The ls command is one of the most fundamental commands in Linux. It displays the contents of a directory, including files and subdirectories. You can use various options to customize the output, such as:

• ls -a: Lists all files, including hidden ones (those starting with a dot)
• ls -l: Displays a long listing format with detailed information like permissions, ownership, size, and modification time
• ls -t: Sorts files and directories by modification time

The cd command is used to navigate between directories. You can change to a specific directory by providing its path as an argument (cd /path/to/directory). Additionally, you can use special shortcuts like . for the current directory and .. for the parent directory.

The mkdir command is used to create new directories. You can specify the name and path of the directory you want to create (mkdir /path/to/new/directory). The -p option allows you to create nested directories in a single command.

The rm command is used to remove files and directories. To remove a file, you simply need to specify its path (rm /path/to/file). To remove a non-empty directory and its contents recursively, you need to use the -r option (rm -r /path/to/directory). Be cautious when using this command, as it can permanently delete data.

The cp command is used to copy files and directories from one location to another. To copy a file, you need to provide the source and destination paths (cp /source/file /destination/path). To copy a directory and its contents recursively, you need to use the -r option (cp -r /source/directory /destination/path).

The mv command is used to move or rename files and directories. To move a file or directory, you need to provide the source and destination paths (mv /source/path /destination/path). To rename a file or directory, you can provide the same source directory and a new name as the destination (mv /path/to/file /path/to/new_name).

The ps command displays information about currently running processes on the system. You can use various options to customize the output, such as showing the full command line (ps -ef) or displaying processes in a user-friendly format (ps aux).

The top command provides a real-time view of the system's running processes, including CPU and memory usage. It allows you to monitor system performance and identify resource-intensive processes.

The kill command is used to terminate a running process by sending a signal. You can specify the process ID (PID) to terminate a specific process (kill pid), or use the -9 option to forcibly terminate a non-responsive process (kill -9 pid).

The chmod command is used to change the permissions of files and directories. Permissions are represented as a three-digit octal number, with each digit corresponding to the permissions for the owner, group, and others, respectively. Common values are:

• 4: Read permission
• 2: Write permission
• 1: Execute permission

For example, chmod 755 file would grant read, write, and execute permissions to the owner, and read and execute permissions to the group and others.

The grep command is a powerful tool for searching and filtering text. It allows you to search for patterns or regular expressions within files or input streams. You can use various options to customize the search behavior, such as case-insensitive search (grep -i) or recursive search (grep -r).

awk is a programming language and text processing utility used for manipulating and transforming structured data, such as text files or command output. It allows you to perform complex operations on input data using pattern-action rules and built-in functions.

The sed command is a powerful stream editor that allows you to perform text transformations on input streams or files. It supports a wide range of editing commands, including substitution, deletion, insertion, and more. sed is often used for tasks such as text filtering, string replacement, and file manipulation.

The uname command displays information about the underlying operating system, including the kernel version, system architecture, and more. The uname -a option provides a detailed overview of the system information.

The df command shows the disk space usage and available space for file systems mounted on the system. It is useful for monitoring disk space utilization and identifying potential issues with disk space.

The free command displays information about the system's memory usage, including the total amount of free and used memory, as well as the swap space utilization.

The ping command is used to test the network connectivity between two devices by sending Internet Control Message Protocol (ICMP) echo request packets and measuring the round-trip time. It is a valuable tool for network troubleshooting and checking if a remote host is reachable.

The ssh command is used to establish a secure encrypted connection between two computers over an insecure network. It is commonly used for remote login, file transfer, and executing commands on remote systems. ssh provides a secure alternative to insecure protocols like Telnet and FTP.

The wget command is a utility for retrieving files from the web using various protocols, including HTTP, HTTPS, and FTP. It supports recursive downloads, mirroring websites, and background downloads. wget is particularly useful for automating download tasks or retrieving files from command-line scripts.

The tar command is used to create, extract, and manipulate archive files, commonly known as tarballs. It can handle both compressed and uncompressed archives. Common options include:

• tar -c: Create a new archive
• tar -x: Extract files from an archive
• tar -z: Use gzip compression/decompression
• tar -j: Use bzip2 compression/decompression

The gzip command is used to compress and decompress files using the Lempel-Ziv coding (LZ77) algorithm. It is commonly used to reduce the size of files for storage or transmission purposes. Common options include:

• gzip file: Compress a file and rename it tofile.gz
• gzip -d file.gz: Decompress a file.gz file

The man command is used to access the manual pages, which provide comprehensive documentation and reference information for various Linux commands, system calls, library functions, and more. It is an invaluable resource for learning about the usage, options, and examples of different commands.

The find command is a powerful tool for searching and locating files and directories based on various criteria, such as name, size, modification time, and permissions. It allows you to perform complex searches and execute actions on the found files or directories.

The alias command is used to create command aliases, which are shortcuts or alternative names for longer commands or command sequences. Aliases can help streamline your workflow and increase productivity by providing concise and memorable names for frequently used commands.