Shulou(Shulou.com)06/02 Report--

What is the top ten common sense of Linux? for this question, this article introduces the corresponding analysis and solution in detail, hoping to help more partners who want to solve this problem to find a more simple and feasible way.

1. GNU and GPL

The GNU Project (also known as the Gernu Project) is a free software collective collaboration project publicly launched by Richard Stallman (Richard Stallman) on September 27th, 1983. Its goal is to create a completely free operating system. GNU is also known as a free software engineering project.

GPL is GNU's General Public license (GNU General Public License,GPL), the concept of "anti-copyright", is one of the GNU protocols, the purpose is to protect GNU software can be freely used, copied, studied, modified and distributed. At the same time, the software must be released in the form of source code.

GNU system combines with Linux kernel to form a complete operating system: a Linux-based GNU system, which is usually called "GNU/Linux", or Linux for short.

2. Linux distribution

A typical Linux distribution includes the Linux kernel, some GNU libraries and tools, command-line shell, X Window systems with a graphical interface and corresponding desktop environments such as KDE or GNOME, and contains thousands of applications ranging from office suites, compilers, text editors to scientific tools.

Mainstream distributions:

Red Hat Enterprise Linux 、 CentOS 、 SUSE 、 Ubuntu 、 Debian 、 Fedora 、 Gentoo

3. Unix and Linux

Linux is based on Unix and belongs to Unix class. Uinx operating system supports multi-user, multi-task, multi-thread and multi-CPU architecture. Linux inherits the design idea of Unix with network as the core, and is a multi-user network operating system with stable performance.

4. Swap partition

Swap partition, or swap area, where the system swaps with Swap when there is not enough physical memory. That is, when the physical memory of the system is insufficient, a part of the space in the hard disk is released for use by the currently running program. When those programs are about to run, restore the saved data from the Swap partition to memory. Programs that are freed of memory space are generally programs that do not operate for a long time.

Swap space should generally be greater than or equal to the size of physical memory, with a minimum of not less than 64m and a maximum of twice the size of physical memory.

5. The concept of GRUB

GNU GRUB (GRand Unified Bootloader referred to as "GRUB") is a multi-operating system boot manager from the GNU project.

GRUB is a boot manager that supports multiple operating systems. In a computer with multiple operating systems, you can use GRUB to select the operating system that users want to run when the computer starts. At the same time, GRUB can boot different kernels on the Linux system partition, and can also be used to pass startup parameters to the kernel, such as entering single-user mode.

6. Buffer and Cache

Cache (cache) A temporary memory located between CPU and memory. The cache capacity is much smaller than memory, but the exchange speed is much faster than memory. By caching file data blocks, Cache solves the contradiction between CPU operation speed and memory reading and writing speed, and improves the data exchange speed between CPU and memory. The larger the Cache cache, the faster the CPU processing.

Buffer (buffer) cache memory, by caching data blocks of disk (Imax O device), speed up the access to data on disk, reduce Imax O, and increase the speed of data exchange between memory and hard disk (or other Imax O devices). Buffer is about to be written to disk, while Cache is read from disk.

7. TCP three-way handshake

The requester sends a SYN (SYN=A) packet, waits for the responder to confirm that the responder receives the SYN, and returns SYN (ACK 1) and its own ACK (K) packet to the requester to receive the SYN+ACK packet from the responder, and sends the acknowledgement packet ACK (Kroom1) to the responder again

The requester and the responder establish a TCP connection, complete the three-way handshake, and begin data transmission.

8. Linux system directory structure

The Linux file system uses a linked tree directory structure, that is, there is only one root directory (usually represented by "/"), which contains information about subordinate subdirectories or files, and subdirectories can contain information about lower-level subdirectories or files.

/: the root of the first hierarchy, the root of the entire file system hierarchy. That is, the entry to the file system, the highest-level directory. / boot: contains the files required by the Linux kernel and the system bootstrap, such as kernel and the initrd;grub system boot manager are also in this directory. / bin: the commands and functions required by the basic system are similar to "/ usr/bin". The files in this directory are executable. Ordinary users can also execute it. / sbin: basic system maintenance commands that can only be used by superusers. / etc: all system configuration files. / dev: device file storage directory. Such as terminals, disks, optical drives, etc. / var: stores frequently changing data, such as logs, emails, etc. / home: the default storage directory for ordinary users. / opt: the directory where third-party software is stored, such as user-defined packages and compiled packages, are installed in this directory. / lib: the library files and kernel modules store directories that contain all the shared library files needed by the system program.

9. Hard links and soft links

Hard links (Hard Link): hard links are links that use the same index node (inode number), that is, you can allow multiple file names to point to the same file index node (hard links do not support directory links or cross-partition links). Delete a hard link without affecting the source file of the index node and multiple hard links under it.

Ln source new-link

Soft links (symbolic links, Symbolic Link): symbolic links are links created in the form of paths, similar to windows shortcut links, symbolic links allow you to create multiple file names to link to the same source file, delete the source file, and all soft links under it will not be available. (soft connection supports directories, cross-partition, cross-file system)

Ln-s source new-link

10. RAID technology

Disk array (Redundant Arrays of independent Disks,RAID), cheap redundant (independent) disk array.

RAID is a technology that combines multiple independent physical hard disks in different ways to form a hard disk group (logical hard disk), which provides higher storage performance and data backup technology than a single hard disk. RAID technology can provide disk crossing function by combining multiple disks together as a logical volume; data can be divided into multiple data blocks (Block) to write / read multiple disks in parallel to improve the speed of accessing disks; fault tolerance can be provided through mirroring or check operations. The specific functions are implemented in different RAID combinations.

In the eyes of users, the disk group composed of RAID is like a hard disk, which can be partitioned, formatted and so on. The storage speed of RAID is much higher than that of a single hard disk, and it provides automatic data backup and good fault tolerance.

RAID level. Different RAID combinations are divided into different RAID levels:

RAID 0: known as Stripping stripe storage technology, all disks are read and written in parallel, which is the simplest form of building a disk array. It only requires more than 2 hard disks, which has a low cost and can provide the performance and throughput of the entire disk. But RAID 0 does not provide data redundancy and error repair functions, so the damage of a single hard disk will lead to all data loss. (RAID 0 simply improves disk capacity and performance, does not provide reliability guarantee for data, and is suitable for environments that do not require high data security.) RAID 1: mirrored storage, data redundancy is achieved by mirroring the data of one disk in two disks to the other. The capacity of data backed up by each other on two disks is only equal to the capacity of one disk. When data is written to one disk, a mirror is produced on another idle disk to maximize the reliability and repairability of the system without affecting performance; when the original data is busy, data can be read directly from the mirror copy (read from the faster one of the two hard drives) to improve read performance. In contrast, RAID 1 is slow to write. RAID 1 generally supports "hot swapping", that is, the removal or replacement of hard drives in the array can be carried out while the system is running, leaving the system without interruption. RAID 1 is the highest unit cost of hard disk in the disk array, but it provides high data security, reliability and availability. When a hard disk fails, the system can automatically switch to the mirrored disk to read and write without the need to reorganize the failed data. RAID 0room1: also known as RAID 10, is actually a combination of RAID 0 and RAID 1, mirroring each disk for redundancy while continuously dividing data in bits or bytes and reading / writing multiple disks in parallel. Through the combination of RAID 0 disk 1, each disk has its own physical mirror disk except for multiple disks, which provides redundancy, allows one disk failure without affecting data availability, and has fast read / write capabilities. RAID 0room1 requires at least 4 hard drives to establish a band set in the disk mirror. RAID 0room1 technology not only ensures the high reliability of data, but also ensures the high efficiency of data reading / writing. RAID 5: a storage solution that takes into account storage performance, data security, and storage costs. RAID 5 can be understood as a compromise between RAID 0 and RAID 1, and RAID 5 requires at least three hard drives. RAID 5 can provide data security for the system, but the degree of protection is lower than that of mirrors, and the utilization of disk space is higher than mirrors. RAID 5 has a data read speed similar to that of RAID 0, but with one more parity information, and writing data is slightly slower than writing to a single disk. At the same time, because multiple data correspond to a parity information, RAID 5 has higher disk space utilization and lower storage cost than RAID 1, so it is a widely used solution at present. What is Linux system Linux is a free-to-use and free-spread UNIX-like operating system, is a POSIX-based multi-user, multi-task, multi-threaded and multi-CPU operating system, using Linux can run major Unix tools, applications and network protocols.

This is the end of the answer to the top ten common sense questions about Linux. I hope the above content can be of some help to you. If you still have a lot of doubts to solve, you can follow the industry information channel to learn more about it.

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.