inetd is the server process for the Internet  standard  ser-
vices.  It  usually  starts  up  at  system  boot  time.

inetd listens for service requests on the TCP or  UDP  ports
     associated  with  each  of the services listed in the 
confi-
     guration file. When a request arrives,  inetd  
executes  the
     server program associated with the service.

     A service can be configured to have "wait"  wait-
status,  in
     which  case,  inetd  waits  for  the  server process 
to exit
     before starting a second server process.  RPC  
services  can
     also be started by inetd.

     inetd provides a number of simple Internet  services  
inter-
     nally.  These include echo, discard, chargen 
(character gen-
     erator), daytime (human-readable time), and  time  
(machine-
     readable  time,  in  the form of the number of seconds 
since
     midnight, January 1, 1900).

Index node to refer file in Unix System

An inode is an entry in a disk table that contains 
information about a file such as its owner, size, and last 
access date. The inode is changed when the file is first 
created and also later if the owner, group, or permissions 
are changed.

I nodes are objects used to record the information about 
files

Inode is a structure contains the information necessary for
a process to access a file.Exist in a static form on disk
and the kernel reads them into an in-core inode. 
consists of 
  - file owner identifier
  - file type
  - file access permissions
  - file access times 
  - number of links to the file
  - table of  contents for the disk address of data in   a file
  - file size

in-core copy of the inode contains
  - status of the in-core inode
  - logical device number of file system
  - inode number
  - pointers to other in-core inodes
  - reference count

Inode Contains all the details about a file like owner, 
permission, type....... etc. But it doesn't Contain  
the "Filename" for the paticular file.

setuid:When setuid permission is set to an executable 
file,if the  user runs this executable file he is granted 
access based on the owner of the file instead of who 
started an executable file.we can set the setuid permission 
on file # chmod 4555 executable_file

setgid:when setgid permission is set to the file in a 
directory,the file belongs to the same group in which the 
directory is a member.we can set the setgid permission on 
file # chmod 2555 executable_file

some of them i know are PERL,TCL/TK,AWK,Python

virtual local area network.
VLANs support logical grouping of network nodes to reduce
broadcast traffic and allow more control in implementing
security policies.

A network of computers that behave as if they are connected 
to the same wire even though they may actually be 
physically located on different segments of a LAN. VLANs 
are configured through software rather than hardware, which 
makes them extremely flexible.

VLAN stands for Virtual Local Area Network it reduce the 
broadcasting in the network. With The Help Of VLAN We Can 
Create A Separate Broadcast Domain in The Switch.

Open Systems Interconnection
There are seven layers 
They are 
Layer 7 - Application Layer 
Layer 6 - Presentation Layer 
Layer 5 - Session Layer 
Layer 4 - Transport Layer 
Layer 3 - Network Layer 
Layer 2 - Data Link Layer 
Layer 1 - Physical Layer

By using netstat command(in linux it works).

switch is a small hardware device that joins multiple
computers together within one local area network (LAN).
Technically, network switches operate at layer two (Data
Link Layer) of the OSI model

switch is a software based physically harware device in 
this communicate same networks, switch is a data 
communicate equipment(DCE),Two types of switch available 
1.manageable switch 2.un(or)non manageable switch.Switch 
every port single collusion domain.ASIC chipset used in 
this device in this working 100mbps speed.

A device that forwards data packets along networks. A 
router is connected to at least two networks, commonly two 
LANs or WANs or a LAN and its ISP?s network. Routers are 
located at gateways, the places where two or more networks 
connect.

A device that finds the best route between any two 
networks, even if there are several networks.Routers 
forward packets from one network to another based on 
network layer information.

Router is a device which is used for communication of 
two diffrent Geogaraphical Area Nwtwork.

It’s like hub. Connect to devices on a network. Communicate 
two or more different network. Different geographical area 
location.

-Router is a Network layer device.
-It select the best path to the network.
-it filter the address.
-it forward protocal to particular address.
-it mantain routing table.
-it communicate to different network.
-it mantain the securite.

it is a external  H/W device like a hub r switch.used for 
connect different lan and wan N/W.

router is network devise use to comnicate two differnt ip 
adderss

Router is a network device, use to communicate two 
diffarent networks.

It’s like hub. Connect to devices on a network. Communicate 
two or more different network. Different geographical area 
location.

Router is the device which route packets on layer 3 of OSI 
model, where as Switch/Bridge works on layer 2. Router is 
more intelligent as compared to Switch. Switch forward 
packets by seeing destination MAc address where as router 
forward packets by destination IP address.

There?s a big difference in the way run levels work on Linux
compared to Solaris. Linux goes straight in at a run-level,
whereas Solaris works up through them (and is better for it,
IMNSHO).

inittab for configuring the run-level; symbolic links;
chkconfig for configuring a service to start; service for
starting them if you don?t fancy running scripts manually.
Perhaps some anecdotes about the actual writing of init scripts.

When an x86 computer is booted, the processor looks at the
end of the system memory for the BIOS (Basic Input/Output
System) and runs it. The BIOS program is written into
permanent read-only memory and is always available for use.
The BIOS provides the lowest level interface to peripheral
devices and controls the first step of the boot process.

The BIOS tests the system, looks for and checks peripherals,
and then looks for a drive to use to boot the system.
Usually it checks the floppy drive (or CD-ROM drive on many
newer systems) for bootable media, if present, and then it
looks to the hard drive. The order of the drives used for
booting is usually controlled by a particular BIOS setting
on the system. Once Linux is installed on the hard drive of
a system, the BIOS looks for a Master Boot Record (MBR)
starting at the first sector on the first hard drive, loads
its contents into memory, then passes control to it.

This MBR contains instructions on how to load the GRUB (or
LILO) boot-loader, using a pre-selected operating system.
The MBR then loads the boot-loader, which takes over the
process (if the boot-loader is installed in the MBR). In the
default Red Hat Linux configuration, GRUB uses the settings
in the MBR to display boot options in a menu. Once GRUB has
received the correct instructions for the operating system
to start, either from its command line or configuration
file, it finds the necessary boot file and hands off control
of the machine to that operating system.

The full form of RPM is Redhat Package Manager.
rpm  is  a  powerful  Package  Manager,  which  can  be used
to build,install, query, verify, update, and erase 
individual  software  packages.  A package consists of an
archive of files and meta-data used to install and erase the
archive files.

RPM means R-Redhat P-Package M-manager
it's just like a .exe file of microsoft. we can use it in 
linux only for installing and upgrading purpose.

RPC is simply known as "Remote Procedure Call". this is the
fundamental in NFS.(Network File System).

RPC is Remote Procedure Call.

It is used by the system to assign the port no. in case of 
a request from client for the processes that do not run on 
booting of system.

Examples. : ftp, telnet etc.

You can see the ftp and telnet in "ps -ef" only when 
somebody try to make a connection using ftp and telnet.

NFS version 2 supports 8KB transfer rate,client can access
unauthorized file they give errors 

NFS Version3 supports 32 kb transfer rate,first check the
permissions after that they give connection permission