Common Linux Commands

1. Keyboard Shortcuts

• Auto-complete
• • Tab
• Cancel current operation
• • Ctrl+C
• Clear screen
• • Ctrl+L
• Jump to beginning of line
• • Ctrl+A
• Jump to end of line
• • Ctrl+E
• Move by word
• • Ctrl+Arrow Keys
• Cut/delete from cursor to beginning of line
• • Ctrl+U
• Cut/delete from cursor to end of line
• • Ctrl+K
• Recall the content after the last [space] of the previous command
• • ESC+.
• Copy
• • Ctrl+Insert
• Paste
• • Shift+Insert

2. Operational Commands

2.1 Software Packages

2.1.1 Utility Package Commands

• Configure official repository update URL
• • curl -s -o /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-7.repo
• Configure third-party EPEL repository update URL
• • curl -s -o /etc/yum.repos.d/epel.repo https://mirrors.aliyun.com/repo/epel-7.repo
• Query software packages
• • yum provides <package-name> -y
• Install software packages
• • yum install <package-name> -y

2.1.2 lrzsz (File Transfer Tool)

• Upload to Linux
• • rz
  • • -E
    • • Auto-rename if a file with the same name exists
    • -y
    • • Overwrite if a file with the same name exists
• Download to Windows
• • sz
  • • -E
    • • Auto-rename if a file with the same name exists
    • -y
    • • Overwrite if a file with the same name exists

2.1.2 tree (Display Directory Tree Structure)

• tree -C
• • Colorized output
• tree -f
• • Show full file paths
• tree -a
• • Show all files, including hidden files
• tree
• • Display files and directories in a tree structure
• tree -L n A
• • Display n levels of directory A

2.1.3 VIM (File Editing Tool)

2.1.3.1 Mode Switching

• Edit Mode
• • Enter edit mode
  • • i I a A
  • Exit edit mode
  • • ESC
• Command Mode
• • Enter command mode
  • • Colon :
    • Save
    • • :w
      • • Save
      • :wq
      • • Save and quit
      • :wq!
      • • Force save and quit
    • Quit
    • • :q
      • • Quit
      • :q!
      • • Force quit
    • Search downward
    • • /pattern
      • • Press n to continue searching
    • Search upward
    • • ?pattern
      • • Press n to continue searching
    • Replace
    • • Global replace
      • • :%s/A/B/g
        • • Replace A with B
        • Local replace
        • • :a,bs/A/B/g
          • • Between lines a and b, replace A with B

2.1.3.2 Keyboard Shortcuts

• End of line
• • $ or End
• Beginning of line
• • 0 or Home
• Last line of file
• • Shift+G
• First line of file
• • gg
• Move cursor to line n
• • n gg
• Move cursor down by n lines
• • n [Enter]
• Copy
• • yy
• Copy multiple lines
• • n yy
• Paste
• • p
  • • Paste on the line below the cursor
• Delete
• • dd
• Delete multiple lines
• • n dd
• Undo
• • u
• Show line numbers
• • :set nu
• Hide line numbers
• • :set nonu

2.1.4 Zabbix Tool

• User login monitoring tool; monitors every minute

2.1.5 apt (Package Manager)

• Update package sources
• • `sudo apt update` — This command updates all existing package information on the system
• Install a package
• • `sudo apt install <packageName>`
• Upgrade packages
• • `sudo apt upgrade` — Note: this command cannot target a specific package; it automatically checks for and upgrades all installed packages. To upgrade a specific package, use `install`, which will update and install the specified package
• Uninstall a package
• • `sudo apt remove <packageName>` — This removes the specified package and its dependent packages, but does not delete configuration files or data.
  • If you want to remove those as well, use `sudo apt-get remove --purge <packageName>`
• Remove leftover dependencies
• • `sudo apt autoremove` — This command likewise cannot target a specific package; it removes packages with missing dependencies and obsolete packages, but again does not delete configuration files or data.
  • To delete those too, use `sudo apt-get autoremove --purge`
• Remove outdated packages
• • `sudo apt autoclean` — This command cleans up outdated packages from the local package cache
• Search for a package
• • `sudo apt search <packageName>` — Searches the system repositories for packages matching the specified name
• List installed packages
• • `sudo apt list --installed` — Lists all packages currently installed on the system
• Show detailed information
• • `sudo apt show <packageName>` — Displays detailed information about the specified package, including version, description, dependencies, and more

2.1.6 yum (Package Manager)

• Update all packages and their dependencies system-wide
• • `yum update`
• Install a package
• • `yum install packageName` — This command automatically installs dependent packages as well
• Uninstall a package
• • `yum remove packageName` — Removes the package and its dependencies
• Upgrade packages
• • `yum upgrade` — Like apt, this command updates all packages on the system and cannot target a specific package
• Search for a package
• • `yum search keyword` — Searches for packages matching the given keyword
• List installed packages
• • `yum list installed` — Lists all packages installed on the system
• Search for a file's owning package
• • `yum provides fileName` — Searches for which package owns the specified file
• Clear cache
• • `yum clean all` — Clears the yum cache and frees up disk space
• Check for available updates
• • `yum check-update` — This command does not automatically upgrade or download any packages; it only checks

3. Common Commands

3.1 Information Viewing

3.1.1 Security Related

• lastlog
• • View login information for various directories
  • • grep
  • Filter by keyword
  • • grep "string" <file-path>
    • • • • • • -v
              • • Invert match — select lines except those containing the quoted content
              • -i
              • • Ignore case of the quoted content
              • -n
              • • Show the line number in the original file for each match
              • grep -E "pattern1 pattern2 ..." <filename>
              • • Filter lines from a file that contain any of the patterns (OR relationship between patterns)
              • grep "string" <source-file> >> <destination-file>
              • • Write the filtered results from the source file into the destination file
          • chattr
          • • File locking
            • • +i
              • • Lock — prevents deletion and modification
                • • When applied to a directory, only protects its immediate child subdirectories, not deeper levels
              • -i
              • • Remove lock
              • =i
              • • Assign
              • a
              • • Allows appending content, but not deletion or modification
              • -R +i
              • • Recursive lock
                • • Enhanced version of +i; protects all subdirectories within the locked directory
              • lsattr
              • • Check whether a file is locked
          • md5sum
          • • Generates a string of special characters based on the file and its contents using a fixed algorithm
        • System Information
        • • Network Related
          • • View IP address
            • • ip addr
              • ifconfig
            • View gateway
            • • ip route
              • route -n
              • netstat -rn
            • View DNS
            • • cat /etc/sysconfig/network-scripts/ifcfg-eth1
            • Test network connectivity
            • • ping <website>
          • System Related
          • • View time
            • • date
              • • date +%F
                • • Display year-month-day
                • date +%Y
                • • Display year only
                • date +%y
                • • Display year only (two-digit)
                • date +%m
                • • Display month only
                • date +%d
                • • Display day only
                • date +%H
                • • Display hour only
                • date +%M
                • • Display minute only
                • date +%S
                • • Display second only
                • date -s "<time>"
                • • Set the time
                • ntpdate ntp2.aliyun.com
                • • Synchronize server time with internet time
            • Find the path of a (binary) command
            • • which <command>
            • View system version
            • • cat /etc/redhat-release
            • View hostname
            • • hostname
              • uname -n
            • View kernel version
            • • uname -r
            • View command history
            • • history
              • • history -d <number>
                • • Delete a history entry by its number
                • history -c
                • • Delete all history entries
                • history
                • • View command history
          • User Related
          • • View user login activity
            • • last
            • Report the most recent login activity for all users
            • • lastlog
            • Clear a user's login information
            • • lastlog -C -u <username>
            • Check current user
            • • whoami
        • File Related
        • • View file contents
          • • cat
            • • cat -n
              • • Display file contents with line numbers
            • less
            • • Enter
              • • Scroll down line by line
              • Space
              • • Scroll down page by page
              • /mysql
              • • Search downward for content containing the string 'mysql' — press n to continue searching downward
              • ?mysql
              • • Search upward for content containing the string 'mysql' — press n to continue searching downward
          • View the first few lines of a file
          • • head
            • • View the first few lines of a file
            • head -n
            • • View the first n lines of a file
          • View the last few lines of a file
          • • tail
            • • View the last 10 lines of a file
            • tail -n
            • • View the last n lines of a file
            • tail -f <filename>
            • • Monitor the tail of a specified file for changes in real time
          • File Information
          • • View file statistics
            • • stat <filename>
            • View current path
            • • pwd
            • View file line count
            • • wc -l
            • View directory
            • • ls (white = file; blue = folder)
              • • ls -l (ll)
                • • Long-format directory listing
                • ls -a
                • • Show all files (including hidden files)
                • ls -t
                • • Sort by modification time
                • ls -r
                • • Reverse order
          • File Content Filtering
          • • grep
            • • grep "string" <file-path>
              • -v
              • • Invert match — select lines except those containing the quoted content
              • -i
              • • Ignore case of the quoted content
              • -n
              • • Show the line number in the original file for each match
              • -w
              • • Search by whole word
              • grep -E "pattern1 pattern2 ..." <filename>
              • • Filter lines from a file that contain any of the patterns (OR relationship between patterns)
              • grep "string" <source-file> >> <destination-file>
              • • Write the filtered results from the source file into the destination file
          • Search
          • • which
            • • Find the path of a binary command
            • find <search-path> <option1> [param1] <option2> [param2] ...
            • • Basic search
              • • -a (default)
                • • Intersection (AND) of options
                • -o
                • • Union (OR) of options
                • !
                • • Negate the search option
                • -name
                • • Search by filename/keyword
                • -type
                • • Search by file type
                  • • b
                    • • block (buffered) special
                      • • Block device — hard disk, optical drive
                    • c
                    • • character
                      • • Character device
                    • d
                    • • directory
                      • • Find directories
                    • f
                    • • regular
                      • • Find regular files
                    • l
                    • • symbolic link
                      • • Symbolic link / shortcut
                    • s
                    • • socket
                      • • Related to inter-process communication
                • -size
                • • Search by size
                  • • +N M
                    • • Larger than N megabytes
                    • N M
                    • • Equal to N megabytes
                    • -N M
                    • • Smaller than N megabytes
                • -mtime
                • • Search by modification time
                  • • +7
                    • • More than 7 days ago
                    • 7
                    • • Exactly 7 days ago
                    • -7
                    • • Within the last 7 days
              • Search and Act
              • • find ... -exec <command> {} \; — {} represents the found items, \; marks the end of the command
                • • find ... -exec rm -rf {} \;
                • find ... | xargs <command> (no filename needed)
                • • find ... | xargs rm -f
                • find ... | xargs -i <command> {} <destination> — -i allows using {} to receive the found files in the subsequent command
                • • find ... | xargs cp {} <destination>
        • User Information
        • • View user information
          • • id <username>
            • whoami
            • • Check current user
          • View user login activity
          • • w
          • View user logs
          • • last
            • lastlog
            • • lastlog
              • • Report the most recent login activity for all users
              • lastlog -C -u <username>
              • • Clear user login information
      • State Control
      • • Network Related
        • • Enable a network interface
          • • ifup <interface-name>
          • Disable a network interface
          • • ifdown <interface-name>
          • Restart all network interfaces
          • • systemctl restart network
          • Graphical network interface configuration
          • • nmtui
        • Account Management
        • • Add a user
          • • useradd <username>
            • • useradd -u <UID> <username>
              • • Add a user and specify the UID
              • useradd <username> -g <group-name>
              • • Add a user and assign them to a group
              • useradd <username> -M
              • • Create a user without creating a home directory
              • useradd <username> -s /sbin/nologin -M
              • • Create a user that is not allowed to log in
                • • Used to provide a user account for running application software
          • Delete a user
          • • userdel <username>
            • • By default, the home directory is not deleted
            • userdel -r <username>
            • • Delete the home directory as well
          • Modify a user
          • • usermod <username>
            • • usermod <username> -s /bin/bash
              • • Change the login shell to /bin/bash
              • usermod <username> -u <UID>
              • • Change the user's UID
          • Change password
          • • echo <password> | passwd --stdin <username>
            • • Change the password of a specified user
            • passwd <username>
            • • Requires root privileges, or to change the current user's password
          • Switch user
          • • su - <username>
          • Execute with administrator privileges
          • • sudo <command>
          • Manage user permissions
          • • visudo
            • • Then: 100gg, yy, p, modify the permission scope, and provide the full path of the command
        • System Control
        • • Shutdown (default: shuts down after 1 minute)
          • • shutdown
            • • -c
              • • Cancel shutdown
              • -h n
              • • Shut down after n minutes
              • now
              • • Shut down immediately
              • -r n
              • • Reboot — defaults to rebooting after 1 minute; n specifies reboot after n minutes
            • halt
            • poweroff
            • init 0
          • Reboot
          • • reboot
            • shutdown -r now
            • init 6
      • Editing
      • • Batch Operations
        • • <command> <filename/foldername>{1..n}
          • • Execute the command on filename/foldername{1..n}
        • Delete
        • • rm <filename>
          • • Delete a file after confirmation
          • rm -f <filename>
          • • Force delete (no confirmation)
          • rm -rf A*
          • • Delete all directories starting with A
          • rm -r <directory>
          • • Delete a directory after confirmation
          • rm -rf <directory>
          • • Force delete a directory
        • Create Files/Folders
        • • touch
          • • touch A B C
            • • Create files A, B, and C
            • touch .A
            • • Create hidden file .A
            • touch -c A
            • • Avoid forcibly creating file A (can be used to update the file's access and modification times)
            • touch -a A
            • • Set file A's access time to the current time
            • touch -m A
            • • Set file A's modification time to the current time
          • mkdir
          • • mkdir A
            • • Create folder A
            • mkdir A{1..n} (note: only two dots)
            • • Create folders A1, A2 ... An
            • mkdir -p A/B/C/D
            • • Create nested directories A/B/C/D
        • Execute a file
        • • ./filename
          • • Execute a file (. means execute, / means the current directory)
        • Change File Attributes
        • • chown
          • • chown -R <user> <file>
            • • Change the user owner of a file
            • chown <user>.<group> <file>
            • • Change both the user owner and group of a file
            • chown .<group> <file>
            • • Change the group owner of a file
        • Change Directory
        • • cd (change directory)
          • • cd A
            • • Change to directory A
            • cd ~
            • • Change to the user's home directory
            • cd -
            • • Change to the previous directory
            • cd .
            • • Change to the current directory
            • cd ..
            • • Change to the parent directory
            • cd ../..
            • • Change to the grandparent directory
        • Copy Files or Directories
        • • cp a A
          • • Copy file a to directory A
          • cp a b
          • • Copy file a and rename it to b
          • cp -r/-a ( -a preserves more attributes than -r )
          • • Copy a directory while preserving attributes
          • cp -t <destination> <source-file>
          • • Swap the order of source and destination
        • Move Files or Directories
        • • mv <source> <directory>
          • • Move the source file to the destination directory
          • mv <source> <filename>
          • • Rename the source file
        • Write text to a specified file
        • • echo "text" >> <filename>
          • • Append to the end of the file
          • echo "text" > <filename>
          • • Overwrite the file's previous contents with the new text
        • Write a sequence of numbers to a specified file
        • • seq n > <filename>
          • • Write numbers 1 through n to the specified file, one number per line
        • Grouping
        • • xargs -n N < <filename>
          • • Group the file's contents into groups of N items each
        • File Permission Changes
        • • chmod
          • • Categories
            • • Permissions
              • • Target
            • u (user)
            • • r — Read
              • • File
                • • Readable
                • Directory
                • • Can list files within the directory
            • g (group)
            • • w — Write
              • • File
                • • Writable
                • Directory
                • • Can create/delete files
            • o (other)
            • • x — Execute
              • • File
                • • Executable
                • Directory
                • • Determines whether you can enter the directory
              • - — None
            • Modification
            • • + — Add permission
              • • - — Remove permission
                • • = — Set permission to
            • -R
            • • Recursive modification
              • • Recursively modify directories and files within a directory
        • Archive and Compression
        • • tar
          • • tar zcvf <destination-path>/<archive-name>.tar.gz <source-path>
            • • Archive
            • tar zxvf <source-path>/<archive-name>.tar.gz
            • • Extract
            • tar zxvf <source-path>/<archive-name>.tar.gz -C <destination-path>
            • • Extract to a specified location
            • tar zcvf <destination-path>/<filename>_$(date +%F).tar.gz <source-path>
            • • Combined archiving (appends the date to the archive filename for easy identification of backup time)
            • tar tf
            • • View
          • unzip <file-name-or-path>
          • • Extract .zip files downloaded from Windows
            • -O
            • • Extract without prompting; overwrites existing files
          • gzip
          • • gzip <filename>
            • • Can only compress files; the original file will be deleted
            • gzip -d <filename>
            • • Can only decompress files; the original compressed file will be deleted
  • Common MySQL Commands
  • • Graphical Database Tool
    • • Navicat
    • Database-Level Operations
    • • Connect to MySQL database
      • • mysql -u<username> -p<password> -h<localhost>
        • • username — the user name
          • password — the corresponding password
          • localhost — the host to connect to
      • Create a database
      • • CREATE DATABASE test_db;
        • • test_db — the name of the database to create
      • Drop a database
      • • DROP DATABASE test_db;
      • Select a database
      • • USE test_db;
      • Query all databases
      • • SHOW databases;
        • • Display all databases
    • Table-Level Operations
    • • Create a table
      • • CREATE TABLE employee ( id INT PRIMARY KEY, name VARCHAR(50), age INT, department VARCHAR(50) );
        • • employee — the name of the table to create
          • id / name / age / department — field names
          • The attributes that follow each field define its properties
          • • INT PRIMARY KEY — indicates this is the table's primary key
            • • A primary key is a field used to uniquely identify each row of data in a table; it must be unique and non-null
            • VARCHAR(50)
            • • Indicates a variable-length character type with a maximum length of 50 characters
            • INT
            • • Represents an integer type, capable of storing signed 32-bit integers ranging from -2,147,483,648 to 2,147,483,647
      • Drop a table
      • • DROP TABLE employee;
      • Insert data
      • • INSERT INTO employee (id, name, age, department) VALUES (1, 'John Smith', 30, 'Sales');
        • • (id, name, age, department)
          • • Specifies the fields to which the subsequent values belong
          • (1, 'John Smith', 30, 'Sales')
          • • Specifies the value corresponding to each field
      • Update data
      • • UPDATE employee SET name = 'John Doe', age = 32 WHERE id = 1;
        • • employee — the name of the table to update
          • SET — followed by the specific fields to update and their corresponding values
          • WHERE — followed by the primary key value that identifies the row to update
      • Show all tables
      • • SHOW tables;
    • Query data
    • • Query all data from a table
      • • SELECT * FROM employee;
        • • * — means query all columns
          • employee — the name of the table to query
      • Sort query results
      • • SELECT * FROM employee ORDER BY age DESC;
        • • ORDER BY — indicates sorting by the age field
          • DESC — descending order
          • ASC — ascending order
      • Group data
      • • SELECT department, COUNT(*) AS employee_count FROM employee GROUP BY department;
        • • COUNT(*) — calculates the number of rows, i.e., the total number of people in each department
          • The AS keyword assigns an alias (employee_count) to the result of the COUNT(*) function, so the result will contain two columns: department and employee_count
          • FROM — specifies which table the data comes from
          • GROUP BY — groups the results by the specified field
        • Example query result
        • • +-------------+---------------------+ | department | employee_count | +-------------+---------------------+ | Sales | 10 | | Marketing | 8 | | Engineering | 15 | | HR | 6 | +-------------+---------------------+
      • Filter query results
      • • SELECT * FROM employee WHERE department = 'Sales';
        • • employee — the table to filter
          • department = 'Sales' — display only rows where the department field value is 'Sales'
      • Join multiple tables
      • • SELECT * FROM employee JOIN department ON employee.department_id = department.id;
        • • JOIN — indicates that the employee and department tables should be joined together
          • employee.department_id = department.id — specifies the condition for joining the two tables by matching these two values
        • Example query result
        • • id name age gender department_id id department_name 1 Alice 23 Female 1 1 Sales 2 Bob 28 Male 2 2 Marketing 3 Charles 31 Male 2 2 Marketing 4 David 25 Male 3 3 Engineering 5 Emma 27 Female 3 3 Engineering 6 Frank 33 Male 3 3 Engineering
      • Create an index
      • • CREATE INDEX age_index ON employee (age);
        • • age_index — the name of the index
          • employee — the name of the table on which to create the index
          • age — creates the index on the age field to speed up data retrieval
        • CREATE INDEX improves data retrieval speed through indexing, making queries faster and more efficient.
        • • In practice, if a table contains a large amount of data and is frequently queried, adding an index on certain fields (such as age) will improve data retrieval efficiency
        • Using indexes
        • • When a query condition includes an indexed column, MySQL will automatically use that index for optimization; you simply need to execute the SELECT command as usual
          • If you have added an age_index index on the employee table, you can use the following SELECT statement to query employees older than 25. When executing this query, MySQL will use the age_index index to quickly locate all employees older than 25 and return the results
          • • SELECT * FROM employee WHERE age > 25;
            • Sub-topic 2
          • In addition to SELECT statements, indexes can also be used in INSERT, UPDATE, and DELETE statements for optimization. For example, to update a specific row in the employee table, you can use the following statement:
          • • UPDATE employee SET age = 30 WHERE id = 1;
    • Data Import and Export
    • • Export data
      • • mysqldump -u<username> -p<password> test_db > backup.sql
        • • test_db — the name of the database whose data to export
          • backup.sql — the file to save the exported data to
      • Import data
      • • LOAD DATA INFILE 'data.txt' INTO TABLE employee;
        • • employee — the table in the database to import data into
          • data.txt — the file from which the data originates