Linux is a free to use and the spread of free Unix-like operating systems, based on POSIX and Unix is a multiuser, multitasking, and support multithreading and multiple CPU operating system. With the development of the Internet, the Linux software enthusiasts from all over the world got, organization, the support of the company.  It besides in server operating system maintained a strong momentum of development, on personal computers, embedded system has a great progress.  Users not only can directly obtain the realization mechanism of the operating system, and can be modified according to the needs of their own to improve the operating system, to maximize its to adapt to the needs of the user.

A brief history of Linux

The birth of the Linux operating system, the development and growth process is always dependent on five important pillars: Unix operating system, MINIX operating system, the GNU project, POSIX standards, and the Internet.

In the 1980 s, the performance of computer hardware, the growing market of PC, at that time, which can be chosen by the computer's operating system Unix, DOS and MacOS which are the main types. Unix is expensive, not running on the PC;DOS is humble, and source code by software vendors strictly confidential;

MacOS is a dedicated to apple computer's operating system. At this point, the computer science is an urgent need to a more perfect, strong, cheap and completely open operating system. Due to the typical operating system for the use of teaching are very few, so at that time in the Netherlands when American professor Andrew S. Tanenbaum writing an operating system, called MINIX, in order to tell the students internal working principle of the operating system. MINIX while is very good, but is just a simple operating system used for teaching purposes, rather than a strong practical operating system, but the biggest advantage is that open source code. Student of computers around the world by studying MINIX source code to run MINIX operating system in the computer, a sophomore students at the university of Helsinki, Finland, Linus Torvalds is one of them, on the basis of absorbing the essence MINIX, Linus wrote in 1991 of his own Linux operating system version for Linux0.01, marks the beginning of the age of Linux. He took advantage of the core of Unix, remove the multifarious core program, make it applicable to general computer x86 system, and on the Internet for everyone to download, launched in 1994, the core of the complete Version1.0, at this point, the Linux gradually become fully functional, stable operating system, and widely used.

The Linux key features

The basic idea

Linux there are two basic ideas: first, everything is a file; Second, each software has certain purposes. The first article in detail is the system of all boil down to a file, including command, hardware and software, operating systems, process equipment and so forth for the operating system kernel, is treated as have their respective characteristic or type of file. As for Linux is based on Unix, is largely because the basic idea of the two is very close.

Completely free

Linux is a free operating system, users can through the Internet or other ways for free, and is free to modify the source code. This is the other operating system. It is because of this, countless programmers from around the world involved in the modification of Linux, written work, the programmer can according to their own interest and inspiration to change, it makes Linux absorb the essence of countless programmers, growing.

Fully compatible with POSIX1.0 standards.

This enables under Linux through corresponding simulator run common DOS, Windows program. This laid the groundwork for users from Windows to Linux. Many users when considering using Linux, just think of before common program under Windows can run normally, it is to eliminate their doubts.

Multi-user, multi-tasking

Linux supports multiple users, each user for your own file equipment have their own special rights, ensure the mutual influence between each user. Multitasking is now one of the main characteristics of computer Linux can run multiple programs at the same time and independently.

Good interface

Linux also has the character interface and graphical interface. In character interface the user can through the keyboard input the corresponding operating instructions. It also provides similar to Windows graphic interface of the X Window system, users can use the mouse to operate. In the X - and in Windows in Windows environment are similar, can be a Linux version of Windows.

Support for multiple platforms

Linux can run on multiple hardware platforms, such as x86, 680 x0, SPARC, Alpha processor platform. In addition Linux is a kind of embedded operating system, can run on the handheld computers, set-top boxes, or game. Released in January 2001, the Linux kernel version 2.4 has been able to fully support Intel64 chip architecture. Linux also supports multiprocessor technology at the same time. Multiple processors work at the same time, make the system performance is greatly improved.

Advantages

1. Linux is composed of many micro kernel, its source code is completely open source;
2. Linux inherits the Unix features, have very strong network function, its support for all Internet protocol, TCP/IPv4, TCP/IPv6 and link layer topology procedures, etc , and can use the Unix network characteristics of developed a new protocol stack;
3. Linux system tool chain is complete, simple operation can configure a suitable development environment, can simplify the development process, reduce the obstacles in developing simulation tools, the system has strong portability;

System kernel routing forwarding

Linux operating system, embedded in the TCP/IP protocol stack protocol software with functions of routing forwarding. Installed in the routing forwarding dependence as the router's host nic, when a piece of card to receive packets, system kernel will according to the packet's destination IP address, query routing table, and then according to the query results to send the packet to another piece of card, the packets sent out at last, through the network card. The host of the process is to complete a the core functions of a router.

By modifying the Linux kernel parameter ip_forward routing function, the way of system use sysctl command configuration and display in the/proc/sys directory kernel parameters. First in the command line, enter: cat/proc/sys/net/ipv4 / ip_forwad, check if the Linux kernel, IP forwarding functions. If the result is 1, which indicates that the routing forwarding functions already open; If the result is 0 that they are not open. For security reasons, the Linux kernel by default packet routing forwarding is prohibited. In a Linux system, there are temporary and permanent forward two methods to enable function.

Temporary enable: this method only for the current session, no longer enabled after system restart. Temporary open command format: sysctl - wnet ipv4. Ip_forward = 1.

Permanent enable: this permanent enable IP forwarding function, by changing the configuration file/etc/sysctl . Conf statement of the "net. Ipv4. Ip_forward = 0", changed to "net. Ipv4. Ip_forward = 1", save the configuration file after executing commands sysctl -p/etc/sysctl. Conf, configuration immediately.

Safety hidden danger and reinforcement measures

User account login and security

Delete the redundant users and user groups. Linux is a multi-user operating system, there are many different accounts, the role of the system after installation is complete operating system, the system will default to not add xu user groups and users, if part of the user or user group does not need, should remove them immediately, otherwise the hackers are likely to take advantage of these accounts, the server to carry out attacks. What keep account, may be determined in terms of the use of the server.

Shut down unnecessary system services. Operating system installation is completed, it will be in the process of installation, can start independent of the various types of service program content, for the long time running server, the operation of the service program, the more the less then the safety of the system. So, the user or user group will need to apply some service procedures that cannot be closed, the performance, the safety of the hoisting system has a great help.

Password security policy. Under Linux, remote login system has two kinds of authentication in the form of: that is the key and password authentication. Among them, the key form of authentication, mainly is the public key is stored on a remote server, the private key is stored locally. When landing system, and then through the local private key, public key, as well as the remote server matching operation of authentication, if authentication matching degree is consistent, the user can login system unobstructed. Such authentication way, will not be threatened by brute force. At the same time, you just need to ensure the safety of the local private key, so that it won't be hackers steal, the attacker is not able to log in to the system by means of such certification. So, it is recommended to use the key system in the form of landed.

Effective application of su , sudo command. The role of the su command is to switch to the user. When the administrator login to the system, use the su command to switch to the super user role to perform some need super authority command. But due to the large super user permissions, at the same time, need to know the super user password management personnel, so the su command has very serious management risk.

Sudo command allows the system to give ordinary users some super powers, and does not need to ordinary users to switch to the super user. On the management, therefore, should be detailed rights allocation mechanism, using sudo commands for each administrator serve its specific administrative privileges.

The remote access and login authentication security

Remote login use SSH to log in. Telnet is a kind of login authentication services, that pose a safety hazard in the above network to transmit content using clear, hackers can easily through the Telnet packets, won the user's login password. And Telnet service program security verification way there is a big security hidden danger, make it become the target of hackers. The SSH service is to encrypt the data transmission, to prevent cheating and IP spoofing, DNS and transmission of data is compressed, to a certain extent to ensure the security of the remote connection by the server.

Embedded Linux

To make the appropriate changes to your Linux and cut, and able to use the system in the embedded system is embedded Linux operating system. Has the following features:

Linux system is completely open, free of charge. It is open, it can be compatible with each other, and other system to realize information interconnection. And it is free to modify the source code, this is what other system does not have.

Advantage of the Linux operating system is the more users and tasks. Ensures that multiple users to use each other ; Multitasking after independence of each other, greatly improve the efficiency, can give full play to performance.

Equipment is independent. As long as the install driver, the driver of the support and help, any user can like using file, to the operation and use of any device, which makes people without considering equipment specific form of existence.