Linux stuff

From Mintarc Forge

Common Commands with examples

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.

ls - List directory contents

The ls command is used to list files and directories in a specified location. It has many options to customize the output.

Examples:

  • ls -l: Long listing format, showing permissions, owner, size, and modification date
  • ls -a: Show all files, including hidden ones (those starting with a dot)
  • ls -R: Recursively list subdirectories
  • ls -lh: Use human-readable file sizes (e.g., 1K, 234M, 2G)
  • ls /etc: List contents of the /etc directory

cd - Change directory

cd is used to navigate the file system. It can use absolute or relative paths.

Examples:

  • cd /home/user: Change to the /home/user directory (absolute path)
  • cd ..: Move up one directory level
  • cd -: Return to the previous directory
  • cd ~: Change to the user's home directory
  • cd Documents/Projects: Change to a subdirectory (relative path)

pwd - Print working directory

pwd displays the full path of the current working directory.

Examples:

  • pwd: Outputs something like /home/user/Documents
  • pwd -P: Print the physical directory, without any symbolic links

mkdir - Create a new directory

mkdir is used to create one or more directories.

Examples:

  • mkdir newdir: Create a directory named "newdir"
  • mkdir -p parent/child/grandchild: Create nested directories
  • mkdir dir1 dir2 dir3: Create multiple directories at once
  • mkdir -m 755 secured_dir: Create a directory with specific permissions

touch - Create an empty file or update file timestamps

touch can create empty files or update the access and modification times of existing files.

Examples:

  • touch newfile.txt: Create a new empty file or update timestamps if it exists
  • touch -t 202502191200 file.txt: Set specific timestamp (YYYYMMDDhhmm)
  • touch -r reference_file target_file: Use timestamps from reference_file

cp - Copy files and directories

cp is used to copy files and directories from one location to another.

Examples:

  • cp file.txt /home/user/backup/: Copy a file to another directory
  • cp -r dir1 dir2: Copy a directory and its contents recursively
  • cp -i *.txt /destination/: Copy all .txt files, prompting before overwrite
  • cp -p source dest: Preserve file attributes (mode, ownership, timestamps)

mv - Move or rename files and directories

mv can move files/directories or rename them.

Examples:

  • mv file.txt newname.txt: Rename a file
  • mv /home/user/doc.txt /tmp/: Move a file to another directory
  • mv dir1 dir2: Rename a directory (if dir2 doesn't exist) or move dir1 into dir2
  • mv -i *.jpg /home/user/Pictures/: Move all .jpg files, prompting before overwrite

rm - Remove files or directories

rm is used to delete files and directories. Use with caution!

Examples:

  • rm file.txt: Delete a file
  • rm -r directory/: Recursively remove a directory and its contents
  • rm -f unwanted_file: Force removal without prompting
  • rm -i *.log: Remove .log files with confirmation for each


rmdir - Remove empty directories

rmdir is used to remove empty directories.

Examples:

  • rmdir empty_folder: Remove an empty directory
  • rmdir -p parent/child/grandchild: Remove nested empty directories

shutdown - Shut down or restart the system

The shutdown command is used to safely bring down or restart a Linux system, allowing for scheduled shutdowns and custom messages to users.

Examples:

  • shutdown now: Shut down the system immediately
  • shutdown -r +10: Reboot the system in 10 minutes
  • shutdown -h 23:30: Schedule a shutdown at 11:30 PM
  • shutdown -c: Cancel a scheduled shutdown
  • shutdown +15 "System maintenance in 15 minutes": Schedule a shutdown with a custom message
  • shutdown -P now: Power off the system immediately

halt - Stop all CPU functions

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.

Examples:

  • halt: Halt the system
  • halt -p: Halt the system and power off
  • halt -f: Force halt without calling shutdown
  • halt -w: Don't actually halt, just write a wtmp record

reboot - Restart the system

The reboot command restarts the system, similar to shutdown -r but more direct.

Examples:

  • reboot: Reboot the system
  • reboot -f: Force an immediate reboot without calling shutdown
  • reboot -w: Don't actually reboot, just write a wtmp record
  • reboot --no-wall: Don't send wall message before rebooting

poweroff - Shut down and power off the system

The poweroff command shuts down the system and turns off the power. It's equivalent to shutdown -P.

Examples:

  • poweroff: Shut down and power off the system
  • poweroff -f: Force power off without calling shutdown
  • poweroff -w: Don't actually power off, just write a wtmp record
  • poweroff --no-wall: Don't send wall message before powering off

SSH Stuff

ssh - Secure Shell for remote system access

sh is used to securely log into remote systems, execute commands on remote machines, and create encrypted tunnels for various network services.

Examples:

  • ssh user@example.com: Connect to example.com as "user"
  • ssh -p 2222 user@example.com: Connect using a non-standard port (2222)
  • ssh -i ~/.ssh/my_key user@example.com: Use a specific private key for authentication
  • ssh user@example.com 'ls -l /tmp': Execute a command on the remote system without entering interactive mode
  • ssh -X user@example.com: Enable X11 forwarding for GUI applications

scp - Secure Copy for file transfer

scp uses SSH to securely copy files between local and remote systems or between two remote systems.

Examples:

  • 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
  • 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
  • scp user1@host1:/file user2@host2:/directory/: Copy a file from one remote host to another

ssh-keygen - Generate SSH key pairs

ssh-keygen creates public/private key pairs for SSH authentication, offering a more secure alternative to password-based logins.

Examples:

  • ssh-keygen -t rsa: Generate an RSA key pair
  • ssh-keygen -t ed25519: Generate an Ed25519 key pair (more secure and efficient)
  • ssh-keygen -t rsa -b 4096: Generate an RSA key with 4096-bit strength
  • ssh-keygen -f ~/.ssh/my_key: Specify a custom filename and path for the key
  • ssh-keygen -p -f ~/.ssh/id_rsa: Change the passphrase of an existing private key

ssh-copy-id - Install SSH key on a remote server

ssh-copy-id securely copies your public key to a remote server's authorized_keys file, enabling key-based authentication.

Examples:

  • 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
  • ssh-copy-id -p 2222 user@example.com: Use a non-standard SSH port

ssh-agent - Manage SSH keys

ssh-agent is a program that holds private keys used for public key authentication, allowing you to use SSH without re-entering your passphrase.

Examples:

  • eval $(ssh-agent): Start the SSH agent
  • ssh-add: Add the default private key to the agent
  • ssh-add ~/.ssh/my_key: Add a specific private key to the agent
  • ssh-add -l: List fingerprints of all identities currently represented by the agent
  • ssh-add -D: Delete all identities from the agent

sftp - Secure File Transfer Protocol

sftp provides an interactive file transfer session with an interface similar to FTP but using SSH for security.

Examples:

  • sftp user@example.com: Start an SFTP session
  • sftp> get remote_file: Download a file from the remote system
  • sftp> put local_file: Upload a file to the remote system
  • sftp> ls: List directory contents on the remote system
  • sftp> !ls: Execute a local command (list local directory contents)

systemd

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.

Examples:

  • systemctl start apache2.service: Start the Apache web server service
  • systemctl stop mysql.service: Stop the MySQL database service
  • systemctl restart sshd.service: Restart the SSH daemon
  • systemctl status nginx.service: Check the status of the Nginx web server
  • systemctl enable cups.service: Enable the CUPS printing service to start at boot
  • systemctl disable bluetooth.service: Prevent the Bluetooth service from starting at boot
  • systemctl reload systemd-journald.service: Reload the systemd journal service configuration
  • systemctl list-units --type=service: List all active service units
  • systemctl is-active postgresql.service: Check if the PostgreSQL service is currently running
  • systemctl is-enabled firewalld.service: Check if the firewall service is set to start at boot
  • systemctl daemon-reload: Reload systemd manager configuration after modifying unit files
  • systemctl list-dependencies apache2.service: Show dependencies of the Apache service
  • systemctl set-default multi-user.target: Change the default system target (runlevel)
  • systemctl poweroff: Shut down the system
  • systemctl reboot: Restart the system
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