Linux operating system and common commands

Ls:list information about the FILEs (the current directory by default).

-l:use a long listing format

[email protected] ~]# ls-l
Total 104
-RW-------. 1 root root 1557 Feb 19:09 anaconda-ks.cfg
Drwxr-xr-x. 2 root root 4096 Feb 07:50 Desktop

File type: the

-: Normal file

D: Catalog file

B: Block device files

C: Character device file

L: Symbolic Link files (symbolic link file)

P: Piping file (pipe)

S: Socket file (socket)

File permissions: mode,9 bits, each three-bit group, respectively, OWNER,GROUP,OTHERS,RWX (read, write, execute), if the bit does not have permission-to indicate

Reference count: The number of times a file has been hard linked

File Owners: Owner

Filegroup: Group

File Size: default unit is byte

File last modified: Last visited, last modified (modified), last changed (changed file properties)

Filename:

-H,--human-readable
With-l, print sizes in human readable format (e.g., 1K 234M 2G)

-A,--all
Do not ignore entries starting with.

Files that start with a. Number in Linux are hidden files

-A,--almost-all
Do not list implied. and..

. Represents the current directory;

.. Represents the parent directory of the current directory;

-D,--directory

list directory entries instead of contents, and do not dereference symbolic links

Displays the properties of the directory itself, not the properties of all files under the directory

-I.,--inode
Print the index number of each file

-R,--reverse
Reverse order while sorting

-R,--recursive
List subdirectories recursively

-s sort by file size

-t Sort by modification time

-x sort alphabetically by entry extension

Cd:change the shell working directory.

-L Force symbolic links to be followed
-P Use the physical directory structure without following symbolic links

The default is to follow symbolic links, as if '-l ' were specified.

CD: Switch to the current user's home directory ($HOME)

CD ~: switch to the current user's home directory

CD ~user: Switch to User's home directory (root only)

CD-: Switch back and forth between the current directory and the previous directory

Pwd:print the name of the current working directory.

Options:
-L PRINT the value of $PWD if it names the current working directory
-P Print the physical directory, without any symbolic links

By default, ' pwd ' behaves as if '-l ' were specified.

Type:display information about command type.

Shell built-in command: Shell builtin

External command: A binary executable program or script with the same name as the command in the file system

Environment variables: named memory space

$PATH

Env:env-run a program in a modified environment

Printenv:printenv-print all or part of environment

Hash:remember or display program locations. Search Time: O (1)

-D Forget the remembered location of each NAME

Date:date-print or set the system date and time

Crystal oscillator, powered by a button battery on the motherboard

Rtc:real Time Clock

Ntp:network Time Protocol

Hardware clock: Clock, Hwclock

System clock: Date

Linux boot after booting through the RTC to read the hardware clock to the system clock, then the kernel is responsible for maintaining the system clock, when the CPU task is busy, the system clock and hardware clock will be out of sync

Date [OPTION] ... [+format]
Date [-u|--utc|--universal] [MMDDHHMM[[CC]YY][.SS]]

How do I get help with my command?

linux commands are divided into built-in commands and external commands

Built-in commands:

#help COMMAND

External command:

# COMMAND--help

# Man COMMAND

# info COMMAND

Man

The standard sections of the manual include:
1 User Commands (/bin:/usr/bin:/usr/local/bin)
2 System Calls
3 C Library Functions
4 Devices and Special Files
5 File Formats and conventions
6 games et. Al.
7 Miscellanea
8 System Administration Tools and Deamons (/sbin:/usr/sbin:/usr/local/sbin)

<>: Required

[]: Optional

... : multiple times can occur

|: Choose one More

{}: Grouping

Name: command names and features brief description

Synopsis: Usage notes, including available options

DESCRIPTION: A detailed description of the command function, including the meaning of the option

Options: The meaning of the option

Files: file associated with the command

EXAMPLES: Examples

See ALSO: Also

With Whatis you can see which chapters the command appears in

which

Whereis

Whatis

Apropos

Linux operating system and common commands