In computer programming, resource management refers to techniques for managing resources for e.
g Memory, %
cpu usage, disk space usage etc.
$ free -m
Line 1: Indicates Memory details like total available RAM, used RAM, Shared RAM, RAM used for
buffers, RAM used of caching content.
Line 2: Indicates total buffers/Cache used and free.
Line 3: Indicates total swap memory available, used swap and free swap memory size available.
BUFFER: A buffer is a temporary location to store data for a particular application and this data is not
used by any other application. This is similar to bandwidth concept. When you try to send burst of
data through network, if your network card is capable of sending less data, it will keep these huge
amounts of data in buffer so that it can send data constantly in lesser speeds.
Cache: In other hand Cache is a memory location to store frequently used data for faster access.
Other difference between a buffer and a cache is that cache can be used multiple times where as
buffer is used single time. And both are temporary store for your data processing.
Shared Ram: Simaltaneously accessed by multiple programs.
Actual Ram= Used RAM (Used Buffer+Used Cache)
Swap space in Linux is used when the amount of physical memory (RAM) is full. If the system needs more memory
resources and the RAM is full, inactive pages in memory are moved to the swap space. While swap space can help
machines with a small amount of RAM, it should not be considered a replacement for more RAM. Swap space is
located on hard drives, which have a slower access time than physical memory.
If M < 2
S = M *2
Else
S = M + 2
uptime gives a one line display of the following information. The current time, how long the system has been
running, how many users are currently logged on, and the system load averages for the past 1, 5, and 15 minutes.
PID lID of the process(4522)
USER The user that is the owner of the process (root)
PR priority of the process (15)
NI The NICE value of the process (0)
nice becomes useful when several processes are demanding more resources than the CPU can provide. In this
state, a higher priority process will get a larger chunk of the CPU.
A niceness of 20 is the highest priority and 19 or 20 is the lowest priority.
VIRT virtual memory used by the process (132m)
RES physical memory used from the process (14m)
SHR shared memory of the process (3204)
S indicates the status of the process: S=sleep R=running Z=zombie (S)
%CPU This is the percentage of CPU used by this process (0.3)
%MEM This is the percentage of RAM used by the process (0.7)
TIME+ This is the total time of activity of this process (0:17.75)
COMMAND And this is the name of the process (bb_monitor.pl)
df h : Disk free (Human readable format)
Linux filesystem types: minix, ext, ext2, ext3, ext4,
Reiserfs, XFS, JFS, xia, msdos, umsdos, vfat, ntfs, proc,
nfs,
LVM is a logical volume manager for the Linux kernel that manages disk drives and similar mass-storage devices.
The extended file system, or ext, was implemented in April 1992 as the first file system created specifically for
the Linux kernel.
NTFS; New technology filesystem, 4
th
extended filesystem
Mounting a filesystem simply means making the particular filesystem accessible at a certain point in the Linux
directory tree. When mounting a filesystem it does not matter if the filesystem is a hard disk partition, CD-ROM,
floppy, or USB storage device. You simply need to know the device name associated with the particular storage
device and a directory you would like to mount it to
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du: estimates disk space usage
Raid:
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Internet server or (web server) - this is a special computer, which is constantly switched on
and connected to the Internet so that each Internet user around the world can access your website
at all times. This computer is built up with selected high quality components, which can endure
incessant work and high load. A web hosting service is a type of Internet hosting service that
allows individuals and organizations to make their website accessible via the World Wide Web.
Web hosts are companies that provide space on a server owned or leased for use by clients,
as well as providing Internet connectivity.
Types of web server:-
A shared web hosting service refers to a web hosting service where many websites reside on
one web server connected to the Internet. Each site "sits" on its own partition, or section/place
on the server, to keep it separate from other sites. This is generally the most economical option
for hosting, as many people share the overall cost of server maintenance.
What is virtualization: It is basically a partitioning of a big system into small one.
A virtual private server (VPS) is a virtual machine which runs its own copy of an operating
system, and customers have superuser-level access to that operating system instance, so they
can install almost any software that runs on that OS. For many purposes they are functionally
equivalent to a dedicated physical server, and being software defined are able to be much more
easily created and configured. They are priced much lower than an equivalent physical server,
but as they share the physical hardware with other VPSs, performance may be lower, and may
depend on the workload of other instances on the same hardware node.
A dedicated hosting service, dedicated server is a type of Internet hosting in which the client
leases an entire server not shared with anyone else. It is dedicated to do specific task.
Note:-An Internet hosting service is a service that runs Internet servers, allowing
organizations and individuals to serve content to the Internet.
VPS HOSTING:
Types of virtualization:
1)Hardware emulation(Out of the context of this topic)-- Emulating(copy) one or more pieces of
hardware into another hardware.
2)Para virtualization(Out of the context):-In paravirtualization there is a layer of hypervizer(A hypervisor
or virtual machine monitor (VMM) is a piece of computer software) on hardware which lets it create
multiple instances of a hardware and on the top of that instances you run your operating system for
e.g xen kvm vmware etc.
3)Containers type virtalization:- In This we modify the kernel, in our case it is a linux kernel to provide
the multiple instances of user space which is called containers. We use OPENVZ which is Open
Virtuozzo, an operating system-level virtualization technology based on the Linux kernel and operating
system.
Instance: If there are multiple server installations on single machine they are identified by instance
name.It is a sigle service allowing many to connect and retreive data from main system.
LXC,FREEBSD jails,openVZ all provides the container type virtalization, etc.
To comparewe can say:-
Hypervisor:- One real hardware, many virtual hardwares and many operating systems.
HyperVM is the most comprehensive virtualization management software in the
industry. It is a multi-server, multi-tiered, multi-platform, multi-virtualization
system allowing you to manage both linux and windows virtualization.
Openvz:-One real hardware, no virtual hardware, one kernel and many user space instances. Dynamic
resorce allocation is a feature of a openvz, we can upgrade and downgrade the memory and hard disk
resources. its a operating system level virtalization so we are using the linux kernel we can do only a
linux based virtualization and we can't install other operating system like windows by this kind of
virtualization.
A modern computer operating system usually segregates virtual memory into kernel space and
user space.
The World Wide Web (abbreviated as WWW or W3,
[1]
commonly known as the Web) is a
system of interlinked hypertext documents that are accessed via the Internet. Hypertext is a text
visible on your computer screen or on any electronic devices. In eays words it is a system of
interlinked documents.
OPENVZ commands:
OpenVZ creates multiple secure, isolated Linux containers ( known as VPSs) on a single
physical server. Each container performs and executes exactly like a stand-alone server; a
container can be rebooted independently and have root access, users, IP addresses, memory,
processes, files, applications, system libraries and configuration files. Lets start, here CTID
representing the ID of a container(VPS Virtual Private Server).
The Internet is a global system of interconnected computer networks that use the
standardInternet protocol suite (TCP/IP) to link several billion devices worldwide. It is an
internationalnetwork of networks that consists of millions of private, public, academic, business,
and government packet switched networks, linked by a broad array of electronic, wireless, and
optical networking technologies. The Internet carries an extensive range of information
resources and services, such as the inter-linked hypertext documents and applications of the
World Wide Web (WWW), the infrastructure to support email, and peer-to-peer networks for file
sharing and telephony.
