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| = Common Commands with examples =
| | A place to get started to understand Linux commands and tools |
| These commands and their usage are used for both the LinuC Level 1 Exam 101 and Exam 102. Using these commands in various scenarios to become proficient in basic command-line tasks, file management, and system administration.
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| == ls - List directory contents ==
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| The ls command is used to list files and directories in a specified location. It has many options to customize the output.
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| Examples:
| | * [https://matomo.mintarc.com/mediawiki/index.php?title=Common_Commands_with_examples Common Commands ] |
| *ls -l: Long listing format, showing permissions, owner, size, and modification date | | * [https://matomo.mintarc.com/mediawiki/index.php?title=SSH_Stuff SSH Stuff] |
| *ls -a: Show all files, including hidden ones (those starting with a dot)
| | * [https://matomo.mintarc.com/mediawiki/index.php?title=Create_monitor_and_terminate_process Create, monitor and terminate process] |
| *ls -R: Recursively list subdirectories
| | * [https://matomo.mintarc.com/mediawiki/index.php?title=SystemD_Stuff SystemD Stuff] |
| *ls -lh: Use human-readable file sizes (e.g., 1K, 234M, 2G)
| | * [https://matomo.mintarc.com/mediawiki/index.php?title=Desktop_environment Desktop Environment] |
| *ls /etc: List contents of the /etc directory
| | * [https://matomo.mintarc.com/mediawiki/index.php?title=Directory_Manipulation_and_Management Directory Manipulation and Management] |
| | | * [https://matomo.mintarc.com/mediawiki/index.php?title=Perform_basic_file_management Perform basic file management] |
| == cd - Change directory ==
| | * [https://matomo.mintarc.com/mediawiki/index.php?title=Hard_and_symbolic_links_Weight Hard and symbolic links Weight] |
| cd is used to navigate the file system. It can use absolute or relative paths.
| | * [https://matomo.mintarc.com/mediawiki/index.php?title=File_placement_and_search File placement and search] |
| | | * [https://matomo.mintarc.com/mediawiki/index.php?title=Process_text_stream_with_filters Process text stream with filters] |
| Examples:
| | * [https://matomo.mintarc.com/mediawiki/index.php?title=Use_streams,_pipes_and_redirects Use streams, pipes and redirects] |
| *cd /home/user: Change to the /home/user directory (absolute path) | | * [https://matomo.mintarc.com/mediawiki/index.php?title=Search_text_files_using_regular_expressions Search text files using regular expressions] |
| *cd ..: Move up one directory level
| | * [https://matomo.mintarc.com/mediawiki/index.php?title=Perform_basic_file_edits_using_an_editor Perform basic file edits using an editor] |
| *cd -: Return to the previous directory
| | * [https://matomo.mintarc.com/mediawiki/index.php?title=Repository_and_Package_Management Repository and Package Management] |
| *cd ~: Change to the user's home directory
| | * [https://matomo.mintarc.com/mediawiki/index.php?title=Debian_package_management Debian package management] |
| *cd Documents/Projects: Change to a subdirectory (relative path)
| | * [[Linux_Kernel|The Linux Kernel]] |
| | | * [[Init_Systems|Explaining Init Systems]] |
| == pwd - Print working directory ==
| | * [[Linux_Virtual_Machines|Linux Virtual Machines]] |
| pwd displays the full path of the current working directory.
| | * [[Mmdebstrap|mmdebstrap]] |
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| Examples:
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| *pwd: Outputs something like /home/user/Documents | |
| *pwd -P: Print the physical directory, without any symbolic links
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| == mkdir - Create a new directory ==
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| mkdir is used to create one or more directories.
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| Examples:
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| *mkdir newdir: Create a directory named "newdir"
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| *mkdir -p parent/child/grandchild: Create nested directories
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| *mkdir dir1 dir2 dir3: Create multiple directories at once
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| *mkdir -m 755 secured_dir: Create a directory with specific permissions
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| == touch - Create an empty file or update file timestamps ==
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| touch can create empty files or update the access and modification times of existing files.
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| Examples:
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| *touch newfile.txt: Create a new empty file or update timestamps if it exists
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| *touch -t 202502191200 file.txt: Set specific timestamp (YYYYMMDDhhmm) | |
| *touch -r reference_file target_file: Use timestamps from reference_file
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| == cp - Copy files and directories ==
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| cp is used to copy files and directories from one location to another.
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| Examples:
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| *cp file.txt /home/user/backup/: Copy a file to another directory
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| *cp -r dir1 dir2: Copy a directory and its contents recursively
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| *cp -i *.txt /destination/: Copy all .txt files, prompting before overwrite
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| *cp -p source dest: Preserve file attributes (mode, ownership, timestamps)
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| == mv - Move or rename files and directories == | |
| mv can move files/directories or rename them.
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| Examples:
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| *mv file.txt newname.txt: Rename a file | |
| *mv /home/user/doc.txt /tmp/: Move a file to another directory
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| *mv dir1 dir2: Rename a directory (if dir2 doesn't exist) or move dir1 into dir2
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| *mv -i *.jpg /home/user/Pictures/: Move all .jpg files, prompting before overwrite
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| == rm - Remove files or directories ==
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| rm is used to delete files and directories. Use with caution!
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| Examples:
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| *rm file.txt: Delete a file | |
| *rm -r directory/: Recursively remove a directory and its contents
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| *rm -f unwanted_file: Force removal without prompting
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| *rm -i *.log: Remove .log files with confirmation for each
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| == rmdir - Remove empty directories ==
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| rmdir is used to remove empty directories.
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| Examples:
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| *rmdir empty_folder: Remove an empty directory
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| *rmdir -p parent/child/grandchild: Remove nested empty directories
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| == shutdown - Shut down or restart the system ==
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| The shutdown command is used to safely bring down or restart a Linux system, allowing for scheduled shutdowns and custom messages to users.
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| Examples:
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| *shutdown now: Shut down the system immediately
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| *shutdown -r +10: Reboot the system in 10 minutes
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| *shutdown -h 23:30: Schedule a shutdown at 11:30 PM
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| *shutdown -c: Cancel a scheduled shutdown
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| *shutdown +15 "System maintenance in 15 minutes": Schedule a shutdown with a custom message
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| *shutdown -P now: Power off the system immediately
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| == halt - Stop all CPU functions ==
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| The halt command stops all CPU functions and brings the system to a halt state. It's similar to shutdown but may not power off the system on all hardware.
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| Examples:
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| *halt: Halt the system
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| *halt -p: Halt the system and power off
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| *halt -f: Force halt without calling shutdown
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| *halt -w: Don't actually halt, just write a wtmp record | |
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| == reboot - Restart the system ==
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| The reboot command restarts the system, similar to shutdown -r but more direct.
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| Examples:
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| *reboot: Reboot the system
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| *reboot -f: Force an immediate reboot without calling shutdown
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| *reboot -w: Don't actually reboot, just write a wtmp record
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| *reboot --no-wall: Don't send wall message before rebooting
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| == poweroff - Shut down and power off the system ==
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| The poweroff command shuts down the system and turns off the power. It's equivalent to shutdown -P.
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| Examples:
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| *poweroff: Shut down and power off the system
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| *poweroff -f: Force power off without calling shutdown
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| *poweroff -w: Don't actually power off, just write a wtmp record
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| *poweroff --no-wall: Don't send wall message before powering off
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| = SSH Stuff =
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| == ssh - Secure Shell for remote system access ==
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| ssh is used to securely log into remote systems, execute commands on remote machines, and create encrypted tunnels for various network services.
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| Examples:
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| *ssh user@example.com: Connect to example.com as "user"
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| *ssh -p 2222 user@example.com: Connect using a non-standard port (2222)
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| *ssh -i ~/.ssh/my_key user@example.com: Use a specific private key for authentication
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| *ssh user@example.com 'ls -l /tmp': Execute a command on the remote system without entering interactive mode
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| *ssh -X user@example.com: Enable X11 forwarding for GUI applications
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| == scp - Secure Copy for file transfer == | |
| scp uses SSH to securely copy files between local and remote systems or between two remote systems.
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| Examples:
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| *scp file.txt user@example.com:/home/user/: Copy a local file to a remote system | |
| *scp user@example.com:/home/user/file.txt .: Copy a remote file to the local system
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| *scp -r directory/ user@example.com:/home/user/: Recursively copy a directory to a remote system | |
| *scp -P 2222 file.txt user@example.com:/home/user/: Use a non-standard SSH port
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| *scp user1@host1:/file user2@host2:/directory/: Copy a file from one remote host to another | |
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| == ssh-keygen - Generate SSH key pairs ==
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| ssh-keygen creates public/private key pairs for SSH authentication, offering a more secure alternative to password-based logins.
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| Examples:
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| *ssh-keygen -t rsa: Generate an RSA key pair
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| *ssh-keygen -t ed25519: Generate an Ed25519 key pair (more secure and efficient)
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| *ssh-keygen -t rsa -b 4096: Generate an RSA key with 4096-bit strength
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| *ssh-keygen -f ~/.ssh/my_key: Specify a custom filename and path for the key
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| *ssh-keygen -p -f ~/.ssh/id_rsa: Change the passphrase of an existing private key
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| == ssh-copy-id - Install SSH key on a remote server ==
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| ssh-copy-id securely copies your public key to a remote server's authorized_keys file, enabling key-based authentication.
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| Examples:
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| * ssh-copy-id user@example.com: Copy the default public key to the remote server | |
| * ssh-copy-id -i ~/.ssh/my_key.pub user@example.com: Specify a particular public key to copy
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| * ssh-copy-id -p 2222 user@example.com: Use a non-standard SSH port
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| == ssh-agent - Manage SSH keys ==
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| ssh-agent is a program that holds private keys used for public key authentication, allowing you to use SSH without re-entering your passphrase.
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| Examples:
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| *eval $(ssh-agent): Start the SSH agent
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| *ssh-add: Add the default private key to the agent
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| *ssh-add ~/.ssh/my_key: Add a specific private key to the agent
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| *ssh-add -l: List fingerprints of all identities currently represented by the agent
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| *ssh-add -D: Delete all identities from the agent
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| == sftp - Secure File Transfer Protocol ==
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| sftp provides an interactive file transfer session with an interface similar to FTP but using SSH for security.
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| Examples:
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| *sftp user@example.com: Start an SFTP session
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| *sftp> get remote_file: Download a file from the remote system
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| *sftp> put local_file: Upload a file to the remote system
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| *sftp> ls: List directory contents on the remote system
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| *sftp> !ls: Execute a local command (list local directory contents)
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| = systemd =
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| == systemctl - Control the systemd system and service manager == | |
| systemctl is the primary command-line tool for interacting with systemd, the init system and service manager for modern Linux distributions. It allows users to manage system services, check their status, and control various aspects of the system.
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| Examples:
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| *systemctl start apache2.service: Start the Apache web server service | |
| *systemctl stop mysql.service: Stop the MySQL database service
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| *systemctl restart sshd.service: Restart the SSH daemon
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| *systemctl status nginx.service: Check the status of the Nginx web server
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| *systemctl enable cups.service: Enable the CUPS printing service to start at boot
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| *systemctl disable bluetooth.service: Prevent the Bluetooth service from starting at boot
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| *systemctl reload systemd-journald.service: Reload the systemd journal service configuration
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| *systemctl list-units --type=service: List all active service units
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| *systemctl is-active postgresql.service: Check if the PostgreSQL service is currently running
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| *systemctl is-enabled firewalld.service: Check if the firewall service is set to start at boot
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| *systemctl daemon-reload: Reload systemd manager configuration after modifying unit files
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| *systemctl list-dependencies apache2.service: Show dependencies of the Apache service
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| *systemctl set-default multi-user.target: Change the default system target (runlevel)
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| *systemctl poweroff: Shut down the system
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| *systemctl reboot: Restart the system
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| = Create, monitor and terminate process =
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| == & - Run a command in the background ==
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| The & symbol is used to run a command or script in the background, allowing you to continue using the terminal.
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| Examples:
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| *long_running_script.sh &: Run the script in the background | |
| *sleep 60 &: Run the sleep command for 60 seconds in the background
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| *nohup command &: Run a command in the background, immune to hangups
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| == bg - Resume suspended jobs in the background ==
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| bg resumes execution of a suspended job in the background.
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| Examples:
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| *bg %1: Resume the first suspended job in the background
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| *bg %vim: Resume the suspended vim job in the background
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| *bg: Resume the most recently suspended job in the background
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| == fg - Bring background jobs to the foreground ==
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| fg brings a background job into the foreground, allowing direct interaction.
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| Examples:
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| *fg %2: Bring the second background job to the foreground
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| *fg %emacs: Bring the background emacs job to the foreground
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| *fg: Bring the most recent background job to the foreground
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| == jobs - Display status of jobs in the current session ==
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| jobs lists the active jobs in the current shell session.
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| Examples:
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| *jobs: List all jobs
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| *jobs -l: List jobs with process IDs
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| *jobs -p: List only process IDs of the active jobs
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| == nohup - Run a command immune to hangups ==
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| nohup allows a command to continue running after the user logs out.
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| Examples:
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| *nohup long_running_script.sh &: Run a script that continues after logout
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| *nohup command > output.log 2>&1 &: Run a command, redirecting output and errors
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| *nohup python script.py &: Run a Python script that persists after terminal closure
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| == screen - Terminal multiplexer == | |
| screen creates a virtual terminal that can be detached and reattached, allowing sessions to persist.
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| Examples:
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| *screen: Start a new screen session
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| *screen -S session_name: Start a named screen session
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| *screen -r: Reattach to a detached screen session
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| *screen -list: List available screen sessions
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| == tmux - Terminal multiplexer ==
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| tmux, like screen, allows for persistent terminal sessions and window management.
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| Examples:
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| *tmux: Start a new tmux session
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| *tmux new -s session_name: Create a named tmux session
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| *tmux attach -t session_name: Attach to an existing session
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| *tmux ls: List active tmux sessions | |
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| == top - Display and update sorted information about processes ==
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| top provides a dynamic real-time view of running system processes.
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| Examples:
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| *top: Display system processes, updating every 3 seconds
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| *top -u username: Show processes for a specific user
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| *top -p 1234,5678: Monitor specific processes by PID
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| == ps - Report a snapshot of current processes ==
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| ps displays information about a selection of the active processes.
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| Examples:
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| *ps aux: Display detailed information about all processes
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| *ps -ef: Show all processes in full format
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| *ps --sort=-%cpu: List processes sorted by CPU usage (descending)
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| == pstree - Display a tree of processes ==
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| pstree shows the running processes as a tree, which is helpful for understanding process relationships.
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| Examples:
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| *pstree: Display process tree
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| *pstree -p: Show process IDs along with the tree
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| *pstree -u: Show user names for each process
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| == uptime - Show how long the system has been running ==
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| uptime displays the current time, system uptime, number of users, and load average.
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| Examples:
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| *uptime: Display system uptime and load | |
| *uptime -p: Show uptime in a pretty format
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| *uptime -s: Display the system up since time
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| == pgrep - Look up or signal processes based on name and other attributes ==
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| pgrep looks through the currently running processes and lists the process IDs which match the selection criteria.
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| Examples:
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| *pgrep firefox: List PIDs of firefox processes
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| *pgrep -u root: List PIDs of processes owned by root
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| *pgrep -l sshd: List PIDs and names of sshd processes
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| == kill - Send a signal to a process ==
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| kill sends a signal to a process, by default the TERM signal to request termination.
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| Examples:
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| *kill 1234: Send SIGTERM to process with PID 1234
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| *kill -9 5678: Send SIGKILL to forcefully terminate process 5678
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| *kill -l: List available signals
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| == pkill - Signal processes based on name and other attributes ==
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| pkill looks up processes based on name and other attributes and sends them a signal.
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| Examples:
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| *pkill firefox: Send SIGTERM to all firefox processes | |
| *pkill -9 httpd: Send SIGKILL to all httpd processes | |
| *pkill -u username: Terminate all processes owned by username | |
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| == killall - Kill processes by name ==
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| killall sends a signal to all processes running any of the specified commands.
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| Examples:
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| *killall nginx: Terminate all processes named nginx
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| *killall -9 apache2: Forcefully kill all apache2 processes
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| *killall -u username bash: Kill all bash processes for a specific user | |
