Linux common commands [Ls/cd/man/type/date/hwclock]

Linux Common commands:

Ls

-L: Long format

File type: the

-: Normal file (f)

D: Catalog file

D: Block device files (blocks)

C: Character device file (character)

L: Symbolic Link files (symbolic link file)

P: Command sleeve file (pipe)

S: Socket file (socket)

File permissions: 9-bit, every 3-bit group, each group: rwx (Read, write, execute)

Number of hard links to files

The owner of the file (Onwer)

Genus Group of files

File size (size), in bytes

The timestamp (timestamp) is displayed by default for the last modified time modify

Access: Access

Modified: Modify (contents of the changed file)

Changes: Change, metadata, metadata (attribute data for a file)

-H: Do unit conversions (change to human readable format)

-A: Show hidden files starting with.

. Represents the current directory Eg:ls = ls.

.. Represents the parent directory

-A: not displayed. And..

-D: Display the directory's own properties

-I: Show index node, inode

-R: Reverse Display

-R: Recursive (Recursive) display

Cd:change Directory

Home directories, home directories, home directory

CD ~username: Enter the home directory of the specified user

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

Command type:

Built-in commands (shell built-in)

External command: There is an executable file that corresponds to the command name in a path on the file system

Environment variables: named memory space

Assigning values to variables

Name=jerry

Path: Using colon-separated paths

O (1)

Type: Shows which type the specified command belongs to

Date: Time Management

LINUX:RTC (real Time clock)

Hardware Clock Clock/hwclock

System Clock Date

Get help with the use of commands:

Internal command:

Help COMMAND

External command:

Command--help (most external commands support this long option)

Command manual: Manual

Man command (almost all commands have man)

Whatis can view chapter information

Man section: (Total 8 sections)

1: User command (/bin,/usr/bin,/usr/local/bin)

2: System call

3: library Call

4: Special files (device files)

5: File Format (configuration file syntax)

6: Game

7: Miscellaneous (Miscellaneous)

8: Management Command (/sbin,/usr/sbin,/usr/local/sbin)

Eg:man 2 read Specifies the read content of the second chapter

[]: Optional

<>: Required

...: can occur multiple times

| : Front and back content, for multiple select one, not all write

{}: Grouping

Mans:

Name: command names and features brief description

Synopsis: Usage notes, including available options

DESCRIPTION: A detailed description of the command function, which may include the meaning of each option

Options: Explaining the meaning of each option

Files: The configuration file associated with this command

BUGS:

EXAMPLES: Working with instances

See ALSO: Another reference

Flip Screen:

Turn back one screen: SPACE

Turn One screen forward: b

Turn back one line: ENTER

Turn One line forward: K

Find:

/keyword backwards

N: Next

N: Previous

? KEYWORD forward

N: Next

N: Previous

Q: Exit

Online Documentation:

Info COMMAND (Info is a supplement to man, not very much)

Document:/usr/share/doc

Google

Official document, Apache,hadoop

Exercise: Get the system's current year, month, day, hour, minute, second separately using date

Hwclock

-W: Write system time to hardware time

-S: Write hardware time to system time

Cal:calendar

Practice:

1. is echo an internal command or an external command?

[[Email protected] ~]# type echo

Echo is a shell builtin

2. How does it work? 、

Mans Echo

Help Echo

3. How to display "The year is 2015." Today is 5 "for two lines?"

Practice:

1. Print internal command or external command?

[[Email protected] ~]# type printf

Echo is a shell builtin

2. How does it work?

3. How to display "The year is 2015." Today is 5 "for two lines?"

File command and its usage

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Linux common commands [Ls/cd/man/type/date/hwclock]