Linux-Essential Root Subdirectories

bin Contains binary programs also known as an executables, which are programs that are ready to run. Most of the basic Unix commands such as ls and cp are in /bin. However, some of the files in /bin are not in binary format because shell scripts perform the tasks of binaries in modern systems. dev Contains device files.  etc The core system configuration directory (pronounced EHT-cee). User password, boot, device, networking,...

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What Is IP Filtering?

IP filtering is simply a mechanism that decides which types of IP packets will be processed normally and which will be dropped or rejected. By dropped we mean that the packet is deleted and completely ignored, as if it had never been received. By rejected we mean that the firewall sends an ICMP response to the sender indicating a reason why the packet was rejected. You can apply many different sorts of criteria to determine which packets you wish to filter. Some examples of these are: Protocol type: TCP, UDP, ICMP, etc. Port number...

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Linux Port Scanning

Listing your open ports and firewall configuration with netstat and iptables is a good start for staying on top of unwanted traffic, but you may want to go a step further with Nmap Network Mapper, a program that scans all of the ports on a machine or network of machines, looking for potential vulnerabilities. Nmap gives you a view from the outside and eliminates guessing which ports are open. Most intruders use Nmap, and you can...

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Configuring IPv6 Networks

At the beginning, IANA gave requestors an entire class A network space thereby granting requestors 16.7 million addressesmany more than necessary. Realizing their error, they began to assign class B networksagain, providing far too many addresses for the average requestor. As the Internet grew, it quickly became clear that allocating class A and class B networks to every requestor did not make sense. Even their later action of assigning class C banks of addresses still squandered address space, as most companies didn't require 254 IP addresses....

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what is IMAP

IMAP, fully documented in RFC 3501, was designed to provide a robust, mobile mail delivery and access mechanism. For more detail on the protocol and how it functions on the network layer, or for additional information on the numerous specification options, please consult the RFC documentation. POP and IMAP tend to be grouped together or compared, which is a bit unfair since they are dissimilar in many ways. POP was created as a simple mail delivery vehicle, which it does very well. Users connect to the server and obtain their messages,...

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TCP/IP Firewall

The combined set of protocols is called the Transmission Control Protocol and Internet Protocol TCP/IPprotocol suite. As a network administrator, it is important that you understand the nature of potential attacks on computer security. We'll briefly describe the most important types of attacks so that you can better understand precisely what the Linux IP firewall will protect you against. You should do some additional reading to ensure that you are able to protect your network against other types of attacks. Here are some of the more...

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Linux Software websites

 Linux Software websites Internet Sites Description ftp.redhat.com Red Hat distribution RPM packages rpmfind.net RPM package repository sourceforge.net Source Forge open source software repository and development site freshmeat.net New Linux software apps.kde.com KDE software applications www.gnome.org GNOME software applications ...

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How to create update or remove symbolic or soft link Linux

Symbolic links , Symlink or Soft link in Unix are very important concept to understand and use in various UNIX operating systems e.g. Linux , Solaris or IBM AIX. Symlinks gives you so much power and flexibility that you can maintain things quite easily.I personally feel that along with find, grep and other UNIX commands, command to create soft link and update soft link i.e. ln -s  is also must for any one working in UNIX machine. Whenever I do scripting or write any UNIX script I always write for symlinks rather than pointing to absolute...

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Common Linux Features?

Multiuser — Not only can you have many user accounts available on a Linux system, you can also have multiple users logged in and working on the system at the same time. Users can have their own environments arranged the way they want: their own home directory for storing files and their own desktop interface (with icons, menus, and applications arranged to suit them). User accounts can be password-protected, so that users can control who has access to their applications and data. Multitasking — In Linux, it is possible to have many...

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What Is an Operating System?

An operating system is made up of software instructions that lie between the computer hardware (disks, memory, ports, and so on) and the application programs (word processors, Web browsers, spreadsheets, and so on). At the center is the kernel, which provides the most basic computing functions (managing system memory, sharing the processor, opening and closing devices, and so on). Besides the kernel, an operating system provides other basic services needed to operate the computer, including: File systems — The file system provides the...

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mkdir and rmdir

You can create and remove directories using the mkdir and rmdir system calls. #include <sys/types.h>#include <sys/stat.h>int mkdir(const char *path, mode_t mode); The mkdir system call is used for creating directories and is the equivalent of the mkdir program. mkdirmakes a new directory with path as its name. The directory permissions are passed in the parametermode and are given as in the O_CREAT option of the open system call and, again, subject to umask. #include <unistd.h>int rmdir(const char *path); The rmdir system call...

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The Shell as a Programming Language

Now that you’ve seen some basic shell operations, it’s time to move on to some actual shell programs. There are two ways of writing shell programs. You can type a sequence of commands and allow the shell to execute them interactively, or you can store those commands in a file that you can then invoke as a program. Interactive Programs Just typing the shell script on the command line is a quick and easy way of trying out small code fragments, and is very useful while you are learning or just testing thing...

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What Is a Shell?

Before jumping in and discussing how to program using a shell, let’s review the shell’s function and thedifferent shells available for Linux. A shell is a program that acts as the interface between you and the Linuxsystem, enabling you to enter commands for the operating system to execute. In that respect, it resembles theWindows command prompt, but as mentioned earlier, Linux shells are much more powerful. For example,input and output can be redirected using < and >, data piped between simultaneously executing programsusing |, and output...

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What is Shell Script

Normally shells are interactive. It means shell accept command from you (via keyboard) and execute them. But if you use command one by one (sequence of 'n' number of commands) , the you can store this sequence of command to text file and tell the shell to execute this text file instead of entering the commands. This is know as shell scrip...

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The Role of the Device Driver

As a programmer, you are able to make your own choices about your driver, andchoose an acceptable trade-off between the programming time required and the flexibilityof the result. Though it may appear strange to say that a driver is “flexible,” welike this word because it emphasizes that the role of a device driver is providingmechanism, not policy. The distinction between mechanism and policy is one of the best ideas behind theUnix design. Most programming problems can indeed be split into two parts: “whatcapabilities are to be provided” (the...

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The kernel

The kernel is a piece of software that, roughly speaking, provides a layer between the hardware and the application programs running on a computer. In a strict, computer-science sense, the term 'Linux' refers only to the kernel - the bit that Linus Torvalds wrote in the early 90s. The kernel of UNIX is the hub of the operating system: it allocates time and memory to programs and handles the filestore and communications in response to system calls. As an illustration of the way that the shell and the kernel work together, suppose...

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