Interview Questions: common linux commands and common linux commands

Interview Questions: common linux commands and common linux commands

Command for displaying directories and files

Ls: Command Used to view all folders.

Dir: command Tree used to display the specified folder and Directory: list the directory content in a Tree chart

Du: displays the directory or file size.

Modify directory, file permissions, owner, and array commands

Chmod: command used to change the permission of a specified file.

Chown: a command used to change the attributes of a file.

Chgrp: command used to change the file group.

Chattr: used to set the permission to delete and modify files.

Lsattr: used to display hidden properties of files or directories.

Create and delete directory commands

Mkdir: used to create a directory

Rmdir: Used to delete an empty directory.

Rm-f: Used to delete directories that are not empty.

Commands for creating, deleting, renaming, and copying files

Touch: Create a new file

Vi: Create a new file

Rm: delete a file or directory

Mv: Command for renaming or Moving Files

Cp: Copy command

Command for displaying file content

Cat: displays all contents of a specified file.

More: display the content of a specified file in the form of pagination

Less: displays the content of a specified file in pagination mode. The difference is that the Operation keys used for more and less paging are different.

Head: used to display the first n rows of the file.

Tail: used to display the last n rows of the file.

Tail-f: displays n rows of data after a file that is automatically refreshed.

SEARCH Command

Find: Find the specified file.

Whereis: Find the specified file source and binary files and manuals.

Which: Used to query the location of a command or Alias.

Locate: quickly finds the specified content in the system database.

Grep: Find the matching strings in the file.

Commands for shutting down and restarting a computer

Shutdown:-r restarts immediately after Shutdown

-K does not actually shut down, but only sends a warning message to all users.

-H: Do not restart after Shutdown

Poweroff: Used to shut down and power off

Init: changes the system running level

Level 0 is used to shut down the system

Level 1 for Single User Mode

Level 2 is used for multi-user usage (without network functions)

Level 3 is used for multi-user usage (with full network functionality)

Level 4 for user-defined use modes

Level 5 indicates the mode when xwindows is enabled

Level 6 is used to restart the system

Reboot: used for computer restart

Halt: Used to shut down the computer system

Compression and Packaging Commands

Tar: Used to package multiple files or directories without compressing them. It also uses commands to unpackage.

Gzip: the extension name ends with .gz.

Gunzip: Used to decompress the gzip compressed file.

Bzip2: Used to compress and decompress files or directories.

Bzcat: used to display the content of the compressed file.

Compress/uncompress: Compress/decompress the. Z File

Zcat: view the compressed file content ending with z or gz.

Gzexe: compresses executable files

Unarg: extract the. arj File

Zip/unzip: decompressed. Zip file

User operation commands

Su: Switch USER commands

Sudo: execute commands as a system administrator

Passwd: used to change the user's password

Change the Directory and view the current directory command

Cd: Enter the working directory

Cd .. : Will return to the upper-level command

Pwd: displays the current user's working directory location

File connection command

Ln: Creates a connection for the source file. If you do not copy the source file, the occupied space is small.

It can be divided into software connection and hard link.

Soft connection: Also known as symbolic connection, which creates a shortcut for a file or directory.

Hard link: place more than one name on a file in different directories for your convenience.

The Ln command parameters are as follows:

-F: when creating a connection, delete the file or directory with the same name as the target object.

-D: allows system administrators to hard-link their directories.

-I: Ask the user before deleting a file or directory with the same name as the target object.

-N: when creating a soft connection, the target object is treated as a normal file.

-S: Creates a soft connection, that is, a symbolic connection.

-V: The file or directory name is displayed before the connection.

-B: Back up the files that will be overwritten or deleted during connection.

Help Command ----- man

Other commands

Who: displays the users in the system.

-The ami displays the current user.

-U: displays the user's actions/work

-S: Display in short format

-V: displays the program version.

Free: view the memory usage of the current system

Uptime: displays how long the system has been running.

Ps: displays the status of transient processes

Top: displays processes dynamically

Pstree: displays all processes in a tree

Date: displays or sets the Date and time of the system.

Last: displays the monthly login system user information

Kill: Kill specific processes.

Logout: exit the system

Useradd/userdel: add or delete a user

Clear: Clear screen

Passwd: Set the User Password

Vi Editor

First, run the vi command to open a file.

Last line mode command:

: N, mwpath/filename Save the specified range document (n table start row, m Table end row)

: Q! Force exit after modifying the file

: Q has not modified the file and exits.

Wq or x save and exit

Dd deletes the row where the cursor is located.

: Set number: displays the row number.

: N jump to n rows

: S replacement string: s/test/test2/g Global replacement/can also be replaced by %

/Search for strings

Common commands for network communication

Arp: network address display and Control

Ftp: File Transfer

Lftp: File Transfer

Mail: Send/receive emails

Mesg: Allows or denies other users from sending messages to their terminals.

MuttE-mail Management Program

Ncftp: File Transfer

Netstat: displays network connection. Route table and network interface information.

Pine: send and receive emails and browse newsgroups

Ping: used to check whether the network is connected smoothly

Ssh: remote login in Safe Mode

Telnet: Remote Logon

Talk: Dialog with another user

Traceroute: displays the path to a host and the time it is used.

Wget: Automatically downloads files from the network

Write: Write information to other user terminals Rlogin: Remote Login

Today, I am asked a linux question when I go out for an interview, and the project will be sent to linux after I enter uat. Therefore, it is necessary to know a few linux commands.

First, it is also the most useful one:

Man looks at the command details. As long as he thinks the command is unclear, man can.

Man ls

Ln create link file

Ln-s sourceName destName

Ls to list objects

-L: displays detailed attributes row by row

-A: lists all objects, including hidden objects starting ".".

Ls-lqt/bin

Cat reads text content

-N: displays the row number.

-B: the row number is displayed and empty rows are ignored.

Cat-n 1.txt

Wc: Count

-L: number of rows

-W: Number of words

-C: number of characters

Wc-l file1 file2... multiple files can be counted

Cp copy file directory

-I: interaction mode. If the target file exists, check whether the file is overwritten.

-R: Copy directory

Cp file1 file2 file3. .. dir indicates copying file1, file2. .. to dir

Cp-r dir1 dir2 dir3. .. dirn copy dir1, dir2, dir3. .. To dirn

View file Types

File test. sh

Move the music video file and change the file name.

-I: interaction mode. If the target file exists, check whether the file is overwritten.

-R: Move the Directory and change the directory name.

Rm delete file

-I: interaction mode. Ask whether to delete it.

Rm-r dir1 dir2 dir3. you can delete multiple

Mkdir create directory

-P: parent. If the parent directory does not exist, the parent directory is created.

Mkdir-p test/test

Rmdir Delete directory

Equivalent to rm-r

Rmdir dir1 dir2 dir3 ....

Rm-r dir1 dir2 dir3 ....

Chmod permission change

Chmod-R 777 DIR changes the permission of all files in the directory to 777, which must be-R

Permission-rwxrwxrwx

421421421

Prefix-indicates that the file type is normal.

The next three digits indicate the owner permission.

The next three digits indicate group permissions.

The last three digits indicate other user permissions.

If a permission is not assigned, use. -Rwxr -- rwx indicates that the group has no write and execution permissions.

The file can be run at night, but indicates whether to allow searching for files in this directory

Chown changes owner

Chgrp Change Group

Command &

Add & to the end of the command to run the command in the background

Find.-name "*. sh "&

Fg puts background processes on the foreground

Fg % 1 place the first job in the background to the foreground

Bg

Put the foreground process in the background

Jobs

Display Background or suspended Processes

Ps

Show all processes

Ps-f displays complete information, including cpu usage time and start time...

Kill

-9 Force end

More: display text content. Press space to continue each screen.

Find/-name "*. sh" | more

Tail displays the following content from the specified position

Tail-f server. log is used to run and view logs on the server.

Tail-10 dos2unix. sh: Check the last 10 lines

Head

Corresponds to tail

Sort sorting

-R Reverse Order

-D dictionary order

Ls | sort-r

Tr character replacement

-D: Delete the specified character ls | tr-d 'log'

Ls | tr 'D' G' converts d to g

At time date job

Regular Scheduling

Compress

-F: compressed file

-V shows the compression ratio.

Compress-vf project.tar: delete project.tar.zand project.tar

Uncompress

-F. decompress the file

-V shows the compression ratio.

Uncompress project.tar. Z deletes project.tarand project.tar. Z.

Tar

-C create a new document

-X unpack

-V: displays the file name being processed.

-F replaces the default file name

Tar-cvf project.tar project/* package all files in the project directory

Tar-xvf project.tar

Crontab

Permission: All Users

Usage:

Crontab [-u user] file

Crontab [-u user] {-l |-r |-e}

Crontab specifies that the user executes the program at a fixed time, that is, the user's time table. -U user is used to set the time table of the specified user. The premise is that you must have the permission (for example, root) to specify the time table of another user. If-u user is not used, the time table is set.