grub configuration file.
• GRUB has the knowledge of the filesystem (the older Linux loader LILO didn’t understand filesystem).
• Grub configuration file is /boot/grub/grub.conf (/etc/grub.conf is a link to this). The following is sample grub.conf of CentOS.

• As you notice from the above info, it contains kernel and initrd image.
• So, in simple terms GRUB just loads and executes Kernel and initrd images.

• Mounts the root file system as specified in the “root=” in grub.conf
• Kernel executes the /sbin/init program
• Since init was the 1st program to be executed by Linux Kernel, it has the process id (PID) of 1. Do a ‘ps -ef | grep init’ and check the pid.
• initrd stands for Initial RAM Disk.
• initrd is used by kernel as temporary root file system until kernel is booted and the real root file system is mounted. It also contains necessary drivers compiled inside, which helps it to access the hard drive partitions, and other hardware.

• Looks at the /etc/inittab file to decide the Linux run level.
• Following are the available run levels
  • 0 – halt
  • 1 – Single user mode
  • 2 – Multiuser, without NFS
  • 3 – Full multiuser mode
  • 4 – unused
  • 5 – X11
  • 6 – reboot
• Init identifies the default init level from /etc/inittab and uses that to load all appropriate programs.
• Execute ‘grep initdefault /etc/inittab’ on your system to identify the default run level
• If you want to get into trouble, you can set the default run level to 0 or 6. Since you know what 0 and 6 means, probably you might not do that.
• Typically you would set the default run level to either 3 or 5.

• When the Linux system is booting up, you might see various services getting started. For example, it might say “starting sendmail …. OK”. Those are the runlevel programs, executed from the run level directory as defined by your run level.
• Depending on your default init level setting, the system will execute the programs from one of the following directories.
  • Run level 0 – /etc/rc.d/rc0.d/
  • Run level 1 – /etc/rc.d/rc1.d/
  • Run level 2 – /etc/rc.d/rc2.d/
  • Run level 3 – /etc/rc.d/rc3.d/
  • Run level 4 – /etc/rc.d/rc4.d/
  • Run level 5 – /etc/rc.d/rc5.d/
  • Run level 6 – /etc/rc.d/rc6.d/
• Please note that there are also symbolic links available for these directory under /etc directly. So, /etc/rc0.d is linked to /etc/rc.d/rc0.d.
• Under the /etc/rc.d/rc*.d/ directories, you would see programs that start with S and K.
• Programs starts with S are used during startup. S for startup.
• Programs starts with K are used during shutdown. K for kill.
• There are numbers right next to S and K in the program names. Those are the sequence number in which the programs should be started or killed.
• For example, S12syslog is to start the syslog deamon, which has the sequence number of 12. S80sendmail is to start the sendmail daemon, which has the sequence number of 80. So, syslog program will be started before sendmail.

• User (u): The owner of file
• Group (g): Other user who are in group (to access files)
• Other (o): Everyone else

• Read (r)
• Write (w)
• Execute (x)

• Read access on a file allows you to view file
• Read access on a directory allows you to view directory contents with ls command

• Write access on a file allows you to write to file
• Write access on a directory allows you to remove or add new files

• Execute access on a file allows to run program or script
• Execute access on a directory allows you access file in the directory

 

STRAIGHT CABLE Color Code        

 One End                 Other End
Orange Light      -      Orange Light          
Orange              -       Orange
Green Light       -       Green Light
Blue                  -         Blue
Blue Light          -       Blue Light
Green                -        Green
Brown Light       -       Brown Light
Brown               -        Brown

CROSSOVER CABLE Color Code

One End             Other End
WhiteGreen     -      WhiteOrange
Green              -      Orange
WhiteOrange   -      WhiteGreen 
Blue                -       Blue
WhiteBlue       -       WhiteBlue
Orange            -       Green 
WhiteBrown    -       WhiteBrown
Brown            -         Brown


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Ubuntu 14.04

Lamp Installation in Ubuntu

Root Password Reset in Ubuntu

Linux Mint 17

Own Blogger Website

Install Free BSD

The following are some important commands that can be used to edit and review command history buffer. It will be useful to practice these commands.

<ctrl> A : Move to the beginning of the command line
<ctrl> E : Move to the end of the command line
<ctrl> F : Move forward one character, same as using "Right Arrow".
<ctrl> B : Move backward one character, same as using "Left Arrow".
<ctrl> P : Repeat Previous command, same as using "Up Arrow".
<ctrl> N : Repeat Next (more recent) command, same as using "Down Arrow".
<esc> B : Moves to beginning of previous word.
<esc> F : Moves to beginning of next word.
<ctrl> R : Creates new command prompt, followed by all the characters typed at the last one.
   

Keyboard Shortcut                          Action

Up Arrow     Displays your previous commands.  (command history)
TAB Key            Completes a partially typed CLI commands.
CTRL+Z             Takes you back to Privileged EXEC Mode.
CTRL+A             Places the cursor at the beginning of a line.
CTRL+E             Places the cursor at the end of a line.
CTRL+R             Redisplays the current command line.
CTRL+W            Erases a word (behind the cursor).
CTRL+U             Erases an entire line.


Here is a summary of Cisco IOS router command prompts:

Router> - User EXEC mode
Router# - Privileged EXEC mode
Router(config)# - Global configuration mode
Router(config-if)# - Interface level configuration mode
Router(config-router)#-Routing engine levelwithinconfigurationmode
Router(config-line)# - Line level (vty, tty, async) within configuration mode


Router#show cdp neighbors

Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
                  S - Switch, H - Host, I - IGMP, r - Repeater



There are two types of configuration files on a router:

Running config - The configuration currently running on the router. Stored in RAM.
Startup config - Saved configuration stored in NVRAM.

To save the running configuration to the startup configuration use the following command.

Router# copy running-config startup-config

or

Router# copy run start


 The various states of an interface :-

Ethernet0 is up, line protocol is up - The interface is functioning correctly.

Ethernet0 is down, line protocol is down - This message usually represents a physical interface problem. The cable may be disconnected. This can also occur if this interface is connected to another router whose interface has been shutdown.

Ethernet0 is up, line protocol is down - The Physical layer connectivity is not the issue. The line protocol being down is either a clocking issue (keepalives) or a mismatch of the frame types being used on connected devices.

Ethernet0 is administratively down, line protocol is down - The interface has been manually shutdown using the shutdown command.

                 WLANs
802.11b           2.4GHz, 11Mbps
802.11n           2.4GHz or 5GHz, 300Mbps
802.11a           5GHz, 54Mbps
802.11g           2.4Ghz, 54Mbps

WEP   ---    Original IEEE wireless security standard.Easily hacked.
WPA   ---    Wireless security standard created by the Wi-Fi 
Alliance. Uses a dynamic key for greatly improved Security over WEP.
Interoperable with different vendors products.
CSMA/CA  ---  Network access method used in wireless networking & uses a proactive algorithm to avoid collisions.
WPA-2   ---   Ratified by the IEEE in 2005 who named it IEEE 802.11i & Uses AES encryption.


                       Protocols

What is the difference between TCP and IP?
IP is a connectionless protocol, it is used for network addressing and is a routed protocol.
TCP is a connection-oriented protocol used for reliable transmission by the Transport layer.

Finds a hardware address from a known IP address?
Address Resolution Protocol (ARP)

RIPv2
Distance vector, 120 admin distance, hop count metric, classless

OSPF
Link state, 110 admin distance, bandwidth metric, classless

IGRP
Distance vector, 100 admin distance, metric bandwidth and delay, classful, Cisco proprietary

Protocol responsible for network addressing and routing through an internetwork
Internet Protocol (IP)

Gather useful information about neighbour devices such as hardware and protocol information
Cisco Discovery Protocol (CDP)

Connectionless protocol at the Transport layer
User Datagram Protocol (UDP)

Layer 2 protocol used to prevent network loops
Spanning Tree Protocol (STP)

RIP
Distance vector, hop count metric, 120 admin distance, classful

Protocol used by a host computer to request its IP address
Reverse Address Resolution Protocol (RARP)

                  
                   Internal Router Components

What is NVRAM(Non-volatile random access memory)?
Stores config and config register

What is ROM ?
Holds POST, bootstrap and mini-IOS

What is Power on self test (POST) ?
Checks hardware and interfaces on start-up
Config register
Controls how router boots

What is Flash ?
 That's Stores in IOS

Mini-IOS
Small IOS used for maintenance

RAM(Random Access Memory)
Holds routing tables and running config

ROM(Read Only Memory) that Stored in ROM, brings up router on boot
Bootstrap

ROM monitor is Used for testing and troubleshooting



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Ubuntu 14.04

Linux Mint 17

Python

Nagios

Oracle Linux 7

Reset Root Password

The Criteria of Password Doesn't Meet Means.

You should not includ any Character in this box (!@$%&*) that means Oracle 

recommended to avoid that type of password. you can use only small character.

This Message is Related to Samba Password Syncing. To Resolve it Follow Below Steps. 

Step1:- sudo su (logging as a Root)

Step2:- pam-auth-update (Press Enter)

Step3:- Deselect the Samba Password Synchronization

Remove crash report files

Step1 :- cd /var/crash 

Step2 :- ls (Just Remove all below crash)

_opt_google_chrome_chrome.1000.crash
_usr_lib_chromium-browser_chromium-browser.1000.crash
_usr_sbin_ulatencyd.0.crash
_usr_share_apport_apport-gtk.1000.crash 

Step3 :- sudo rm /var/crash/* 

Turn off apport. 

After removing the old crash reports, if you still get the same error message, then you can completely turn off apport to get rid. Edit the configuration file at /etc/default/apport.

Step4 :- gksudo gedit /etc/default/apport

# set this to 0 to disable apport, or to 1 to enable it
# you can temporarily override this with
# sudo service apport start force_start=1
enabled=1

Step5 :- enabled=0

Step6 :- sudo restart apport 

Error :- oracle is not in the sudoers file.  This incident will be reported.
 you can fix this error not only in ubuntu 14.04 but also in ubuntu 12.04 / 12.10.

Ans :- To give the sudo permission to a oracle we need to add the user to the file /etc/sudoers file.

Step1 :- sudo su (logging as a Root)

Step2 :- sudo nano /etc/sudoers or sudo vi /etc/sudoers

Step3 :- Add Line

            

 oracle ALL = (ALL)ALL (under the user privilege specification section)

Step4 :- Save and Exit

Note :- In place of Ubuntu you can right any name, just replace it

Thanking You

Hope U Like it............

Oracle Linux 7

Fedora 20 in Virtual box

Nagios 4.0.7

Roboform in linux

Ubuntu server 12.04

Zimbra Desktop 7