Directory Operations

Displaying and Navigating Directories

• pwd: Show the current working directory.
• clear: Clear the terminal screen.
• cd ~: Navigate to the current user's home directory.
• cd /: Navigate to the root directory.
• cd -: Return to the previous directory visited.
• cd ..: Move up one directory level.
• Ctrl+R: Search through command history by typing any character from a command.

Viewing Directory Contents

• ll: List detailed contents of the current directory.
• ls: List basic contents of the current directory.

Creating Directories

• mkdir aaa: Create a directory named aaa in the current directory.
• mkdir /usr/aaa: Create a directory named aaa in the specified /usr directory.

Searching for Files and Directories

• find / -name 'b': Search the root directory (including subidrectories) for files and directories named exactly b.
• find / -name 'b*': Search the root directory (including subdirectories) for files and directories starting with b.

Renaming and Moving Directories

• mv original_directory new_name: Rename a directory; e.g., mv test001 test.
• mv /aaa /bb: Move the aaa directory from the root to the bb directory.
• mv bbbb usr/bbb: Move the bbbb directory from the current directory to usr, renaming it to bbb.
• mv bbb usr/aaa: Move the bbb directory from the current directory to usr, renaming it to aaa.

Copying Directories

• cp /usr/tmp/aaa /usr: Copy the aaa directory from /usr/tmp to /usr.

Deleting Directories

• rm -r /bbb: Delete the /bbb directory with confirmation for each file.
• rm -rf /bbb: Force delete the /bbb directory and all its subdirectories without prompts.

File Operations

Deleting Files

• rm -r a.java: Delete a.java in the current directory with confirmation.
• rm -rf a.java: Force delete a.java in the current directory.
• rm -rf ./a*: Force delete all files starting with a in the current directory.
• rm -rf ./*: Force delete all files in the current directory (use with caution).
• rm –f *.txt: Force delete all files with .txt extension.

Creating Files

• touch test: Create an empty file named test.

Editing Files with vi/vim

Modes in vim

• Command Mode: Default mode when vim starts; press Esc multiple times to return to this mode from any other mode.
• Insert Mode: Press i to enter; allows text input; press Esc to return to Command Mode.
• Ex Mode: Press : to enter; cursor moves to the bottom for saving, quitting, or executing commands.

Common Commands in Command Mode

• i: Insert text before the cursor.
• o: Insert a new line below the current line.
• dd: Delete the entire current line.
• yy: Copy the current line to the buffer.
• n+yy: Copy n lines to the buffer.
• p: Paste buffer contents after the cursor.
• u: Undo the last operation.
• r: Replace the current character.
• /: Search for a keyword.

Common Commands in Ex Mode

• :w: Save changes.
• :q: Quit vim.
• :q!: Force quit without saving changes.
• :x: Save and quit, equivalent to :wq.
• :set number: Display line numbers.
• :! system_command: Execute a system command and show results.
• :sh: Switch to the command line; use Ctrl+D to return to vim.

Output and Viewing Commands

• echo: Display input content; e.g., echo "liuyazhuang" >> liuyazhuang.txt appends text to a file.
• cat: Display file contents or merge multiple files; e.g., cat test.txt shows content, cat test.txt test2.txt > readme.txt merges files.
• head: Display the first few lines of a file (default 10); e.g., head -n 20 filename shows first 20 lines.
• tail: Display the last few lines of a file (default 10); e.g., tail -f filename continuously displays new content (useful for logs).
• more: Page through file content downward only; e.g., ls -al | more.
• less: Page through file content with up/down navigation; e.g., ls -al | less.

Hard Links and Soft Links

Creating Soft Links

• ln -s test.txt link_1: Create a soft link named link_1 pointing to test.txt.
• ln -sf test.txt link_2: Force replace an existing soft link with link_2.
• ln -sv /opt/test1 /opt/test2: Create a soft link for a directory.

Creating Hard Links

• ln real.txt link_2: Create a hard link named link_2; modifications affect the source file.

Compression and Decompression

Using tar

• tar -cvf start.tar a.java b.java: Create a tar archive start.tar from specified files.
• tar -cvf start.tar ./*: Archive all files in the current directory.
• tar -zcvf start.tar.gz a.java b.java: Create a gzipped tar archive.
• tar -zcvf start.tar.gz ./*: Gzip archive all files in the current directory.
• tar -xvf start.tar: Extract start.tar to the current directory.
• tar -xvf start.tar -C /usr/local: Extract to a specified directory.
• tar -zxvf start.tar.gz: Extract a gzipped tar archive to the current directory.
• tar -zxvf start.tar.gz -C /usr/local: Extract to a specified directory.

Using zip and unzip

• zip lib.zip tomcat.jar: Compress a single file into lib.zip.
• zip -r lib.zip lib/: Compress a directory into lib.zip.
• zip -r lib.zip tomcat-embed.jar xml-aps.jar: Compress multiple files into lib.zip.
• unzip file1.zip: Extract a zip archive.
• unzip -d /usr/app/ test.zip: Extract test.zip to a specified directory.

Search Commands

Using grep

• ps -ef | grep sshd: Find processes related to SSH service.
• ps -ef | grep sshd | grep -v grep: Exclude the grep process itself.
• ps -ef | grep sshd -c: Count the number of specified processes.

Using find

• find . -name "*.log" -ls: Find .log files in the current directory with details.
• find /root/ -perm 600: Find files in /root/ with permission 600.
• find . -type f -name "*.log": Find regular files ending with .log.
• find . -type d | sort: List and sort all directories in the current directory.
• find . -size +100M: Find files larger than 100MB.
• find . -name *liuyazhuang*: Find files containing "liuyazhuang" in their name.
• find / -perm 777: Find all files with permission 777.

Using locate

• locate keyword: Quickly search for files or folders by keyword.

Yum Commands

• yum install iptables-services: Install a package.
• yum list: List all installed packages.
• yum search package_name: Search for a package in repositories.
• yum update package_name.rpm: Update all installed RPM packages.
• yum update package_name: Update a specific package.
• yum remove package_name: Remove a package.
• yum clean all: Clear all cached packages and headers.

System Services

• service iptables status: Check the status of iptables service.
• service iptables start: Start the service.
• service iptables stop: Stop the service.
• service iptables restart: Restart the service.
• chkconfig iptables off: Disable service auto-start on boot.
• chkconfig iptables on: Enable service auto-start on boot.

User Management

• su - username: Switch user and change directory.
• exit: Log out of the current account.
• Note: Using su without a username switches to root, but it is not recommended for security reasons.
• which: Find the location of a command; e.g., which ls outputs /bin/ls.
• /etc/passwd: File storing user information.
• /usr/bin/passwd: Program for changing user passwords.

Other Commands

Process Management

• ps -ef: View all running processes.
• kill pid or kill -9 pid: Terminate a process (force kill with -9).

Network Commands

• ifconfig or ifconfig | more: View network interface information.
• netstat -an: View current system ports.
• netstat -an | grep 8080: Search for a specific port.
• setup: Configure network settings.
• service network restart: Restart network services.
• chkconfig iptables off: Disable firewall auto-start.
• iptables -L: List firewall rules.
• iptables -F: Flush firewall rules.
• service iptables stop: Stop the firewall service.

File Permissions

• chmod 777: Change file permissions to read, write, and execute for all.

System Information

• Ctrl + L: Clear the terminal screen.
• du -lh: Check disk usage of directories.
• free: View system memory usage.
• df -lh: Check filesystem partition usage.
• date: View or set the system time; e.g., date +%Y--%m--%d for formatted output.
• date -s: Set the system time.
• uptime: Check system uptime.

Network Connectivity

• ping www.baidu.com: Test connectivity to a host.
• telnet baidu.com 80: Check if a remote port is open; "Connected" indicates success.