Linux Common environment variables, file types, rights Management

von Neumann system 1 input device -"2 memory (memory)-"3 Operator -"4 controller -"5 output device

Linux Common environment variables:

( same environment variable name for different users but different content )

1. Path command search paths

Export path= $PATH: path to/2016_ program

2. Home user home directory

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3. histsize history command

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4. LOGNAME The login name of the current user

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5. HOSTNAME host name

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6. What Shell does the shell use for the current user?

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7. lang/languge Language-related environment variables

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8. MAIL

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9. PS1

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PS2 affiliated prompt >

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1 echo

2 Export to set a new environment variable

Export hello= "HELLO" ( yes . quotation marks )

3 env Display all environment variables

4 Set shows locally-defined shell variables

5 unset

6 readonly Setting read-only environment variables

Linux File Types

1 Common Files (regular file) [-]

① Plain Text file (ASCII)

② binary file (binary executable file )

③ Data Format File

2 contents (directory) [d]

3 Connection File (link) [l]

(Soft connection equals shortcut)

( hard Connect )

4 device and device files ( All Files in the computer )

Block device files that store files such as hard disks [b]

Character device file keyboard mouse printer [c]

5 Sockets (sockets) [s]

6 Pipe (FIFO, pipe) [P]

Linux Extensions

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Linux does not use extensions and extensions just to make it easier for users to differentiate between different types of files

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Bin Save Command

Home User name folder

Lost+found Temporary file Delete file

MNT Mount

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Proc system Process information CPU Memory-related information

SYS and proc overlap reaction hardware and software information (sys new version must support proc boss for historical reasons)

Dev

Lib Library file

NET Network

SELinux set up the network

var log system Boot information, etc.

Boot kernel startup-related files

Root Super User working directory /root

TMP temp file

How the Shell works

General users cannot directly operate the core (kernel) must communicate through shell shells

Shell : command-line interpreter

1 translate the user's commands to the core (kernel) processing.

2 at the same time, the core processing results are translated to the user.

The shell does not execute the command itself but runs with the child process.

Child process failure does not affect itself because once the shell hangs up, the user cannot communicate with the kernel.

How the shell runs the program

The Shell creates a new process with fork , runs the user-specified program in the new process with the EXECV function cluster, and finally the shell

Wait for the new process to end with the wait command. the Wait system is called at the same time as the kernel gets the eject state or sequence of signals to tell how the child process ended.

Linux Rights Management

1 category (people) of file visitors

the owner of a file and file directory u---user

b user of the group that owns the file and file directory:g---group

C other users o---Others

2 types of file access rights (things properties)

A basic permissions

I- read (R/4)

II write (w/2)

III execution (X/1)

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This article is from the "City Hunter" blog, please be sure to keep this source http://alick.blog.51cto.com/10786574/1773117

Linux Common environment variables, file types, rights Management