Linux Learning-General Command use 2

Hashed Hash : Once an external command has been run, it is hashed into the cache and can be read quickly the next time it runs.

Look at the cat's file location and find its environment variable, the default environment variable is/usr/bin/cat. Its highest-priority environment variable location is/usr/local/sbin

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Because the default is the/usr/bin/cat path, the cache record is also under this path.

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Copy the default path/usr/bin/cat to the highest priority/usr/local/sbin/cat, and implement the Cat feature here to find the hash or follow the original path. Because/usr/bin/cat is already used in the cache record as the default path. If you want/usr/local/sbin/cat to take effect, you need to clear the cache before you use the Cat command

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Clear the cache, use the Cat command to discover that the path has been changed to/usr/local/sbin/cat

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To restore the original default path, the following method:

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Enable-n CD

Enable CD

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Because the internal instruction is disabled, the external command is still in, CENTOS6 does not support

Command usage Trivia

[email protected] tmp]# ls \
> L \
> Yum.log//For longer commands can be displayed on a branch

[[email protected] tmp] #ls;p wd;ifconfig//For short commands can be executed together and take effect separately

Loginout =ctrl + d//exit current Login
Systemctl Restart network//restart NIC

Date cal Usage

Date: Displays dates and times
Date-u//Show GMT

Clock: Show Hardware time
Synchronization Time Method:
CLOCK-S//Hardware-based quasi-sync time
CLOCK-W//With system time quasi-synchronization time

Default format: Date month day hour divided by year. seconds
Date 091811302012.20
For example:

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Cal: The command that displays the date
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Religious reasons.

Modify system Boot Display content

Cat/etc/issuevi/etc/issue

\s
Kernel \ r on an \m
STOP!!! This is MY MY ///Added to character interface line entry will appear.

Screen installation and use

CentOS 7 Command Installation
You can choose to see if the screen is installed on your computer.
Type screen
If not installed, there are two ways to install it:
1: Check that the disc has been mounted, locate the screen-4.1.0-0.21.20120314git3c2946.el7.x86_64.rpm file in the packages package and double-click Install;
2;DF view disc is already mounted

DF rpm-i/run/media/root/centos7\7\x86_64/packages/screen-4.1.0-0.21.20120314git3c2946.el7.x86_64.rpm

Test starts after successful installation
Test purpose: To help users solve system application problems
Test completion Prerequisites: Both sides have to log on to the same server, and use the same account, on two different computers to achieve

Help side:

Type screen screen screen-s zcl184

Help side:

which screen screen-lsscreen-x zcl1840

After the connection, both can be operated on a single desktop.
If either side exits exit then the link is interrupted.
Create a background program through screen to prevent interruptions. For example, the upgrade program runs in the background.
Simulation via infinite loop Yes command

1:screen
2:yes
3:ctrl + A//pause press D to turn Yes Infinite loop program into the background
4:screen-ls//view to Background process program number and random user name Pts-0.centos7
5:screen-x name should be user//After joining the original background run program is displayed on the desktop
6:screen-r session//Restore a process: If a background process is not added after the user name, if there are multiple add the corresponding process name, you can restore the process or CTRL + C end Process
7: If the process is finished, screen-r there is no screen tobe resumed exit

Variable: Represents a collection of some strings
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Add "\" to turn to meaning, ' strong reference, ' ' weak reference
0

ECHO-E//Can let the following string display some special functions
For example:
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The \c parameter only takes effect when E is added

echo Command options:

-N does not wrap characters at the end of the line
-E If the following character appears in the string, it is handled in particular, not as a general text output:
\a issued a warning sound;
\b Backspace key
\c finally not add the line break symbol;
\ n Wraps and the cursor moves to the beginning of the line;
\ r The cursor moves to the beginning of the line, but does not wrap;
\ t Insert tab;
\ \ insert \ Character
\0NNN insert ASCII character represented by NNN (octal)
Echo-e "\033[43;31mabcd\033[0m"//43 represents background color, 31 is font color
\XHH Insert the ASCII character represented by the HH (hex)

Linux Learning-General Command use 2