A summary of the first phase of Linux learning

Source: Internet
Author: User


1. The Dev directory role

DEV is the acronym for Devices. Here the main storage device, CD-ROM, hard disk (under Linux, all files).

2. tmp directory Permissions

The permissions for the/tmp directory are 1777, the last one for other users is t, the sticky bit (sticky), is the special permission in Linux, the corresponding number is 1, meaning in the/tmp directory, only the owner or root of the file can delete or move the file.

3. Tar Command Summary

-Z: compression via zip tool;

-C: (create) creates a compressed package;

-V: (verbose) shows the execution process;

-F: (file) The name of the compressed package;

-T: (list) Displays the contents of the compressed package;

-X: (extract) extracts files from the package.

4. RAID0 RAID1 RAID5 RAID10 Advantages and disadvantages and application scenarios

RAID 0: Split the contiguous data into blocks, scattering the data block's read/write requests to each disk to achieve "simultaneous" read/write purposes.

Minimum disk requirements: 1 blocks

Advantages: The highest utilization rate, 100%, the fastest read and write.

Cons: Unable to back up data, once an error occurs, all data is lost.

Application scenario: Suitable for large-scale concurrent read and write, but the data security requirements are not high, such as MySQL slave (data block from the library), cluster node RS (waiter)

RAID 1: Maximum availability and repair of user data is guaranteed.

It's only 2 disks.

Advantage: Write two disks at the same time for full data backup.

Cons: Lowest utilization, 50%, slow read and write speed.

Scenario: A business that applies to data that is important and uninterrupted.

Compromise of RAID 5:raid 0 and RAID 1.

3 disks or more, utilization is (n-1)/n*100% (n≥3)

Pros: Allows error to occur, data security is lower than RAID 1, disk space utilization is higher than RAID 1

Disadvantage: Only one disk can be allowed to be lost, write performance is not high

Application scenario: MySQL master-slave library can be, storage can also, ordinary server in order to reduce maintenance costs, but also maintain a certain degree of redundancy and read performance can do RAID 5

RAID 10: Also known as RAID 1+0, is a combination of RAID 1 and RAID 0 standards, first by RAID 0 divided into two groups, and then the two groups by RAID 1 mirroring

4 Disks, Utilization 50%

Advantages: Read and write fast, can fault-tolerant, can back up data

Cons: High cost

Application scenario: For applications that require high performance, high fault tolerance, but small capacity requirements, not bad for money

5. AWK Countdown second column awk How to say

awk ' Nr==3{print $ (NF-1)} '

Where $NF represents the last column, the penultimate list is-1, the third column is 2, and so on, and the Countdown nth column (n-1)

A summary of the first phase of Linux learning

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