Basic linux commands

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Basic Commands

1. pwd: Print the current working directory.
2. ls: List files and directories in the current directory.
   • ls -l: List files in long format (detailed view).
   • ls -a: Show hidden files (those starting with .).
3. cd: Change the current directory.
   • cd ..: Go up one directory.
   • cd ~: Go to the home directory.
4. mkdir <directory_name>: Create a new directory.
5. rmdir <directory_name>: Remove an empty directory.
6. rm <file_name>: Remove a file.
   • rm -r <directory_name>: Remove a directory and its contents recursively.
7. touch <file_name>: Create a new empty file or update the timestamp of an existing file.
8. cp <source> <destination>: Copy files or directories.
   • cp -r <source_directory> <destination_directory>: Copy a directory recursively.
9. mv <source> <destination>: Move or rename files or directories.
10. cat <file_name>: Concatenate and display the contents of a file.
11. less <file_name>: View the contents of a file one page at a time.
12. head <file_name>: Display the first 10 lines of a file.
13. tail <file_name>: Display the last 10 lines of a file.
    • tail -f <file_name>: Continuously monitor the end of a file for new lines.

System Information

1. df -h: Show disk space usage in a human-readable format.
2. du -h <directory_name>: Show disk usage of a directory and its subdirectories.
3. top: Display active processes and system resource usage.
4. htop: Enhanced version of top with a user-friendly interface (needs to be installed).
5. uname -a: Display system information (kernel version, architecture, etc.).
6. free -h: Show memory usage in a human-readable format.
7. lscpu: Display information about the CPU architecture.

User Management

1. whoami: Display the current logged-in user.
2. adduser <username>: Create a new user.
3. deluser <username>: Delete a user.
4. passwd <username>: Change the password for a user.
5. su <username>: Switch to another user (requires password).
6. sudo <command>: Execute a command with superuser (admin) privileges.

Package Management (APT)

1. sudo apt update: Update the package list.
2. sudo apt upgrade: Upgrade installed packages to their latest versions.
3. sudo apt install <package_name>: Install a new package.
4. sudo apt remove <package_name>: Remove an installed package.
5. sudo apt search <package_name>: Search for a package in the repositories.
6. sudo apt show <package_name>: Show details about a package.

Networking

1. ifconfig: Display network interfaces and their configurations (deprecated; use ip).
2. ip a: Show all network interfaces and their IP addresses.
3. ping <hostname>: Check connectivity to a host by sending ICMP echo requests.
4. traceroute <hostname>: Show the route packets take to a network host.
5. netstat -tuln: Display active network connections and listening ports.
6. curl <url>: Fetch content from a URL.

File Permissions

1. chmod <permissions> <file_name>: Change the permissions of a file or directory.
   • chmod 755 <file_name>: Set read, write, and execute permissions for the owner, and read and execute permissions for group and others.
2. chown <user>:<group> <file_name>: Change the ownership of a file or directory.

Searching and Finding Files

1. find <directory> -name <file_name>: Search for files in a directory hierarchy.
2. grep <pattern> <file_name>: Search for a specific pattern in a file.
3. locate <file_name>: Quickly find the location of a file (requires mlocate package to be installed).

System Control

1. shutdown: Shut down the system.
   • shutdown -h now: Shut down immediately.
2. reboot: Restart the system.
3. systemctl <action> <service_name>: Control system services (start, stop, restart, enable, disable).

Miscellaneous

1. history: Show the command history.
2. clear: Clear the terminal screen.
3. echo <text>: Display a line of text.

4. man <command>: Display the manual page for a command, providing details on its usage.

File and Directory Operations

1. find <directory> -type f -name <file_name>: Find files by name in a specific directory.
2. find <directory> -type d -name <directory_name>: Find directories by name.
3. cp -i <source> <destination>: Copy files with confirmation before overwriting.
4. mv -i <source> <destination>: Move files with confirmation before overwriting.
5. rm -i <file_name>: Remove a file with confirmation.
6. mkdir -p <directory_path>: Create a directory and parent directories as needed.
7. tree: Display a directory structure in a tree format (requires installation).
8. rename <expression> <replacement> <files>: Rename files based on a regex expression (use with caution).

Text Processing

1. sort <file_name>: Sort lines in a text file.
2. uniq <file_name>: Report or omit repeated lines in a file.
3. wc <file_name>: Count lines, words, and characters in a file.
4. cut -d <delimiter> -f <field_number> <file_name>: Extract specific fields from a file.
5. awk '{print $1}' <file_name>: Process and analyze text files (prints the first column).
6. sed 's/<pattern>/<replacement>/' <file_name>: Stream editor for filtering and transforming text.

System Monitoring and Management

1. vmstat: Report virtual memory statistics.
2. iostat: Report CPU and I/O statistics (requires installation).
3. mpstat: Show CPU usage (requires installation).
4. uptime: Show how long the system has been running and load averages.
5. ps aux: Display a snapshot of current processes with detailed information.
6. kill <pid>: Terminate a process by its process ID.
7. killall <process_name>: Terminate all processes by name.
8. pkill <pattern>: Kill processes based on a pattern.

User and Group Management

1. groups <username>: Display the groups a user belongs to.
2. usermod -aG <group_name> <username>: Add a user to a group.
3. chgrp <group_name> <file_name>: Change the group ownership of a file.
4. visudo: Safely edit the sudoers file to manage user privileges.

Networking

1. ifup <interface>: Bring a network interface up (e.g., ifup eth0).
2. ifdown <interface>: Bring a network interface down (e.g., ifdown eth0).
3. ip route: Show the routing table.
4. nslookup <domain>: Query DNS to obtain domain name or IP address mapping.
5. wget <url>: Download files from the web.
6. scp <source> <destination>: Securely copy files between hosts over SSH.
7. ssh <username>@<host>: Connect to a remote server via SSH.
8. iptables -L: List firewall rules (requires sudo privileges).
9. hostname: Display the current hostname of the system.
10. curl -I <url>: Fetch the HTTP headers of a URL.

Disk and Filesystem Management

1. lsblk: List all block devices (disks and partitions).
2. fdisk -l: List disk partitions (requires sudo).
3. mount <device> <mount_point>: Mount a filesystem.
4. umount <mount_point>: Unmount a filesystem.
5. fsck <device>: Check and repair a filesystem.
6. dd if=<input_file> of=<output_file>: Convert and copy files (often used for disk images).
7. truncate -s 0 <file_name>: Reduce the size of a file to zero bytes.
8. xfs_repair <device>: Repair an XFS filesystem (requires the device to be unmounted).

Package Management (Advanced)

1. sudo apt autoremove: Remove unnecessary packages that were automatically installed.
2. sudo apt list --upgradable: List packages that can be upgraded.
3. sudo dpkg -i <package.deb>: Install a .deb package manually.
4. sudo dpkg --configure -a: Reconfigure packages that were not configured correctly.
5. apt-cache search <package_name>: Search for a package in the repository cache.

Backup and Compression

1. tar -czvf <archive_name>.tar.gz <directory>: Create a compressed tarball.
2. tar -xzvf <archive_name>.tar.gz: Extract a compressed tarball.
3. zip <zip_file>.zip <file1> <file2>: Create a zip archive.
4. unzip <zip_file>.zip: Extract a zip archive.
5. rsync -av <source> <destination>: Sync files and directories between locations.

Miscellaneous

1. alias <shortcut>='<command>': Create an alias for a command.
2. unalias <shortcut>: Remove an alias.
3. date: Display the current date and time.
4. cal: Show the calendar for the current month.
5. bc: Basic calculator for mathematical operations.
6. ssh-keygen: Generate SSH key pairs for secure authentication.

Permissions and Ownership

1. chmod +x <file_name>: Make a script executable.
2. stat <file_name>: Display detailed file or filesystem status.
3. getfacl <file_name>: Get file access control lists (requires installation).
4. setfacl -m u:<username>:rwx <file_name>: Set file access control lists for specific users.