Download Linux Concepts and key ideas

Linux Definitions, Concepts and Key Ideas
(adapted from various books and from white papers on various web sites)
What is an operating system? What is a kernel?
An operating system is made up of software instructions that lie between the computer
hardware and the application software. At the center is the kernel, which functions to
control processes, handles memory management, and manages software and hardware
communications. Besides the kernel, an operating system also provides other basic
services such as file systems, device drivers, user interfaces and system services.
What is UNIX?
UNIX was originally born in 1969 at Bell Labs, and grew and evolved through the years.
In the early 1980s, AT&T began to market UNIX, and also distributed it free to
universities. UNIX began to be used more and more throughout the world. As multiple
ports of UNIX started appearing, AT&T standardized what the different ports had to be
able to do to still be called UNIX. To that end, compliance with the Portable Operating
System Interface for UNIX (POSIX) and the AT&T UNIX System V Interface Definition
(SVID) defined whether an operating system was UNIX or not. Some of the major
operating systems that are POSIX compliant, and thus UNIX, are Solaris, Linux, AIX,
and HP-UX.
What is Linux?
Linux is a free Unix-type operating system originally created by Linus Torvalds in
August of 1991 when he was a student at the University of Helsinki. He wrote it partly
from scratch and partly by using publicly available software. He then released it to the
internet and asked others to work with it, fix it and enhance it. Developed under the
GNU General Public License, the source code for Linux is freely available to everyone.
Although much of the code for Linux started from scratch, the blueprint for what the code
would do was created to follow POSIX standards.
What is open source?
In general, ‘open source’ refers to any program whose source code is made freely
available for use or modification. Open source software is usually developed as a public
collaboration project and is made freely available, as are patches and fixes.
The Open Source community is a loose collection of highly capable and dedicated
individuals who donate their time and energy to developing and maintaining software
made publicly available. The major pieces of software produced and supported by this
community is of very high quality. Some well-known examples of open source software
are Linux, Sendmail, Apache and DNS.
What is a distribution? What is a boxed version?
When Linus Torvalds first developed Linux, the operating system basically consisted of
his kernel and some GNU tools. With the help of other developers, Linus added more and
more tools and applications.
With time, individuals, university students and companies began distributing Linux with
their own choice of packages bound around Linus' kernel. This is where the concept of
the "distribution" was born. The object of a distribution is to make the hundreds of
unrelated software packages that make up Linux work together as a cohesive whole.
A distribution is sometimes also called a ‘boxed version’. Since Linux itself is free, what
you buy is the CD, the collected set of packages, printed documentation and usually some
type of support (a phone number to call to help with installation, for example).
You can buy a boxed version of Linux from companies such as Red Hat, SuSE, Caldera,
MandrakeSoft and many others. You can also download Linux for free from any number
of companies and individuals. There are distributions of all types and for practically any
kind of computing endeavor.
What is Clustering?
Clustering is most widely recognized as the ability to combine multiple systems in such a
way that they provide services a single system could not. Clustering is used to achieve
higher availability, scalability and easier management. Higher Availability can be
achieved by use of "failover" clusters, in which resources can automatically move
between 2 or more nodes in the event of a failure. Scalability can be achieved by
balancing the load of an application across several computer systems. Simpler
management can be attained through the use of virtual servers, as opposed to managing
each individual computer system.
What are High Availability Clusters?
High availability clustering joins together two or more servers to help ensure against
system failures including planned shutdowns (e.g., maintenance, backups) and unplanned
outages (e.g., system failure, software failure, operator errors). The group of connected
systems is known as a cluster.
What is a Beowulf or High Performance Computing Clusters?
Beowulf or High Performance Computing Cluster (HPCC) combines multiple Symmetric
Multi-Processor (SMP) computer systems together with high-speed interconnects to
achieve the raw-computing power of classic "big-iron" supercomputers. These clusters
work in tandem to complete a single request by dividing the work among the server
nodes, reassemble the results and present them to the client as if a single-system did the
work.
What is IP Load Balancing?
Server farms that can distribute requests to the same application among multiple
independent servers are referred to as "load balancing". The term load balancing applies
to clusters that include some number of nodes processing requests for the same type of
application, often web servers, streaming media servers, terminal servers, or read only
FTP and file servers. There are software-based mechanisms to perform load balancing, as
well as appliance-based mechanisms.
What are Scalable Clusters?
Scalable Clusters provide the freedom of adding compute nodes in a cluster in order to
increase the joint resources of processing. This can add to the power of computation since
processors within a cluster can communicate data more efficiently and hence it also can
reduce the average memory access time. This is particularly attractive when running
parallel applications.
What is Oracle Real Application Clusters (RAC)?
Oracle RAC is a parallel database clustering technology from Oracle that runs under
Linux and is an option of Oracle9i Enterprise Edition. RAC enables IT organizations to
acquire key competitive advantages from a technical and business standpoint:
Scalability: RAC is an active-active cluster with shared storage, whereby multiple servers
can work in parallel on the same set of data. Through a cluster interconnect technology
called CacheFusion, up to 8 database server nodes are connected over a private Gigabit1
interconnect, and are sharing database storage, using SCSI or Fiber Channel technology.
This allows the customer to add nodes as growth requirements increase. The maximum
configuration supported by Dell is eight PowerEdgeTM 8450 servers (8 CPU, 16GB of
memory per server), which combined provide the capacity of a 64-CPU database system
and up to 128MB (16GB per server) of shared memory across the server nodes.
Availability: RAC, in addition to providing performance and scaling beyond a single
server, delivers fault tolerance and helps deliver maximum uptime. Dell, Oracle and
EMC have worked together on making the cluster fully redundant so that the database
can remain up and running in the event of a component failure in the cluster (server,
switch, disk, interconnect, etc).
What is the Linux Virtual Server?
The Linux Virtual Server is a highly scalable and highly available server built on a
cluster of real servers, with the load balancer running on the Linux operating system. The
architecture of the cluster is transparent to end users. End users only see a single virtual
server. The Linux Virtual Server can be used to build highly scalable and high available
network services, such as a scalable web, mail or media service. The real servers may be
interconnected by high-speed LAN or by geographically dispersed WAN. The front-end
of the real servers is a load balancer, which schedules requests to the different servers and
make parallel services of the cluster to appear as a virtual service on a single IP address.
Scalability is achieved by transparently adding or removing a node in the cluster. High
availability is provided by detecting node or daemon failures and reconfiguring the
system appropriately.