Basic knowledge points

Linux matters needing attention

1. Linux Case sensitive
2. Is saved as a file
3. Linux File types are distinguished by no extension

Compressed package ：“.gz” 、“.bz2”、".tar.bz2”
Binary packages ：.rpm
Web page file ：.htm1、.php
Script files :：.sh
The configuration file ：.conf

Linux Built in and external commands

Linux There are two kinds of commands: internal command and external command ：

• Internal orders

Built in commands and shell Is one. , The built-in command is called into memory when the system starts , It's memory resident .

They act as shell The components of the tool exist , There is no need to derive child processes to execute , There is no need to open the program file .

So the execution speed of built-in commands should be faster , It's more efficient .

• External command

External command is the software function of the system , Read in the memory from the hard disk when the user needs it

External commands are also called file system commands , yes bash shell Outside the program , It is not shell Part of . External commands are generally located in /bin、/usr/bin、/sbin or /usr/sbin in .

When executing external commands ,Linux The system will create a sub process （ This operation is called derivation ）.

When a process must perform a derivation ,Linux The system needs to consume data to set the environment of the new sub process .

• Discrimination method

1、help

cd Is an internal command

ls Is an external command

• type