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The difference between hard link and soft link is somewhat confusing. It confuses the beginning and sometimes experienced system administrators as well. In this article I’m trying to explain the difference between the two theoretically and practically as well. Before starting I’ll layout foundation by just explaining some simple necessary terms.
What is Link Anyways
The link is nothing but just the shortcut to a file or directory. The ln command does the purpose of creating links to files or directories. Now from I’ll use the term file, even for directories. After all unix treats everything as a file in OS environment.
What is Inode Then
Inode is a data structure which stores the information of files, directories, devices, filesystem objects etc. So, for any file existing in a unix system, an inode will be there. Any file can be recognized by its inode number. I’ll tell you how to see inode number of files. Unix deals with any objects like files, directories, devices, filesystem objects with the help of inodes.
What is There in An Inode
Following are the contents of an inode for every file:
User and group ownership.
User permissions on files like read, write and execute.
Type of file.
File length in bytes.
Number of links to file.
Access privileges.
Time of last access and last modification.
Time of last inode change.
Pointers to the file’s data.
File allocation information.
Direct and indirect extent information.
How To See The Inode Number Associated With File
To see the inode number, you need to issue ls command with -i option.
Below is the usage: wiw_labs: $ ls -li maps maps_soft_link maps_hard_link 64232 -rw-r–r– 2 lab_user lab_user 91 May 15 06:09 maps 64232 -rw-r–r– 2 lab_user lab_user 91 May 15 06:09 maps_hard_link 64234 lrwxrwxrwx 1 lab_user lab_user 4 May 15 06:09 maps_soft_link -> maps
What Do I Have To Do With Inodes
When a link is created to a file, we have two options:
Assigning fresh inode to the new link.
Assigning inode of the original file to the link, for which we are creating a link.
What is A Soft Link
When we create a soft link, a fresh inode is assigned to the link. So the original file and soft link will have different inode numbers. The new inode points to the original inode. So, whatever data we access through the soft link, is retrieved from the original file through original inode. That means if we delete the original file, the soft link won’t be able to show you the data of file, the original inode is freed up as a result of original file deletion. If still you have doubt, wait for the practical demo.
What is A Hard Link
When we create a hard link, the original inode is assigned to the link. The original file and hard link will be having same inode number. So, imagine we delete the original file. The data is still accessible, because we still have the original inode. It’s not gone anywhere.
Practically Demonstrated Commands
Below I’m pasting the outputs I created after running the commands to show you the demo.
Here I’ve taken three cases:
Case 1: Original file is deleted and then we cat both soft and hard links.
Case 2: Hard link is deleted and we cat both original file and soft link.
Case 3: Soft link is deleted and we cat both original file and hard link.
Original file is maps and its contents as: A quick brown fox jumps over the lazy dog. This line has all english alphabets from A - Z.
Normally its required to gather important information of unix machines. The prtconf command is specifically used in Aix and Solaris operating systems. The information required normally is:
System model.
Machine serial number.
Processor type, number of processors and clock speed of processors.
Network information.
File system information.
Paging space information.
Devices information.
Total memory size.
The explanation will be on the basis of AIX.
Now, information on prtconf command will be represented in the form of question and answers.
How To Gather General Machine Information
Using the command prtconf alone provides the whole information of machine.
The sample is given below. Some actual values have been replaced with other values for the sake of security.
wiw_labs: $ prtconfSystem Model: IBM,9133-55AMachine Serial Number: 06F865GProcessor Type: PowerPC_POWER5Number Of Processors: 4Processor Clock Speed: 1499 MHzCPU Type: 64-bitKernel Type: 64-bitLPAR Info: 1 galaxy198Memory Size: 4096 MBGood Memory Size: 4096 MBPlatform Firmware level: Not AvailableFirmware Version: IBM,SF240_338Console Login: enableAuto Restart: trueFull Core: falseNetwork InformationHost Name: galaxy198IP Address: 192.168.10.29Sub Netmask: 255.255.255.0Gateway: 192.168.10.1Name Server: 192.168.19.28Domain Name: foo.comPaging Space InformationTotal Paging Space: 8192MBPercent Used: 1%Volume Groups Information==============================================================================rootvg:PV_NAME PV STATE TOTAL PPs FREE PPs FREE DISTRIBUTIONhdisk0 active 525 383 109..24..42..99..109==============================================================================INSTALLED RESOURCE LISTThe following resources are installed on the machine.+/- = Added or deleted from Resource List.* = Diagnostic support not available.Model Architecture: chrpModel Implementation: Multiple Processor, PCI bus+ sys0 System Object+ sysplanar0 System Planar* vio0 Virtual I/O Bus* vsa0 U9133.55A.06F865G-V1-C0 LPAR Virtual Serial Adapter* vty0 U9133.55A.06F865G-V1-C0-L0 Asynchronous Terminal* pci2 U787B.001.DNWCF4C-P1 PCI Bus* pci7 U787B.001.DNWCF4C-P1 PCI Bus+ ent2 U787B.001.DNWCF4C-P1-T9 2-Port 10/100/1000 Base-TX PCI-X Adapter (14108902)+ ent3 U787B.001.DNWCF4C-P1-T10 2-Port 10/100/1000 Base-TX PCI-X Adapter (14108902)* pci8 U787B.001.DNWCF4C-P1 PCI Bus+ usbhc0 U787B.001.DNWCF4C-P1 USB Host Controller (33103500)+ usbhc1 U787B.001.DNWCF4C-P1 USB Host Controller (33103500)* pci9 U787B.001.DNWCF4C-P1 PCI Bus+ fcs2 U787B.001.DNWCF4C-P1-C1-T1 FC Adapter* fcnet2 U787B.001.DNWCF4C-P1-C1-T1 Fibre Channel Network Protocol Device* fscsi2 U787B.001.DNWCF4C-P1-C1-T1 FC SCSI I/O Controller Protocol Device+ mem0 Memory+ proc0 Processor+ proc2 Processor+ proc4 Processor+ proc6 Processor
How To Get The Processor Clock Speed
For this issue the command with -s parameter. wiw_labs: $ prtconf -s
How To Get CPU Type
To know if the cpu type is 32 bit or 64 bit, issue the command with -c parameter. wiw_labs: $ prtconf -c
How To Know The Type of Kenel
To know which type of kernel is in use 32 bit or 64 bit, issue the command with -k parameter. wiw_labs: $ prtconf -k
How To Get The LPAR Information of Machine
To know what is the LPAR partition number and partition name, issue with -L. wiw_labs: $ prtconf -L
If its not LPAR, then “-1 NULL” will be returned.
How To Get The Physical Memory Size of Machine
To know the physical memory size of the machine, issue the command with -m flag. wiw_labs: $ prtconf -m
How To Get The Details of All Physical Devices of The Machine
To know the Vital Product Data of all physical devices internal or attached to the machine, use -v option. wiw_labs: $prtconf -v
Almost all of the information gathered by above commands is shown above in the output of prtconf command.
The question about the difference between a website and a blog is often quite confusing. The starters in web world often Google from site to site in their bewilderment. So, was I, while I was struggling to juggle out the difference between website and the blog. Here I’m trying to explain the difference between the both according to my understanding and experience in web technologies. But one thing is for sure that you won’t understand it till you start one website or blog.
There are various points of views to see websites and blogs. So far as I have perceived, the difference between these two are different for different people. But to me No Difference. Confusing? Let me explain. If at end of the post, you feel still in doubt then feel free to contact me or comment on this post and I’ll be writing back to you.
I’ll take two cases:
Your aim is to sell the products or services.
Your aim is to write your articles and showcase these.
Now let’s discuss the difference between the two in a general sense.
What Are Websites
On the website you will be putting up information of their products and services. Here are the features of websites:
The information normally does not change too frequently on a website.
Generally Visitors are not allowed to present their view point on products or services information presented on website.
Chronology is not of much importance to a website. Anything updated on website is hardly of any importance in context to the date of information.
The sections and categories play a vital role in website information presentation.
Websites normally fall under the category of Content Management Systems.
Then What Are Blogs
The blogs are acronyms for web logs. These are a sort of a journal. The main features of blogs are:
On blogs you will be putting up articles about their products like news, information of products upgrades etc. etc. These are also referred to as Blog Posts. Normally anything under the sun can be presented in blogs. The only condition is it should be information only.
The visitors can present their view points on the information given on blog. The mode of communication from visitor’s side is generally the comments on articles.
The information is organized mainly on chronological basis.
The information changes very frequently on blogs as compared to sites. The dates play more important role than the categorization of information in categories and sections.
The blogs normally include podcasts/videos etc. as well. So visitors feel close to the service providers.
Normally no products are sold on blogs.
How Does The Difference Apply To You
You simply have to find, which category you fall in.
If you want to sell anything then you should make two things separate, website and blog.
If you just want to write articles and present the information to your visitors then this difference should not bother you. The technology has merged the difference between the two to quite an extent. With the help of different software extensions, the websites can act as blogs and vice versa.
A Piece of Advice For Starters
If you are a starter in the web world and you want to write, then here is the piece of advice for you. It’s not the number of posts that matters, but it’s the quality of content which matters. So write posts on your blog which are long lasting. Normally your posts should be immune to the time. Anytime visitors read your post, it should be as useful to them as it was on the first day of writing. I hope I made my point.
Textures and patterns are essential elements in a good room design. They help to bring harmony and synchronization in the design. The texture is mostly seen in the wall covering products. In addition to the conventional methods of painting, we have distressed painting, hand painting, and roller texture where primary colors like red, green and yellow are used with a little silver as a background. Pattern is the combination of motifs like lines, shapes, colors and textures to form a composition. Effective use of patterns can make a larger room appear small, and a small room larger. Combination of textures and patterns help in demarcating spaces and also lend continuity to the room. Here are a few tips, with which you can experiment with different textures and patterns :
Patterns in multi shades, with diagonal lines criss- crossing each other randomly, serves to keep eyes busy. But these patterns may give a cluttering impression in small areas so are recommended for large rooms only.
Vertical stripes in pattern for rooms with low ceiling create the illusion of height.
In a narrow room, horizontal stripes set closer to each other give the illusion of width.
Large areas usually look good with large prints while small areas should have smaller prints, like close lines, close dots etc.
Using similar patterns in two or more consecutive rooms creates an open plan look. Sudden difference in pattern breaks the continuity of the design, and hence distracts the eye.
A rough texture absorbs more light while a smooth texture reflects light. This can be used in the design of various rooms. A rough texture gives a more rustic look and adds a natural feel as compared to areas with a smooth, glossy finish. However, areas with smooth and glossy finish are easier to clean. This works well in places that need to cleaned more often, such as kitchen and bathroom. On the other hand, rough surfaces tend to accumulate dust more often, making them difficult to clean.
In my last post on web hosting I discussed about what is web hosting and why do we need that. Now in this post I’m gonna discuss more about web hosting.
Web Hosting Defined
When you want to display your web content on Internet, you need to put this web content on some server. This is called web hosting. The professional companies which provide the servers for putting up this content are called web hosts or web hosting providers.
What Does It Take To Start Web Hosting
It takes nothing except free registration on some popular hosting providers, choose some unique page name for you and start writing your stuff. The famous providers are:
If you just want to write articles etc. And don’t want anything else in return you can write the articles and submit these to various websites like ezinearticles.com, articlebase.com etc. And so on.
Prerequisites of Web Hosting
If you want to seriously use your website for any purposes including your business then you need to give it enough thinking. These are the prerequisites for starting your own website.
Domain Name.
Web Hosting Service.
Some Content Management System.
And/or Blogging Software
And/or E-Commerce Software.
And/or some Wiki software.
Some e-mail system to start sending and receiving mails in your name.
Some visitor tracking systems and so on.
Registering Your Domain Name
Once you decided to have a domain name in your name, you need to register a domain. To register a domain you need to contact a domain registrar. Normally people go to GoDaddy.com
You can go to google either. But they also go to GoDaddy. It’s normally a $10/annum cost. With some web-hosting providers, you get domain name for free till you host with them. I personally recommend to register your own domain, so that you are not bound with any host provider.
Types of Web Hosting
Once you have domain name, you need to host your content on some server. For that you find some web hosting provider. As per cost Web hosting is mainly of two types: free and paid.
Free Web Hosting
For free web hosting you can go to google.com. They provide free web hosting. But you can not use databases with them. You can create your web site of only static content. Which is not what you want. You are left with very little or no flexibility.
Paid Web Hosting
Paid hosting is also of two types.
Shared hosting.
Dedicated hosting.
Shared Hosting
In shared hosting you share the server resources with other users. It’s all seamless to the users. And no one can enter other’s domain. With shared web hosting, you get the following things with the package:
Sometimes free domain name.
Web space to store your content. You may get anywhere from 500MB to unlimited storage, depending upon the hosting providers.
Databases like MYSQL, SQLLITE, MSSQL etc. Hosting providers provide from 2 to 100 to unlimited number of databases. Some hosting providers even restrict the size of databases as well.
E-Mail facility. Normally its all included.
Sub-domains for managing your website hierarchy in a more meaningful way. These are also varying in number from 100 to unlimited.
Control Panel to manage your web-services.
Sometimes you can get shell access, if you need to run native operating system commands.
The advantage of shared hosting is that, you don’t need to bother about the management and security of the operating system and the resources. Also this is good service for the starters.
Dedicated Hosting
Dedicated hosting has several types:
Virtual Private Server(VPS) Hosting.
Dedicated Server Hosting.
Hybrid Server Hosting.
The terms will be discussed in some other post. I’m just listing what you get with Dedicated Hosting:
Web space. Normally 8GB+ is provided.
Database Server like MYSQL, SQLLITE, MSSQL pre-installed.
For control panels you need to pay extra.
E-Mail facility will have to configured manually if you don’t get control panel.
Unlimited sub-domains can be configured.
Unlimited domains can be configured.
Server security has to be taken care of by yourself. Otherwise pay more.
Full root login with shell access is provided. So, you need to do everything of your own.
Normally rates are more as compared to shared hosting.
You need to be more expert at setting up your web hosting on dedicated severs.
We are forced to stay indoors during the hot summer months, so we should attempt to make our home interiors cooler and soothing so that staying indoors doesn’t become painful. Here are a few tips by which you can turn your home into a cool haven and beat the scorching heat, without having to invest much.
Windows :
To start with, change your old windows , as old windows tend to make the house hot by allowing heat transfer into the rooms. Consider putting up good quality vinyl or wood windows, and windows that use low e-glazing on the glass, which cuts down on UVs and heat entering the rooms from outside. Also consider putting horizontal blinds or shutters on windows. When using blinds, position them so the sunlight is directed upwards towards the ceiling. This imitates the effect of a skylight by providing natural sunlight without having much impact on the cooling. Wood blinds are preferable to metal blinds as metal blinds tend to conduct heat into a room.
Light : Lighting is another important aspect, to be taken into consideration. During summer months, try to minimize overhead lighting as it generates heat. To read or study, you can use a table lamp instead of switching on an overhead light. Every time you turn on an overhead light, you not only burn energy through the light source, but also generate heat that your AC or fan must work harder to cool. Try using Compact fluorescent light bulbs instead of the standard incandescent bulbs, as they use less energy and produce less heat.
Upholstery : The type and color of fabric also determines the amount of heat produced in a room. You should go for light colored fabric slipcovers during the summer months , like white muslin slipcovers for the upholstery. Similarly, heavy wool carpets should be rolled up in the summer and light colored cotton rugs or durries can replace them, as they tend to accumulate less heat than the haavy carpets. This follows the basic principle that dark colors absorb and hold heat while light colors reflect heat.
Plants :
Placing some plants indoors can also give a cooler effect to the room. Glossy evergreens like dracaenas and ficus plants are big enough to be used as stand alone plants. They also fit well into a large living room or a large dining area. Select plants with glossy leaves and elegant shapes. Place them in attractive containers to add beauty to the room. Brass containers give an ancient look while terracotta ones bring in an earthy feel to the ambience.
Waterstructure : These days its quite a fashion to install a water structure inside the house. A small fountain inside your home or even a terracotta container filled with water and sprinkled with flower petals will make your home feel cooler.
SUID programs in Unix based systems are one of the most dangerous things you can every have one your systems. Today I’m gonna discuss the dangers of SUID programs in Unix based system. For system security, often it’s suggested to keep minimum or no suid programs in the systems. Here is a brief introduction and practicle demo of the dangers of SUID programs. I start from the definition and then explain a bit about these programs and then give an example to make you understand.
What Are SUID Programs
SUID programs are those programs which run with the permissions and privileges of root user at the time of execution. So, when the program is executed, it’s granted the privileges of root user.
SUID Programs Are Always Binary Programs
SUID bit can be set only on binary programs. Shell scripts can not be made SUID in any way, because these are ascii not binary.
How To Make A Program SUID
To make a program an SUID program, you need to change the permissions of this program and add suid bit. This is how you will make program suid. We’ll take the example of vi program.
Dangers of SUID Program Step By Step
I’m going to give you step by step demo of the dangers of suid, which you can replicate on your respective system.
vi command is accessible to everyone on the system. So, whosoever is going to run vi command, will become root while the program is running. Now, see what a potential hacker can do with this small negligience.
So, do
wiw_labs:$vi /etc/passwd
Now, change the id and gid to 0. This makes the hacker a root user.
Now, switch to hacker account again and check id.
wiw_labs:$su - hacker
Password:
wiw_labs:$id
uid=0(root) gid=0(root) groups=0(root)
Now, notice the, hacker has become the root.
Now again run the commands for which (s)he was denied the permission to run as normal user.
wiw_labs:$/etc/init.d/apache2 restart
* Restarting web server apache2 apache2: Could not reliably determine the server’s fully qualified domain name, using 127.0.0.1 for ServerName
apache2: Could not reliably determine the server’s fully qualified domain name, using 127.0.0.1 for ServerName
[ OK ]
wiw_labs:$/etc/init.d/mysql restart
* Stopping MySQL database server mysqld [ OK ]
* Starting MySQL database server mysqld [ OK ]
* Checking for corrupt, not cleanly closed and upgrade needing tables.
By now it must be obvious to you, that if the hacker can do this thing, then (s)he can do much more dangers to your system, e.g (s)he runs this command rm -fr * then the whole system can be wiped out.
How to make money online is everyone’s dream. Here is a small video showing how to make money online with MySpace.com. Watch out this video to know more.
You know that our TCP/IP world operates in IP addresses because computers don’t understand words. But human beings understand their language(words) better. So, to make it easy for both computers as well as humans, DNS works as a layer in between. DNS will translates IP addresses, which are understandable by computers to meaningful names for humans. Similarly it will translate names to IP addresses for computers. I’m not going in much detail, but presenting this video for those who want to understand DNS. This 8 minute video introduces you to the concepts of DNS and the components. A must watch for the absolute beginners.
